INTERLOCKED STEPPED RETAINING RING BACKGROUND Field [0001] Embodiments provided in this application are generally related to substrate processing systems used in semiconductor device manufacturing, and more particularly to a retaining ring used in chemical mechanical planarization (CMP) of surfaces. Description of the Related Art [0002] An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulating layers on a silicon substrate. One fabrication step involves depositing a filler layer over a non-planar surface, and planarizing the filler layer until the non-planar surface is exposed. After planarization, portions of the conductive layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. [0003] Planarization typically requires that the substrate be mounted on a carrier or polishing head of a CMP apparatus with a retaining ring. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad can be either a standard pad or a fixed-abrasive pad. A polishing liquid, such as a slurry includes abrasive particles and is applied to the surface of the polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. [0004] Retaining rings typically include an upper ring bonded to a lower ring. The upper ring is coupled to the carrier head, and the lower ring interacts with the polishing pad. On occasion, the forces experienced during repeated processing events can cause failure of the bond, and subsequent delamination between the upper and lower rings. This separation often results in complete failure of the retaining ring. [0005] Accordingly there is a need in the art for a two part retaining ring that does not delaminate under typical processing loads. SUMMARY [0006] One embodiment of the present disclosure is directed to a retaining ring assembly. The retaining ring assembly generally includes an annular upper portion and an annular lower portion. The annular upper portion includes an opposing interlocking recess, disposed between a first gap feature and a second gap feature. The opposing interlocking recess includes a first opposing interlocking recess wall positioned at a first angle and a second opposing interlocking recess wall positioned at a second angle. The annular lower portion includes a lower portion surface, a step feature disposed on the lower portion surface between an inner wall of the retaining ring and the first gap feature, and an interlocking feature, disposed on the lower portion surface between the first gap feature and the second gap feature. The interlocking feature includes a first interlocking feature wall positioned at the first angle, wherein the first angle is formed by the first interlocking feature wall relative to the lower portion surface, and a second interlocking feature wall at the second angle, wherein the second angle is formed by the second interlocking feature wall relative to the lower portion surface. [0007] One embodiment of the present disclosure is directed to a retaining ring assembly. The retaining ring assembly generally includes an annular lower portion and an annular upper portion. The annular lower portion includes an upper surface, a step feature, and an interlocking feature. The annular upper portion includes a lower surface, an opposing step recess, wherein the opposing step recess is recessed into the lower surface, a first gap feature, wherein the first gap feature is in contact with the upper surface of the annular lower portion, an interlocking recess, wherein the opposing interlocking recess is recessed into the lower surface, a second gap feature wherein the second the gap feature is in contact with the upper surface of the annular lower portion, and an adhesive disposed between the interlocking feature and the opposing interlocking recess, and disposed between the step feature and the opposing step recess. [0008] One embodiment of the present disclosure is directed to a method of forming a retaining ring. The method generally includes selectively depositing a thin film of adhesive onto an upper surface of an annular lower portion of the retaining ring, wherein selectively depositing a thin film comprises depositing a thin film on a surface and walls of an interlocking feature and a surface and wall of a step feature, and pressing the annular lower portion together with an annular upper portion of the retaining ring such that the interlocking feature and step feature are positioned within an opposing interlocking recess of the annular upper portion and an opposing step recess of the annular upper portion. BRIEF DESCRIPTION OF THE DRAWINGS [0009] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of the disclosure and are therefore not to be considered limiting of its scope, as the disclosure may admit to other equally effective embodiments. [0010] Figure 1 is an axonometric, partial cross-sectional view of a retain ring, according to one embodiment. [0011] Figure 2 is a cross-sectional view of a retaining ring, according to one embodiment. [0012] Figure 3A-3D are cross-sectional views of each region of the retaining ring in FIG.2. [0013] Figure 4 is an exploded view of the cross-sectional profile of the upper portion and the lower portion of the retaining ring according to one embodiment. [0014] Figure 5 is a method of assembling a retaining ring, according to one embodiment. [0015] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. DETAILED DESCRIPTION [0016] Embodiments provided in this application are generally related to substrate processing systems used in semiconductor device manufacturing, and more particularly to a retaining ring used in the chemical mechanical planarization (CMP) of surfaces. [0017] A retaining ring is generally an annular ring that can be secured to a carrier head of a CMP apparatus. Typically a retaining ring comprises two portions coupled to each other to form the retaining ring. Here, the retaining ring comprises an upper portion with a top surface, coupled to a lower portion with a flat bottom surface. Generally, the upper portion and the lower portion comprise different materials, as the polishing pad wears away the bottom surface of the lower portion of the retaining ring during processing. An adhesive (e.g., an epoxy) is used to join the two different materials together. Although the upper and lower portions do not initially delaminate, under certain processing conditions, and/or repeated use, the two portions can separate and cause the retaining ring to fail. [0018] To prevent delamination, and subsequent ring failure, the disclosed retaining ring comprises a thick step on the interior diameter, and an interlocking feature. The thick step on the interior diameter helps prevent delamination of the interior diameter, while the interlocking feature helps prevent delamination of the outer diameter. By including an interlocking step feature in addition the adhesive solution, the disclosed retaining ring design significantly improves the durability of the retaining ring, and reduces the likelihood of catastrophic failure due to delamination. [0019] Figure 1 is an axonometric, partial cross-sectional view of a retain ring 100, according to one embodiment. Here, the retaining ring 100 comprises an upper portion 110, formed of a rigid metal, such as stainless steel, and a lower portion 105 formed of a chemically resistant polymer material, such as polyphenylene sulfide (PPS). The upper portion 110 further comprises an upper surface 114 and a lower surface 112. The lower portion 105 further comprises a lower portion upper surface 108 and a bottom surface 106. The lower portion 105 includes an annular step feature 120 and annular interlocking feature 130 secured to the upper portion 110 by use of a thin layer of adhesive 115. [0020] The lower portion 105 further comprises a step feature 120 and an interlocking feature 130 (e.g., a dovetail). The step feature 120 and the interlocking feature 130 are used to prevent shear forces between the upper portion 110 and the lower portion 105 from causing failure of the thin layer of adhesive 115. [0021] The upper surface 114 of the upper portion 110 generally includes holes 125, with screw sheaths to receive fasteners, such as bolts, screw, or other hardware, for securing the retaining ring 100 to the carrier head (not shown). The holes 125 can be evenly spaced around the carrier head. Additionally, one or more alignment features (not shown) can be located on the upper surface 114 of the upper portion 110. If the retaining ring 100 has an alignment aperture, the carrier head can have a corresponding pin that mates with the alignment aperture when the carrier head and retaining ring are properly aligned. [0022] In some configurations, the bottom surface 106 of the lower portion 105 may have one or more recesses 145 that extend from an inner diameter D _in of the lower portion 105 to the outer diameter Dout of the lower portion 105 for allowing slurry or air to pass from the interior of the retaining ring 100 to the exterior of the retaining ring 100, or from the exterior to the interior, of the retaining ring 100 during polishing. [0023] As previously mentioned, the upper portion 110 and the lower portion 105 can be attached with a thin layer of adhesive 115. Typically, the thin layer of adhesive 115 includes either a two-part slow curing epoxy, or a high temperature epoxy solution. [0024] During polishing, the friction between the polishing pad and the retaining ring 100 creates a side load which can skew the upper portion 110 away from the lower portion 105. This action tends to pull the upper portion 110 away from the lower portion 105. In addition, a side load caused by the substrate pushing against the inner diameter D _in of the lower portion 105 increases the tension (e.g., peel force) at the inner diameter D _in of the retaining ring 100 between the upper portion 110 and the lower portion 105 of the retaining ring 100. [0025] Figure 2 is a cross-sectional view of the retaining ring 100, according to one embodiment. Here, the retaining ring 100 includes four regions: a step region 220, a first gap region 225, an interlocking region 230, and a second gap region 235. Each region is centered on a specific feature. [0026] The step region 220 includes the step feature 120, an opposing step recess 221 and part of a first gap feature 270. Here, the step feature 120 is disposed on the lower portion upper surface 108 between the inner wall 102 of the retaining ring 100 and the first gap feature 270. The step feature 120 extends vertically from the lower portion 105 into the opposing step recess 221 of the upper portion 110. The opposing step recess 221 is recessed into the upper portion 110. The opposing step recess 221 is positioned to receive the step feature 120. A thin layer of adhesive 115 separates the step feature 120 from the opposing step recess 221 and the first gap feature 270. [0027] The first gap region 225 includes the first gap feature 270, the lower portion upper surface 108, part of the step feature 120, part of the opposing step recess 221, part of the interlocking feature 130, and part of an opposing interlocking recess 231. Here, the first gap feature 270 is disposed between the step feature 120 and the interlocking feature 130 along a lower reference plane LRP. The first gap feature 270 is in physical contact with the lower portion upper surface 108 at the lower reference plane LRP. The lower reference plane LRP is coincident with the lower portion upper surface 108, and cuts horizontally from the inner wall 102 to the outer wall 103 of the retaining ring 100. [0028] The interlocking region 230 includes the interlocking feature 130, an opposing interlocking recess 231, part of the first gap feature 270, and part of a second gap feature 275. Here, the interlocking feature 130 is disposed on the lower portion surface 108 between the first gap feature 270 and the second gap feature 275. The interlocking feature 130 extends vertically from the lower portion 105 into the opposing interlocking recess 231 of the upper portion 110. Thus, the opposing interlocking recess 231 is recessed into the upper portion 110. The opposing interlocking recess 231 is positioned to receive the interlocking feature 130. The opposing interlocking recess 231 is separated from the interlocking feature 130 by a thin layer of adhesive 115. [0029] The second gap region 235 includes the second gap feature 275, the lower portion surface 108, part of the interlocking feature 130 and part of the opposing interlocking recess 231. Here, the second gap feature 275 is disposed between the interlocking feature 130 and the outer wall 103 along the lower reference plane LRP. The second gap feature 275 is in physical contact with the lower portion surface 108. [0030] Figures.3A-3D are cross-sectional views of each region of the retaining ring 100 in FIG.2. As seen in FIG.3A, the step feature 120 has a step feature wall 327A. The step feature wall 327A extends vertically from the lower portion surface 108 into the opposing step recess 221 of the upper portion 110 and terminates at a step feature surface 108A. The step feature wall 327A is joined with the step feature surface 108A at a 90 degree angle. The step feature wall 327A includes a rounded base 350 that joins the step feature wall 327A to the lower portion surface 108. Although the rounded base 350 slopes inward, the rounded base 350 can be curved at any angle. In some configurations, the step feature wall 327A can be tapered, such that it extends away from a starting point at an angle of more or less than 90 degrees. In addition, in some configurations, the joint between the step feature wall 327A and the step feature surface 108A is a rounded edge, or a joining angle of more or less than 90 degrees. [0031] The opposing step recess 221 includes an opposing step recess wall 317A, and an opposing step recess surface 112A. In this configuration, the opposing step recess wall 317A and the opposing step recess surface 112A are separated from the step feature wall 327A and the step feature surface 108A, by a gap in which a the thin layer of adhesive 115. As seen in FIG.3A, the thin layer of adhesive 115 is selectively disposed between the step feature surface 108A and the opposing step recess surface 112A. The thin layer of adhesive 115 is also disposed between the step feature wall 327A and the opposing step recess wall 317A. [0032] As seen in FIG.3B, the first gap feature 270 is in physical contact with the upper surface 108 of the lower portion 105. Here, the first gap feature 270 is in physical contact with the upper surface 108 of the lower portion 105 to fix the spacing between the step feature 120 and the opposing step recess 221, and the interlocking feature 130 and the opposing interlocking recess 231. The physical contact between the first gap feature 270 and the upper surface 108 of the lower portion 105 prevents the step feature surface 108A from contacting the opposing step recess surface 112A and an interlocking feature surface 108C from contacting an opposing interlocking recess surface 112C. As discussed further in FIG.4, the height of the first gap feature 270 can be adjusted to alter the size of the space between the step feature 120 and the opposing step recess 221, and the interlocking feature 130 and the opposing interlocking recess 231. [0033] Unlike the step feature 120, a thin layer of adhesive 115 is not needed between a first gap feature surface 112B of the upper portion 110 and a first gap feature surface 108B of the lower portion. In this configuration, the purpose of the first gap feature 270 is to fix the spacing of the interlocking feature 130 and the opposing interlocking recess 231, and the step feature 120 and the opposing step recess 221, and not to adhere the first gap feature 270 to the lower portion 105. Even though a thin layer of adhesive 115 is not needed, and no space is available for the adhesive 115 to deposit, a monolayer of adhesive (not shown) may be present. In some configurations, adhesive 115 deposited on nearby feature may spill over onto the first gap feature 270. In those configurations, a monolayer of adhesive may remain on the first gap feature surface 112B after the upper portion 110 and lower portion 105 are joined together. [0034] Although there is no space between the first gap feature surface 112B of the upper portion and the first gap feature surface 108B of the lower portion, a space is present on both sides of the first gap feature 270. The space between the first gap feature 270 and the first interlocking feature wall 327B ₁ and the step feature wall 327A allows for a thin layer of adhesive 115 to be disposed between the first gap feature 270 and the first interlocking feature wall 327B1 and the step feature wall 327A. When joined together, the space between the first interlocking feature wall 327B ₁ and the step feature wall 327A prevents the unwanted displacement of the thin layer of adhesive 115. As seen further in FIG. 3B, the first interlocking feature wall 327B1 extends outwardly from the lower portion surface 108 at an angle θ and terminates at the interlocking feature surface 112C. The angle θ of the first interlocking feature wall 327B1 can be any angle on an X-Y plane greater than 0 and less than 90 degrees. For example, the angle θ can be between about 60 degrees and about 30 degrees, such as about 60 degrees, about 55 degrees, about 50 degrees, about 45 degrees, about 40 degrees, about 35 degrees or about 30 degrees. The interlocking feature 130 is further discussed in FIG.3C below. [0035] As seen in FIG.3C, the interlocking feature 130 extends vertically from the lower portion surface 108 into the interlocking recess 231 of the upper portion 110. The interlocking feature 130 has a first interlocking feature wall 327B ₁ and a second interlocking feature wall 327B ₂ . The first interlocking feature wall 327B ₁ is disposed adjacent to the first gap feature 270. The second interlocking feature wall 327B2 is disposed adjacent to the second gap feature 275. Both the first interlocking feature wall 327B ₁ and the second interlocking feature wall 327B ₂ extend vertically into the upper portion 110 at an angle θ of between 60 degrees and 30 degrees relative to the adjacent surface. The first interlocking feature wall 327B1 extends vertically between the lower reference plane LRP and the interlocking feature surface 108C. The second interlocking feature wall 327B2 extends vertically between the lower reference plane LRP and the interlocking feature surface 108C. Both the first interlocking feature wall 327B ₁ , and the second interlocking feature wall 327B ₂ terminate at the interlocking feature surface 108C and form an interlocking feature 130 (i.e., dovetail). The height and width of the interlocking feature 130 are further discussed in FIG. 4. As seen in FIG. 3C the first interlocking feature wall 327B ₁ extends in a first direction along an X-Y plane away from a first point at an angle θ of between 60 degrees and 30 degrees in the positive X direction and positive Y direction. For example, the first interlocking feature wall 327B1 can extend vertically from a starting point positioned on an X-Y axis in the positive Y direction, at an angle θ of 45 degrees relative to the surface of the first gap region (positioned along the positive X axis). The second interlocking feature wall 327B2 extends in a second direction along an X-Y plane away from a second point at an angle in the negative X direction and positive Y direction. For example, the second interlocking feature wall 327B2 can extend vertically from a starting point positioned on an X-Y axis in the positive Y direction, at an angle of 45 degrees relative to the surface of the second gap region (positioned along the negative X axis). The angle θ of the first interlocking feature wall 327B1, and the angle θ second interlocking feature wall 327B2 can be the same, but do not have to be. The angle θ of either the first interlocking feature wall 327B ₁ or the second interlocking feature wall 327B ₂ or both can be any angle on an X-Y plane greater than 0 and less than 90 degrees. For example, the angle θ can be between about 60 degrees and about 30 degrees, such as about 60 degrees, about 55 degrees, about 50 degrees, about 45 degrees, about 40 degrees, about 35 degrees or about 30 degrees. [0036] The opposing interlocking recess 231 includes a first opposing interlocking recess wall 317B ₁ , and a second opposing interlocking recess wall 317B ₂ . The opposing interlocking recess 231 further includes the opposing interlocking recess surface 112C. The first opposing interlocking recess wall 317B1, the second opposing interlocking recess wall 317B ₂ , and the opposing interlocking recess surface 112C are separated from the first interlocking feature wall 327B1, the second interlocking feature wall 327B2, and the interlocking feature surface 108C by the thin layer of adhesive 115. As seen in FIG. 3C, the thin layer of adhesive 115 is selectively disposed between the interlocking feature surface 108C and the opposing interlocking recess surface 112C. A thin layer of adhesive 115 is also selectively disposed between the first interlocking feature wall 327B ₁ , and the second interlocking feature wall 327B ₂ , and the first opposing interlocking recess wall 317B ₁ and the second opposing interlocking recess wall 317B2. [0037] As seen further in FIG. 3C, the interlocking feature surface 108C is separated from the opposing interlocking recess surface 112C by a thin layer of adhesive 115. The thin layer of adhesive 115 extends along the interlocking feature surface 108C. The thin layer of adhesive 115 also separates the first interlocking feature wall 327B ₁ from the first gap feature 270 of the upper portion 110, and separates the second interlocking feature wall 327B2 from the second gap feature 275. [0038] As seen in FIG.3D, the second gap feature 275 is in physical contact with the lower portion 105. Here, the second gap feature 275 is in physical contact with the lower portion 105 to fix the spacing between the interlocking feature 130 and the opposing interlocking recess 231. The physical contact between the second gap feature 275 and the lower portion 105 prevents the interlocking feature surface 108C from contacting the opposing interlocking recess surface 112C. As discussed further with respect to FIG.4, the height of the second gap feature 275 can be adjusted to alter the size of the space between the interlocking feature 130 and the opposing interlocking recess 231. [0039] Unlike the interlocking feature 130, a thin layer of adhesive 115 is not needed between the second gap feature surface 112D of the upper portion and the second gap feature surface 108D of the lower portion 105. In this configuration the purpose of the second gap region 235 is to fix the spacing of the interlocking feature 130, and not to adhere the second gap feature 275 to the lower portion 105. Even though a thin layer of adhesive 115 is not needed, and no space is available for the adhesive to deposit, a monolayer of adhesive (not shown) may be present. In some configurations, adhesive deposited on nearby features may spill over onto the first gap feature. In those situations, a monolayer of adhesive may remain on the second gap feature surface 112D after the upper portion 110 and lower portion 105 are joined together. [0040] FIG.4 is an exploded view of the cross-sectional profile of the upper portion 110 of the retaining ring 100 and the lower portion 105 of the retaining ring 100 according to one embodiment. As seen in FIG.4, the lower portion 105 includes the step feature 120, and the interlocking feature 130. The upper portion 110 includes the opposing step recess 221, the first gap feature 270, the opposing interlocking recess 231, and the second gap feature 275. [0041] The step feature 120 includes a step feature height SFH and a step feature width SFW. The step feature height SFH is the vertical length of the step feature measured from the lower reference plane LRP to the step feature surface 108A. The step feature width SFW is the horizontal length of the step feature 120 measured from the inner wall 102 to step feature wall 327A. In this configuration, the step feature height SFH is greater than the step feature width SFW. Typically, the ratio of the step feature height SFH to the step feature width SFW is about 2:1. However, the ratio (of the step feature height SFH to the step feature width SFW) can be any ratio so long as the step feature height SFH is greater than the step feature width SFW. For example, the ratio (of the step feature height SFH to the step feature width SFW) can be about 1.25: 1, about 1.5: 1, about 1.75:1, about 2:1, about 2.25:1, about 2.5:1, about 2.75:1, or about 3:1. [0042] The interlocking feature 130 includes an interlocking feature height IFH and an interlocking feature width IFW. The interlocking feature height IFH is the vertical length of the interlocking feature measured from the lower reference plane LRP to the interlocking feature surface 108C. The interlocking feature width IFW is the horizontal length of the interlocking feature 130 measured from the first interlocking feature wall 327B ₁ to the second interlocking feature wall 327B ₂ . In this configuration, the interlocking feature width IFW is greater than the interlocking feature height IFH. Typically, the ratio of the interlocking feature width IFW to the interlocking feature height IFH is about 1:5. However, the ratio (of interlocking feature height IFH to the interlocking feature width IFW) can be any ratio so long as the interlocking feature width IFW is greater than the interlocking feature height IFH. For example, the ratio (of interlocking feature height IFH to interlocking feature width IFW) can be about 1:3, about 1:3.5, about 1:4, about 1:4.5, about 1:5.5, or about 1:6. The interlocking feature width IFW further includes an inner interlocking feature width IFWin and an outer interlocking feature width IFW _out . The length of the inner interlocking feature width IFW _in is measured horizontally from the point where the first interlocking feature wall 327B1 meets the lower reference plane LRF, to the point where the second interlocking feature wall 327B ₂ meets the lower reference plane LRF. The length of the outer interlocking feature width IFW _out is measured horizontally from the point where the first interlocking feature wall 327B1 meets the interlocking feature surface 108C to the point where the second interlocking feature wall 327B2 meets the interlocking feature surface 108C. For the interlocking feature to properly snap into position, the length of the inner interlocking feature width IFWin must be shorter than the outer interlocking feature width IFW _out . [0043] Typically, the step feature height SFH is greater than the interlocking feature height IFH, by a ratio (of the step feature height SFH to the interlocking feature height IFH) of about 2:1. However, the ratio of the step feature height SFH to the interlocking feature height IFH can be any ratio so long as the step feature height SFH is greater than the interlocking feature IFH. For example, the step feature height SFH to interlocking feature height IFH ratio can be about 1.25: 1, about 1.5: 1, about 1.75:1, about 2:1, about 2.25:1, about 2.5:1, about 2.75:1, or about 3:1. In addition, the interlocking feature width IFW is typically greater than the step feature width SFW by a ratio (of interlocking feature width IFW to step feature width STF) of about 5:1. However, the ratio of the interlocking feature width IFW to the step feature width SFW can be any ratio so long as the interlocking feature width IFW is greater than the step feature width SFW. For example, the ratio of the interlocking feature width IFW to the step feature width STW can be about 6:1, about 5.5:1, about 4.5:1, about 4:1, or about 3.5:1. [0044] As seen further in FIG.4, the opposing step recess 221 is recessed into the upper portion 110 and includes an opposing recess height OSRH and an opposing step recess width OSRW. The opposing step recess height OSRH is the vertical length measured from an upper reference plane URP to the opposing step recess surface 112A. The opposing step recess width OSRW is the horizontal length measured from the opposing step recess wall 317A to the inner wall 102. [0045] To form a space for a thin layer of adhesive 115 to be deposited between the step feature 120 and the opposing step recess 221, the opposing step recess height OSRH, and the opposing step recess width OSRW must be different than the step feature height SFH and step feature width SFW. For example, as shown and describe, the vertical length of the opposing step recess height OSRH is greater than the vertical length of the step feature height SFH, and the horizontal length of the opposing step recess width OSRW is greater than the horizontal length of the step feature width SFW. [0046] Furthermore, the opposing interlocking recess 231 is recessed into the upper portion 110 and includes an opposing interlocking recess height OIRH and an opposing interlocking recess width OIRW. The opposing interlocking recess height OIRH is the vertical length measured from the upper reference plane URP to the opposing interlocking recess surface 112C. The opposing interlocking recess width OIRW is the horizontal length of the opposing interlocking recess 231 measured from the first opposing interlocking recess wall 317B1 to the second opposing interlocking recess wall 317B ₂ . The opposing interlocking recess width OIRW further includes an inner opposing interlocking recess width OIRW _in and an outer opposing interlocking recess width OIRWout. The length of the opposing inner interlocking recess width OIRWin is measured horizontally from the point where the first opposing interlocking recess wall 317B ₁ meets the upper reference plane URF, to the point where the second opposing interlocking recess wall 317B2 meets the upper reference plane URF. The length of the outer opposing interlocking recess width OIRW _out is measured horizontally from the point where the first opposing interlocking recess wall 317B1 meets the opposing interlocking recess surface 112C to the point where the second opposing interlocking recess wall 317B ₂ meeting the opposing interlocking recess surface 112C. [0047] To form a space for a thin layer of adhesive 115 to be deposited between the interlocking feature 130 and the opposing interlocking recess 231, the opposing interlocking recess height OIRH, and the opposing interlocking recess width OIRW must be different than the interlocking feature height IFH and the interlocking feature width IFW. Typically the vertical length of the opposing interlocking recess height OIRH is greater than the vertical length of the interlocking recess height IRH, and the horizontal length of the opposing interlocking recess width OIRW is greater than the interlocking feature width IFW. [0048] To allow the interlocking feature 130 to securely fasten the lower portion 105 to the upper portion 110, the inner opposing interlocking recess width OIRWin is shorter than the outer interlocking recess width OIRW _out . The shorter width creates a barrier to joining the lower portion 105 to the upper portion 110 by requiring that the two portions be forcefully snapped into position. This act of snapping the interlocking feature 130 together with the opposing interlocking recess 231 securely fastens the lower portion 105 to the upper portion 110. [0049] FIG.5 is a method of assembling a retaining ring, such as the retaining ring 100, according to one embodiment. The method 500 generally includes selectively depositing a thin film on selective features. [0050] At activity 501, the method 500 includes selectively depositing a thin film of adhesive 115 onto the upper surface 108 of the lower portion 105. Here selectively depositing the thin layer of adhesive 115 comprises depositing the thin layer of adhesive 115 on the step feature wall 327A and the step feature surface 108A and depositing the thin layer of adhesive 115 on the interlocking feature walls 327B and interlocking feature surface 108C. [0051] At activity 502, the method 500 includes pressing the lower portion 105 together with the upper portion 110 such that the interlocking feature 130 and step feature 120 are positioned within the opposing interlocking recess 231 of the upper portion 110 and the opposing step 221 of the upper portion. [0052] While the foregoing is directed to embodiments of the present disclosure, other and future embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.