Brushes may be used to gently abrade desired surfaces, including in some cases pads for chemical - mechanical polishing. This process of pad conditioning is an important component of wafer planarization, and defects introduced by pad conditioning can affect the end state of the wafer.

Summary

In one aspect, the present description relates to a pad conditioning brush. The pad conditioning brush includes a carrier layer and a plurality of brush bristles extending from the carrier layer. The plurality of brush bristles are abrasive particle-free, and the carrier layer and the plurality of brush bristles form a unitary body. The pad conditioning brush has sufficient stiffness to texture a chemical mechanical polishing pad with a hardness of 20 Shore A.

In another aspect, the present description relates to a method of conditioning a chemical mechanical polishing pad. The method includes providing a chemical mechanical polishing pad, providing a pad conditioning brush, contacting the pad conditioning brush to the chemical mechanical polishing pad, and texturing the chemical mechanical polishing pad. The pad conditioning brush includes a carrier layer and a plurality of brush bristles extending from the carrier layer. The plurality of brush bristles are abrasive particle-free, and the carrier layer and the plurality of brush bristles form a unitary body. The pad conditioning brash has sufficient stiffness to texture a chemical mechanical polishing pad with a hardness of 20 Shore A.

In yet another aspect, the present description relates to a method of conditioning a chemical mechanical polishing pad. The method includes providing a pad conditioner including a unitary working surface that is metal-free and abrasive particle-free, providing a chemical mechanical polishing pad, contacting the pad conditioner to the chemical mechanical polishing pad, and texturing the chemical mechanical polishing pad.

Brief Description of the Drawings

FIG. 1 is a schematic top plan view of a pad conditioning brush.

FIG. 2 is a schematic side elevation cross-section of a pad conditioning brash.

FIG. 3 is a graph showing the residual concentration of slurry on a pad for no brash, Comparative Example 1, Example 1, and Example 2.

FIG. 4 is a graph showing the residual concentration of slurry on the brash for Comparative Example 1, Example 1, and Example 2.

FIG. 5 is a graph showing the pad wear rate and bristle wear rate for Examples 3-5.

FIG. 6 is a graph showing the oxide removal rate across 200 wafers for Comparative Example 2, Example 6, and Example 7 during a ceria polishing process.

FIG. 7 is a graph showing defect rates across 200 wafers for Comparative Example 2, Example 6, and Example 7 after a ceria polishing process. Detailed Description

Conventional pad conditioners such as those including a bulk abrasive material have certain challenges as wafer polishing processes become less tolerant of damage or errors introduced by the components. For example, abrasive grains (such as diamonds) may become loose as the pad conditioner wears and may deposit those extremely hard grains into the overall polishing system. Particularly for an in- situ process, wherein the chemical -mechanical polishing (CMP) pad is being conditioned and polishing a wafer simultaneously, introducing foreign material may have downstream effects. For example, it may enter the slurry and become part of the abrasive system in contact with the wafer. While the wafer polishing mechanism needs to be very carefully controlled, the introduction of a foreign abrasive object may cause scratches or otherwise introduce defects into the process. Metal ions in conventional pad conditioners may also react with other polishing system components and result in contamination or other downstream defects.

Alternatively, brushes made through a flocking process or otherwise where the bristles are attached by an adhesive to a surface of a brush carrier have utility within polishing processes as well. The material, dimensions, and density of the bristles may be tuned to achieve a wide range of desired parameters and may be especially suitable for soft pads. However, similarly to conventional abrasive pad conditioning disks, bristles can become detached from the surface of the conditioning brush and enter the abrasive system in contact with the wafer. This also may result in scratches or other defects on the otherwise polished wafer.

Pad conditioning brushes as described herein may surprisingly provide many of the advantages of a conventional brush while significantly reducing the defect rate when used in a polishing system. Surprisingly, these brushes — while in some embodiments being abrasive particle -free, and in some embodiments being metal-ion free (for purposes of this description, metal-ion free means that less than 1 ppm of trace metals are present) — still demonstrate sufficient stiffness to texture chemical mechanical polishing pads on par with conventional pad conditioners. And, the pad conditioning brushes being a unitary body (including carrier layer and bristles) means that bristles will not fall out because of delamination or adhesive failure, in many embodiments greatly reducing the risk of broken bristles or separated bristles entering the abrasive system in contact with the wafer.

FIG. 1 is a schematic top plan view of a pad conditioning brush. Pad conditioning brush 100 includes carrier layer 110 with top surface 120. Bristles 122 extend from top surface 120 of carrier layer 110. Pad conditioning brush 100 may be any overall shape and size. Typically, a pad conditioner size may be prescribed by the particular polishing system in use. In some embodiments, the pad conditioning brush may be approximately 3-6 inches in diameter. In some embodiments, the pad conditioning brush may be 3.75, 4, or 4.25 inches in diameter. In some embodiments, the pad conditioning brush may have a substantially circular shape to avoid asymmetries or vibrations at high rotational speeds. Although these are typical shapes and sizes for current pad conditioners, the shape and size of the pad conditioning brush is not particularly limited While not expressly illustrated, the pad conditioning brush may include mechanisms for attachment to a suitable polishing apparatus, including mechanical means for securely attaching the pad conditioning brush to a pad conditioner arm, including mounting points, retaining rings, or adhesives. In some embodiments, pad conditioning brush may include a rigid backplane in which the carrier layer is mounted. This backplane may be formed from any suitable material and along with the carrier layer may have any suitable dimension depending on the particular application, e.g., for easy substitution with heavier, conventional conditioning disks. For example, in some embodiments the pad conditioning brush may include a stainless steel frame as a backplane. The carrier layer may be adhered or otherwise attached (including with a mechanical or frictional fit) to the backplane. Either the carrier layer or the backplane may be selected for one or more mechanical or material properties, like stiffness, thermal conductivity, or chemical resistance.

Carrier layer 110 has at least one major surface, representing in FIG. 1 by top surface 120. Protruding or extending out of carrier layer 110 (in particular, from top surface 120) are bristles 122. In some embodiments, carrier layer 110 and bristles 122 are formed from the same process and formed from the same material. In some embodiments, carrier layer 110 and bristles 122 are formed from the same material. In some embodiments, bristles are on both major surfaces of the carrier layer. Bristles 122 may have any suitable shape, size, and distribution on top surface 120. In some embodiments, bristles 122 may vary one or more of their size, shape, and density along one or more directions in the plane of top surface 120. For example, the size of bristles 122 may change as a function of distance from the center of pad conditioning brush 100. The change can be smooth, step-wise, or even pseudorandom. In some embodiments, pad conditioning brush 100 is divisible into zones, which each zone containing bristles having certain properties in common. The zones may be any shape, such as portions of arc (e.g. pie- or wedge-shaped segments), zones bounded by inner and outer radii (e g., rings or annular sections) or even a combination of each. In some embodiments, a zone near the outermost section of pad conditioning brush 100 may include taller bristles. These bristles may preferentially interact with a pad during a break-in period, until those bristles are worn such that the height is even with other bristles on the pad conditioning brush. In some embodiments, there may be one or more sections of pad conditioning brush 100 that substantially do not contain bristles. These areas may be left substantially free of bristles in order to accommodate other functional parts of the pad conditioning brush: e.g., a centered hole to accommodate a spindle. In some embodiments, more than 1000 bristles are present on the pad conditioning brush. In some embodiments, more than 1500 bristles are present on the pad conditioning brush. In some embodiments, more than 2000 bristles are present on the pad conditioning brush. In some embodiments, more than 2500 bristles are present on the pad conditioning brush. In some embodiments, more than 3000 bristles are present on the pad conditioning brush.

In some embodiments, carrier layer 110 and bristles 122 form a unitary body. In some embodiments, the carrier layer and the bristles are formed during the same injection molding process or even step. In some embodiments, the carrier layer and the bristles contain substantially no adhesive to remain attached to one another.

Ranges of suitable dimensions and shapes for bristles 122 are more completely described in conjunction with the schematic side elevation cross-section of FIG. 2. FIG. 2 shows pad conditioning brush 200 including carrier layer 210 and bristles 222 extending from top surface 220 of the pad conditioning brush. Each bristle can be roughly characterized as having a height, h, shown in FIG. 2 as extending from the top surface (not including a bristle) of carrier layer 210 to the tip peak of the bristle. The bristle in FIG. 2 is illustrated as having a flat truncated peak but a myriad of geometries and tip shapes are contemplated. For example, bristles may include a sharp peak, a multi-tip peak, a beveled peak, a rounded peak, a square peak, a sloped peak, a roughened peak or the like. In some embodiments, the bristle tapers away from the top surface of the carrier layer. In some embodiments, this taper is a straight taper (as in a cone or pyramid) and in some embodiments this taper is more complex, having a non-linear taper or more than one degree of taper incorporated into its shape.

The bristles may also be characterized as having a base width. The base width, illustrated in FIG. 2 as w, may be described as the dimension of the bristle having the greatest extent. In a circular or substantially circular shape, this may be equal to the diameter of the bristle. In more complicated elliptical or polygonal shapes, the base width may not be equal to but may be approximated by the equivalent circular diameter (e.g., the diameter of a circle having the same area as the actual base of the bristle) of the shape at its base. Each of the height, the base width, and the ratio between the two (referred to as the aspect ratio of the bristle) are important in designing and selecting the appropriate geometry depending on the desired application and performance. In some embodiments, the bristles have a tip width (i.e., the minimum width in a tapered shape) which may be used as the basis for the aspect ratio, instead of the base width. In some embodiments, the average between the base width and the tip width may be used as the basis for the aspect ratio. In some embodiments, the maximum aspect ratio for a bristle for any of its widths (i.e., for a tapered shape, typically the width at the tip) may be used. As the aspect ratio may be used as a parameter to measure mechanical properties and manufacturability (particularly the tendency for bristles to break in manufacturing or be otherwise unmoldable, with the higher the aspect ratio, the higher the difficulty), the definition of the ratio may depend on the particular application and requirements. In some embodiments, the bristle heights may be between 1 mm and 10 mm. In some embodiments, the bristle heights may be between 1 mm and 5 mm. In some embodiments, the bristle heights may be between 2 mm and 4 mm. In some embodiments, the bristle heights may be between 3 and 4 mm. In some embodiments, suitable aspect ratios for bristles may be greater than 1.5: 1. In some embodiments, suitable aspect ratios for bristles may be from between 1.5:1 and 8:1. In some embodiments, suitable aspect ratios for bristles may be from between 1: 1 and 10: 1. In some embodiments, suitable aspect ratios for bristles may be from between 1:1 and 20: 1.

For injection molding processes, the particular geometry and design of the bristles may be limited by practical considerations. For example, a bristle design that tapers toward the top surface of the carrier layer, even assuming a frictionless mold and no adhering, may be difficult or impossible to remove with conventional molding techniques without significantly damaging the integrity and fidelity of the molded features. The skilled person will also recognize that some mold designs may not have high reproducibility because the material filling the mold may not reliably fill the entire volume of the cavity. Certain features may be theoretically possible but commercially impractical: for example, multi-part molds that can be disassembled to release the molded parts. Overall, the bristles may have a regular shape, including cylindrical, conical, tetrahedral, or other shapes including a polygonal cross section. In some embodiments, the bristles may have an irregular shape or include a combination of shapes (either from bristle to bristle or within a single bristle). For example, a bristle may include a cross section having both a curved portion and a straight portion.

Using an injection molding process, the bristles and the carrier layer may be formed from any suitable material. In some embodiments, the material includes a thermoplastic material. In some embodiments, the material includes a thermoset or elastomeric material. In some embodiments, the material is hydrophobic. In some embodiments, the material is hydrophilic. In some embodiments, the material includes a polyolefin. In some embodiments, the material includes polypropylene. In some embodiments, the material includes a polystyrene. In some embodiments, the material includes polyurethane. In some embodiments, the material includes polyphenylene sulfide. In some embodiments, the material includes polyaryletherketone. In some embodiments, the material includes polyether ether ketone. In some embodiments, the material includes a polyester. In some embodiments, the material includes polyethylene. In some embodiments, the material includes polyethylene terephthalate. In some embodiments, the material includes a polyamide. In some embodiments, the material includes an aliphatic polyamide. In some embodiments, the material includes a nylon. In some embodiments, the material includes a fluorinated polymer. In some embodiments, the bristles include a second material at least partially overlaying the first material. These configurations may be useful to provide a break-in period with the pad conditioning brush wherein the second material wears away, exposing the first material underneath.

In some embodiments, the material for the injection molding process may be selected for its rheological, processing, and/or ultimate mechanical properties. For example, the material for the injection molded process may have a sufficiently low glass transition temperature (in its bulk) or melting point such that the material can be properly manipulated and molded. In some embodiments, the material for the injection molding process has a flexural modulus between 0.1 GPa and 5.0 GPa. In some embodiments, the material for the injection molding process has a flexural modulus between 0.1 GPa and 2 GPa. In some embodiments, the material for the injection molding process has a flexural modulus between 0.2 GPa and 1.8 GPa. In some embodiments, the material for the injection molding process has a hardness of at least 30 Shore A. In some embodiments, the material for the injection molding process has a hardness of at least 50 Shore A. In some embodiments, the material for the injection molding process has a hardness of at least 75 Shore A. In some embodiments, the material for the injection molding process has a hardness of at least 100 Shore A. In some embodiments, the material for the injection molding process has a hardness between 50 Shore A and 100 Shore D. In some embodiments, the material for the injection molding process has a hardness between 50 Shore A and 150 HRR (Rockwell Hardness, R scale).

The formation of an appropriate and suitable mold for injection molding are not limited and may be performed through any conventional process. For example, etching, machining, ablating, microreplicating, electrical discharge machining, sintering, molding, embossing, or others may be used. Additive manufacturing processes such as 3D printing may also be used. The material for the mold is not particularly limited but should be selected to be compatible with the process requirements for the material to be molded. In some embodiments, treatments are provided on the surface of the finished mold at the time or formation or before molding of each part to aid in mold life and also help with release. Suitable release agents and treatments for injection mold parts that reduce the surface energy may include polytetrafluoroethylene coatings, nickel boron plating, polyfluoropolyether silane coatings, waxes, electroplating treatments, silicone coatings, chromium nitrate coatings, plasma treatments and other surface modifying processes, and any other suitable treatments and coatings including combinations thereof.

The material used for the injection molding process may include one or more impact modifiers. These impact modifiers may modify the mechanical properties of the resulting carrier layer and bristles. Any suitable impact modifiers may be used and may include elastomers or rubbers such as EPDM (ethylene propylene diene monomer) rubber, modified EPDM including maleic anhydride -modified EPDM terpolymer, or polyethylene octene co-maleic acid. In some embodiments, the impact modifier may be present in between 5 and 10 weight percent of the overall material. In some embodiments, the impact modifier may be present in between 5 and 70 weight percent of the overall material.

The material use for the injection molding process may include a pigment or colorant. In multishot injection molding processes, materials having different colors may be used to impart a visual indication of surface wear as color of one pigment is worn off and allows another color or level of transparency/ opacity to be visible beneath.

In some embodiments, the material used for the injection molding process may include one or more stiffening fibers. These stiffening fibers are fibers having a higher modulus than the base resin in which they are included. These fibers may include, for example, one or more of an aramid fiber or a carbon fiber. In some embodiments, the stiffening fibers may include a meta-aramid fiber. In some embodiments, the stiffening fibers may include a para-aramid fiber. In some embodiments, the stiffening fibers may include a poly( -phcnylcne-2.6-bcnzobisoxazolc) fiber. These fibers may have any suitable dimension and may be provided in any suitable concentration. In some embodiments, the material may include between 10 and 20 weight percent of a stiffening fiber. In some embodiments, the material may include between 10 and 50 weight percent of a stiffening fiber. In some embodiments, the material may include between 15 and 20 weight percent of a stiffening fiber. In some embodiments, the stiffening fibers may be less than 100 micrometers in diameter. In some embodiments, the stiffening fibers may be less than 50 micrometers in diameter. In some embodiments, the stiffening fibers may be less than 30 micrometers in diameter. In some embodiments, the stiffening fibers may be less than 20 micrometers in diameter. Short or long fiber pieces may be appropriate depending on the application (“short” meaning in this context shorter than 0.5 mm and “long” meaning greater than 0.5 mm). To achieve a sufficiently strong interface between the fiber and the rest of the material, adhesion promoters may be used on the fiber or within the material used for injection molding. The selection of the material in addition to the design of the geometry of the bristles can be altered and tuned to reach the desired performance characteristics.

While injection molding is in some embodiments an economical and easily reproduceable manufacturing process, other manufacturing techniques and processes are possible for forming the bristles and pad conditioning brushes described herein. For example, 3D-printing (or other additive manufacturing), compression molding, thermoforming, vacuum molding, rotational molding, laser drilling, diamond turning, etching, machining, ablating, microreplication, electrical discharge machining, sintering, embossing, or other suitable processes may be used to form brushes described herein. The materials used in those processes may be similar to or exhibit similar properties to those described as suitable for injection molding processes described herein.

Pad conditioning brushes as described herein may be suitable for use in both in-situ and ex-situ polishing machines, for any suitable type of pad, and with any suitable type of slurry. For example, in some embodiments, pad conditioning bmshes described herein may be suitable for use in processes including ceria-based and colloidal silica slurries. Pad conditioning brushes described herein may alternatively or additionally be suitable for use in buffing processes.

In some embodiments, pad conditioning brushes described herein may have sufficient stiffness to texture a chemical mechanical polishing pad with a hardness of 80 Shore A. In some embodiments, pad conditioning brushes described herein may have sufficient stiffness to texture a chemical mechanical polishing pad with a hardness of 65 Shore D.

Examples

Materials used in the examples were as follows:

Example pad conditioning disks were formed with the following bristle design characteristics:

Injection molding inserts

Inserts were produced from T-7075 aluminum and the bristle shapes were plunge machined with taper cutters to form the inverse of the desired brush and bristle geometry. No polishing was done before or after machining. A release coating was provided on the completed inserts to aid with mold release. Bristle features were formed as through holes to be injection molded with a backing plate in order to allow for tip venting.

Cleaning of ceria slurry from a pad

A commercially available pad brush (not injection molded) was obtained: PB33A (from 3M Company, St. Paul, Minn.) (Comparative Example 1). To compare with the brush, two injection molded pad conditioning brushes were formed:

Example 1: Nylon 12 + 50 weight percent impact modifier; design B.

Example 2: Nylon 12 + 70 weight percent impact modifier; design B.

Commercial ceria slurry, AGC 333 from AGC Electronic Materials (Tokyo, Japan) was used to polish SiC>2 wafers on a benchtop Bruker CP4 polisher (Billerica, Mass.). A 30.5” IC1010 pad (available from DuPont, Wilmington, Del.) was cut into 9” disks and were used as the pads on the benchtop polisher. A break-in was done with a 3M SI 22 conditioner at 6 pounds downforce for 30 mins. After the break-in, the pad was rinsed with water for 5 minutes and then a TEOS wafer was polished for 5 minutes in the presence of the slurry for 2 minutes. The slurry flow rate was 50 mL/min. One of the pads was rinsed with deionized water post-polish as was used as a “no brush” control. The post-polish DIW rinse was repeated along with using the different exemplary and comparative brushes to clean the pad. The pads and brushes were analyzed to measure the concentration of slurry remaining on the pads. The results are shown in FIG. 3. As can be seen, the brushes performed substantially the same as the conventional brushes.

The brushes were also measured to determine the concentration of slurry remaining on the brush. Keeping the brush clean while cleaning the pad is a useful attribute. The risk of redepositing debris back on the pad (and ultimately contacting the wafer) is relatively high, thus increasing the potential for defects on the wafers. The results are shown in FIG. 4. As can be seen, the injection molded brushes performed better than the conventional brush.

Bristle and pad wear rate

Three injection molded pad conditioning brushes were formed:

Example 3: Nylon 6,10 + 5 weight percent impact modifier; design B

Example 4: Nylon 6,10 + 10 weight percent impact modifier and 15 weight percent aramid fiber; design B.

Example 5: Nylon 6,10 + 10 weight percent impact modifier and 19 weight percent carbon fiber; design B.

A 30.5” IC 1010 pad (available from DuPont, Wilmington, Del.) was cut into 9” disks and were used as the pads on the benchtop Bruker CP4 polisher (Billerica, Mass.). Each brush was run with 6 pounds downforce for a duration of 3 hours. The platen and brush rotation speeds were set to 57 and 61 rpm, respectively. The deionized water flow rate was set to 30 mL/min.

The pad wear was measured using the height sensor on the CP4 polisher and the bristle wear was characterized by measuring the bnstle height before and after the test, using a KEYENCE VR5200 (Itasca, Ill .) structured light microscope . The results are shown in FIG. 5. As can be seen, the examples without the stiffening fibers had approximately the same pad wear rate as the examples with the stiffening fibers; however, the bristle rate was much less for each of the examples with stiffening fibers. In particular, the carbon fiber containing example showed the lowest bristle wear rate.

Ceria polishing process

A commercially available diamond abrasive was obtained: 3M S122 Diamond Pad Conditioner (available from 3M Company, St. Paul, Minn.) (Comparative Example 2). To compare with the conditioner, two injection molded pad conditioning brushes were formed:

Example 6: Nylon 6,10 + 10 weight percent impact modifier and 15 weight percent aramid fiber; design C.

Example 7: Nylon 6,10 + 10 weight percent impact modifier and 19 weight percent carbon fiber; design C.

Commercial ceria slurry, AGC 333 from AGC Electronic Materials (Tokyo, Japan) was used to polish SiC>2 wafers on APPLIED MATERIALS REFLEXION LK CMP polisher (available from Applied Materials, Santa Clara, Cal ). A 30.5” IC1010 pad (available from DuPont, Wilmington, Del.) was used. All conditioners were run at 100% in-situ at a 6 pounds downforce. A break-in was done with the pad at 6 pounds downforce for 30 mins. Platen and head speeds were set to 87 and 93 rpm, respectively, during the polish. The wafer average downforce was 3 psi and was for a duration of 1 min. The process was continued for 200 wafers where the polish rate was logged after each wafer. Removal rates are shown in FIG. 6.

As can be seen, Example 7 had a comparable removal rate to the diamond Comparative Example 2, and Example 6 had a higher oxide removal rate. The polish rates for each example were relatively stable over a run of 200 wafers (and no more unstable than Comparative Example 2).

Defect incidence per wafer was also measured using a SP2 defect inspection system (available from KLA Corporation, Milpitas, Cal.), with a threshold of 120 nm. Results are shown in FIG. 7. As can be seen, Example 7 had a comparable defect rate to the diamond pad conditioner Comparative Example 2, while Example 6 had a much lower defect count. The performance of Example 6 is even more surprising considering the increased oxide removal rate demonstrated over the same testing period.

Pad conditioning brushes as described herein may enable flexibility with process parameters. For example, enabling superior oxide removal rate over conventional conditioning options may enable other parameters, such as downforce, to be reduced, increasing component lifetime without giving up relative performance.