Polishing head assembly that holds the recess and cap

Abstract

To provide a polishing apparatus that optimizes flatness parameters by modulating the wafer thickness shape in a polishing process.SOLUTION: A polishing head assembly 400 for polishing of semiconductor wafers includes a polishing head 210 and a cap 240. The polishing head has a recess 238 along a bottom portion 214. The recess has a recessed surface 216. The cap is positioned within the recess, and includes an annular wall 250 secured to the polishing head, and a floor 242 joined to the annular wall at a joint. The floor extends across the annular wall, and has a top surface 244 and a bottom surface 246. The top surface is disposed at a distance from the recessed surface to form a chamber 202 between the top surface and the recessed surface. A deformation resistance of a portion of the floor proximate to the joint 290 is weakened to allow the portion of the floor proximate to the joint to deflect relative to the polishing head by a change of pressure in the chamber.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims priority based on U.S. Provisional Patent Application No. 63 / 265951, filed on December 23, 2021. All disclosures of the application on which the priority is based are hereby incorporated by reference in their entirety into this application.

[0002] This disclosure generally relates to the polishing of semiconductor wafers, particularly to a polishing head assembly having recesses and caps.

Background Art

[0003] Semiconductor wafers are typically used in the manufacture of integrated circuit (IC) chips on which circuits are printed. First, circuits are printed in a miniaturized state on the surface of the wafer. Then, the wafer is diced into circuit chips. For these miniaturized circuits, the front and back surfaces of each wafer are required to be extremely flat and parallel to ensure proper printing of the circuits over the entire surface of the wafer. To achieve this, after the wafer is cut from an ingot, grinding and polishing processes are commonly used to improve the flatness and parallelism of the front and back surfaces of the wafer. When the wafer is polished as a preparation for printing miniaturized circuits by an electron beam lithography process or a photolithography process (hereinafter, "lithography"), particularly good finish is required. The surface of the wafer on which the miniaturized circuits are printed needs to be flat.

[0004] A polishing machine typically includes a circular or annular polishing pad mounted on a turntable or platen for rotational drive around a vertical axis passing through the center of the pad, and a mechanism for holding the wafer and pressing the wafer into the polishing pad. The wafer is typically attached to the polishing head, for example, using the surface tension of a liquid or vacuum / suction. A polishing slurry, typically containing chemical abrasives and polishing particles, is applied to the pad to increase the polishing interaction between the polishing pad and the wafer surface. This type of polishing operation is typically called chemical mechanical polishing (CMP).

[0005] During operation, the pad rotates, and the wafer is brought into contact with the pad by the polishing head and pressed against the pad. For example, after polishing hundreds of wafers, if the pad becomes worn, the pad is no longer flat and instead has worn annular bands that form depressions along the polishing surface of the pad, thus reducing the wafer's flatness parameter. Such pad wear affects the wafer's flatness and can cause "dishing" or "doming," or a combination thereof, resulting in a "W-shape."

[0006] When the wafer flatness becomes unacceptable, worn polishing pads are replaced with new ones. Frequent pad replacement adds significant costs to the operation of the polishing equipment, not only due to the number of pads that need to be purchased, stored, and disposed of, but also due to the considerable amount of downtime required to replace the polishing pads.

[0007] Therefore, there is a need for polishing equipment that can optimize flatness parameters by adjusting the wafer thickness shape in doming, dishing, and + / -W shaped polishing processes.

[0008] This background technology section is intended to introduce readers to various aspects of the technology that may be relevant to the various aspects of the disclosure described and / or claimed below. This discussion is intended to be useful in providing readers with background information to better understand the various aspects of the disclosure. Therefore, these statements should be read in this context and should not be understood as an admission of prior art. [Overview of the Initiative]

[0009] In one embodiment, a polishing head assembly for polishing a semiconductor wafer includes a polishing head and a cap. The polishing head has a recess along its bottom. The recess has a concave surface. The cap is positioned within the recess. The cap comprises an annular wall fixed to the polishing head and a floor joined to the annular wall at a joint. The floor extends across the annular wall and has an upper surface and a lower surface. The upper surface is positioned at a distance from the concave surface, forming a chamber between the upper surface and the concave surface. The deformation resistance of the portion of the floor adjacent to the joint is weakened to allow the portion of the floor adjacent to the joint to flex relative to the polishing head due to pressure changes within the chamber.

[0010] In another embodiment, a polishing head assembly for polishing a semiconductor wafer includes a polishing head and a cap. The polishing head has a top and a recess along its bottom. The recess has a concave surface. Multiple holes extend from the top through the concave surface. The cap is positioned within the recess. The cap has an annular wall having multiple openings corresponding to the multiple holes. The multiple holes and corresponding openings receive fasteners for fastening the annular wall to the concave surface. The cap has a floor joined to the annular wall at a joint. The floor extends across the annular wall. The floor has an upper surface and a lower surface. The upper surface is positioned at a distance from the concave surface, forming a chamber between the upper surface and the concave surface. The floor can flex relative to the polishing head due to pressure changes within the chamber. The deformation resistance of the portion of the floor adjacent to the joint is weakened to allow the portion of the floor adjacent to the joint to flex relative to the polishing head.

[0011] In other embodiments, a polishing head assembly for polishing semiconductor wafers includes a polishing head and a cap. The cap comprises an annular wall fixed to the polishing head and a floor bonded to the annular wall at a joint. The polishing head and the cap define a chamber between the polishing head and the floor of the cap. The floor is formed of a metallic material that can flex relative to the polishing head in response to pressure changes within the chamber. The thickness of at least one of the annular wall and the floor is reduced near the joint, thereby reducing the deformation resistance of the floor near the joint.

[0012] Various improvements exist to the features described in relation to the embodiments described above. Similarly, further features may be incorporated into the embodiments described above. These improvements and additional features may exist individually or in any combination. For example, various features described below in relation to any of the illustrated embodiments may be incorporated into any of the embodiments described above, individually or in any combination. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic front view of a part of the polishing apparatus. [Figure 2] Figure 2 is a cross-sectional view of a polishing head assembly adapted for use with the polishing apparatus shown in Figure 1. [Figure 3] Figure 3 is a cross-sectional view of the polishing head assembly shown in Figure 1, which has a floor that is only partially deflected downwards. [Figure 4] Figure 4 is a cross-sectional view of an exemplary polishing head assembly adapted for use with the polishing apparatus shown in Figure 1. [Figure 5] Figure 4 is a cross-sectional view of another exemplary polishing head assembly adapted for use with the polishing apparatus shown in Figure 1. [Figure 6]Figure 6 is a cross-sectional view of yet another exemplary polishing head assembly adapted for use with the polishing apparatus shown in Figure 1. [Figure 7] Figure 7 is a cross-sectional view of another exemplary polishing head assembly adapted for use with the polishing apparatus shown in Figure 1. [Figure 8] Figure 8 is a cross-sectional view of yet another exemplary polishing head assembly adapted for use with the polishing apparatus shown in Figure 1.

[0014] Similar reference numerals in various drawings indicate the same elements. [Modes for carrying out the invention]

[0015] Generally, in embodiments of this disclosure, suitable substrates “wafers” (which may be referred to as “semiconductor wafers” or “silicon wafers”) include, for example, single-crystal silicon wafers, such as silicon wafers obtained by cutting wafers from single-crystal silicon ingots formed by the Czochralski process or the float-zone method. Each wafer has a central axis, a front surface, and a rear surface parallel to the front surface. The front and rear surfaces are generally perpendicular to the central axis. The front and rear surfaces are joined by their periphery. The wafers may have any diameter suitable for use by those skilled in the art, and include, for example, wafers with diameters of 200 mm, 300 mm, 300 mm or more, or 450 mm.

[0016] In one embodiment, a pre-roughly polished semiconductor wafer having a rough front and rear surface is first subjected to an intermediate polishing operation in which the front surface of the wafer is polished (leaving the rear surface untouched) to improve the flatness parameter or to smooth the front surface and remove handling scratches. To perform this operation, the wafer is placed against a polishing head assembly. In this embodiment, the wafer is held in place against the polishing head assembly by surface tension. The wafer is placed on the turntable of the polishing machine with the front surface of the wafer in contact with the polishing surface of the polishing pad.

[0017] The polishing head assembly attached to the polishing machine can move vertically along an axis extending through the wafer. While the turntable is rotating, the polishing head assembly moves relative to the wafer and biases the wafer towards the turntable, pressing the front surface of the wafer against the polishing surface of the polishing pad.

[0018] A conventional polishing slurry containing polishing particles and a chemical etching solution is applied to the polishing pad. The polishing pad acts the slurry on the surface of the wafer, removing material from the front surface of the wafer, resulting in a surface with improved smoothness. As an example, an intermediate polishing operation preferably removes less than about 1 micron of material from the front side of the wafer.

[0019] The wafer then undergoes a final polishing operation. In the final polishing operation, the front surface of the wafer is polished to remove fine or "micro" scratches caused by large-sized colloidal silica such as Syton® from DuPont Air Products Nanomaterials in an intermediate step, resulting in a highly reflective and damage-free front surface of the wafer. In the intermediate polishing operation, generally more material is removed from the wafer than in the final polishing operation. The wafer may be polished to a finish using the same polishing machine used to intermediate polish the wafer as described above. However, a separate polishing machine may be used for the final polishing operation. The final polishing slurry typically has an ammonia base and a low concentration of colloidal silica is injected between the polishing pad and the wafer. The polishing pad acts the final polishing slurry on the front surface of the wafer, removing remaining scratches and haze, leaving the front surface of the wafer generally highly reflective and damage-free.

[0020] Referring to FIG. 1, a portion of a polishing apparatus is schematically shown and generally designated 100. The polishing apparatus 100 may be used to polish the front surface of a semiconductor wafer W. It is contemplated that other types of polishing apparatuses may be used.

[0021] The polishing apparatus 100 includes a wafer holding mechanism, for example, a template having a backing film 110 and a holding ring 120, a polishing head assembly 130, and a turntable 140 having a polishing pad 150. The backing film 110 is disposed between the polishing head assembly 130 and a holding ring 120 that receives the wafer W. The holding ring 120 has at least one circular opening for receiving the wafer W to be polished.

[0022] In this embodiment, the wafer W is attached to and held against the polishing head assembly 130 by surface tension. To form the surface tension, the wet-saturated backing film 110 is attached to the polishing head assembly 130 with a pressure-sensitive adhesive. The backing film 110 and the holding ring 120 form a template or a "wafer holding template". The backing film 110 is generally a soft polymer pad or other suitable material.

[0023] Next, when the wafer W is pressed against the wet-saturated backing film 110, most of the water or other suitable liquid is removed or squeezed out. By squeezing out the water, the wafer is held on the backing film 110 by the surface tension and the atmospheric pressure acting on the exposed surface of the wafer. By squeezing out the water, the wafer is attached to the polishing head assembly 130.

[0024] A part of the polishing head assembly 130 has sufficient flexibility to deform in response to a change in the pressure applied to the polishing head assembly 130, and has sufficient rigidity not to deform when the wafer is pushed into the wet-saturated template. The surface tension provides a constant holding force on the surface of the wafer. Due to this constant holding force, any deformation of the polishing head assembly 130 adjacent to the wafer is directly converted into a proportional deformation of the wafer. <0000!01> The retention of the wafer W by surface tension has a function different from other known mechanisms for holding a wafer against a polishing head assembly using a flexible film or vacuum. A flexible film, as is known in the art, deforms to form a space or vacuum pocket between the wafer and the flexible film when the wafer is pressed on it. These vacuum pockets allow the film to pick up the wafer. Other films have vacuum holes connected to a vacuum to create a low-pressure area for picking up the wafer.

[0026] The polishing apparatus 100 applies force to the polishing head assembly 130, causing it to move vertically and raise or lower the polishing head assembly 130 relative to the wafer W and the turntable 140. An upward force raises the polishing head assembly 130, and a downward force lowers the polishing head assembly 130. As described above, the downward vertical movement of the polishing head assembly 130 relative to the wafer W applies polishing pressure to the wafer to bias the wafer against the polishing pad 150 on the turntable 140. When the polishing apparatus 100 increases the downward force, the polishing head assembly 130 moves vertically downward, increasing the polishing pressure.

[0027] A portion of the polishing head assembly 130, the polishing pad 150, and the turntable 140 rotate at a rotational speed selected by a suitable drive mechanism (not shown) as known in the art. The rotational speeds of the polishing pad and the turntable may be the same or different. In some embodiments, the polishing apparatus includes a controller (not shown) that allows an operator to select the rotational speeds of both the polishing head assembly 130 and the turntable 140, and the downward force applied to the polishing head assembly.

[0028] Referring to Figure 2, a polishing head assembly 200 adapted for use with the polishing device 100 is shown. The polishing head assembly 200 comprises a polishing head 200, a cap 240, and a band 270. The polishing head 210 and / or cap 240 are preferably made from a metallic material such as aluminum or steel, or may be made from other suitable structural materials. For example, the polishing head 210 and / or cap 240 may be made from cast aluminum (e.g., MIC6® aluminum casting sheet available from Alcoa). Alternatively, the cap 240 may be made from a ceramic material such as alumina, a plastic material, or a stainless steel material with a corrosion-resistant coating such as diamond-like carbon.

[0029] The polishing head 210 has a top 212 and a bottom 214 that are substantially parallel to each other. The polishing head 210 has a platform 220 and an annular member 230 extending downward from the platform 220. A concave surface 216 is formed at the bottom 214 of the polishing head 210 by the annular member 230 extending downward from the platform 220. The annular member 230 has an outer surface 232 that is substantially perpendicular to the top 212 and bottom 214 of the polishing head 210. The outer surface 232 of the annular member 230 forms the periphery of both the polishing head 210 and the polishing head assembly 200. The annular member 230 has an inner surface 234 that is angled with respect to the outer surface 232 such that the annular member 230 is thinnest at the bottom 214 of the polishing head 210. This taper of the annular member 230 provides a more rigid top section adjacent to the platform 220. In other embodiments, the inner surface 234 may be substantially parallel to the outer surface 232.

[0030] The cap 240 has a floor 242 and an annular wall 250 extending upward along the perimeter of the floor. The annular wall 250 has an outer surface 252 that fits with the inner surface 234 of the annular member 230. Therefore, the outer surface 252 of the annular wall 250 is angled to fit with the inner surface 234 of the annular member 230. The outer surface 252 of the annular wall 250 is attached to the inner surface 234 of the annular member 230 of the polishing head 210 with an adhesive (not shown). The adhesive may be epoxy glue.

[0031] The floor 242 extends across a bottom opening formed by the annular member 230. The floor 242 has a top surface 244 and a bottom surface 246. A chamber 202 is formed between the top surface 244 of the floor 242 and the concave surface 216 of the polishing head 210. The annular member 230 and the annular wall 250 define the radial boundary of the chamber 202. The platform 220 and the overlapping annular member 230 and annular wall 250 are thicker and more rigid than the floor 242.

[0032] The metal used in the polishing head assembly 200 can contaminate the wafer by becoming a source of metal ions through the polishing chemicals or slurry. To prevent metal from the cap 240 from contaminating the slurry and wafer, a template having a backing film (e.g., backing film 110 shown in Figure 1) and a retaining ring (e.g., retaining ring 120 shown in Figure 1) may be used to provide a barrier between the slurry and the cap 240. The backing film 110 is generally a thin, flexible polymer pad or other suitable material. The backing film 110 preferably comprises two or more material layers (not shown). For example, the backing film 110 may have an adhesive layer, a thin plastic film layer, and a thin polyurethane foam or other nonwoven material layer (e.g., felt). The adhesive layer seals the backing film 110 to the bottom surface 246 of the cap 240. The thin plastic film layer provides a protective barrier between the cap 240 and the slurry and / or wafer W. A layer having polyurethane foam or a nonwoven material (e.g., felt) contacts the wafer and provides a surface similar to a polishing pad (such as the polishing pad 150 shown in Figure 1). The retaining ring 120 extends downward from the backing film 110 and is generally made of plastic material. The wafer is received by the retaining ring 120 and held against the backing film 110 by surface tension. Thus, the wafer does not come into direct contact with the cap 240.

[0033] To prevent metal from the polishing head assembly 200 from contaminating the slurry and wafer, the polishing head 210 and cap 240 are surrounded by a band 270 that forms a barrier to prevent the slurry from coming into contact with the metal and contaminating the wafer. The annular member 230 has a side recess 238 extending inward from the outer surface 232 at the bottom 214. The tab 248 extends outward from the annular wall 250 of the cap 240, opposite to the floor 242. The tab 248 and the side recess 238 each receive the band 270 and are sealed to the band 270 with an adhesive such as epoxy glue. The band 270 may overlap the backing film 110 and / or retaining ring 120 of the template to form a seal between the band 270 and the backing film 110 and / or retaining ring 120 in order to prevent metal contamination during the polishing process from the polishing head 210. Band 270 is made from plastics such as polyetherimide (e.g., ULTEM resin 1000, available from Saudi Basic Industries Corporation (SABIC)), polyetheretherketone, polyphenylene sulfide, or polyethylene terephthalate.

[0034] The polishing head assembly 200 is mounted on a spindle (not shown) of the polishing apparatus 100. The spindle is a tube having a center passage (not shown). The center passage opens at one end to the polishing head assembly 200 and is connected at the other end to a rotary connector (not shown). To regulate the pressure in the chamber 202, a pressurizing source (not shown) is provided through the center passage and connected to a chamber passage 222 (for example, via a quick-connect fitting plug). The chamber passage 222 extends through the platform 220 into the chamber 202. The pressurizing source (not shown) supplies a pressurizing medium or pressurizing fluid to and from the chamber 202 through the spindle (not shown). The pressurizing source may provide an air supply source to increase or decrease the pressure in the chamber 202 of the polishing head assembly 200.

[0035] The floor 242 is a semi-rigid "flex plate" made of the same material as the cap 240 (e.g., a metallic material). The floor 242 is fitted to deform or flex precisely to change the pressure distribution and polishing pressure profile, and has sufficient rigidity due to surface tension to mount and remove wafers on and off the backing film 110. The configuration of the floor 242 is such that it does not deform substantially during mounting of wafers onto the polishing head assembly 200. The floor 242 may be substantially flat in its initial or unflexed state. The floor 242 temporarily flexes in a direction perpendicular to the polishing surface when the polishing pressure increases and when the pressure in the chamber 202 increases. The cap 240 does not permanently deform or flex under pressure. The floor 242 has the ability to transition between a pressurized, flexed or downwardly curved shape (shown in Figure 3), a flat shape substantially parallel to the bottom surface of the polishing head 210 (shown in Figure 2), and an upwardly curved or convex shape (not shown), based on the amount of pressurizing medium or fluid supplied to the chamber 202 and the polishing pressure. When the pressure inside the chamber 202 is adjusted and the floor 242 deforms, the wafer can be directly deformed by the uniformly distributed surface tension that mounts and holds the wafer on the backing film 110. By increasing or decreasing the pressure inside the chamber 202, the surface of the floor 242 and the wafer can be made to bulge outward, maintain flatness, or retract.

[0036] Pressure changes within the chamber 202 cause changes to a given or predetermined polishing pressure P. A pressurizing source (not shown) may be connected to a controller (not shown) for monitoring and adjusting the pressure within the chamber 202. The controller may include a pressure regulator (not shown). The pressure may be manually adjusted based on the general wafer shape of the incoming lot, or it may be electrically controlled on a lot-by-lot or wafer-by-wafer basis. In some embodiments, a characteristic wafer profile is obtained from a lot of wafers, and the downward pressure applied to the wafer by the polishing head assembly 200, and the distribution of that pressure, are changed by adjusting the pressure within the chamber 202. Preferably, the change in polishing pressure may be in the range of about 0.7P to about 1.3P. Thus, the change in polishing pressure P by changing the pressure within the chamber 202 provides the operator with the ability to adjust the control variable and the polished shape of the wafer. In some embodiments, the predetermined polishing pressure may be in the range of 1.0 psi to 4.0 psi. In other embodiments, the predetermined polishing pressure may be less than 6.0 psi.

[0037] Referring to Figure 3, the polishing head assembly 200 shown in Figure 2 is shown with a portion 280 of the floor 242 of the cap 240 deflected into a downward dome shape as a result of an increase in pressure within the chamber 202. The change in the shape of the floor 242 results in a change in the force distribution of the polishing pressure across the wafer (e.g., wafer W shown in Figure 1), which in turn causes the wafer to bend accordingly. The change in force distribution causes a change in the rate of material removal from the wafer. Generally, the removal rate increases when the von Mises stress acting between the wafer and the polishing pad 150 (shown in Figure 1) increases. The deflected portion 280 of the floor 242 in response to the change in pressure within the chamber 202 increases or decreases these von Mises stresses when the pressure within the chamber 202 increases or decreases.

[0038] However, it has been observed that the removal of material from the wafer by the polishing head assembly 200 decreases significantly near the wafer edge. This is a result of the non-uniform stress distribution across the floor 242, particularly the low von Mises stress exerted between the wafer edge and the polishing pad 150. These von Mises stresses generally cannot be increased, even when the pressure in the chamber 202 of the polishing head assembly 200 is increased.

[0039] The reason for the non-uniform stress distribution is that the floor 242 of the polishing head assembly 200 does not flex completely and uniformly in response to an increase and / or decrease in pressure within the chamber 202. This is due to non-uniform deformation resistance across the floor 242. As shown in Figure 3, the floor 242 is joined to the annular wall 250 at joint 290. Joint 290 acts as a hinge, allowing the floor 242 to flex temporarily around the hinge without permanently deforming relative to the polishing head 210. Due to the semi-rigidity of the floor 242, portion 280 of the floor 242 has adequate deformation resistance, allowing portion 280 to flex in response to pressure changes within the chamber 202. However, the deformation resistance increases in portion 282 of the floor 242 adjacent to joint 290. As a result, portion 282 does not flex in response to pressure changes within the chamber 202. Therefore, even if the pressure in the chamber 202 increases, there is no increase corresponding to the von Mises stress exerted between the wafer edge attached to portion 282 of the floor 242 and the polishing pad 150. The non-uniform von Mises stress distribution during polishing with the polishing head assembly 200 results in a non-uniform removal profile in the polished wafer. Furthermore, portion 282 may define the periphery of the floor 242 and extend radially from the joint 290 to portion 280 for a distance of up to approximately 30 mm. Thus, the non-uniform removal profile may cover a considerable portion of the wafer, leading to unacceptable flatness of the wafer.

[0040] The thickness of the annular wall 250 adjacent to the joint 290 and / or the thickness of the floor 242 adjacent to the joint 290 are thought to contribute to the relatively high deformation resistance of portion 282 of the floor 242. The thickness of the annular wall 250 adjacent to the joint 290 is typically about 8 mm. The thickness of the annular wall 250 is measured as the distance between the outer surface 252 and the inner surface 253 of the annular wall 250. The thickness of portion 282 of the floor 242 is typically about 5 mm to about 7 mm. The thickness of the floor 242 is measured as the distance between the top surface 244 and the bottom surface 246.

[0041] Referring to Figure 4, an exemplary polishing head assembly 400 adapted for use with the polishing device 100 is shown. The polishing head assembly 400 includes the elements and components of the polishing head assembly 200 shown in Figure 2 and described above. The annular wall 250 of the cap 240 includes a first portion 254 that is joined to the floor 242 to form a joint 290, and a second portion 256 extending from the first portion 254. The first portion 254 is defined by a notch 255 formed on the inner surface 253 of the annular wall 250 at the joint 290. The notch 255 may be U-shaped or substantially circular. The radius of the notch 255 is preferably greater than 1 mm, for example, 1 mm to about 3 mm, or about 2.5 mm. The first portion 254 of the annular wall 250 has a thickness less than the thickness of the second portion 256. The thickness of the first portion 254 depends on the radius of the notch 255. Preferably, the radius of the notch 255 is such that the thickness of the first portion 254 does not become less than 1.5 mm. For example, the thickness of the first portion 254 may preferably be about 2 mm to about 5 mm, or about 3 mm. The notch 255 forms a fillet 257 at the joint 290. Reducing the thickness of the first portion 254 and / or forming the fillet 257 via the notch 255 preferably weakens the deformation resistance of the portion 282 (shown in Figure 3) of the floor 242 adjacent to the joint 290.

[0042] Forming notches 255 and / or fillets 257 to reduce the deformation resistance of portion 282 of floor 242 may be adequately performed using computer numerical control (CNC) milling. Generally, notches 255 and / or fillets 257 cannot be formed using conventional machining techniques used to flatten floor 242 of cap 240, such as conventional lapping processes. However, it is considered that modifications can be made to conventional machining techniques to form notches 255 and fillets 257. CNC milling may also be used to provide portion 282 of floor 242 having a thickness of about 5 mm to about 6 mm, for example, 5.5 mm. Floor 242 may preferably have a continuous thickness extending across the entire diameter of floor 242 between the annular walls 250. Alternatively, the thickness of floor 242 may vary across the diameter of floor 242 between the annular walls 250.

[0043] Referring to Figure 5, another exemplary polishing head assembly 500 adapted for use with the polishing device 100 is shown. The polishing head assembly 500 includes the elements and components of the polishing head assembly 200 shown in Figure 2 and described above. The inner surface 253 of the annular wall 250 is also angled inward toward the fillet 257 formed in the joint 290. Preferably, the thickness of the annular wall 250 at the joint 290 is reduced to a thickness of about 3 mm to about 5 mm, or about 3 mm. The inner surface 253 may be angled to match the outer surface 252 so that the thickness of the annular wall 250 is constant. Alternatively, the inner surface 253 may be angled so that the thickness of the annular wall 250 tapers inward toward the joint 290, and the annular wall 250 has its thinnest thickness at the joint 290. By reducing the thickness of the annular wall 250 at the joint 290 and / or forming a fillet 257, the deformation resistance of the portion 282 (shown in Figure 3) of the floor 242 adjacent to the joint 290 is suitably reduced.

[0044] To reduce the deformation resistance of portion 282 of the floor 242, forming an angled profile of the inner surface 253 and forming a fillet 257 to reduce the thickness of the annular wall 250 may preferably be performed using computer numerical control (CNC) milling. Generally, the fillet 257 and the angled profile of the inner surface 253 cannot be formed using conventional machining techniques used to flatten the floor 242 of the cap 240, such as conventional lapping processes. However, it is considered that modifications can be made to conventional machining techniques to form the fillet 257 and the angled profile of the inner surface 253. CNC milling may also be used to provide portion 282 of the floor 242 having a thickness of about 5 mm to about 6 mm, for example, 5.5 mm. The floor 242 may preferably have a continuous thickness extending across the entire diameter of the floor 242 between the annular walls 250. Alternatively, the thickness of the floor 242 may vary across the diameter of the floor 242 between the annular walls 250.

[0045] Referring to Figure 6, another exemplary polishing head assembly 600 adapted for use with the polishing device 100 is shown. The polishing head assembly 600 includes a polishing head 610, a cap 640, and a band 670. The polishing head 610 and / or cap 640 may preferably be made of a metallic material such as aluminum or steel, or of other suitable structural materials. For example, the polishing head 610 and / or cap 640 may be made of cast aluminum (e.g., MIC6® aluminum casting sheet available from Alcoa). Alternatively, the cap 640 may be made of a ceramic material such as alumina, a plastic material, or a stainless steel material with a corrosion-resistant coating such as diamond-like carbon.

[0046] The polishing head 610 has a top 612 and a bottom 614 that are substantially parallel to each other. The polishing head 610 has a platform 620 and an annular member 630 extending downward from the platform 620. A concave surface 616 is formed at the bottom 614 of the polishing head 610 by the annular member 630 extending downward from the platform 620. A hole 618 extends from the top 612 through the platform 620 and the concave surface 616.

[0047] The annular member 630 has an outer surface 632 that is substantially perpendicular to the top 612 and bottom 614 of the polishing head 610. The outer surface 632 of the annular member 630 forms the periphery of both the polishing head 610 and the polishing head assembly 600. The annular member 630 has an inner surface 634 that is substantially parallel to the outer surface 632.

[0048] The cap 640 has a floor 642 and an annular wall 650 extending upward along the perimeter of the floor. The annular wall 650 has an outer surface 652 substantially parallel to the inner surface 634, which fits with the inner surface 634 of the annular member 630. The outer surface 652 of the annular wall 650 may be attached to the inner surface 634 of the annular member 630 of the polishing head 610 with an adhesive (not shown). The adhesive may be epoxy glue. The annular wall 650 extends upward toward a shoulder 692. The shoulder 692 has a top edge 694 that fits with the concave surface 616 of the polishing head 610. An opening 658 is formed in the shoulder 692 at the top edge 694, corresponding to the hole 618. The cap 640 is attached to the polishing head 610 by receiving fasteners (not shown), such as screws, through the holes 618 and the corresponding openings 658, and by securing the top edge 694 of the shoulder 692 to the concave surface 616. The fasteners may preferably be formed from plastic or metal materials having a corrosion-resistant coating. Additionally or alternatively, at least a portion of the top 612 of the polishing head 610 may be covered by a lid (not shown) to prevent polishing chemicals or slurry from coming into contact with the fasteners and / or entering the holes 618 during the polishing process. The shoulder 692 may have an O-ring (not shown) that forms a seal when the top edge 694 is secured to the concave surface 616.

[0049] The floor 642 extends across the bottom opening formed by the annular member 630. The floor 642 has a top surface 644 and a bottom surface 646. A chamber 602 is formed between the top surface 644 of the floor 642 and the concave surface 616 of the polishing head 610. The annular member 630 and the annular wall 650 define the radial boundary of the chamber 602. The platform 620 and the overlapping annular member 630 and annular wall 650 are thicker and more rigid than the floor 642.

[0050] The metal used in the polishing head assembly 600 can contaminate the wafer by becoming a source of metal ions through the polishing chemicals or slurry. To prevent metal from the cap 640 from contaminating the slurry and wafer, a template having a backing film (e.g., backing film 110 shown in Figure 1) and a retaining ring (e.g., retaining ring 120 shown in Figure 1) may be used to provide a barrier between the slurry and the cap 640. The backing film 110 is generally a thin, flexible polymer pad or other suitable material. The backing film 110 preferably comprises two or more material layers (not shown). For example, the backing film 110 may have an adhesive layer, a thin plastic film layer, and a thin polyurethane foam or other nonwoven material layer (e.g., felt). The adhesive layer seals the backing film 110 to the bottom surface 646 of the cap 640. The thin plastic film layer provides a protective barrier between the cap 640 and the slurry and / or wafer W. A layer having polyurethane foam or a nonwoven material (e.g., felt) contacts the wafer and provides a surface similar to that of a polishing pad (such as the polishing pad 150 shown in Figure 1). The retaining ring 120 extends downward from the backing film 110 and is generally made of a plastic material. The wafer is received by the retaining ring 120 and held against the backing film 110 by surface tension. Thus, the wafer does not come into direct contact with the cap 640.

[0051] To prevent metal from the polishing head assembly 600 from contaminating the slurry and wafer, the polishing head 610 and cap 640 are surrounded by a band 270 that forms a barrier to prevent the slurry from coming into contact with the metal and contaminating the wafer. The annular member 630 has a lateral recess 638 extending inward from the outer surface 632 and an inner recess 639 extending inward from the inner surface 634 at the bottom 614. The tab 648 extends outward from the annular wall 650 of the cap 640, opposite to the floor 642. Each of the tab 648, the lateral recess 638, and the inner recess 639 is received by a band 670 and sealed to the band 670 with an adhesive such as epoxy glue. The band 670 may overlap the backing film 110 and / or retaining ring 120 of the template to form a seal between the band 670 and the backing film 110 and / or retaining ring 120, in order to prevent metal contamination from the polishing head 610 during the polishing process. The band 670 is made from a plastic such as polyetherimide (e.g., ULTEM resin 1000, available from Saudi Basic Industries Corporation (SABIC)), polyetheretherketone, polyphenylene sulfide, or polyethylene terephthalate.

[0052] The band 670 does not have to be a single piece and may be made of two or more segments. For example, the band 670 may be made of three, four, five, or six segments. In these embodiments, the band 670 may be sealed to each other at segment joints (not shown) and may be sealed to the polishing head 610 and / or cap 640 using an adhesive such as epoxy glue. To prevent the seal between the band 670 and the polishing head 610 and / or cap 640 from loosening due to adhesive failure, the band 670 may have connecting members for securing the band 670 to the polishing head assembly 600. For example, the band 670 may have dovetail joints 672 that form a joint with an inner recess 639 formed on the inner surface 634 of the annular member 630 and a member extending above the tab 648. The dovetail joints 672 may be used in addition to, or in place of, adhesive to secure the band 670 to the polishing head 610 and / or cap 640.

[0053] Similar to the polishing head assembly 200 described in detail herein, the chamber 602 is pressurized with a pressurizing medium or fluid. The chamber 602 may be connected to a pressurizing source (not shown) to provide the pressurizing medium or fluid to the chamber 602, as described herein for the polishing head assembly 200. The pressurizing source (not shown) is connected to the chamber passage 622 (e.g., via a one-touch fitting plug). The chamber passage 622 extends through the platform 620 into the chamber 602. Similar to the floor 242 described in detail herein, the floor 642 is a semi-rigid “flex plate” that is adapted to deform precisely to change the pressure distribution and polishing pressure profile and has sufficient rigidity by surface tension to mount and remove wafers on and off the backing film 110. The floor 642 can temporarily flex against the polishing head 610 without permanent deformation. The flexing of the floor 642 is caused by adjusting the pressure in the chamber 602. In embodiments in which the shoulder portion 692 includes an O-ring (not shown), a seal formed at the connection between the apex portion 694 and the concave portion 616 may prevent the pressurized medium or fluid from leaking from the chamber 602, thereby maintaining a given pressure within the chamber 602.

[0054] In addition to the shoulder portion 692, the annular wall 650 of the cap 640 includes a first portion 654 that is joined to the floor 642 to form a joint 690. The floor 642 may temporarily flex around the joint 690 in response to pressure changes in the chamber 602. The first portion 654 may be connected to the shoulder portion 692 by a second portion 656 that extends between the first portion 654 and the shoulder portion 692. The thickness of the annular wall 650 is greatest at the shoulder portion 692, as shown in Figure 6. The first portion 654 is defined by a notch 655 formed in the annular wall 650 at the joint 690. The notch 655 may be U-shaped or substantially circular. Thus, the first portion 654 has a thinner thickness than the second portion 656. For example, the thickness of the first portion 654 may be about 3 mm to about 5 mm, or about 3 mm. The notch 655 forms a fillet 657 at the joint 690. Reducing the thickness of the first portion 654 and / or forming the fillet 657 via the notch 655 favorably weakens the deformation resistance of the portion of the floor 642 adjacent to the joint 690 (the portion that cannot substantially flex in response to pressure changes in the chamber 602). This portion of the floor may extend radially from the joint 690 toward the center of the floor 642 for a distance of up to approximately 30 mm.

[0055] Forming notches 655 and / or fillets 657 in the portion of the floor 642 adjacent to the joint 690 to reduce deformation resistance may preferably be done using computer numerical control (CNC) milling. Generally, notches 655 and / or fillets 657 cannot be formed using conventional machining techniques used to flatten the floor 642 of the cap 640, such as conventional lapping processes. However, it is considered that modifications can be made to conventional machining techniques to form notches 655 and fillets 657. CNC milling may also be used to provide a portion of the floor 642 adjacent to the joint 690 having a thickness of about 5 mm to about 6 mm, for example, 5.5 mm. The floor 642 may preferably have a continuous thickness extending across the entire diameter of the floor 642 between the annular walls 650. Alternatively, the thickness of the floor 642 may vary across the diameter of the floor 642 between the annular walls 650. For example, the floor 642 may have a thickness that tapers inward from the center of the floor 642 toward the joint 690, as described in more detail herein.

[0056] Referring to Figure 7, another exemplary polishing head assembly 700 adapted for use with the polishing device 100 is shown. The polishing head assembly 700 includes the elements and components of the polishing head assembly 600 shown in Figure 6 and described above. In this example, a portion 659 of the annular wall 650 extending between the shoulder 692 and the fillet 657 has an inner surface 653 angled with respect to the outer surface 652. The thickness of the portion 659 of the annular wall 650 tapers inward from the shoulder 692 toward the joint 690 such that the annular wall 650 has its thinnest thickness at the joint 690. Preferably, the thickness of the annular wall 650 at the joint 690 is reduced to a thickness of about 3 mm to about 5 mm, or about 3 mm. By reducing the thickness of the annular wall 650 from the shoulder 692 toward the joint 690 and / or by forming a fillet 657, the deformation resistance of the portion of the floor 642 adjacent to the joint 690 (otherwise, the portion that would not be substantially able to flex in response to pressure changes in the chamber 602) is preferably reduced. This portion of the floor may extend radially from the joint 690 toward the center of the floor 642 for a distance of up to approximately 30 mm.

[0057] To reduce the deformation resistance of the portion of the floor 642 adjacent to the joint 690, forming an angled profile on the inner surface 653 and forming a fillet 657 to reduce the thickness of the annular wall 650 may preferably be done using computer numerical control (CNC) milling. Generally, the fillet 657 and the angled profile on the inner surface 653 cannot be formed using conventional machining techniques used to flatten the floor 642 of the cap 640, such as conventional lapping processes. However, it is considered that modifications can be made to conventional machining techniques to form the fillet 657 and the angled profile on the inner surface 653. CNC milling may also be used to provide a portion of the floor 642 adjacent to the joint 690 having a thickness of approximately 5 mm to approximately 6 mm, for example, 5.5 mm. The floor 642 may preferably have a continuous thickness extending across the entire diameter of the floor 642 between the annular walls 650. Alternatively, the thickness of the floor 642 may vary across the diameter of the floor 642 between the annular walls 650. For example, the floor 642 may have a thickness that tapers inward from the center of the floor 642 toward the joint 690 (as shown in Figure 8).

[0058] Referring to Figure 8, another exemplary polishing head assembly 800 adapted for use with the polishing device 100 is shown. The polishing head assembly 800 is shown in Figures 6 and 7, respectively, and includes elements and components similar to those of the polishing head assemblies 600 and / or 700 described above. To reduce the deformation resistance of the portion of the floor 642 adjacent to the joint 690, the thickness of the floor 642 tapers inward from the radial center C of the floor 642 toward the joint 690. Thus, the thickness of the floor 642 is thickest at the center C and thinnest at the joint 690. The thickness of the floor 642 may taper from about 5 mm to 6 mm, or about 5.5 mm, at the center C, to about 3 mm to about 4 mm, or about 3 mm, at the joint 290. Tapering the thickness of the floor 642 so that the thickness of the floor 642 adjacent to the joint 690 is reduced preferably weakens the deformation resistance of the portion of the floor 642 adjacent to the joint 690 (otherwise, the portion that would not be substantially able to flex in response to pressure changes in the chamber 602). This portion of the floor 642 adjacent to the joint 690 may extend radially for a distance of up to approximately 30 mm from the joint 690 toward the radial center C of the floor 642.

[0059] In the exemplary polishing head assembly 800, the annular wall 650 of the polishing head assembly 800 may or may not have additional features to reduce the deformation resistance of the portion of the floor 642 adjacent to the joint 690, as described herein. For example, a portion 659 of the annular wall 650 extending between the shoulder 692 and the corner 696 may have an inner surface 653 substantially parallel to the outer surface 652 such that the thickness of the portion 659 is substantially constant. Alternatively, the thickness of the portion 659 may be thinner at the joint 690. For example, the inner surface 653 may be angled with respect to the outer surface 652 such that the thickness of the portion 659 of the annular wall 650 tapers inward from the shoulder 692 toward the joint 690 (as shown in Figure 7). Furthermore, the corners 696 at the joint 690 between the inner surface 653 of the annular wall 650 and the top surface 644 of the floor 642 may be angular or chamfered (i.e., a fillet 657 may be formed as shown in Figures 6 and 7). Preferably, the thickness of the annular wall 650 at the joint 690 may be about 8 mm, or it may be thinner to about 3 mm to about 5 mm, or about 3 mm.

[0060] To reduce the deformation resistance of the portion of the floor 642 adjacent to the joint 690, forming a tapered profile of the floor 642 may preferably be performed using computer numerical control (CNC) milling. Generally, a tapered profile of the floor 642 cannot be formed using conventional machining techniques used to flatten the floor 642 of the cap 640, such as conventional lapping processes. However, it is considered that modifications can be made to conventional machining techniques to form a tapered profile of the floor 642.

[0061] The described embodiment reduces the deformation resistance of the floor of the cap of the polishing head assembly (the portion that would otherwise be substantially unable to deform in response to pressure changes within the chamber of the polishing head assembly). The embodiment enables a more uniform removal profile on the polished wafer. By weakening the floor portion (the portion that would otherwise be substantially unable to flex in response to pressure changes within the chamber), the distribution of von Mises stress between the wafer and the polishing pad becomes more uniform during polishing. In particular, the von Mises stress between the wafer edge and the polishing pad can be better controlled to fine-tune the removal profile near the wafer edge.

[0062] As used herein, the terms “about,” “substantially,” “essentially,” and “approximately,” when used in relation to a range of dimensions, density, temperature, or other physical or chemical properties or characteristics, mean to include any variations that may exist in the upper and / or lower limits of the property or characteristic. Such variations include, for example, variations resulting from rounding, measurement methods, or other statistical variations.

[0063] When describing elements of this disclosure or embodiments thereof, the articles “a,” “an,” “the,” and “said” are intended to indicate that there is one or more elements. The terms “comprising,” “including,” and “having” are intended to indicate comprehensiveness and that additional elements other than those listed may exist. The use of terms indicating specific orientations (e.g., “top,” “bottom,” “side,” “down,” “up,” etc.) is for explanatory convenience and does not require a specific orientation of the described article.

[0064] Because various modifications are possible in the above-described structure and method without departing from the scope of this disclosure, all matters included in the above description and shown in the accompanying drawings are intended to be interpreted as illustrative rather than restrictive.

Claims

1. A polishing head assembly for polishing semiconductor wafers, A polishing head having a recess along the bottom, the recess having a concave surface, A cap placed in the recess and Equipped with, The aforementioned cap is An annular wall fixed to the polishing head, having a first portion having a first thickness and a second portion extending from the first portion and having a second thickness, The floor is joined to the annular wall at the joint. Equipped with, The aforementioned floor extends across the annular wall, The floor has an upper surface and a lower surface. The upper surface is positioned at a distance from the concave surface, and a chamber is formed between the upper surface and the concave surface. The first portion of the annular wall is joined to the floor, A polishing head assembly wherein the first thickness is thinner than the second thickness, such that the deformation resistance of the portion of the floor adjacent to the joint is weaker compared to the other portions of the floor, and the portion of the floor adjacent to the joint flexes relative to the polishing head due to pressure changes in the chamber.

2. The polishing head assembly according to claim 1, wherein the first thickness is approximately 3 mm to approximately 5 mm.

3. The polishing head assembly according to claim 2, wherein the first thickness is approximately 3 mm.

4. The polishing head assembly according to claim 1, wherein the floor has a continuous thickness of approximately 5 mm to approximately 6 mm.

5. The polishing head has a top and a hole extending from the top through the concave surface, The annular wall further comprises a shoulder portion extending from the second portion and having an opening corresponding to the hole, The polishing head assembly according to claim 1, wherein the hole and the corresponding opening receive fasteners for fixing the shoulder of the annular wall to the concave surface of the polishing head.

6. The polishing head assembly according to claim 1, wherein the annular wall is positioned so that its first thickness is close to the joint, and the annular wall is tapered inward toward the joint from the second thickness to the first thickness so as to reduce the deformation resistance of the portion of the floor close to the joint.

7. The polishing head assembly according to claim 6, wherein the first thickness of the annular wall adjacent to the joint is approximately 3 mm to approximately 5 mm.

8. The polishing head assembly according to claim 6, wherein the first thickness of the annular wall adjacent to the joint is approximately 3 mm.

9. The polishing head assembly according to claim 6, wherein the floor has a continuous thickness of approximately 5 mm to approximately 6 mm.

10. The polishing head assembly according to claim 1, wherein the thickness of the floor is thinnest in the portion of the floor adjacent to the joint, and the floor is tapered inward toward the joint so as to reduce the deformation resistance of the portion of the floor adjacent to the joint.

11. The polishing head assembly according to claim 10, wherein the thickness of the floor is thickest at the center of the floor.

12. The polishing head assembly according to claim 11, wherein the thickness of the floor in the portion adjacent to the joint is approximately 3 mm, and the thickness of the floor in the center is approximately 5 mm to approximately 6 mm.

13. The polishing head assembly according to claim 1, wherein the cap is made of a metal material.

14. The polishing head assembly according to claim 1, wherein the annular wall is fixed to the polishing head with adhesive.

15. A polishing head assembly for polishing semiconductor wafers, A polishing head comprising a top, a recess having a concave surface along the bottom, and a plurality of holes extending from the top through the concave surface, A cap placed in the recess and Equipped with, The aforementioned cap is An annular wall having multiple openings corresponding to the multiple holes, The floor is joined to the annular wall at the joint. Equipped with, The plurality of holes and the corresponding plurality of openings receive fasteners for fixing the annular wall to the concave surface. The aforementioned floor extends across the annular wall, The floor has an upper surface and a lower surface. The upper surface is positioned at a distance from the concave surface, and a chamber is formed between the upper surface and the concave surface. The floor can bend relative to the polishing head due to pressure changes within the chamber. A polishing head assembly in which the deformation resistance of the portion of the floor adjacent to the joint is weakened compared to the rest of the floor, so as to allow the portion of the floor adjacent to the joint to flex relative to the polishing head.

16. The polishing head assembly according to claim 15, wherein the thickness of the floor is thinnest in the portion of the floor adjacent to the joint, and the floor is tapered inward toward the joint so as to reduce the deformation resistance of the portion of the floor adjacent to the joint.

17. The polishing head assembly according to claim 16, wherein the thickness of the floor in the portion adjacent to the joint is approximately 3 mm, and the thickness of the floor in the center of the floor is approximately 5 mm to approximately 6 mm.

18. The polishing head assembly according to claim 15, wherein the cap is made of a metal material.

19. A polishing head assembly for polishing semiconductor wafers, A polishing head having a platform and a hole extending through the platform, A cap having an annular wall fixed to the polishing head and a floor joined to the annular wall at a joint, wherein the annular wall has an opening corresponding to the hole, and the hole and the corresponding opening receive a fastener to fix the annular wall to the platform of the polishing head, Equipped with, The polishing head and the cap define a chamber between the polishing head and the floor of the cap. The floor is made of a metal material that can flex relative to the polishing head in response to pressure changes within the chamber. A polishing head assembly wherein the thickness of at least one of the annular wall and the floor is reduced in proximity to the joint, thereby weakening the deformation resistance of the floor in the vicinity of the joint compared to other parts of the floor.

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