POLISHING HEAD ASSEMBLIES FOR POLISHING SEMICONDUCTOR WAFERS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]The application claims the benefit of U.S. Provisional Patent Application No. 63/669,552, filed Jul. 10, 2024 and claims the benefit of U.S. Provisional Patent Application No. 63/729,571, filed Dec. 9, 2024. Both applications are incorporated herein by reference in their entirety.

TECHNICAL FIELD

[0002]The field of the disclosure relates to polishing heads for single side polishing of silicon wafers.

BACKGROUND

[0003]Semiconductor wafers are commonly used in the production of integrated circuit (IC) chips on which circuitry are printed. The circuitry is first printed in miniaturized form onto surfaces of the wafers. The wafers are then broken into circuit chips. This miniaturized circuitry requires that front and back surfaces of each wafer be extremely flat and parallel to ensure that the circuitry can be printed over the entire surface of the wafer. To accomplish this, grinding and polishing processes are commonly used to improve flatness and parallelism of the front and back surfaces of the wafer after the wafer is cut from an ingot. A particularly good finish is required when polishing the wafer in preparation for printing the miniaturized circuits on the wafer by an electron beam-lithographic or photolithographic process (hereinafter “lithography”). The wafer surface on which the miniaturized circuits are to be printed must be flat.

[0004]Polishing machines typically include a circular or annular polishing pad mounted on a turntable or platen for driven rotation about a vertical axis passing through the center of the pad and a mechanism for holding the wafer and forcing it into the polishing pad. The wafer is typically mounted to the polishing head using for example, liquid surface tension or vacuum/suction. A polishing slurry, typically including chemical polishing agents and abrasive particles, is applied to the pad for greater polishing interaction between the polishing pad and the surface of the wafer. This type of polishing operation is typically referred to as chemical-mechanical polishing (CMP). During operation, the pad is rotated and the wafer is brought into contact with and forced against the pad by the polishing head.

[0005]Silicon wafers typically undergo a final polishing process after completion of a double side polishing process. It is desirable to make the wafer as flat as possible after final polishing. In order to achieve a flat wafer after final polishing, the removal profile in final polishing should match the thickness variation profile of the wafer after double side polishing as closely as possible. Most double side polishing processes can be tuned to either achieve a flat thickness variation profile, a “W” shape thickness variation profile or a smooth dome shape thickness variation profile.

[0006]A need exists for polishing heads having a removal profile that matches the profile of the double side polished wafer to achieve a flatter wafer after final polishing. (e.g., smooth dome-type removal profiles that match the smooth dome-type thickness variation profile of the post double side polished wafer).

[0007]This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

SUMMARY

[0008]One aspect of the present disclosure is directed to a polishing head assembly for polishing a semiconductor wafer. The polishing head assembly includes a polishing head, a cap, and a template for securing the semiconductor wafer to the polishing head assembly. The cap is connected to the polishing head. The cap and polishing head form a chamber therebetween. The cap includes a floor. The template is connected to the floor. The template has a central axis, a circumferential edge, and a radius. The radius extends from the central axis to the circumferential edge. The template has a thickness that varies along the radius of the template.

[0009]Another aspect of the present disclosure is directed to a polishing head assembly for polishing a semiconductor wafer. The polishing head assembly includes a polishing head, a cap, a template for securing the semiconductor wafer to the polishing head assembly, and a template support. The cap is connected to the polishing head. The cap and polishing head form a chamber therebetween. The cap includes a floor. The template has a central axis, a circumferential edge, and a radius. The radius extends from the central axis to the circumferential edge. The template support is disposed between the cap and template. The template support is connected to the floor.

[0010]Yet another aspect of the present disclosure is directed to a polishing head assembly for polishing a semiconductor wafer. The polishing head assembly includes a polishing head, a cap, and a template for securing the semiconductor wafer to the polishing head assembly. The cap is connected to the polishing head. The cap and polishing head form a chamber therebetween. The cap includes a floor that is made of metal. The floor has a central axis, a circumferential edge, and a radius. The radius extends from the central axis to the circumferential edge. The floor has a thickness of at least 8 mm along the entire radius of the floor. The template is connected to the floor.

[0011]Various refinements exist of the features noted in relation to the above-mentioned aspects of the present disclosure. Further features may also be incorporated in the above-mentioned aspects of the present disclosure as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments of the present disclosure may be incorporated into any of the above-described aspects of the present disclosure, alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic view of a polishing apparatus;

[0013]FIG. 2 is a cross-section view of a polishing head assembly adapted for mounting and use in the polishing apparatus shown in FIG. 1;

[0014]FIG. 3 is a detailed cross-section view of a polishing head assembly having a template that varies in thickness radially;

[0015]FIG. 4 is an exploded cross-section view of the polishing head assembly of FIG. 3;

[0016]FIG. 5 is a detailed cross-section view of another embodiment a polishing head assembly having a template that varies in thickness radially;

[0017]FIG. 6 is an exploded cross-section view of the polishing head assembly of FIG. 5;

[0018]FIG. 7 is a detailed cross-section view of another embodiment a polishing head assembly having a template that varies in thickness radially;

[0019]FIG. 8 is an exploded cross-section view of the polishing head assembly of FIG. 7;

[0020]FIG. 9 is a detailed cross-section view of another embodiment a polishing head assembly;

[0021]FIG. 10 is a graph of the contact pressure profile of the polishing head assembly of FIGS. 3-4;

[0022]FIG. 11 is a graph of the contact pressure profile of the polishing head assembly of FIGS. 5-6;

[0023]FIG. 12 is a graph of the contact pressure profile of the polishing head assembly of FIGS. 7-8;

[0024]FIG. 13 is a graph of the contact pressure profile of the polishing head assembly of FIG. 9; and

[0025]FIG. 14 is a graph of the contact pressure profile of the polishing head assembly of FIG. 9 at a lower chamber pressure.

[0026]Corresponding reference characters indicate corresponding parts throughout the drawings.

DETAILED DESCRIPTION

[0027]Provisions of the present disclosure relate to polishing head assemblies for single side polishing of semiconductor wafers. In some embodiments, the polishing head assemblies provide a smooth domed removal profile. The thickness of the polishing floor and the template on which the wafer is mounted is varied along the radius to modulate the stiffness and thereby control the contact pressure profiles to adjust the actual removal profiles in the polishing process. In some embodiments, a template support is used to modulate the stiffness.

[0028]Generally, and in embodiments of the present disclosure, suitable “semiconductor wafers” (which may also be referred to as “wafers” or “silicon wafers”) that may be polished by the polishing head assemblies described herein include single crystal silicon wafers, such as, for example, silicon wafers obtained by slicing the wafers from single crystal silicon ingots formed by the Czochralski method or the float zone method. Each wafer includes a central axis, a front surface, and a back surface parallel to the front surface. The front and back surfaces are generally perpendicular to the central axis. A circumferential edge joins the front and back surfaces. The wafers may be any diameter suitable for use by those of skill in the art including, for example, 200 millimeter (mm), 300 mm, greater than 300 mm or even 450 mm diameter wafers.

[0029]In some embodiments, a semiconductor wafer that has previously been rough polished so that it has rough front and back surfaces (i.e., double-side polished) is first subjected to an intermediate polishing operation in which the front surface of the wafer, but not the back surface, is polished to improve flatness parameters or to smooth the front surface and remove handling scratches. To carry out this operation, the wafer is placed against a polishing head assembly. The wafer is retained in position against the polishing head assembly by surface tension. The wafer also is placed on a turntable of a polishing machine with the front surface of the wafer contacting the polishing surface of a polishing pad.

[0030]A polishing head assembly mounted on the machine is capable of vertical movement along an axis extending through the wafer. While the turntable rotates, the polishing head assembly is moved against the wafer to urge the wafer toward the turntable, thereby pressing the front surface of the wafer into polishing engagement with the polishing surface of the polishing pad.

[0031]A conventional polishing slurry containing abrasive particles and a chemical etchant is applied to the polishing pad. The polishing pad works the slurry against the surface of the wafer to remove material from the front surface of the wafer, resulting in a surface of improved smoothness. As an example, the intermediate polishing operation preferably removes less than about 1 micron of material from the front side of the wafer.

[0032]The wafer is then subjected to a finish or “final” polishing operation in which the front surface of the wafer is finish polished to remove fine or “micro” scratches caused by large size colloidal silica, such as Syton® from DuPont Air Products Nanomaterials, LLC, in the intermediate step and to produce a highly reflective, damage-free front surface of the wafer. The intermediate polishing operation generally removes more of the wafer than the finishing polishing operation. The wafer may be finish polished in the same polishing machine used to intermediate polish the wafer as described above. However, a separate polishing machine may also be used for the finish polishing operation. A finish polishing slurry typically has an ammonia base and a reduced concentration of colloidal silica is injected between the polishing pad and the wafer. The polishing pad works the finish polishing slurry against the front surface of the wafer to remove any remaining scratches and haze so that the front surface of the wafer is generally highly-reflective and damage free. The polishing head assemblies described herein may be used to polish the semiconductor wafer in an intermediate polishing step or in a finish polishing step.

[0033]Referring to FIG. 1, a portion of a polishing apparatus is shown schematically and indicated generally at 100. The polishing apparatus 100 may be used to polish a front surface of a semiconductor wafer W. It is contemplated that other types of polishing apparatus may be used.

[0034]The polishing apparatus 100 includes a polishing head assembly 130 that forms a chamber 102, a wafer holding mechanism 146, and a turntable 140 having a polishing pad 150. The wafer holding mechanism 146 includes a template (or “backing film”) 118 and a retaining ring 120. The template 118 is located between a polishing head assembly 130 and the retaining ring 120 to secure a wafer W. The retaining ring 120 has at least one circular opening to receive the wafer W to be polished therein.

[0035]The wafer W in this embodiment is attached to and retained against the polishing head assembly 130 by surface tension. To form the surface tension, the wet template 118 is attached to the polishing head assembly 130 with a pressure sensitive adhesive. The template 118 is generally a soft polymer pad or other suitable material.

[0036]The wafer W is then pressed into the wet saturated template 118 to remove or squeeze out the majority of the water or other suitable liquid. Squeezing out the water causes the wafer to be retained on the template 118 by surface tension and the atmospheric pressure on the exposed surface of the wafer. This squeezing out of the water mounts the wafer to the polishing head assembly 130.

[0037]A portion of the polishing head assembly 130 is flexible enough to deform in response to a change in pressure applied to the polishing head assembly 130, and stiff enough not to deform when the wafer is pressed into the wet saturated template 118. The surface tension provides a constant retaining force over the surface of the wafer W. This constant retaining force causes any deformation of the polishing head assembly 130 adjacent to the wafer to be directly translated into proportional deformation of the wafer W.

[0038]The retention of the wafer W by surface tension functions differently than other known mechanisms that use flexible membranes or vacuums to retain the wafer against the polishing head assembly. Flexible membranes, as known in the art, deform to create space or vacuum pockets between the wafer and the flexible membrane when the wafer is pushed thereon. These vacuum pockets allow the membrane to pick up the wafer. Other membranes have vacuum holes, which are connected to a vacuum to create low pressure areas to pick up wafers.

[0039]The polishing apparatus 100 applies a force to the polishing head assembly 130 to move the polishing head assembly 130 vertically to raise and lower the polishing head assembly 130 with respect 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 discussed above, the downward vertical movement of the polishing head assembly 130 against the wafer W provides the polishing pressure to the wafer to urge the wafer into the polishing pad 150 of the turntable 140. As the polishing apparatus 100 increases the downward force, the polishing head assembly 130 moves vertically lower to increase the polishing pressure.

[0040]A portion of the polishing head assembly 130 and the polishing pad 150 and turntable 140 are rotated at selected rotation speeds by a suitable drive mechanism (not shown) as is 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 100 includes a controller (not shown) that allows the operator to select rotation speeds for both the polishing head assembly 130 and the turntable 140, and the downward force applied to the polishing head assembly.

[0041]With reference to FIG. 2, a polishing head assembly 200 adapted for mounting and use in the polishing apparatus 100 is shown. The polishing head assembly 200 includes a polishing head 210, a cap 240, and a band 270. The polishing head 210 and/or cap 240 are suitably made of a metallic material, such as aluminum or steel, or may be made of another suitable structural material. For example, the polishing head 210 and/or cap 240 may be made of cast aluminum (for example, MIC6® Aluminum Cast Plate available from Alcoa.) Alternatively, the cap 240 may be made of a ceramic material, such as alumina, a plastic material, or a stainless steel material with anti-corrosion coating, such as, for example, diamond-like carbon.

[0042]The polishing head 210 has a top 212 and a bottom 214 that are substantially parallel with each other. The polishing head 210 has a platform 220 and an annular member 230 extending downwardly from the platform 220. A recessed surface 216 is formed in the bottom 214 of the polishing head 210 by the annular member 230 extending downwardly from the platform 220. The annular member 230 has an outside surface 232 that is substantially perpendicular to the top 212 and bottom 214 of the polishing head 210. The outside surface 232 of the annular member 230 forms the circumference of both the polishing head 210 and the polishing head assembly 200. The annular member 230 has an inside surface 234 that is angled with respect to the outside surface 232 such that the annular member 230 is thinnest at bottom 214 of the polishing head 210. This tapering of the annular member 230 provides a stiffer top section adjacent the platform 220. In other embodiments, the inside surface 234 may be substantially parallel to the outside surface 232.

[0043]The cap 240 has a floor 242 (which may also be referred to as “plate 242”) and an upwardly extending annular wall 250 along the perimeter of the floor 242. The annular wall 250 has an outer surface 252 that mates with the inside surface 234 of the annular member 230. As such, the outer surface 252 of the annular wall 250 is also angled to match the inside surface 234 of the annular member 230. The outer surface 252 of the annular wall 250 is attached to the inside surface 234 of the annular member 230 of the polishing head 210 with an adhesive (not shown). The adhesive may be an epoxy glue.

[0044]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 recessed surface 216 of the polishing head 210. The annular member 230 and the annular wall 250 determine the radial boundaries of the chamber 202. The platform 220 and the overlapping annular member 230 and annular wall 250 are thicker and are adapted to be more rigid than the floor 242.

[0045]Metal used in the polishing head assembly 200 has the potential to contaminate the wafer by being a source of metal ions through the polishing chemicals or slurry. To prevent the metal from cap 240 from contaminating the slurry and the wafer, a template 118 (FIG. 1) and retaining ring 120 (FIG. 1) may be used to create a barrier between the slurry and the cap 240. The template 118 is generally a thin soft polymer pad or other suitable material. The template 118 may suitably include two or more layers of material (not shown). For example, the template 118 may have an adhesive layer, a thin plastic film layer, and a thin polyurethane foam, or other non-woven material (e.g., felt), layer. The adhesive layer seals template 118 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. The layer comprising polyurethane foam or non-woven material (e.g., felt) contacts the wafer and provides a surface similar to that a polishing pad (such as polishing pad 150 shown in FIG. 1). The retaining ring 120 extends downwardly from template 118 and is generally a plastic material. The wafer is received within the retaining ring 120 and is retained against template 118 by surface tension. As such, the wafer does not directly contact the cap 240.

[0046]To prevent metal from the polishing head assembly 200 from contaminating the slurry and the wafer, the polishing head 210 and cap 240 are circumscribed with a band 270 that forms a barrier to prevent the slurry from contacting the metal and contaminating the wafer. The annular member 230 has a side recess 238 that extends inwardly from the outside surface 232 at the bottom 214. A tab 248 extends outwardly from the annular wall 250 of cap 240 opposite the floor 242. The tab 248 and the side recess 238 each receive the band 270 and may be sealed thereto with an adhesive, such as epoxy glue. The band 270 may overlap the template 118 and/or the retaining ring 120 of the wafer holding mechanism 146 to form a seal therebetween to prevent metal contamination from the polishing process from contacting the polishing head 210. The band 270 may be made of plastic, such as polyetherimide (for example, ULTEM™ Resin 1000 available from Saudi Basic Industries Corporation (SABIC)), polyether ether ketone, polyphenylene sulfide, or polyethylene terephthalate.

[0047]The polishing head assembly 200 is attached to a spindle (not shown) of the polishing apparatus 100. The spindle is a tube with a center passage (not shown). The center passage opens to the polishing head assembly 200 at one end and is connected with a rotary connector (not shown) at the other end. To adjust the pressure within the chamber 202, a pressurizing source (not shown) is provided through the center passage and connects to a chamber passageway 222 (e.g., via a quick disconnect coupling plug). The chamber passageway 222 extends through the platform 220 to chamber 202. The pressurizing source (not shown) supplies a pressurized media or fluid to and from the chamber 202 through the spindle (not shown). The pressurizing source may provide a pneumatic supply for increasing or decreasing the pressure within the chamber 202 of the polishing head assembly 200.

[0048]The floor 242 is a semi-rigid “flex plate” that may be made of the same material as the cap 240 (e.g., a metallic material). The floor 242 is adapted to be precisely deformed or deflected to change the pressure distribution and polishing pressure profile, and still be rigid enough to mount and demount the wafer on the template 118 by surface tension. The rigidity of the floor 242 is such that it does not substantially deform during the mounting of a wafer on the polishing head assembly 200. The floor 242 may be substantially flat in an initial or un-deflected state. The floor 242 temporarily deflects in a direction that is perpendicular to the polishing surface as the polishing pressure is increased and as the pressure within chamber 202 is increased.

[0049]The cap 240 is not permanently deflected or deformed by the pressure. The floor 242 has the ability to transition to a pressurized deflected or downwardly curved shape, to a flat shape that is substantially parallel with a bottom surface of the polishing head 210 (shown in FIG. 2), and to an upwardly curved or convex shape (not shown), based on the amount of pressurized media or fluid supplied to the chamber 202 and the polishing pressure. The evenly distributed surface tension mounting and retaining the wafer on the template 118 provides direct deformation of the wafer when the pressure in the chamber 202 is adjusted and the floor 242 is deformed. Increasing or decreasing the pressure within the chamber 202 can thereby cause the surface of the floor 242 and wafer to balloon outwardly, remain flat, or be drawn in.

[0050]The change of pressure within chamber 202 causes a change to a given or predetermined polishing pressure P. The pressurizing source (not shown) may be connected with 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 can be adjusted either manually, based on general wafer shape of the incoming lot, or may be electronically controlled lot by lot, or even wafer by wafer. 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 is varied by adjusting pressure in the chamber 202. Suitably, the change in polishing pressure may range from about 0.7 P to about 1.3 P. Thus, a change in polishing pressure P by changing the pressure within chamber 202 provides an operator with a control variable and the ability to adjust the polished shape of the wafer. In some embodiments, the predetermined polishing pressure may range from 1.0 psi to 4.0 psi. In other embodiments, the predetermined polishing pressure may be less than 6.0 psi.

[0051]Referring now to FIGS. 3-4, an embodiment of a polishing head assembly 300 of the present disclosure is shown. The polishing head assembly 300 of FIGS. 3-4 may correspond to the polishing head assembly 200 as described above and include the same or similar components with differences described below. The components shown in FIGS. 3-4 that are analogous to those of FIG. 2 are designated by the corresponding reference number of FIG. 2 plus “100” (e.g., part 223 becomes 323). The polishing head assembly 300 includes a polishing head 310 and a cap 340 that is connected to the polishing head 310 (e.g., by adhesive or fasteners). The polishing head 310 and cap 340 form a chamber 302 therebetween. The cap 340 includes a floor 342.

[0052]The polishing head assembly 300 includes a template 318 for securing the semiconductor wafer to the polishing head assembly 300. The template 318 is connected to the floor 342 (e.g., by any of the methods described above). The template 318 (FIG. 4) has a central axis A₃₁₈, a circumferential edge 354 and a radius R₃₁₈ that extends from the central axis A₃₁₈ to the circumferential edge 354. The template 318 has a thickness that varies along the radius R₃₁₈. For example, the thickness increases from the central axis A₃₁₈ to the circumferential edge 354. In the illustrated embodiment, the template 318 comprises a step 360 (i.e., the thickness undergoes a step change) disposed between the central axis A₃₁₈ and the circumferential edge 354. The thickness increases along the radius R₃₁₈ from a center thickness T₁ to an edge thickness T₂. In other embodiments, the template 318 decreases in thickness along its radius from the circumferential edge 354 toward the central axis A₃₁₈). In the illustrated embodiment, the step 360 extends to the circumferential edge 354 of the template 318. In some other embodiments, the template 318 changes thickness continuously along at least a portion of the radius R₃₁₈ (i.e., a taper in which the template and floor have matching angled interfaces as opposed to a step change in thicknesses).

[0053]The step 360 has a width W₃₆₀. The width W₃₆₀ of the step 360 is at least 5% of the radius R₃₁₈ of the template 318. In other embodiments, the width W₃₆₀ of the step 360 is at least 10% of the radius R₃₁ of the template 318 or at least 15%, from 5% to 35%, or from 5% to 30% of the radius R₃₁₈ of the template 318. The thickness of the template 318 increases by at least 25%, at least 50% or at least 60% (e.g., from 25% to 100% or from 50% to 100%) at the step 360 ((T₂−T₁)/T₁). The thickness of the step 360 may range from 1 mm to 20 mm and the width may range from 5 mm to 100 mm; however, other thicknesses and widths are contemplated by the present disclosure.

[0054]The floor 342 may have a shape that matches the profile of the template 318. As shown FIG. 4, the floor 342 has a central axis A₃₄₂, a circumferential edge 362 and a radius R₃₄₂ that extends from the central axis A₃₄₂ to the circumferential edge 362. The floor 342 has a thickness that varies along the floor 342. For example, the floor 342 may decrease in thickness from its central axis A₃₄₂ to the circumferential edge 362 of the floor 342. In the illustrated embodiment, the floor 342 includes a floor recess 366. As shown in FIG. 3 the step 360 is disposed within the floor recess 366.

[0055]Another embodiment of the polishing head assembly 400 is shown in FIGS. 5-6 of the application. The polishing head assembly 400 of FIG. 5 may correspond to the polishing head assembly 200 as described above and include the same or similar components with differences described below. The components shown in FIG. 5-6 that are analogous to those of FIG. 2 are designated by the corresponding reference number of FIG. 2 plus “200” (e.g., part 223 becomes 423). The polishing head assembly 400 includes a polishing head 410 and a cap 440 that is connected to the polishing head 410. The polishing head 410 and cap 440 form a chamber 402 therebetween. The cap 440 includes a floor 442.

[0056]The polishing head assembly 400 includes a template 418 for securing the semiconductor wafer to the polishing head assembly 400. The template 418 (FIG. 6) has a central axis A₄₁₈, a circumferential edge 454 and a radius R₄₁₈ that extends from the central axis A₄₁₈ to the circumferential edge 454. The template 418 has a thickness T₄₁₈.

[0057]A template support 464 is disposed between the floor 442 and the template 418 (e.g., at least partially along the radius of the template 418). The template support 464 is connected to the floor 442. The template support 464 has a central axis A₄₆₄, a circumferential edge 468 and a radius R₄₆₄ that extends between the central axis A₄₆₄ to the circumferential edge 468. As shown in FIG. 6, the radius R₄₆₄ of the template support 464 is less than the radius R₄₁₈ of the template 418. For example, the radius R₄₆₄ of the template support 464 may be less than 99% of the radius R₄₁₈ of the template 418 or less than 97.5%, less than 95%, from 80% to 99%, or from 90% to 99% of the radius R₄₁₈ of the template 418. The thickness of the template support may be at least 2.5% of the thickness of the floor 442 or at least 5%, at least 10% or at least 25% of the thickness of the floor 442 (e.g., from 2.5% to 50%, from 5% to 50% of the thickness of the floor 442). In example embodiments, the Young's Modulus of the template support 464 may range between 0.3-500 MPa and/or the thickness may vary between 0.1 mm and 10 mm or 0.1 mm to 5 mm.

[0058]The floor 442 forms a floor recess 472. As shown in FIG. 5, the template support 464 is disposed in the floor recess 472.

[0059]The template 418 and the template support 464 may be made of different materials. The template support 464 and the floor 442 may also be made of different materials. The template support 464 may have a Young's Modulus less than the Young's Modulus of the floor 442. The template support 464 may have a Young's Modulus greater than the Young's Modulus of the template 418. The template support 464 may be made of rubber or ULTEM or other materials (e.g., soft/medium/hard materials).

[0060]Another embodiment of the polishing head assembly 500 is shown in FIGS. 7-8 of the application. The polishing head assembly 500 of FIGS. 7-8 may correspond to the polishing head assembly 200 as described above and include the same or similar components with differences described below. The components shown in FIG. 7-8 that are analogous to those of FIG. 2 are designated by the corresponding reference number of FIG. 2 plus “300” (e.g., part 223 becomes 523). The polishing head assembly 500 includes a polishing head 510 and a cap 540 that is connected to the polishing head 510. The polishing head 510 and cap 540 form a chamber 502 therebetween. The cap 540 includes a floor 542.

[0061]As shown in FIGS. 7-8, the polishing head assembly 500 includes a template support 564 disposed between the floor 542 and the template 518. The template support 564 may be similar to the template support 464 shown in FIGS. 5-6 (e.g., with a smaller radius than template support 464). The template support 564 is connected to the floor 542 and is disposed within a first floor recess 572.

[0062]The radius R₅₆₄ of the template support 564 is less than the radius R₅₁₈ of the template 518. For example, the radius R₅₆₄ of the template support 564 may be less than 95% of the radius R₅₁₈ of the template 518 or less than 90%, less than 85%, from 60% to 95%, or from 70% to 95% of the radius R₅₁₈ of the template 518. The thickness of the template support 564 may be at least 2.5% of the thickness of the floor 542 or at least 5%, at least 10% or at least 25% of the thickness of the floor 542 (e.g., from 2.5% to 50%, from 5% to 50% of the thickness of the floor 542).

[0063]The template 518 includes a step 560 at which the thickness of the template 518 increases. The step 560 may be similar to step 360 shown in the embodiment of FIGS. 3-4. The step 560 is disposed in a second floor recess 566. The step 560 may extend to the circumferential edge 554 (FIG. 8) of the template 518. The step 560 may have a width that at least 5% of the radius R₅₁₈ of the template 518 or at least 10%, at least 15%, from 5% to 35%, is from 5% to 30% of the radius R₅₁₈ of the template 518. In some embodiments, the thickness of the template 518 increases by at least 25%, at least 50% or at least 60% (e.g., from 25% to 100% or from 50% to 100%) at the step 360.

[0064]Another embodiment of a polishing head assembly 600 of the present disclosure is shown in FIG. 9. The polishing head assembly 600 of FIG. 9 may correspond to the polishing head assembly 200 as described above and include the same or similar components with differences described below. The components shown in FIG. 9 that are analogous to those of FIG. 2 are designated by the corresponding reference number of FIG. 2 plus “400” (e.g., part 223 becomes 623). The polishing head assembly 600 includes a polishing head 610 and a cap 640 that is connected to the polishing head 610 (e.g., by adhesive or fasteners). The polishing head 610 and cap 640 form a chamber 602 therebetween. The cap 640 includes a floor 642. The floor 642 has a central axis A₆₄₂, a circumferential edge 672 and a radius R₆₄₂ that extends from the central axis A₆₄₂ to the circumferential edge 672.

[0065]The polishing head assembly 600 includes a template 618 for securing the semiconductor wafer to the polishing head assembly 600. The template 618 is connected to the floor 642 (e.g., by any of the methods described above).

[0066]In the illustrated embodiment, the floor 642 is made of metal (e.g., aluminum alloy or stainless steel) and has a thickness T₆₄₂ of at least 8 mm along the entire radius R₆₄₂ of the floor 642. In other embodiments, the thickness T₆₄₂ of the floor 642 is from 8 mm to 15 mm, from 8 mm to 12 mm, from 8 mm to 10 mm, from 8 mm to 9 mm, or about 8.5 mm. In the illustrated embodiment, the pressure in the chamber may be less than 1000 Pa or, as in other embodiments, less than 750 Pa, less than 500 Pa, from 250 Pa to 1000 Pa, or from 250 Pa to 750 Pa.

[0067]Compared to conventional polishing head assemblies, the polishing head assemblies of the present disclosure have several advantages. By adding a step to the template, the contact pressure profile may be improved such as by a smooth dome-shaped removal profile. Embodiments having a template support and or increased floor thickness (e.g., 8 mm or more) may also result in improved removal profiles (e.g., smooth dome-shaped removal profile). In the disclosed embodiments, the polishing head is less stiff and deforms more which results in a higher contact pressure and more removal of the material at and near the outer edge. The thickness and width of the template step may be tuned to achieve the desired contact pressure. In embodiments having a template support, the thickness and/or Young's Modulus of the template support may be tuned to achieve a desired contact pressure profile.

EXAMPLES

[0068]The processes of the present disclosure are further illustrated by the following Examples. These Examples should not be viewed in a limiting sense.

Example 1: The Effect of Using a Template Having a Step on the Removal Profile

[0069]For embodiments of the present disclosure, FEM simulations were conducted and a comparison of the contact pressure profiles as a function of radius were performed. In the process of record, a flat polishing plate and template of constant thickness at all radii was used.

[0070]A polishing head similar to FIGS. 3-4 with a reduced thickness by 0.4 mm at the outer edge (radius >120 mm) was simulated. A comparison of the contact pressure profile of this design and the process of record is shown in FIG. 10.

[0071]As can be seen in FIG. 10, the contact pressure profile is more convex as compared to the original profile which enables more removal of material from the outer edge.

Example 2: The Effect of Using a Template Support on the Removal Profile

[0072]The polishing head assembly of FIG. 5 was simulated by FEM. The floor of the cap (i.e., polishing plate) was made thinner by 0.4 mm for radius <140 mm. An additional template support of thickness (T=0.4 mm) and Young's Modulus (Y=7.5 MPa) was added between the polishing plate and the template as shown in FIG. 5.

[0073]A comparison of the contact pressure profile for this assembly and the process of record is shown below in FIG. 11. As shown in FIG. 11, the contact pressures profiles for this embodiment is a smooth more upwardly curve or convex as compared to the original design.

Example 3: The Effect of Using a Template Having a Step and a Template Support on the Removal Profile

[0074]The polishing head assembly of FIG. 7 was simulated by FEM. In this embodiment, the polishing plate and template thickness varies along the radius along with an additional template support between the plate and the template.

[0075]A comparison of the contact pressure profile for this assembly and the process of record is shown in FIG. 12. Using a thinner plate at the edge along with a template support also provided a more convex contact pressure profile as compared to the original design as shown below in FIG. 12.

Example 4: The Effect of Using a Thicker Floor on the Removal Profile

[0076]Another embodiment of the polishing head as shown in FIG. 9 was simulated by FEM. The polishing plate was made stiffer by increasing the thickness of the floor to 8.5 mm at all radii.

[0077]A comparison of the contact pressure profile for this assembly and the POR is shown below in FIG. 13. Using a thicker polishing plate, a smoother convex contact pressure profile can be achieved.

[0078]It is difficult to generate a flat contact pressure profile using the POR and achieve a similar removal rate as seen in its domed profile. But at a lower chamber pressure, the embodiment of FIG. 9 also showed capability of generating a flat contact pressure profile. FIG. 14 shows a comparison of the “domed” and “flat” contact pressures profiles achieved by the POR and the “flat” profile achieved by the embodiment of FIG. 9. The normalized contact pressure profiles shown in the figures were offset a by a fixed amount to separate plots for each combination.

[0079]At low chamber pressures a “nearly” flat contact pressure profile may be achieved in the original design, where the contact pressure variation from the center to the edge (r=145 mm) for the original assembly is around 1730 Pa. In the embodiment of FIG. 9, a more uniformly flat profile can be achieved on lowering the chamber pressure. The contact pressure variation from center to the edge (r=145 mm) for the embodiment of FIG. 9 was around 481 Pa. The average contact pressure was similar for the three profiles shown above which would result in a similar removal rate, but the embodiment of FIG. 9 at a lower chamber pressure provides a flatter contact pressure profile with a lower contact pressure variation from center to the edge (r=145 mm) resulting in a more uniform contact pressure distribution along the plate.

[0080]FEM simulations results illustrate the ability of all designs to modulate the contact pressure profiles for adjusting the actual removal profiles. A given desired contact pressure profiles can be achieved by tuning the polishing plate thickness and width, template support's material, thickness, and width.

[0081]As used herein, the terms “about,” “substantially,” “essentially” and “approximately” when used in conjunction with ranges of dimensions, concentrations, temperatures or other physical or chemical properties or characteristics is meant to cover variations that may exist in the upper and/or lower limits of the ranges of the properties or characteristics, including, for example, variations resulting from rounding, measurement methodology or other statistical variation.

[0082]When introducing elements of the present disclosure or the embodiment(s) thereof, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” “containing,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of terms indicating a particular orientation (e.g., “top,” “bottom,” “side,” etc.) is for convenience of description and does not require any particular orientation of the item described.

[0083]As various changes could be made in the above constructions and methods without departing from the scope of the disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawing[s] shall be interpreted as illustrative and not in a limiting sense.