Field of the invention

This disclosure relates to an apparatus, system and method for at least partially neutralizing an acid solution.

The disclosure also relates to the apparatus, system and method for the neutralization of highly corrosive and gassing acids with a strong exothermic reactive behaviour, as for example Peroxymonosulfuric acid, (H2S05), also known as Piranha Etch or Sulfuric Peroxide Mixture (SPM).

Background of the invention

Several types of strong acids are used in the industry as cleaning or etching agents, where after the application of these acids a complex and aggressive residue remains, that is often hard to neutralize for disposal or to post-process for reuse. The use of these acids leads to high waste footprints, complex and expensive disposal procedures, and destruction or loss of valuable materials.

A relevant example can be found in the semiconductor industry, where large quantities of silicon wafers are produced. The wafer serves as the substrate for microelectronic devices built in and over the wafer and undergoes many microfabrication processes steps such as doping or ion implantation, etching, deposition of various materials, and photolithographic patterning.

Repeated etching and cleaning steps are required to produce the micro-structures required for the final silicon semiconductor products. A powerful etching solution used here is the so-called Piranha or SPM (sulfuric peroxide mix) solution. This solution can clean organic material from wafers and oxidize most metals. The powerful chemical action that makes it a favourite for resist strip and for the cleaning of wafers with organic residue also makes it difficult to use. High quality silicon wafer cleaning equipment designed to handle the corrosive chemicals safely is required for carrying out piranha etch safely and effectively.

A piranha solution or Sulfuric Peroxide Mixture (SPM) is made up of a mixture of sulfuric acid and hydrogen peroxide. The most common ratio is approximately three parts acid to one-part peroxide but solutions of up to seven parts acid to one part peroxide are sometimes used. The resulting solution is highly exothermic and is prepared by slowly adding the peroxide to the acid. The mixture heats up rapidly and is often used at temperatures of around 130 degrees C. Once operating temperature and the desired concentration are reached, the wet bench equipment has to heat the solution to maintain the temperature and keep the etch rate constant. The Sulfuric Peroxide Mixture (SPM) applied during processing in the semiconductor industry typically comprises of between 70-80% sulfuric acid, between 8-11% hydrogen peroxide, and between 9-22% water. The Sulfuric Peroxide Mixture (SPM) sulfuric acid processed in an apparatus according to the disclosure, so after being used in a semiconductor industrial production process, will typically comprise between 70-75% sulfuric acid, between 3-5% hydrogen peroxide, and between 20-27% water.

The solution removes trace organic contaminants and strip residue while oxidizing metals. The underlying surfaces are hydroxylated making them hydrophilic or attractive to water, a characteristic that can be used in subsequent silicon semiconductor manufacturing process steps.

After using the SPM solution for etching and cleaning, the remaining residue still contains a significant amount of peroxide dissolved in a strong sulfuric acid, making it difficult to handle, treat, and store. The residue solution cannot be reused for the etching process, as its effectiveness is reduced, and the solution is contaminated with traces of metals and dissolved CO2. Direct disposal is not allowed for environmental reasons; the high content of sulfuric acid also represents a significant economic value, making recycling of this acid a key driver for the semiconductor industry. Because the SPM residue solution is still highly reactive and exothermic, the solution cannot be transported to a waste treatment site, thus requiring local storage and neutralization at the semiconductor plant.

Neutralization of a Piranha solution is achieved by reducing (ideally completely removing) its peroxide content. Removing the peroxide content is based on decomposing the peroxide in water and oxygen, according to the following reaction:

In the last 20 years, many SPM-neutralization processes have been designed, tested and applied. Some examples of working principles of these neutralization processes are:

(1) Natural decay: an SPM-solution will very slowly lose its peroxide content overtime.

(2) Dilution: mixing the SPM solution with extra sulfuric acid will reduce the peroxide component in the residue to below 1%, at which point the solution can be transported and post-treated as sulfuric acid.

(3) Inserting a reactant: mixing the SPM solution with a material that reacts with the peroxide accelerates the peroxide breakdown. Examples of used materials are activated carbon, manganese or hydrochloric acid.

(4) Treatment with UV light: exposing the SPM solution to UV light causes the peroxide to break down. An SPM neutralization process variation according to method (3) is known from the Korean document KR 102047212 Bl. In this document the residue SPM mixture is brought into contact with an activated carbon matrix, and more particularly an active carbon matrix impregnated with an iron salt, which matrix is used to accelerate the decomposition of peroxide. A method for manufacturing of the matrix is described, as well as the type of process packing. As this method is based on the use of a reactant, the resulting process outputs of neutralized SPM and oxygen gas both need cleaning post-processing steps before they can be further treated or recycled. The use of a specialty consumable as impregnated active carbon combined with the need of special process packaging and required post-processing cleaning steps of the neutralization results makes this variation complex and subject to high costs, for materials but also for process maintenance and control.

A further system is known from the American document US 9278860 B2. This document relates to another neutralization process variation according to method (3), making use of hydrochloric acid as reactant. The chlorine component reacts with the peroxide, providing a controlled breakdown of the chlorine in a controlled manner, avoiding an uncontrolled exothermic reaction of the SPM solution. However, the chlorine-based reaction with the peroxide produces a chloride-based toxic gas, which has to be post-treated for safe disposal. The reaction process between the chlorine and peroxide is a slow process, requiring time and constant mixing to achieve a sufficient peroxide decomposition grade. Moreover, to assure complete reaction of the peroxide, a surplus of hydrochloric acid has to be dosed, which leads to a residual presence of hydrochloric acid in the neutralised SPM solution.

The four neutralization methods listed above all result in peroxide decomposition, but application of neutralization methods in the semiconductor industry has been proven difficult to apply or non-cost effective because of (a combination of) the following factors: long process time, danger of uncontrolled exothermic neutralization reactions, high use of expensive or dangerous consumables, large physical process footprints, and the need of extensive post-treatment steps on the neutralized SPM or possible waste flows resulting from the neutralization process.

Neutralization methods according to method (3) currently seem most applied in the semiconductor industry but are not optimal as explained above.

Although the present description will generally refer to SPM hereafter for ease of explanation, it will be understood that the disclosure may be applied to various other types of acid solutions.

It is an object of the disclosure to provide an apparatus, system and method for neutralization of an acid solution wherein one or more of the above described disadvantages of the prior art have been at least partially removed. Furthermore there is a need for a controlled neutralization process for acid solutions, especially SPM residue solutions of any peroxide concentration, where the neutralization has a reduced footprint and/or is of low-complexity so it can be applied on-site with minimal peripheral demands.

Embodiments

According to a first aspect an apparatus for at least partially neutralizing an acid solution, especially a sulfuric peroxide mixture (SPM) is provided, the apparatus comprising:

- a vessel for holding the acid solution, comprising:

- a supply unit for supplying the acid solution to the vessel; and

- a disposal unit for of disposing of the at least partially neutralized acid solution from the vessel;

- a plurality of contactor modules, each comprising a catalyst module, arranged in series inside the vessel in a flow direction between the supply unit and the disposal unit; and

- a heating unit for heating one or more of the catalyst modules.

The heating unit may be configured to generate heat in the one or more contactor modules and to allow the transfer of the generated heat from the one or more contactor modules into the acid solution flowing along the one or more contactor modules.

The contactor module (or at least the outer surface thereof which, in use, is in contact with the acid solution, is at least partially made of catalyst material. Preferably this catalyst material is essentially not reacting with the acid solution or reacts with the acid solution to a very low extent.

In an embodiment of the present disclosure a contactor module is configured to allow flow of the acid solution through the contactor module, for instance through liquid passages like openings, channels and the like, as will be explained later. This may allow for a direct and efficient contact between the (heated or non-heated) catalyst material and the acid solution.

In embodiments of the present disclosure the supply unit and disposal unit are arranged so as to cause an upward flow of acid solution supplied through the supply unit towards the disposal unit. In further embodiments the supply unit and disposal unit are arranged at opposite ends of the vessel, wherein preferably the supply unit is arranged near the bottom of the vessel and the disposal unit is arranged near the top of the vessel. In other embodiments the supply unit and disposal unit may be arranged at the same end of the vessel, wherein preferably both the supply unit and disposal unit are arranged near the top of the vessel.

In embodiments of the present disclosure the heating unit is configured to heat only a subset of the plurality of contactor modules. When, for instance, the vessel is arranged in upright position and the acid solution flows in upward direction along the contactor modules, the subset of heated contactor modules may be the one or more modules arranged in a bottom section of the vessel while the remaining non-heated contactor modules are arranged in the top section of the vessel.

In embodiments of the present disclosure the apparatus comprises a gas disposal unit for disposing of gas from the vessel. The gas disposal unit may comprise a gas outlet, for instance a gas outlet arranged at the top side of the vessel so that gas (for instance oxygen) may escape automatically as a result of the overpressure caused by the gas production inside the vessel.

In embodiments of the present the contactor modules are positioned vertically in series, such that the apparatus is configured to, when acid solution is supplied via the supply unit, cause a substantially vertical flow, in particular a turbulent flow, of acid solution passing each of the contactor modules in series.

In embodiments of the present disclosure the heating unit is comprised of an electrically conductive portion of the contactor module. The electrically conductive portion of the contactor module, optionally an electrically conductive portion of the catalyst module, may be configured to be connected to an electric power supply. In this manner the one or more catalyst modules connected to the electric power source may be heated by causing an electric current in the respective electrically conductive portion(s). The electrically conductive portion of a contactor module may be formed by at least a part of the contactor module that is connected (through wiring) to a voltage source or current source in order to be able to drive a current through the catalyst module so as to heat the contactor module.

In embodiments of the present disclosure the heating unit may comprise one or more electromagnetic coils configured to heat the one or more catalyst modules (or at least the catalyst material thereof) by electromagnetic induction. In certain embodiments each of the one or more electromagnetic coils is arranged outside the vessel, preferably around the wall of the vessel, more preferably horizontally around the vessel (for instance, when the vessel is arranged in the upright position), surrounding at least one of the contactor modules. In this manner electromagnetic induction may create electrical currents to flow inside the contactor module causing the catalyst material in the contactor module to be effectively heated up without the material of the coils being present in the acid solution.

In embodiments of the present disclosure each contactor module may be arranged within an associated electromagnetic coil. For instance, when the vessel is oriented in an upright position, each contactor module may have a coil positioned at the same height level as the contactor module itself. By selectively operating (e.g. energizing) individual coils of the heating unit one or more of the contactor modules may be heated in a selective manner. For instance, the degree of heating of individual contactor modules may be varied, by appropriately energizing individual coils.

In embodiments of the present disclosure the vessel comprises a first side and an opposite second side, wherein the first side of the vessel comprises a removable top lid. In use, the first side preferably is the top side of the vessel. The apparatus may further comprise a centring unit attached to the top lid and arranged to support and/or to centre the one or more contactor modules inside the vessel. The centring unit may comprise an elongated element comprising an internal channel arranged to connect first side of the vessel to the supply unit via the internal channel. The elongated element may be a tube extending in a generally vertical direction inside the vessel.

In embodiments of the present disclosure the plurality of contactor modules are locked in place by a retainer at the end of the centring unit.

In embodiments of the present disclosure a plurality of contactor modules are spaced apart in the flow direction in order to provide a predetermined amount of catalyst-free space between each subsequent pair of contactor modules.

In embodiments of the present disclosure a contactor module comprises a catalyst module and a carrier structure. The carrier structure may comprise the earlier-mentioned liquid passages. The carrier structure furthermore is preferably made of a different material. This may avoid or at least reduce heating of the carrier structure itself. The carrier structure may be made of non magnetic material so that in principle no heat is generated inside the carrier structure in case the heating unit is configured to heat the contactor module by induction heating. The catalyst module may comprise a catalyst material which is essentially non-reactant with the acid solution and is suitable for inductive heating. In specific embodiments the catalyst material is a metal-based material such as platinum, gold, or rhodium. More specifically, in case the acid solution is an SPM solution, each catalyst module may comprise a catalyst material which causes an accelerated peroxide decomposition and which is suitable for inductive heating, for instance platinum (Pt), gold (Au), or rhodium (Rh), preferably platinum.

In embodiments of the present disclosure the catalyst material of a catalyst module comprises one or more thin strips of a single material, preferably a thin strip of platinum (Pt) material. The catalyst module may be comprised of at least one of a number of concentric ring- shaped strips and spiral-shaped strips. In these embodiments the carrier support may be generally ring-shaped for properly supporting the ring-shaped or spiral-shaped strips of catalyst material. Furthermore one or more mechanical spacers may be provided for maintain a predefined distance between neighbouring contactor modules.

In embodiments of the present disclosure the apparatus further comprises a discharge unit located near the bottom side of the vessel and configured to discharge the neutralized acid solution completely after processing.

According to another aspect a system for at least partially neutralizing an acid solution, is provided, wherein the system comprises a plurality of apparatuses as defined herein. The plurality of apparatuses may be connected in series with a disposal unit of a first apparatus in fluid connection through one or more flow elements, for instance flow pipes and flow valves, with a supply unit of a second, subsequent apparatus. The disposal unit of the second apparatus may be in fluid connection through one or more flow elements with a supply unit of a third, subsequent apparatus etc. In this manner a series arrangement of interconnected vessels may be realized wherein in every further apparatus the acid solution may be further neutralized.

Such system may further comprise a feedback flow element arranged to allow at least a part of the at least partially neutralized acid solution in the last apparatus in the series of apparatus to be fed back to the first apparatus. This allows for a batch wise process wherein the acid solution is guided two or more times (i.e. in multiple passes) through the series of vessels. This batch wise process has a number of important advantages, as will be explained later.

In embodiments of the present disclosure the disposal unit of the last apparatus of the series is connected to the supply unit of the first apparatus of the series by the feedback flow element, wherein the feedback flow element may comprise a pump arranged to pump at least partially neutralized acid solution from the last apparatus to the first apparatus.

According to another aspect a method of at least partially neutralizing an acid solution in an apparatus is provided, wherein the method comprises: supplying the acid solution to the vessel in which a plurality of contactor modules, each comprising a catalyst module, are arranged in series in a flow direction; heating one or more of the catalyst modules so as to heat the acid solution; causing the acid solution to flow through the vessel in the flow direction past each of the contactor modules, so as to be at least partially neutralize the acid solution; and disposing of the at least partially neutralized acid solution from the vessel.

According to an embodiment the acid solution is Sulfuric Peroxide Mixture, SPM. According to an embodiment the heating is performed by electromagnetic induction. According to an embodiment the flow direction runs from the bottom to the top of the vessel, and wherein acid solution is caused to flow in the flow direction by rising oxygen bubbles arising from neutralization and/or by the heating by the catalyst modules.

According to an embodiment the method comprises performing the neutralization process repeatedly on the same acid solution in a plurality of vessels which are connected to each other in series guiding the acid solution consecutively through the series of vessels.

According to an embodiment partially neutralized acid solution is fed from the last vessel of the series of vessels to the first vessel and the guiding of acid solution through the series of vessels is repeated (multiple pass process).

As discussed above the apparatus may comprise a contactor module, comprising a non reactant material, where said material acts as chemical catalyst with respect to the neutralization process. The contactor module consists of a carrier structure for the catalyst, and the catalysts itself. The layout of the contactor module is such that the acid solution can flow freely through it, allowing for direct contact between the surface of the catalyst and the acid solution. Several contactor modules are placed inside an acid- and temperature resistant container, where the container is equipped with installation and orientation means for defined positioning of the contactor modules. Said container is also equipped with interfaces for supply of non-neutralized acid solution, disposal of neutralized acid solution, and evacuation of gas that is formed during the neutralization process. Such container also allows for the installation of process monitoring and control equipment.

As a further aspect of the disclosure, said contactor module is used as a heating means, allowing heat transfer from the contactor module material into the acid solution. The layout of the contactor module here is such that the acid solution can flow freely through it, allowing for direct contact between the heated catalyst and the acid solution. The direct and local supply of heat to the acid solution, from the surface of the catalyst, results in a stronger and more effective neutralization process, while the type of local heating allows for a robust and fast neutralization process control, avoiding sudden uncontrolled exothermic decompositions.

As a still further aspect of the disclosure, the required physical and material properties of the contactor module in the function of catalysts are adjusted to comply with the required physical and material properties of the contactor module in the function of heating element, where the resulting properties allow the contactor modules to be installed in a container as defined in the first aspect of the disclosure.

In embodiments of the present disclosure the method of heating of the contactor module may be defined as heating by electric current in the contactor catalyst material. Although not discarded, other heating processes based on using a foreign heat carrying material (i.e. hot water) are deemed less suitable, making the contactor module very large and complex in layout, while also introducing a possible contaminant and moreover an important safety hazard in case there is a leak in the contactor module. Heating of the contactor module by electric current can be done by directly connecting said module to an electric power source, using wiring. This would require an extra interface in the module-carrying container, and it would also require an acid-resistant type of connection, as the connection is routed to the interior part of the container where the acid solution is present. As a preferred embodiment, the heating of the contactor module is achieved by use of an electromagnetic induction process. Here, an external coil, located outside the container, is provided with a strong alternating electrical current. Because of this current, the coil creates a magnetic field around its circumference, where said magnetic field is also present inside the container. By designing the contactor module inside the container such that it will act as a coil, inside the catalyst material in the contactor module another electric current will be generated. This current will cause the catalyst material to heat up, where the amount of heat and heating grade will be determined by the catalyst material used, the current in the primary (outside) coil, and the electromagnetic coupling between the primary (outside) and secondary (contactor module) coil. The functioning and dynamics of an inductive heating process is expected to be known by the skilled person and will not be further elaborated.

In a further embodiment, the contactor module is designed and configured for the neutralization of an SPM solution with a peroxide content between 1% and 10%. When combining the requirements of a non-reactant catalyst with the requirement that the catalyst should be suitable for inductive heating, metal-based materials catalysts can be used. Some applicable examples of such catalysts are (but such catalysts are not limited to) Gold (Au), Platinum (Pt) and Rhodium (Rh). Although all three comply with the requirements, it is determined by testing with an inductive heating setup that Platinum has best performance specifications as catalyst, but also as inductive heating element, mainly because of the magnetic properties of Pt. In a preferred embodiment, the contactor module catalyst surface is therefore made of Platinum.

In a still further embodiment, the contactor module is comprised of a carrier structure to maintain the catalyst material in position and in shape, and the catalyst material itself. It would be preferable to make the carrier structure the catalyst, so one type of material covers both functions. Although possible, practical testing has shown that this leads to several complications. First of all, the carrier design must be sufficient strong and stiff to maintain the shape and position of the catalyst material in the container, but also to maintain any loads resulting from the SPM flow around it, and the electrical and thermal loads acting on it. This requires a significant mass of material to be applied to the carrier structure; in the case the carrier is made of Pt, this results in a significant cost. Second, making the carrier out of catalyst, also means that the carrier structure will couple to the magnetic field applied by the primary induction coil. This results in a heating of the carrier structure as well, which causes heat power loss to the catalysts surfaces that are meant to introduce heat to the SPM solution. As a result, in a preferred embodiment, the carrier structure is made from a different material than the catalyst, in particular the carrier structure material is based on a non-magnetic material so the induction field is not affected. It goes without saying that the carrier material must also be SPM-resistant.

In another embodiment, the design and layout of the catalyst is such that it results in the largest outer surface per acid volume contained within a contactor module. This condition assures that ratio of the volume of acid per surface catalyst is lowest, which is important for optimal neutralization and also for maintaining the neutralization process under control. A small acid volume per surface unit will limit the exothermic response of this volume when subjected to the catalyst and heat transfer at the same time. A second requirement for the design and layout comes from the induction heating: for correct and optimal coupling with the magnetic field, the catalyst must have a certain shape and mass that allow for a maximum resulting current inside the catalyst. As the catalyst is made from an expensive material, as a third requirement it is desirable to have a maximum outer surface with respect to the total mass of the catalyst, although this requirement is not process-driven.

Combining above requirements, in a preferred embodiment the catalyst is designed as a thin strip of Pt, which is rolled up into a spiral shape, where the strip height orientation is vertical. The thickness of this strip is such that it cannot maintain shape and needs a supporting structure. The density of the spiral (number of turns per total horizontal covering surface of the spiral) is chosen such that the space between the turns of the spiral does not allow for touching of the turns between each other; this would result in a short circuit when subjected to induction heating, and probable catalyst failure. The use of a spiral shape for the catalyst implies that the required carrier structure is best made in (but embodiments are not limited to) a circular shape, for maximum support of the catalyst.

In another embodiment, the contactor module with the carrier structure and the catalyst installed is designed such that the contactor modules can be stacked on top of each other, around a vertical supporting tube located in the middle of the container. The carrier structure comprises of mechanical spacing means for maintaining a distance between each contactor module, when stacked. This allows for selective induction heating of a contactor module, by installing this particular contactor module within the external primary coil of the inductive heating, while the preceding and following contactor module are not or less affected by the induction coil magnetic field. This allows for a stack of contactor modules that acts over its full length as a catalyst, but only partly as heating elements. The spacing means of the carrier structure also assure that the catalyst surfaces of each contactor module do not touch each other, avoiding the risk of a short circuit when subject to induction heating.

In a preferred embodiment, the contactor modules are stacked in a vertical orientation within the container, where the container has a cylindrical shape, to correctly accommodate the circular contactor modules, to assure maximum SPM contact with the catalyst surfaces. To position and maintain the contactor modules within the container, a vertically placed tube is positioned inside the container, in the centre of said container. The contactor modules are placed over this centre tube, using the carrier structure of each module. Said centre tube can be installed such that it is supported at the bottom of the container, but in a preferred installation the tube is attached to the top lid of the vessel of the container.

In one implementation, the vessel contains a stack of multiple contactor modules, and is equipped with a top lid, whose primary function is to close off the top side of the vessel. Furthermore, a tube is attached inside said top lid, in the centre of the top lid or, in other embodiments, off-centre, with this tube being hollow so as to create a fluid transportation channel inside the tube. The length of the tube is such that when the top lid is positioned on top of the vessel, the bottom end of the tube does not touch the bottom of the vessel. In the top lid an SPM supply line is connected such that the SPM can enter the centre tube channel, flow down to the bottom of the tube and flow out at this location into the bottom of the vessel. This results in a flow of fresh SPM from the bottom of the vessel towards the top of the vessel: experiments have shown that such bottom-to-top flow, combined with the oxygen bubbles that form in the SPM, results in a steady turbulent SPM flow over the contactor modules, resulting in a more effective neutralization process of the SPM. The turbulent upward SPM flow is driven by the rising oxygen bubbles and the heat the SPM receives from the different contactor modules, which results in another driving force coming from the convection effect.

In another aspect of this implementation, the top lid is equipped with a gas disposal unit for the releasing oxygen from the SPM, and the vessel is equipped with a sidewall positioned SPM disposal unit as well. The position of the side disposal unit for the SPM is set such that the maximum level of the SPM always ensures an SPM-free space between the maximum SPM level and the bottom of the top lid. This creates a pocket where released oxygen and possible droplets of SPM can separate, so that only oxygen flows out of the top lid gas disposal unit. If certain embodiments, additional separation means like membranes are installed in the gas disposal unit, to assure that SPM cannot exit.

After the SPM is neutralized, the volume inside the vessel needs to be drained out. This could be achieved by applying a suction force on the SPM inlet that runs through the centre tube. This will result in removal of the SPM volume that is stored above the bottom end of the centre tube; a small volume of SPM will remain in the vessel, when the liquid level of SPM falls below the bottom end of the centre tube. Therefore, as a preferred means of draining, a drain exit in the bottom or lower side wall of the vessel is used, which will allow for gravity-assisted complete draining of the vessel.

In another implementation, the stack of contactor modules is located around the centre tube which is attached to the top lid. The bottom of said centre tube is equipped with a removable retaining means. This allows for easy installation and removal of the contactor modules placed on the centre tube, before the top lid is installed on the vessel. All required contactor modules can be installed on the centre tube of the top lid, after which the retainer is placed to keep the contactor modules in place. Now the top lid, including all the contactor modules positioned correctly, can be placed in its position on the vessel, resulting in the correct placement of the SPM supply tube, the oxygen exit, and the contactor modules inside the vessel.

Another aspect of above implementation is the use of part of the stack of contactor modules as catalyst modules only, against the use of the remaining part of the contactor modules as catalyst and heating means. As the neutralization of SPM is an exothermic process, not all contactor modules need to be used for heating. When the SPM has reached a certain temperature the formed exothermic heat results in maintaining or even rising the temperature of the SPM. With a preferred flow for the SPM from bottom to top of the vessel, this aspect therefore comprises the use of contactor modules as catalyst and heating in the lower section of the vessel, against just catalyst modules in the middle and top section of the vessel. To achieve this, around the lower section of the vessel one or more induction coils are installed, around the outside perimeter of the vessel. The position of these external coils is such, that when the top lid is installed on top of the vessel, the contactor modules that are dedicated to the function of catalyst and heating element are located and aligned correctly with these induction coils. The correct location for a contactor module is determined by the contactor module horizontal centre line being at the same position vertical position as the induction coil horizontal centre line. When operating the induction coil, the contactor modules that are correctly aligned with the induction coil will heat up and dissipate this heat by means of their catalyst coils into the SPM flowing through the contactor modules. Any contactor modules that are not correctly aligned with the external induction coil, but that are within a distance of 10 cm of such a coil, will be heated up but with lesser intensity, and effect that is acceptable within the SPM neutralization process.

A single vessel and resulting stack of contactor modules can be dimensioned such that the complete neutralization process can take place inside this single vessel. Although resulting in much less need for supporting hardware and tubing, a single-vessel solution requires materials with unusual dimensions, resulting in high costs and/or a high vertical footprint. Therefore, in a preferred implementation, multiple vessels are used in series, to achieve the correct process length for sufficient neutralization of the SPM.

In this implementation, multiple vessels, with a minimum of two, are connected to each other by their means of SPM inlets and outlets. More in particular, the sidewall outlet of each vessel connects to the inlet of the following vessel. This could be done by standard tubing and assisted by pumping means in case level or pressure differences have to be overcome; however, by placing the vessels on the same level and introduction of an SPM-inlet in the sidewall of the vessel, the flow of SPM does not need pumping means as the vessels are now openly communicating. The clear advantage here, apart from not needing expensive pumping means, is that the SPM flow does not receive any pressurization which could result in uncontrolled neutralization or degassing effects.

According to a previous aspect, each vessel in series-stack of vessels could be equipped with either catalyst and heating contactor modules, just catalyst modules, or a combination of both. Experiments have shown that a most stable and controllable neutralization process is achieved by locating the required heating at the start of the process, preferably at the bottom of the first vessel. In this way the SPM is heated to a certain temperature first, where after the SPM flows through the catalyst contactor modules, using the thermal energy and the presence of catalyst to neutralize itself, releasing oxygen in the same process. This does not exclude that heating units are located in other vessels also: a preferred variation of the process can contain heating units in the last vessel of a series-stack of vessels. When the SPM has almost reached full neutralization, it is beneficial to heat the SPM to higher temperatures to get the last part of hydrogen peroxide out in a more time efficient way. This additional heating was not possible at the start of the process, as the SPM still has its exothermic properties here. Additional heating in the last vessel is therefore only applicable if the SPM has reached a hydrogen peroxide content of less than 1%.

A series-stack of vessels can be setup such that the SPM is fully neutralized when reaching the last vessel. The neutralization process is then based on a single pass, which leads to a simple configuration of the process itself. However, the number of vessels in a single-pass process depends on the amount of hydrogen peroxide content of the incoming SPM. The higher this content, the more vessels are needed. To make a single-pass process applicable for a variable peroxide content, it is necessary to install the maximum number of vessels that are needed for the highest expected peroxide content. Experiments have shown that for a single-pass neutralization process to be applicable in atypical semicon fab process, it is necessary to install between 5 and 8 vessels in series, with heating units in at least the first vessels but likely also in the last vessel. It goes without saying that this leads to a SPM-neutralization process that requires an important investment: not only are multiple special-material made vessels necessary, also an important amount of heating and/or catalyst contactor modules must be installed. The catalyst in these modules adds the larger part of the high costs of such a solution.

In a preferred variation, the neutralization process can be setup in a batch-wise configuration. Here between 1 and maximum 3 vessels are used, with heating units located in the first vessel (not ruling out heating units in another vessel). The series-stack of vessels is now used for a first pass treatment of the SPM, resulting in a partially neutralized SPM as output from the last vessel in the stack. The SPM output is then recirculated back to the first vessels, using a pumping means. The partially neutralized SPM is now again run through the stack of vessels, receiving heat and exposure to the catalyst, resulting in a partially-neutralized SPM with a hydrogen peroxide content at the output of the last vessel, which is lower than the peroxide content in the first vessels. Without further detailed explanation, it is obvious that this process of recirculation can be repeated until the necessary neutralization grade of the SPM is reached, where after the neutralized SPM is evacuated out of the installation. A fresh batch of SPM is loaded into the installation, and the batch wise neutralization process can be executed again.

This batch wise process has an important economic advantage, as fewer vessels and thus fewer contactor modules are used. The introduction of pumping means, together with the required control valves and tubing is found to be lower in costs (capital and operational) than the usage of extra vessels. At the same time, experiments have shown that the batch wise process allows for a better heat introduction and thus temperature control of the SPM during neutralization. Exposing the fresh SPM to a first limited temperature rise by using the conductive heating unit leads to a better controlled initial neutralization process, as the exothermic reaction of the active fresh SPM is limited. Each time the SPM is recycled, having a lower hydrogen peroxide content, the heat transfer can be set higher, because the exothermic capacity of the already partially processed SPM is now lower. This leads to a most controllable and most efficient (timewise) neutralization process. In case this is deemed necessary, the last (or previous) vessel in the batch wise process can still be equipped with additional heating units so as to boost the neutralization process even more.

Further elaborating the batch wise process, it can be determined that this type of process needs a fresh SPM input to fill the system, and a neutralized SPM output to remove the SPM from the system when the process is finished. It was earlier derived that the treated SPM output must provide a way to drain the vessels, when the preferred internal SPM flow direction from bottom to top is used. In a first configuration, the SPM input and output can both be separately achieved by using a pumping means for input and a pumping means for output, each equipped with corresponding valves for correct functioning. To run the batch wise neutralization process itself, another pumping means would be required, bringing the total number of pumps to three. This configuration makes the complete neutralization process operable, but the introduction of several pumping means with their valves makes the process also more complex, with more parts that could fail. As safety is a major concern when working with SPM, it is determined that a process with fewer active components is preferred.

Such an optimum process configuration is found by using the pumping means for the batch wise process also as SPM supply and as SPM disposal pump. This is achieved by introducing a so- called 3 -way valve before the pump (in the suction line), and another 3 -way valve aft of the pump (in the pressure line) (or three 2-way valves). The valve on the suction side of the pump can act as supply valve, connecting it to an external fresh SPM-containing vessel. When this side of the valve is active, the pump will pull in fresh SPM, and introduce it in the contactor-modules containing vessels, until these are filled. Then the 3-way valve in the suction line closes, connecting the suction side of the pump to the outlet of the last vessel. The pump, when operative, now circulates SPM through the vessels, making the neutralization process work. When the SPM is neutralized completely, the 3-way valve in the pressure line, which has been set to pass the SPM back into the process vessels, is now set to the external disposal position. When the pump is now operated, the neutralized SPM is pumped out of the vessels and into an external collection vessel.

As stated before, it is necessary to drain the process vessels as a separate step, as the SPM inside the vessels cannot be taken out when the preferred internal SPM bottom-to-top flow is used. The draining via an output located in the bottom area of each vessel, as described before, can be achieved by using gravity as driving force, draining the neutralized SPM content of each vessel separately or combined, into an external collection means, by operating a valve that opens or closes the draining output. When combining the drains of all vessels in the process, it will be important to install a valve in each of the draining lines, so as to avoid that a shortcut route for non-neutralized SPM exists, which allows SPM to bypass the contactor modules in the vessels.

Gravity-driven SPM draining is a simple, cost-effective, and robust method. However, it can be a preferred configuration to combine the draining of the vessels with the pump that is used to drive the batch wise neutralization process. As described before, this single pump is used to supply the vessels with fresh SPM for neutralization, to circulate the SPM during the batch wise neutralization process, and to evacuate the neutralized SPM from the lines and part of the vessels after the batch wise process is completed. By draining the neutralized SPM content of all the vessels into the suction side of the pump, the SPM can be pumped out of the vessels and other process components in a controlled and safe manner.

During the neutralization process oxygen is released inside the vessels, where the volume of oxygen released per vessel might differ, depending on the neutralization grade of the SPM in each vessel. The released oxygen is evacuated from each vessel through a direct exit in the top lid of each vessel, without any pumping means or other additional driving force: experiments have demonstrated that the production of oxygen in the SPM mixture itself generates a light overpressure over the SPM top level, which assures removal of the oxygen through the provided exit. The exits of the oxygen of all vessels used in the process can therefore be combined into one gas disposal unit, if this is deemed better.

Fig. 1 shows a schematic representation of a generalized SPM neutralization process 100. The chemistry behind the neutralization of SPM is already explained in the background to this disclosure; process 100 highlights the main external inputs that lead to neutralization, and their respective impact on a batch of SPM 101.

First, heat treatment of the acid solution is a working principle which will accelerate the peroxide decomposition. An acid solution container may be maintained at a high temperature (for example 175 °C) or sulfuric acid solutions with a small quantity of peroxide may be used, in which case preheating the acid solution to 30-80 °C will lead to evaporation of the peroxide and partial decomposition.

A first input 102, leading to the introduction of heat into SPM batch 101, has an important effect on the neutralization, as the breakdown of hydrogen peroxide accelerates with higher temperatures. As this breakdown is an exothermic reaction, the generation of heat in the SPM itself will accelerate the breakdown process even more. It goes without saying that this effect could be beneficial for a faster breakdown, but that it also comprises an important risk when too much heat is either applied externally or generated inside the SPM batch 101, which can lead to an uncontrolled breakdown reaction in an explosive manner. This is especially the case when the starting hydrogen peroxide concentration of a% in 101 is high, where between 5% and 8% is considered extremely high, and between 2% and 5% is considered high, and between 1% and 2% moderate. SPM with a hydrogen peroxide content below 1% is considered of a lower risk and apt for post-processing, where a concentration below 0.1% is considered neutralized.

The prior art contains no clear descriptions of any type of heating method for this application. Heating methods for acid solutions may be developed based on the use of special- material heat exchangers (using special metal alloys or plastics), or the use of electric heating elements that are covered with an acid-resistant material. The heating step and the catalyst step could take place in separate environments and therefore in a non-combined manner, but this may make the overall neutralisation process unsuitable because of long process times or insufficient neutralisation grade.

Second, inserting a catalyst is another working principle. Several materials which are non reacting catalysts will cause an accelerated peroxide decomposition when introduced in the SPM solution. Highly concentrated sulfuric acid may be regenerated from piranha solution waste in case a metal catalyst (Pt, Ni, Zr, Au, Rh, and/or combination thereof) is used to degrade the peroxide. Such a catalyst may have a granular form, bar-like form etc.

A second input 103, being the addition of a catalyst or reactant to the SPM batch 101 with hydrogen peroxide content b%, where b < a, has another important effect on the breakdown process. Generally spoken, a reactant has a stronger effect than a catalyst, as the reactant becomes an active part of the breakdown process and is as such a consumable. The catalyst is an accelerator by mere presence but is not consumed in the breakdown process. The presence of heat (i.e. temperature) has again a positive effect on either reactant or catalyst effectiveness. It can therefore be stated that the sequence of the first input 102 followed by the second input 103 on batch 101 is deemed more effective than the other way around. It can be understood that the value of concentration b% of hydrogen peroxide in batch 101 is of the same importance for the breakdown process as a result of the second input 103, as it is for concentration a% with the first input 102. Application of a reactant generally leads to the presence of reactant (or remains thereof) in the neutralized SPM, which may raise the need for a post-treatment process of the neutralized SPM. Application of a catalyst will not cause this.

Using a preheating (to for example 120°C), the residual concentration of peroxide may be strongly reduced in a short period of time, compared to less reduction in a much longer time without a metal catalyst. In both cases the resulting sulfuric acid concentration may be over 60%.

The last input 104 is the total process time given to the neutralization process. SPM has a natural decay which will cause full breakdown of the hydrogen peroxide if the SPM is left standing for a long enough time. In the process 100, the third input 104 is important when applied over the previous neutralization steps resulting from the first and second inputs 102 and 103. Heat application has a stronger neutralization effect when applied over a longer time (leading to a higher temperature of the batch 101); longer presence of the batch 101 to a catalyst or reactant will also have a positive effect on the breakdown process.

Although these principles may lead to a feasible neutralisation method, currently there is no known solution based hereon available for the semiconductor industry. In the art, a problem is the control over the process: the heating step in combination with a catalyst, applied on a relevant volume of SPM solution, might quickly lead to uncontrolled exothermic behaviour and decomposition of the SPM solution.

A secondary result from the neutralization process driven by and under the influence of inputs 102, 103 and 104, is the production of heat and gas 105 in batch 101. The neutralization process is exothermic, and the decomposition of hydrogen peroxide leads to the formation of oxygen that will evacuate from the batch 101. The magnitude and timewise formation of either heat and/or oxygen depends on a combination of factors. A degassing device may be used to discharge generated oxygen gas. A fdter (such as a hydrophobic membrane) may be used to separate vapour peroxide from sulfuric acid resulting from the process.

Following from Fig.1, it can be stated that the correct combination and application of inputs 102, 103 and 104 on batch 101 will result in a controlled hydrogen peroxide breakdown process, resulting in a continuous and controlled lowering of the peroxide content, with a% > b% > c% > d%. Although not mandatory, a preferred order of application of inputs on batch 101 for an optimized and controllable neutralization process has been determined as 102 - 103 - 104.

Fig. 2 shows a representation of a volume of SPM 101, containing a body 201 which is considered either a catalyst or a heat transfer element. Volume 101 is subject to a flow, meaning that the SPM incoming at the bottom of volume 101 flows upward with flow speed Fi, where the SPM has temperature Ti and the SPM is containing a hydrogen peroxide concentration of x%.

Body 201 is shaped such that the SPM in volume 101 can flow freely over the surfaces on both sides of body 201; distribution of the SPM over these surfaces is considered homogeneous for this example purpose. After passing alongside body 201, the SPM exits volume 101 with a temperature T2, with flow rate F2 and with a hydrogen peroxide concentration of y%.

If body 201 is considered to be a catalyst, shaped as a flat and thin surface, it can be assumed that the effect of the presence of body 201 on the SPM flow is marginal. As a result, it can be stated that Fi = F2. Because 201 is a catalyst for the breakdown of hydrogen peroxide, it follows that concentration x > y, where the difference between x and y is defined as AC _cat = x-y. Because of the exothermic properties of the breakdown reaction of hydrogen peroxide, we can also state that Ti < T2. The difference of temperatures is defined as AT _cat = T2 - Ti.

When considering body 201 as a heat transfer body, with a energy supply 202, where it is assumed that as a result of this energy supply body 201 reaches a temperature that is higher than Ti, we can determine that the flow of SPM over body 201 is again subject to a hydrogen peroxide breakdown as a result of the heat transfer 102 from the surface of 201 into SPM volume 101, without any significant effect on the flow of SPM through volume 101. The resulting hydrogen peroxide concentration gradient as a result of this heat transfer is defined as AC _tem = x-y, and the resulting temperature difference is AT _tem = T2 - Ti.

As a next step, body 201 is now considered to be a heat transfer body, made out of a catalyst material. An example material for such a body would be (but materials are not limited to) platinum: this metal is found to be a catalyst for the breakdown reaction of hydrogen peroxide, while it can also contain a significant amount of thermal energy. It would be expected that a body

201 which is now a heated catalyst has a combined effect on the breakdown of hydrogen peroxide, denominated as AC _tot , which in a simple way could be expressed as AC _tot = AC _cat + AC _tem .

However, experiments have demonstrated that the overall effect of combining catalyst and heat transfer on hydrogen peroxide breakdown is larger than the sum of each separate effect. A plausible cause for this unexpected effect is found in a literature study on the working principle of using platinum as a catalyst for the breakdown of hydrogen peroxide in SPM. In short, platinum binds oxygen to its surface, therefore disrupting the chemical balance in the hydrogen peroxide, leading to the breakdown of hydrogen peroxide and formation of water and oxygen. However, the oxygen binding to the surface of the platinum form a blanket over the surface, lowering the amount of exposed platinum surface available for more oxygen atoms to bind to. When heating the platinum surface, the bound oxygen is assumed to be releasing from the platinum surface at a faster rate than when the platinum surface is not heated. This can be caused by an effect of the heat on the binding force between oxygen and platinum atoms, making this force lower. Another plausible effect can be found in the increase of the oxygen volume over the surface under the influence of the heat. This might promote the faster formation of larger oxygen bubbles on the platinum surface, which will release into the SPM flow over the platinum surface under the known effect of buoyancy of a gas in a liquid.

Fig. 3A indicates an embodiment 300 which consists of a stack of catalyst elements 201, wherein the stacking is done in a horizontal manner (although the invention is not limited to this manner). The elements 201 are considered to be all heated catalysts, therefore an energy supply

202 is connected to one element 201. To make all elements 201 of the heated type, an internal energy supply 203 is introduced between the first heated element and subsequent elements. Regarding the dimensioning of element 201 and their relative positions the following is considered: to minimize the effect of element 201 on the flow of SPM, the thickness f of element 201 is preferably at mostl mm, more preferably with a maximum 0.1 mm, with a preferred minimum thickness of 0.05 mm. The distance between elements 201 is defined as d , where the preferred maximum value of d is set to 20 mm, but the value is more preferably lower than 10 mm, with a minimum of 1 mm. The height of element 201 is defined as f, where fi preferably has a value between 2 mm and 20 mm, more preferably between 5 mm and 10 mm. The width of element 201 is defined as e in this embodiment the exact value of e is not substantially restricted, depending mostly on the total volume of SPM that one wants to treat per time unit.

In Fig. 3B, stack 300 is now placed in a SPM volume 101, where two stacks 300 are placed in a vertical orientation, for explanatory purposes of the significance of parameter h (the vertical distance between two stacks 300). In theory, one could consider making element 201 with a large height f , so as to expose the flowing SPM to a large surface of catalyst while receiving heat from said surface. However, experiments have shown that this can lead to a situation of over exposure , meaning that the SPM is exposed to heat and catalyst for a too long time, leading to an uncontrolled breakdown of hydrogen peroxide as a result of the additional heating of the SPM from the exothermic effect. Said over-exposure results in a violent boiling of the SPM over the surface of element 201, leading to loss of contact between the SPM and the surface of 201, temperatures in the SPM that can endanger the consistency of supporting materials (melting), and even the creation of evaporated hydrogen peroxide instead oxygen.

To avoid such uncontrolled and possibly dangerous effects during the neutralization of SPM, using several bodies 300 of elements 201, stacked in a vertical position (vertical meaning in the flow direction of the SPM), with a space h between each body 300 is deemed preferable. The volume space created by distance h allows agitated SPM to release heat and oxygen while not being in the presence of elements 201, making this a controlled process. Distance h is therefore defined such that the SPM with the highest concentration of hydrogen peroxide, with its respective flowrate, is subject to enough volume space without the presence of elements 201 so as to controllably breakdown part of its hydrogen peroxide content, assuring a controlled and safe and controlled exposure of said SPM to the next body 300 of elements 201. A preferred order of magnitude of the range for distance h is, 10 mm to 50 mm, although the invention is not limited to these magnitudes.

Considering above description of the preferred embodiment of a vertical stacking of several bodies 300 in an SPM volume 101, Fig. 3C also shows an embodiment 301, consisting of a top view of a possible configuration of body 300. SPM flow for this embodiment 301 is supposed to be in the direction towards the viewer. Elements 201 in this embodiment have the shape of a closed circle with radius R _e , where distance e is now defined by the formula e = 2aR _e . Each circle has a thickness t and a height f , and distance d between each circle follows from the difference in value of radius between one circle and its subsequent circle. To provide the outer body 300 (the largest circle) in embodiment 301, energy supply 202 is indicated. To supply the remaining bodies 300 with energy supply for heating, connection 203 is drawn. Fig. 3D shows another and preferred embodiment 302: here body 300 is shaped as a continuous spiral with again thickness T and a height f Distance d is now set by the offset chosen for the spiral, e is now the total length of the spiral. The spiral is placed perpendicular to the SPM flow. A first important advantage of embodiment 302 is the simplicity of introduction of energy supply 202 for heating of the spiral: this only requires one connection as indicated. As the spiral is a continuous shape, further connections 203 are not necessary. Another important advantage regarding this energy supply and the spiral shape comes from a particular and preferred type of energy supply: no-contact induction heating. It is assumed the working principle of induction heating is known to the skilled reader; experiments have shown that heating by induction of a set of concentric circles as shown in embodiment 301 is subject to very low efficiency, leading to uneven heating of each circle, while needing a large energy supply because of losses. A spiral as indicated in embodiment 302 allows for a controlled and vey efficient heating of the spiral with induction heating: efficiencies of 80% or higher have been measured in experiments, where it needs to be noted that the effect of using an open-end spiral or a closed-end spiral is important. When both ends of the spiral are brought into (electrical) contact with each other, the conductivity efficiency improves considerably, where the efficiency of an open-end spiral was still found to be higher than the efficiency of the stack of concentric circles as shown in embodiment 301. For application of conductive heating means, the material of the element 201 must have magnetic properties. In previous examples platinum was used as material for 201: this metal is a catalyst for the breakdown reaction of hydrogen peroxide, and it has sufficient magnetic properties to be heated by induction.

Fig. 4 shows a schematic representation of an embodiment 400, containing a catalyst and heating element 201 (shown lifted out of their position for clarity), element supports 401, and interlinking members 402 between supports 401, where the members 402 are equipped with liquid passage means 403. In the centre section of embodiment 400, a centring unit 404 is located, which connects to the two inner members 402. It must be noted that for simplicity the drawing of 400 is setup as a symmetric object around its vertical centre axis: in the case that element 201 is in the spiral configuration as previous indicated in Fig. 3 as embodiment 302, the embodiment 400 will clearly not be symmetrical around its centre axis. The positioning and fixation of element 201 in support 401 can be achieved as shown in Fig. 4, by means of a slit with dimensions such that element 201 is clamped into position, but it is obvious others means of positioning and fixation can also be applied, like for example clamping by screws. The connection between support 401 and interlinking member 402 can be either permanent or removable, which is also applicable for the connection between the most inner interlinking members and the centring unit 404. The same approach is taken for the overall design of the carrying and support structure with respect to strength and stiffness: the design must be made such that acting forces on said structure resulting from SPM flow, deformation from thermal processes, or magneto-electric effects from conductive heating can be dealt with so as to avoid structural failure or out-of-tolerance deformation of said structure.

An important feature of Fig.4 is the difference between the material of element 201 (which must be a catalyst to SPM, have thermal conductivity properties, and must be magnetic to a sufficient degree for conductive heating), and the material(s) of members 401, 402 and 404. Members 401, 402 and 404 could be made of different materials, but a more obvious choice is to make the complete catalyst carrying structure of the same material. Whatever material choice is made for these members, an important condition is that said material does not interfere with the conductive heating means, and that said material is SPM-resistant. If the members were made of an electrically conductive material, they would pickup part of the magnetic field generated by the conductive heating means, thus taking away thermal power from catalyst elements 201. This would downgrade the efficiency of element 201 acting as a catalyst and heat transfer element at the same time. It is therefore deemed imperative that the catalyst element carrying and supporting structure with members 401, 402 and 404 is made of a non-magnetic SPM-resistant material. Examples of such a material can be found in the field of fluorine-carbon plastics, where polytetrafluoroethylene or PTFE is a typical material that complies with above requirements.

Fig. 5A shows a schematic representation of a complete embodiment 400, consisting of the combined catalyst and the supporting members. In the following figure and explanatory text, this embodiment will also be referred to as catalyst module.

Fig. 5B indicates the basic setup of neutralization process means 500 for the controlled neutralization of SPM using a catalyst body that can serve as heating transfer means also. The catalyst with supporting and positioning means is indicated in a schematic manner as catalyst module 400, where it is assumed said embodiment is constructed and shaped such that it allows for conductive heating. The vessel is represented as a cylindrical closed tank 501, with an interior supporting and centring member 502, which preferably is (but is not limited to) a cylindrical member also. Tank 501 is provided with an SPM supply unit 505, a gas disposal unit 506, and an SPM disposal unit 507. Exact shape and location of said means is not to scale in Fig. 5. Around centring member 502 a set of catalyst modules 400 is now positioned, where the number of modules in this figure is for clarifying purposes only. Modules 400 must be positioned inside vessel 501 such that they are centred, where it can be advantageous to have modules 400 touching the inner side of the walls of tank 501, for SPM flow guidance. This however is not strictly necessary. With respect to vertical positioning, it can be understood that the exact vertical position of each module 400 in each tank may be varied, as long as these modules are within the SPM volume. However, as was explained previously, the vertical position of each module 400 with respect to adjacent modules can be important to provide enough catalyst-free space for the SPM to neutralize in a controlled and correct manner. This inner spacing between modules can be set and fixed by using spacer means between modules 400, or, by shaping the centring unit of module 400 (member 404 in Fig.4) such that stacking the modules vertically leads to the desired spacing between modules.

Another consideration regarding the vertical position of (some of) the modules 400 in tank 501 follows from the application of conductive heating. To generate an electro-magnetic field inside tank 501, external coils 503 and 504 are placed outside and around tank 501, in such a way that they can heat the two bottom modules 400. For clarity reasons only two coils are drawn here, but the number of coils (and thus the number of heated modules 400) can be higher than two, but no less than one, if deemed necessary for the neutralization process. Experiments have shown that the most effective electro-magnetic coupling between outside coils 503 and 504 and the respective modules 400 takes places when the module 400 is placed at the same vertical position as the outside coil, when looking at their horizontal centre lines. A last remark regarding Fig. 5 is aimed at the exact configuration of modules 400 inside tank 501: following from this figure one could deduce that all modules 400 in tank 501 are exactly the same in terms of materials, dimensions and configuration. Although this could apply to materials used in modules 400, it can alternatively be deemed necessary to for example change certain configurations or dimensions in the modules that are subjective to conductive heating, so as to be able to withstand loads resulting from thermal deformation or electro-magnetic effects.

Fig. 6 shows a preferred embodiment 514 of neutralization process means 500. For clarity, just four modules 400 are shown, but the applied number of modules in a tank 501 can be adjusted to process requirements and dimensions of said tank. Again, also for clarity, only two external conductive heating coils 503 and 504 are indicated, resulting in the two bottom modules 400 being of the heated type, and therefore possibly different in certain aspects of configuration than the non- heated modules 400.

With respect to the location and application of supply and disposal interfaces, Fig. 6 shows the use of a removable top lid 510 to tank 501. A removable top lid provides easy access to tank 501 and the inside content; to assure correct positioning and fixation of top lid 510 on tank 501, the top lid and tank will be equipped with the necessary means, which for clarity purposes are not shown in Fig.6. In top lid 510 oxygen disposal 506 is located, in the shape of a hole through the lid. Attached to the centre of the bottom side of the top lid is centring and support member 508. Said member differs from previous member 502 shown in Fig. 5, in the way that member 508 is equipped with an internal channel for fluid transport. Top lid 510 has SPM supply hole 505 placed in the centre of the top lid, such that supply 505 aligns with the liquid channel inside member 508. Said member is not attached to the interior of the bottom of tank 501 but is only attached to top lid 510. Member 508 has a length such that when top lid 510 is placed on top of tank 501, the end part of member 508 remains at a short distance (5-20 mm) from the bottom of the tank. The channel inside member 508 now forms a supply for SPM at the bottom of tank 501. By placing the SPM disposal exit 507 in the top region of tank 501, a flow of SPM with direction bottom -to-top is generated inside tank 501. Experiments have shown that this flow direction is preferred with respect to the neutralization process stability and control. The main cause for this preferred flow direction is linked to the formation of oxygen bubbles in the heated SPM: these bubbles combined with the heat create a strong vertical upward flow (caused by convection), with a turbulence gradient that allows for better exposure of the SPM to all the modules’ 400 catalyst surfaces. However, it can be determined that for certain SPM concentrations a top-to-bottom flow is preferred: this can be realized by for example the obvious operation of reversing the function of 507 and 505.

As a result of the positioning of SPM supply 505 at the bottom of tank 501 and SPM disposal exit 507 at the top section, a volume of SPM is retained in the tank. To evacuate this volume, when neutralization is ready, a first option is to use SPM supply 505 (through member 508) now as an evacuation means, by applying a suction force on it. A preferred option is to place an additional disposal exit 512 at the bottom part of tank 501. Opening 512 will drain the retained SPM out of tank 501 without the need for any pumping means.

At the bottom part of member 508 a retainer 509 is placed: this retainer can be easily removed and installed on member 508. By removing retainer 509, modules 400 can be installed around member 508, as was explained before in Fig. 5B. Placing of said modules can be done when top lid 510 is removed from tank 501. After loading member 508 with the necessary number of modules 400, retainer 509 is positioning and fastened, to lock said modules in place. Now the top lid, including the modules 400 can be placed as one unit on tank 501. The location of the retainer 509 is such that the modules that are used as heating transfer means are now positioned correctly with respect to external induction coils 503 and 504. This correct position is indicated in Fig. 6 by induction coil centre line 511; this centre line must align with the horizontal centre line of catalyst elements 201 in the respective module 400 that is located inside said induction coil.

Execution of the complete neutralization process in a single process vessel 500 (or preferred embodiment 514) is possible but would require many modules 400. Experiments have shown that for a variable SPM concentration between 3% and 6% hydrogen peroxide content, the number of modules 400 needed would vary between 15 to 40. Stacking such amounts of modules in one single tank 501 would require a tank height that does not match the available sizes of raw material, will lead to a high physical vertical process footprint and will have a negative effect on the robustness and controllability of the process, as exothermic effects can directly affect the SPM volumes in the upper part of the tank. Experiments have shown that placing several process means 500 (or suitably 514) with a limited amount of modules 400 (for example between 10 and 14 modules per tank) in series will lead to a more efficient footprint of the process, while maintaining a controlled and robust neutralization process. To place two process means 500 (or 514) in series would mean that the SPM disposal exit 507 of the first means 500 would have to be connected to the SPM supply unit 505 of the second process means 500. Such connection could lead to the necessity of pumping means between the two vessels, or for example to placing the second means lower than the first, so the SPM transfer could be driven by gravity. A preferred series connection is shown in Fig. 7, where the first vessel of embodiment 514 is connected to a second vessel 700. Said second vessel has a modified top lid 702, where SPM supply 505 is removed. Instead, the SPM supply is now moved to the side of the vessel, as supply 703 in Fig.7. Supply 703 is located such that it is connected with the internal channel in member 508, so as to provide SPM to the bottom of the vessel, as described in previous figures. This preferred SPM supply configuration now allows for series connection of multiple vessels without the need of pumping means between said vessels.

The SPM transport 701 between vessels is based on the overflowing of SPM from one vessel into the next. As a remark: the first vessel in Fig. 7 is indicated as embodiment 514 but can also be a vessel of a 700-embodiment.

Fig. 8 shows a 3-vessel series stack 800, with peripheral means to transform said series stack into a functional and applicable batch wise SPM-neutralization process.

SPM pumping means 801 is introduced, where said pump output or pressure port is connected to the SPM supply port in the first vessel in the series stack by SPM transport line 808. The inlet or suction port of pump 801 is connected to the SPM disposal exit of the last vessel in the series stack by SPM transport line 807. In this way pump 801 can recycle the SPM several times over the series stack, until the desired neutralization grade is reached.

Furthermore, circuit 806 is introduced, allowing for oxygen removal from all vessels comprised in the series stack, by connecting all oxygen exits in said vessels in parallel onto one single exit. It was explained before that the oxygen evacuation can be driven by the neutralization process pressure itself, but assistance of for example pumping means in this circuit can be required by the process operator because of safety issues. However, such pumping means are not indicated in Fig. 8 for clarity.

Circuit 809 with single-way valves 804 and 805 allows for draining of the vessels implied in installation 800; the draining process from each vessel is assumed to be gravity-assisted, although pumping means could also be used if deemed necessary. In Fig. 8 the draining circuit is connected to 4-way valve 803 : this preferred configuration allows the drained liquid to be pumped out of the installation 800 by using pump 801 in combination with 3-way valve 802. When the draining circuit is activated by opening valves 804 and 805, valve 803 will set itself to the position where the drained liquid can enter the suction side of pump 801. Pump 801 is started, and on the pressure side of the pump valve 802 will switch to a position where the drained liquid is exiting the installation using outflow line 810. In this manner, the installation and lines can be drained completely after the neutralization process is finished, or whenever it is deemed necessary to evacuate all liquid from installation 800.

In a similar way, pump 801 in combination with valve 803 and valve 802 can be used to fill the vessels and lines of installation 800. When activating this filling procedure, valve 803 switches to a position where liquid intake 811 is connected to the suction side of the pump. At the same time, valve 802 switches to the position where the pressure side of the pump is now connected with intake line 808 that is connected to the inlet of the first vessel. When liquid input line 811 is connected to a tank containing SPM, starting the pump 801 will now result in SPM being pumped into vessel 514, and subsequently into proceeding vessels 700 (by means of the overflow connections 701). Level sensing means 814 detects when the last vessel is filled and stops pump 801. When the last vessel is filled, valve 803 switches to the position where the last vessel outlet line 807 is connected to the suction side of pump 801. The system is now ready to start a batch wise neutralization process.

When the batch wise neutralization process is started, induction heating coils 503 and 504 are activated to heat up the SPM solution inside the vessel around which the coils are installed. In Fig. 8 said induction coils are indicated as present in the first and the last vessel, this is for illustration purposes only. The exact location and the total amount of induction coils used in installation 800 depends among other things on the volume of SPM that has to be neutralized, and the concentration of hydrogen peroxide in this volume when the neutralization process is started.

The exact method of control of the induction heating depends on several parameters, for example the concentration of hydrogen peroxide in the SPM, the total volume of SPM stored in a vessel, the total amount of vessels implied, the amount of modules 400 installed in each vessel, and the flow of the SPM through the vessels.

Without describing the complete control logic for an installation 800 as shown in Fig. 8, it is mentioned here that the main control logic regarding the induction heating is based on temperature sensing at certain location(s) in the neutralization process, by means of the introduction of SPM-resistant temperature sensors 812. For illustration purposes, in Fig. 8 a sensor 812 is positioned in the intake line 808, so the temperature of the SPM before it enters vessel 514 is measured, which is the temperature of the SPM before exposure to induction heating at the bottom of said vessel. It can be understood that such temperature reading can serve as input for a power supply to the induction coils, where a higher temperature reading results in a lower power input to said coils. A temperature reading close to the boiling point of the hydrogen peroxide in the SPM solution could even result in temporal removal of power supply to the induction heating, to avoid uncontrolled exothermic neutralization of the SPM.

Above control strategy is based on the known and measured response of SPM to heating as a function of its temperature. To enable such control strategy, it is necessary to know the actual concentration of hydrogen peroxide in an SPM solution; for this purpose, a sensor 813 is installed which can measure this concentration. The location in output line 807 of this sensor in Fig. 8 is for illustration purposes only, here sensor 813 would measure the resulting hydrogen peroxide concentration of the SPM after a neutralization pass through all vessels. The actual measured concentration of hydrogen peroxide, in combination with its temperature measured by sensor 812, can be used to set the induction coil power supply. As a secondary result, the sensor 813 can also be used to measure when the remaining concentration of hydrogen peroxide has fallen below a certain desired level during the neutralization process, indicating that the neutralization process is completed.

As the measurement of the concentration of hydrogen peroxide in an SPM solution is a complex and costly process, an alternative control strategy can be based on (but control strategies are not limited to) temperature measurement only. Here, in the installation of Fig. 8 an additional temperature sensor 815 is introduced, at a position which is for illustration purposes only. Sensor 815 is positioned such, that it can measure the SPM temperature at a location downstream of the induction coils. With this setup, the power supply to the induction coils can be controlled by either the difference between the temperature of sensor 812 and 815, and/or by the absolute reading of both sensors. The concentration of hydrogen peroxide concentration in the SPM is not known in this control management strategy but it can derived from the response of the SPM to heat input as measured by temperature difference. An SPM solution with a relatively high content of hydrogen peroxide will need less heat input to generate a higher temperature difference over the coil, because of a stronger exothermic reaction.

From experiments performed by applicant it has been shown that in an apparatus wherein the contactor modules serve both for induction heating and as catalyst by including a catalyst module the rate of heating the Piranha etch or sulfuric peroxide mixture may become too high; or even uncontrollable. This introduces a risk of the neutralisation process running in an explosive manner. The use of induction heating further requires a degree of magnetic permeability of the material of the contactor module and included catalyst module, which is satisfied by certain precious metals, such as platinum, gold and rhodium. During the catalyst process oxygen is bound to the surface of each catalyst module, which oxygen is then prevented from recomposing with water to form peroxide again. Hence, the neutralisation reaction runs in proximity of the catalyst module faster and in a more defined manner than in prior art apparatuses. As a result, the surface of the catalyst module may become covered or even saturated by oxygen thereby reducing the effectiveness of the peroxide neutralisation process. In further experiments, applicant has shown that the heating of the catalyst module increases the release of oxygen from the catalyst surface, as indicated by small bubbles growing on the surface of the catalyst module until released and rising to the upper surface of the solution. In this manner; the oxygen escapes the solution instead of flowing back in the mixture and recomposing with water to peroxide.