Polishing head assembly having recess and cap

Abstract

This invention discloses a grinding head assembly for grinding semiconductor wafers, comprising a grinding head and a cover. The grinding head has a groove along a bottom. The groove has a concave surface. The cover is positioned within the groove. The cover includes an annular wall fixed to the grinding head and a base plate engaged to the annular wall at a joint. The base plate extends across the annular wall and has an upper surface and a lower surface. The upper surface is spaced from the concave surface to form a chamber therebetween. A portion of the base plate near the joint exhibits reduced deformation resistance to allow that portion of the base plate near the joint to be deflected relative to the grinding head by a pressure change within the chamber.

Description

Technical Field

[0001] The present invention is generally related to the grinding of semiconductor wafers, and more specifically, to a grinding head assembly having a groove and a cover. Prior Technology

[0002] Semiconductor wafers are commonly used in the production of integrated circuit (IC) chips for printed circuit systems. The circuit system is first printed in miniaturized form onto the surface of the wafer. Next, the wafer is cleaved into circuit chips. This miniaturized circuit system requires extremely flat and parallel front and back surfaces of each wafer to ensure that the circuit system can be properly printed across the entire surface of the wafer. To achieve this, grinding and polishing processes are typically used to improve the flatness and parallelism of the front and back surfaces of the wafer after it has been cleaved from a wafer ingot. A particularly good surface finish is required when grinding wafers in preparation for printing miniaturized circuits on the wafer using an electron beam lithography or photolithography process (hereinafter referred to as "lithography"). The wafer surface to be printed with the miniaturized circuits must be flat.

[0003] A polishing machine typically includes a circular or annular polishing pad mounted on a turntable or pressure plate, driven to rotate 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. An polishing slurry, typically containing chemical abrasives and abrasive particles, is applied to the pad for greater polishing interaction between the pad and the wafer surface. This type of polishing operation is commonly referred to as chemical mechanical polishing (CMP).

[0004] During operation, the pad rotates and the wafer contacts the pad and is forced against the pad by the grinding head. When the pad wears (for example, after several hundred wafers), the wafer flatness parameter degrades because the pad is no longer flat and has a wear ring band, forming a depression along the grinding surface of the pad. This pad wear affects wafer flatness and can cause a "dimple" or "bump" or a combination thereof resulting in a "W-shape".

[0005] When the flatness of the wafer becomes unacceptable, a new polishing pad should be used to replace the worn polishing pad. Frequent pad replacements not only increase the cost of operating the polishing equipment due to the large number of pads that need to be purchased, stored, and disposed of, but also due to the significant downtime required to change polishing pads.

[0006] Therefore, a polishing apparatus is needed that can optimize flatness parameters by modulating the wafer thickness shape in the polishing process of bumps, depressions, and + / - w-shaped processes.

[0007] This [Prior Art] section is intended to introduce to the reader various forms of art that may be associated with various aspects of the present invention, which will be described and / or claimed below. This discussion is believed to help provide the reader with background information to facilitate a better understanding of one of the various aspects of the present invention. Therefore, it should be understood that these statements are read in this context and not as an admission of prior art. Summary of the Invention

[0008] In one embodiment, a polishing head assembly for polishing semiconductor wafers includes a polishing head and a cover. The polishing head has a groove along a bottom. The groove has a concave surface. The cover is positioned within the groove. The cover includes an annular wall fixed to the polishing head and a base plate engaged to the annular wall at a joint. The base plate extends across the annular wall and has an upper surface and a lower surface. The upper surface is spaced from the concave surface to form a chamber therebetween. A portion of the base plate near the joint experiences reduced deformation resistance to allow that portion of the base plate near the joint to be deflected relative to the polishing head by a pressure change within the chamber.

[0009] In another embodiment, a polishing head assembly for polishing semiconductor wafers includes a polishing head and a cover. The polishing head has a top and a recess along a bottom. The recess has a concave surface. Holes extend from the top through the concave surface. The cover is positioned within the recess. The cover includes an annular wall having apertures corresponding to the apertures. The apertures and corresponding apertures receive fasteners to secure the annular wall to the concave surface. The cover also includes a base plate engaged at a joint with the annular wall. The base plate extends across the annular wall. The base plate has an upper surface and a lower surface. The upper surface is spaced from the concave surface to form a chamber therebetween. The base plate is deflectable relative to the polishing head by a pressure change within the chamber. A portion of the base plate near the joint experiences reduced deformation resistance to allow that portion of the base plate near the joint to deflect relative to the polishing head.

[0010] In another embodiment, a polishing head assembly for polishing semiconductor wafers includes a polishing head and a cover. The cover has an annular wall fixed to the polishing head and a base plate engaged with the annular wall at a joint. The polishing head and the cover define a chamber between the polishing head and the base plate of the cover. The base plate is made of a metallic material capable of deflecting relative to the polishing head in response to a pressure change in the chamber. The thickness of at least one of the annular wall and the base plate decreases near the joint to reduce deformation resistance of the base plate near the joint.

[0011] Various modifications exist relative to the features described in the above-mentioned specifications. Further features may also be incorporated into the above specifications. These modifications and additional features may exist individually or in any combination. For example, the various features discussed below with respect to any of the embodiments illustrated in the figures may be incorporated individually or in any combination into any of the above specifications. Simple Explanation of the Diagram

[0012] Figure 1 is a partial schematic diagram of a grinding device;

[0013] Figure 2 is a cross-sectional view of a grinding head assembly adapted for installation and use in the grinding apparatus shown in Figure 1;

[0014] Figure 3 is a cross-sectional view of one of the grinding head assemblies shown in Figure 1, featuring a base plate with only partial downward deflection;

[0015] Figure 4 is a cross-sectional view of a grinding head assembly adapted for installation and use in the grinding apparatus shown in Figure 1;

[0016] Figure 5 is a cross-sectional view of another example of a grinding head assembly adapted for installation and use in the grinding apparatus shown in Figure 1;

[0017] Figure 6 is a cross-sectional view of another example of a grinding head assembly adapted for installation and use in the grinding apparatus shown in Figure 1;

[0018] Figure 7 is a cross-sectional view of another example of a grinding head assembly adapted for installation and use in the grinding apparatus shown in Figure 1;

[0019] Figure 8 is a cross-sectional view of another example of a grinding head assembly adapted for installation and use in the grinding apparatus shown in Figure 1; and

[0020] The same element symbols in various diagrams indicate the same element. Implementation

[0021] This application claims priority to U.S. Provisional Patent Application No. 63 / 265,951, filed December 23, 2021, the entire contents of which are incorporated herein by reference.

[0022] Typically, and in embodiments of the present invention, the suitable substrate "wafer" (which may also refer to a "semiconductor wafer" or "silicon wafer") comprises a single-crystal silicon wafer, such as a silicon wafer obtained by dicing a single-crystal silicon ingot formed, for example, by the Czochralski method or the floating zone method. Each wafer includes 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. A circumferential edge joins the front and rear surfaces. The wafer can be of any diameter suitable for use by those skilled in the art, including, for example, 200 mm, 300 mm, greater than 300 mm, or even 450 mm diameter wafers.

[0023] In one embodiment, a semiconductor wafer that has been previously rough-polished to have one of its rough front and rear surfaces first undergoes an intermediate polishing operation, wherein the front surface, but not the rear surface, is polished to improve flatness parameters or to smooth the front surface and remove treatment 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 also placed on a turntable of a polishing machine, wherein the front surface of the wafer contacts the polishing surface of a polishing pad.

[0024] A grinding head assembly mounted on the machine can move vertically along an axis extending through the wafer. As the turntable rotates, the grinding head assembly moves against the wafer to push the wafer toward the turntable, thereby pressing the front surface of the wafer into grinding engagement with the grinding surface of the grinding pad.

[0025] A conventional polishing slurry containing abrasive particles and a chemical etchant is applied to a polishing pad. The polishing pad applies the slurry to the surface of the wafer to remove material from the front surface of the wafer, resulting in a surface with improved smoothness. As an example, intermediate polishing operations preferably remove material smaller than about 1 micrometer from the front side of the wafer.

[0026] Next, the wafer undergoes a precision polishing operation, in which the wafer's front surface is precision polished to remove fine or "micro" scratches caused by large-area colloidal silica (such as Syton® from DuPont Air Products Nanomaterials, LLC) in the intermediate steps, resulting in a highly reflective, undamaged front surface of the wafer. Intermediate polishing operations typically remove more wafer material than precision polishing operations. Precision polishing of the wafer can be performed in the same polisher used for intermediate polishing, as described above. However, a separate polisher can also be used for precision polishing operations. A precision polishing slurry typically contains an amino base and a reduced concentration of colloidal silica is injected between the polishing pad and the wafer. The polishing pad allows the precision polishing slurry to act on the wafer's front surface to remove any remaining scratches and haze, resulting in a typically highly reflective and undamaged front surface.

[0027] Referring to Figure 1, a portion of a polishing apparatus is schematically shown and is generally indicated by 100. Polishing apparatus 100 can be used to polish one front surface of a semiconductor wafer W. Other types of polishing apparatus may be used upon careful consideration.

[0028] The polishing apparatus 100 includes a wafer holding mechanism, such as a template including a backing film 110 and a retaining ring 120, a polishing head assembly 130, and a turntable 140 having a polishing pad 150. The backing film 110 is located between the polishing head assembly 130 and the retaining ring 120 for receiving a wafer W. The retaining ring 120 has at least one circular opening for receiving the wafer W to be polished therein.

[0029] In this embodiment, the wafer W is attached to and held against the polishing head assembly 130 by surface tension. To create surface tension, a pressure-sensitive adhesive is used to attach a wet-saturated backing film 110 to the polishing head assembly 130. The backing film 110 and the retaining ring 120 form a template or "wafer holding template". The backing film 110 is typically a soft polymer pad or other suitable material.

[0030] Next, the wafer W is pressed into a wet-saturated backing film 110 to remove or squeeze out most of the water or other suitable liquid. The squeezing out of water causes the wafer to remain on the backing film 110 due to surface tension and atmospheric pressure on the exposed surface of the wafer. This squeezing out of water then mounts the wafer to the grinding head assembly 130.

[0031] A portion of the polishing head assembly 130 is sufficiently flexible to deform in response to changes in pressure applied to it, and sufficiently rigid to remain undeformed when the wafer is pressed into a wet saturated stencil. Surface tension provides a constant holding force on the surface of the wafer. This constant holding force causes any deformation of the polishing head assembly 130 adjacent to the wafer to be directly translated into proportional deformation of the wafer.

[0032] The function of holding the wafer W by surface tension differs from other known mechanisms that use flexible films or vacuum to hold the wafer against the grinding head assembly. As known in this art, when the wafer is pushed onto a flexible film, the flexible film deforms to create a space or vacuum cavity between the wafer and the flexible film. These vacuum cavities allow the film to pick up the wafer. Other films have vacuum holes connected to a vacuum to create a low-pressure region for wafer pickup.

[0033] The polishing apparatus 100 applies a force to the polishing head assembly 130 to vertically move the polishing head assembly 130 relative to the wafer W and the turntable 140, raising and lowering the polishing head assembly 130. An upward force raises the polishing head assembly 130, and a downward force lowers the polishing head assembly. As discussed above, the downward vertical movement of the polishing head assembly 130 against the wafer W provides polishing pressure to the wafer to push it into the polishing pad 150 of the turntable 140. When the polishing apparatus 100 increases the downward force, the polishing head assembly 130 moves vertically downward to increase the polishing pressure.

[0034] A portion of the grinding head assembly 130, the grinding pad 150, and the turntable 140 are rotated at a selected rotational speed by a suitable drive mechanism (not shown) as known in the art. The rotational speeds of the grinding pad and the turntable may be the same or different. In some embodiments, the grinding apparatus 100 includes a controller (not shown) that allows an operator to select the rotational speeds of both the grinding head assembly 130 and the turntable 140, as well as the downward force applied to the grinding head assembly.

[0035] Referring to Figure 2, the figure shows a grinding head assembly 200 adapted for installation and use in one of the grinding apparatuses 100. The grinding head assembly 200 includes a grinding head 210, a cover 240, and a belt 270. The grinding head 210 and / or the cover 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 grinding head 210 and / or the cover 240 may be made of cast aluminum (e.g., MIC6® Aluminum Cast Plate, available from Alcoa). Alternatively, the cover 240 may be made of a ceramic material (such as alumina), a plastic material, or a stainless steel material with an anti-corrosion coating (such as, for example, diamond-like carbon).

[0036] The grinding head 210 has a top 212 and a bottom 214 that are substantially parallel to each other. The grinding head 210 has a platform 220 and an annular member 230 extending downward from the platform 220. A concave surface 216 is formed in the bottom 214 of the grinding 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 grinding head 210. The outer surface 232 of the annular member 230 forms the circumference of both the grinding head 210 and the grinding head assembly 200. The annular member 230 has an inner surface 234 that is angled relative to the outer surface 232, such that the annular member 230 is thinnest at the bottom 214 of the grinding 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.

[0037] The cover 240 has a base plate 242 and an annular wall 250 extending upward along the periphery of the base plate. The annular wall 250 has an outer surface 252 that mates with the inner surface 234 of the annular member 230. Therefore, the outer surface 252 of the annular wall 250 is also angled to conform to the inner surface 234 of the annular member 230. An adhesive (not shown) is used to attach the outer surface 252 of the annular wall 250 to the inner surface 234 of the annular member 230 of the grinding head 210. The adhesive may be an epoxy resin.

[0038] The base plate 242 extends across a bottom opening formed by the annular member 230. The base plate 242 has a top surface 244 and a bottom surface 246. A chamber 202 is formed between the top surface 244 of the base plate 242 and the concave surface 216 of the grinding 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 the annular wall 250 are thicker and adapted to be more rigid than the base plate 242.

[0039] Metals used in the polishing head assembly 200 may contaminate the wafer as a source of metal ions through polishing chemicals or slurry. To prevent metal contamination of the slurry and wafer from the cover 240, a template comprising 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) can be used to create a barrier between the slurry and the cover 240. The backing film 110 is typically a thin soft polymer pad or other suitable material. The backing film 110 suitably comprises two or more layers of material (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 non-woven material (e.g., felt) layer. The adhesive layer seals the backing film 110 to the bottom surface 246 of the cover 240. The thin plastic film layer provides a protective barrier between the cover 240 and the slurry and / or wafer W. A layer of polyurethane foam or nonwoven material (such as felt) contacts the wafer and provides a surface similar to a polishing pad (such as polishing pad 150 shown in Figure 1). A retaining ring 120 extends downward from the backing film 110 and is typically made of plastic. The wafer is received by the retaining ring 120 and held against the backing film 110 by surface tension. Therefore, the wafer does not directly contact the cover 240.

[0040] To prevent metal contamination of the slurry and wafer from the grinding head assembly 200, the grinding head 210 and the cover 240 are externally connected using a strip 270 forming a barrier to prevent the slurry from contacting the metal and contaminating the wafer. The annular member 230 has a side groove 238 extending inward from the outer surface 232 at the bottom 214. A tab 248 extends outward from the annular wall 250 of the cover 240 opposite to the base plate 242. Both the tab 248 and the side groove 238 receive the strip 270 and can be sealed to the strip 270 using an adhesive (such as epoxy resin). The strip 270 can overlap with the template backing film 110 and / or retaining ring 120 to form a seal therebetween to prevent metal contamination from the grinding process of the grinding head 210. The 270 is made of plastic, such as polyetherimide (e.g., ULTEM™ Resin 1000, available from SABIC), polyetheretherketone, polyphenylene sulfide, or polyethylene terephthalate.

[0041] The grinding head assembly 200 is attached to a spindle (not shown) of the grinding apparatus 100. The spindle is a tube having a central channel (not shown). The central channel is open at one end to the grinding head assembly 200 and connected at the other end to a rotary connector (not shown). To adjust the pressure within the chamber 202, a pressurizing source (not shown) is provided through the central channel and connected to a chamber passage 222 (e.g., via a quick-disconnect coupling plug). The chamber passage 222 extends through the platform 220 to the chamber 202. The pressurizing source (not shown) supplies a pressurizing medium or fluid to and from the chamber 202 via the spindle (not shown). The pressurizing source may provide a pneumatic supply for increasing or decreasing the pressure within the chamber 202 of the grinding head assembly 200.

[0042] The base plate 242 is a semi-rigid "flexible plate" made of the same material as the cover 240 (e.g., a metallic material). The base plate 242 is adapted to precisely deform or deflect to alter the pressure distribution and grinding pressure profile, while remaining sufficiently rigid to mount and remove wafers on the backing film 110 by surface tension. The rigidity of the base plate 242 ensures that it does not substantially deform during the mounting of a wafer onto the grinding head assembly 200. The base plate 242 can remain substantially flat in an initial or undeflected state. As the grinding pressure increases and the pressure within the chamber 202 increases, the base plate 242 temporarily deflects in a direction perpendicular to the grinding surface. The cover 240 is not permanently deflected or deformed by pressure. Depending on the amount of pressurized medium or fluid supplied to chamber 202 and the grinding pressure, the substrate 242 can be transformed into a pressurized deflection or downward bending shape (shown in Figure 3), a flat shape substantially parallel to one bottom surface of the grinding head 210 (shown in Figure 2), and an upward bending or convex shape (not shown in the figure). When the pressure in chamber 202 is adjusted and the substrate 242 deforms, the uniformly distributed surface tension of the wafer mounted and maintained on the backing film 110 provides direct deformation of the wafer. Increasing or decreasing the pressure within chamber 202 can thereby cause the surface of the substrate 242 and the wafer to expand outward, remain flat, or be sucked in.

[0043] Pressure variations within chamber 202 cause variations in a given or predetermined polishing pressure P. A pressure source (not shown) may be connected to a controller (not shown) for monitoring and adjusting the pressure within 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 feed batch, or it may be electronically controlled batch-by-batch, or even wafer-by-wafer. In some embodiments, a characteristic wafer profile is obtained from a plurality of wafers, and the downward pressure applied to the wafer by the polishing head assembly 200 and the distribution of that pressure are varied by adjusting the pressure within chamber 202. Suitablely, the variation in polishing pressure may range from about 0.7 P to about 1.3 P. Therefore, varying the polishing pressure P by changing the pressure within chamber 202 provides an operator with a control variable and the ability to adjust the polishing profile 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.

[0044] Referring to Figure 3, which shows the polishing head assembly 200 of Figure 2, a portion 280 of the base plate 242 of the cover 240 deflects into a downward dome shape due to the increased pressure within the chamber 202. This change in the shape of the base plate 242 causes a change in the force distribution of the polishing pressure across a wafer (e.g., wafer W shown in Figure 1), thereby causing the wafer to bend in response. This change in force distribution also causes a change in the rate at which material is removed from the wafer. Typically, the removal rate increases when the Von Mises stress applied between the wafer and the polishing pad 150 (shown in Figure 1) increases. The portion 280 of the base plate 242, deflected in response to a pressure change within the chamber 202, increases or decreases this Von Mises stress as the pressure within the chamber 202 increases or decreases.

[0045] However, we have observed a significant reduction in material removal from the wafer by the polishing head assembly 200 near the wafer edge. This is a result of a non-uniform stress distribution across the substrate 242, and specifically, lower Von Mises stress is applied between the wafer edge and the polishing pad 150. Even when the pressure within the chamber 202 of the polishing head assembly 200 increases, these Von Mises stresses typically do not increase.

[0046] The uneven stress distribution is caused by the base plate 242 of the grinding head assembly 200 not deflecting completely and uniformly in response to increases and / or decreases in pressure within the chamber 202. This is attributed to the uneven deformation resistance across the base plate 242. As shown in Figure 3, the base plate 242 engages with the annular wall 250 at a joint 290. The joint 290 acts as a hinge around which the base plate 242 can temporarily deflect without permanent deformation relative to the grinding head 210. Due to the semi-rigidity of the base plate 242, a portion 280 of the base plate 242 has a suitable deformation resistance to allow the portion 280 to deflect in response to a pressure change within the chamber 202. However, the deformation resistance increases at the portion 282 of the base plate 242 near the joint 290. Therefore, the portion 282 does not deflect in response to a pressure change within the chamber 202. Therefore, increasing the pressure within chamber 202 does not cause a corresponding increase in Von Mises stress applied between the edge of the wafer mounted to portion 282 of base plate 242 and the polishing pad 150. During polishing using the polishing head assembly 200, the uneven distribution of Von Mises stress in the polished wafer produces an uneven removal profile. Furthermore, portion 282 defines a periphery of base plate 242 and can extend from connector 290 to portion 280 by a radial distance of up to approximately 30 mm. Therefore, the uneven removal profile can cover a large portion of the wafer, resulting in unacceptable flatness of the wafer.

[0047] It is believed that the thickness of the annular wall 250 near the joint 290 and / or the thickness of the base plate 242 near the joint 290 contributes to a relatively high deformation resistance of a portion 282 of the base plate 242. The thickness of one portion of the annular wall 250 near the joint 290 is typically about 8 mm. The thickness of the annular wall 250 is measured as a distance between the outer surface 252 and an inner surface 253 of the annular wall 250. The thickness of one portion 282 of the base plate 242 is typically from about 5 mm to about 7 mm. The thickness of the base plate 242 is measured as a distance between the top surface 244 and the bottom surface 246.

[0048] Referring now to Figure 4, an example of a grinding head assembly 400 adapted for installation and use in a grinding apparatus 100 is shown. The grinding head assembly 400 includes the elements and components shown in Figure 2 and the aforementioned grinding head assembly 200. Additionally, the annular wall 250 of the cover 240 includes a first portion 254 joined to the base plate 242 to form a connector 290 and a second portion 256 extending from the first portion 254. The first portion 254 is defined by a recess 255 formed in an inner surface 253 of the annular wall 250 at the connector 290. The recess 255 may be U-shaped or substantially circular. The radius of the recess 255 is suitably greater than 1 mm, for example, from greater than 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 recess 255. Suitablely, the radius of the notch 255 is such that the thickness of the first portion 254 is not reduced to less than 1.5 mm. For example, the thickness of the first portion 254 can be suitable from about 2 mm to about 5 mm, or about 3 mm. The notch 255 also 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 appropriately weakens the deformation resistance of one of the portions 282 of the base plate 242 approaching the joint 290 (shown in Figure 3).

[0049] Computer numerical control (CNC) milling can be appropriately performed to form the notch 255 and / or fillet 257 to reduce the deformation resistance of portion 282 of the base plate 242. Generally, the notch 255 and / or fillet 257 cannot be formed using conventional machining techniques (such as a conventional fine grinding process) for the base plate 242 of the flattened cover 240. However, conventional machining techniques can be modified with careful consideration to form the notch 255 and fillet 257. Alternatively, CNC milling can be used to provide a portion 282 of the base plate 242 having a thickness of from about 5 mm to about 6 mm (e.g., 5.5 mm). The base plate 242 can suitably have a continuous thickness extending across the entire diameter of the base plate 242 between the annular walls 250. Alternatively, the thickness of the base plate 242 can vary across the diameter of the base plate 242 between the annular walls 250.

[0050] Referring to Figure 5, another example of a grinding head assembly 500 adapted for installation and use in a grinding apparatus 100 is shown. The grinding head assembly 500 includes the elements and components shown in Figure 2 and the aforementioned grinding head assembly 200. Additionally, the inner surface 253 of the annular wall 250 is angled inward toward the fillet 257 formed at the connector 290. Suitablely, the thickness of the annular wall 250 at the connector 290 is reduced to a thickness of approximately 3 mm to approximately 5 mm or approximately 3 mm. The inner surface 253 may be angled to conform to the outer surface 252 such that the thickness of the annular wall 250 remains constant. Alternatively, the inner surface 253 may be angled such that the thickness of the annular wall 250 tapers inward toward the connector 290 along the annular wall 250, such that the annular wall 250 has a minimum thickness at the connector 290. Reducing the thickness of the annular wall 250 at the joint 290 and / or forming a fillet 257 appropriately weakens the deformation resistance of one portion 282 of the base plate 242 approaching the joint 290 (shown in Figure 3).

[0051] Computer numerical control (CNC) milling can be used to appropriately perform the forming of an angled profile of the inner surface 253 to reduce the thickness of the annular wall 250, and to form a fillet 257 to reduce the deformation resistance of the portion 282 of the base plate 242. Generally, conventional machining techniques (such as a conventional fine grinding process) for the base plate 242 of the flattened cover 240 cannot be used to form the fillet 257 and the angled profile of the inner surface 253. However, conventional machining techniques can be modified with careful consideration to form the fillet 257 and the angled profile of the inner surface 253. Alternatively, CNC milling can be used to provide a portion 282 of the base plate 242 having a thickness of from about 5 mm to about 6 mm (e.g., 5.5 mm). The base plate 242 can appropriately have a continuous thickness extending across the entire diameter of the base plate 242 between the annular walls 250. Alternatively, the thickness of the base plate 242 can vary across the diameter of the base plate 242 between the annular walls 250.

[0052] Referring now to Figure 6, another example of a grinding head assembly 600 adapted for installation and use in a grinding apparatus 100 is shown. The grinding head assembly 600 includes a grinding head 610, a cover 640, and a belt 670. The grinding head 610 and / or the cover 640 are suitably made of a metallic material (such as aluminum or steel), or may be made of another suitable structural material. For example, the grinding head 610 and / or the cover 640 may be made of cast aluminum (e.g., MIC6® Aluminum Cast Plate, available from Alcoa). Alternatively, the cover 640 may be made of a ceramic material (e.g., alumina), a plastic material, or a stainless steel material with an anti-corrosion coating (such as, for example, diamond-like carbon).

[0053] The grinding head 610 has a top 612 and a bottom 614 that are substantially parallel to each other. The grinding head 610 has a platform 620 and an annular member 630 extending downward from the platform 620. A concave surface 616 is formed in the bottom 614 of the grinding 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 through the concave surface 616.

[0054] The annular member 630 has an outer surface 632 that is substantially perpendicular to the top 612 and bottom 614 of the grinding head 610. The outer surface 632 of the annular member 630 forms the circumference of both the grinding head 610 and the grinding head assembly 600. The annular member 630 has an inner surface 634 that is substantially parallel to the outer surface 632.

[0055] The cover 640 has a base plate 642 and an annular wall 650 extending upward along one periphery of the base plate. The annular wall 650 has an outer surface 652 that mates with the inner surface 634 of the annular member 630 and is substantially parallel to the inner surface 634 of the annular member 630. An adhesive (not shown) can be used to attach the outer surface 652 of the annular wall 650 to the inner surface 634 of the annular member 630 of the grinding head 610. The adhesive may be epoxy resin. The annular wall 650 extends upward to a shoulder 692. The shoulder 692 has a top edge 694 that mates with the concave surface 616 of the grinding head 610. An aperture 658 is formed in the shoulder 692 at the top edge 694 and corresponds to an aperture 618. Hole 618 and corresponding aperture 658 receive fasteners (not shown) (such as screws, for example) to attach the cover 640 to the grinding head 610 by securing the top edge 694 of shoulder 692 to concave surface 616. The fasteners may suitably be formed of a plastic or metal material with an anti-corrosion coating. Alternatively, a cover (not shown) may cover at least a portion of the top 612 of the grinding head 610 to prevent grinding chemicals or slurry from contacting the fasteners and / or entering the hole 618 during a grinding process. Shoulder 692 may also include an O-ring (not shown) that forms a seal when the top edge 694 is secured to concave surface 616.

[0056] A base plate 642 extends across a bottom opening formed by an annular member 630. The base plate 642 has a top surface 644 and a bottom surface 646. A chamber 602 is formed between the top surface 644 of the base plate 642 and the concave surface 616 of the grinding head 610. The annular member 630 and 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 adjusted to be more rigid than the base plate 642.

[0057] Metals used in the polishing head assembly 600 may contaminate the wafer as a source of metal ions through polishing chemicals or slurry. To prevent metal contamination of the slurry and wafer from the cover 640, a template comprising 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 create a barrier between the slurry and the cover 640. The backing film 110 is typically a thin soft polymer pad or other suitable material. The backing film 110 suitably comprises two or more layers of material (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 non-woven material (e.g., felt) layer. The adhesive layer seals the backing film 110 to the bottom surface 646 of the cover 640. The thin plastic film layer provides a protective barrier between the cover 640 and the slurry and / or wafer W. A layer of polyurethane foam or nonwoven material (such as felt) contacts the wafer and provides a surface similar to a polishing pad (such as polishing pad 150 shown in Figure 1). A retaining ring 120 extends downward from the backing film 110 and is typically made of plastic. The wafer is received by the retaining ring 120 and held against the backing film 110 by surface tension. Therefore, the wafer does not directly contact the cover 640.

[0058] To prevent metal contamination of the slurry and wafer from the grinding head assembly 600, the grinding head 610 and the cover 640 are externally connected using a strip 670 forming a barrier to prevent the slurry from contacting the metal and contaminating the wafer. The annular member 630 has a side groove 638 extending inward from the outer surface 632 and an inner groove 639 extending inward from the inner surface 634 at the bottom 614. A tab 648 extends outward from the annular wall 650 of the cover 640 opposite to the base plate 642. The tab 648, side groove 638, and inner groove 639 each receive the strip 670 and can be sealed to the strip 670 using an adhesive (such as epoxy resin). The strip 670 can overlap with the template backing film 110 and / or retaining ring 120 to form a seal therebetween to prevent metal contamination from the grinding process of the grinding head 610. The 670 is made of plastic, such as polyetherimide (e.g., ULTEM™ Resin 1000, available from SABIC), polyetheretherketone, polyphenylene sulfide, or polyethylene terephthalate.

[0059] The band 670 may be non-monomeric and 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 together at the segment joints (not shown) and sealed to the grinding head 610 and / or the cover 640 using an adhesive (such as epoxy resin). To prevent the seal between the band 670 and the grinding head 610 and / or the cover 640 from loosening due to adhesive failure, the band 670 may include an interlocking member to secure the band 670 to the grinding head assembly 600. For example, the band 670 may include a dovetail 672 that forms a joint with an inner groove 639 formed on the inner surface 634 of the annular member 630 and an upwardly extending member of the tab 648. In addition to an adhesive or as an alternative, the dovetail 672 may be used to secure the band 670 to the grinding head 610 and / or the cover 640.

[0060] Similar to the polishing head assembly 200 described in detail herein, a pressurizing medium or fluid is used to pressurize chamber 602. Chamber 602 may be connected to a pressurizing source (not shown) to provide the pressurizing medium or fluid to chamber 602, as described herein with respect to polishing head assembly 200. The pressurizing source (not shown) is connected to a chamber passage 622 (e.g., via a quick-disconnect coupling plug). Chamber passage 622 extends through platform 620 to chamber 602. Similar to the base plate 242 described in detail herein, base plate 642 is a semi-rigid "flexible plate" adapted to precisely deform to change the pressure distribution and polishing pressure profile while remaining sufficiently rigid to mount and remove wafers from backing film 110 by surface tension. Base plate 642 can be temporarily deflected relative to polishing head 610 without permanent deformation. Adjusting the pressure in chamber 602 causes deflection of base plate 642. In an embodiment where the shoulder 692 includes an O-ring (not shown), a seal formed at the junction of the top edge 694 and the concave surface 616 prevents the pressurized medium or fluid from leaking from the chamber 602, thereby maintaining a given pressure in the chamber 602.

[0061] Except for the shoulder 692, the annular wall 650 of the cover 640 includes a first portion 654 that engages with the base plate 642 to form a joint 690, the base plate being temporarily deflectable about the joint 690 in response to a pressure change within the chamber 602. The first portion 654 is connected to the shoulder 692, wherein a second portion 656 extends between the first portion 654 and the shoulder 692. The thickness of the annular wall 650 is greatest at the shoulder 692, as shown in FIG6. 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 thickness less than that of the second portion 656. For example, the thickness of the first portion 654 may be from about 3 mm to about 5 mm, or about 3 mm. The notch 655 also forms a rounded corner 657 at the joint 690. By reducing the thickness of the first portion 654 through the notch 655 and / or forming the fillet 657, the deformation resistance of a portion of the base plate 642 near the connector 690 is appropriately weakened; otherwise, it would not be able to respond to a pressure change within the chamber 602 and deflect. This portion of the base plate may extend radially from the connector 690 to the center of the base plate 642 by up to approximately 30 mm.

[0062] Computer numerical control (CNC) milling can be appropriately performed to form the notch 655 and / or fillet 657 to reduce deformation resistance of the portion of the base plate 642 approaching the connector 690. Generally, the notch 655 and / or fillet 657 cannot be formed using conventional machining techniques (such as a conventional fine grinding process) used for the bottom 642 of the flattened cover 640. However, conventional machining techniques can be modified with careful consideration to form the notch 655 and fillet 657. Alternatively, CNC milling can be used to provide a portion of the base plate 642 approaching the connector 690 with a thickness of from about 5 mm to about 6 mm (e.g., such as 5.5 mm). The base plate 642 may suitably have a continuous thickness of one full diameter extending between the annular walls 650. Alternatively, the thickness of the base plate 642 may vary across the diameter of the base plate 642 between the annular walls 650. For example, base plate 642 may have a thickness that tapers inward from one center of base plate 642 to joint 690, as described in further detail herein.

[0063] Referring to Figure 7, another example of a grinding head assembly 700 adapted for installation and use in a grinding apparatus 100 is shown. The grinding head assembly 700 includes the elements and components shown in Figure 6 and the aforementioned grinding head assembly 600. 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 relative to the outer surface 652. The thickness of the portion 659 of the annular wall 650 gradually decreases inward from the shoulder 692 toward the joint 690, such that the annular wall 650 has a minimum thickness at the joint 690. Suitablely, the thickness of the annular wall 650 at the joint 690 is reduced to a thickness of approximately 3 mm to approximately 5 mm or approximately 3 mm. Reducing the thickness of the annular wall 650 from the shoulder 692 toward the connector 690 and / or forming a rounded corner 657 appropriately weakens the deformation resistance of a portion of the base plate 642 approaching the connector 690, otherwise it would not be able to respond to a pressure change within the chamber 602 and deflect. This portion of the base plate may extend radially up to approximately 30 mm from the center of the connector 690 toward the base plate 642.

[0064] Computer numerical control (CNC) milling can be appropriately performed to form the angled profile of the inner surface 653 to reduce the thickness of the annular wall 650, and to form the fillet 657 to reduce the deformation resistance of the portion of the base plate 642 approaching the connector 690. Generally, conventional machining techniques (such as a conventional fine grinding process) used for the bottom 642 of the flattened cover 640 cannot be used to form the fillet 657 and the angled profile of the inner surface 653. However, conventional machining techniques can be modified with careful consideration to form the fillet 657 and the angled profile of the inner surface 653. Alternatively, CNC milling can be used to provide a portion of the base plate 642 approaching the connector 690 with a thickness of from about 5 mm to about 6 mm (e.g., such as 5.5 mm). The base plate 642 can appropriately have a continuous thickness extending across the entire diameter of the base plate 642 between the annular walls 650. Alternatively, the thickness of the base plate 642 can vary across the diameter of the base plate 642 between the annular walls 650. For example, the base plate 642 may have a thickness that tapers inward from one center of the base plate 642 to the joint 690 (shown in Figure 8).

[0065] Referring to Figure 8, another example of a grinding head assembly 800 adapted for installation and use in a grinding apparatus 100 is shown. The grinding head assembly 800 includes similar elements and components to those shown in Figures 6 and 7, and the aforementioned grinding head assemblies 600 and / or 700. To reduce deformation resistance in the portion of the base plate 642 approaching the connector 690, the thickness of the base plate 642 gradually decreases inward from a radial center C toward the connector 690. Therefore, the thickness of the base plate 642 is greatest at center C and decreases to a minimum at the connector 690. The thickness of the base plate 642 may decrease from approximately 5 mm to 6 mm or approximately 5.5 mm at center C to approximately 3 mm to approximately 4 mm or approximately 3 mm at the connector 290. The thickness of the base plate 642 is gradually reduced to decrease the thickness of the base plate 642 near the connector 690, thereby appropriately weakening the deformation resistance of a portion of the base plate 642 near the connector 690, which would otherwise be unable to respond to a pressure change within the chamber 602 and deflect. This portion of the base plate 642 near the connector 690 can extend radially from the connector 690 toward the radial center C of the base plate 642 by up to approximately 30 mm.

[0066] In the example grinding head assembly 800, the annular wall 650 of the grinding head assembly 800 may or may not include additional features to reduce deformation resistance of the portion approaching the base plate 642 of the connector 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 decrease at the connector 690. For example, the inner surface 653 may be angled relative 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 connector 690 (as shown in FIG. 7). Additionally, the corner 696 at the connector 690 between the inner surface 653 of the annular wall 650 and the top surface 644 of the base plate 642 may be angled or may be rounded (i.e., forming the rounded corner 657 shown in FIG. 6 and FIG. 7). Appropriately, the thickness of the annular wall 650 at the joint 690 may be about 8 mm, or may be reduced to a thickness of about 3 mm to about 5 mm or about 3 mm.

[0067] Computer numerical control (CNC) milling can be used to properly form the tapered profile of the base plate 642 to reduce deformation resistance in the portion of the base plate 642 approaching the joint 690. Generally, the tapered profile of the base plate 642 cannot be formed using conventional machining techniques for the base plate 642 of the flattened cover 640, such as a conventional fine grinding procedure. However, with careful consideration, conventional machining techniques can be modified to form the tapered profile of the base plate 642.

[0068] The described embodiment reduces the deformation resistance of a base plate of a cover of a grinding head assembly, which would otherwise be substantially unable to deform in response to pressure changes within a chamber of the grinding head assembly. The embodiment achieves a more uniform removal profile on a grinding wafer. By reducing portions of the base plate that would otherwise be substantially unable to deform in response to pressure changes within the chamber, the distribution of Von Mises stress applied between the wafer and a grinding pad during grinding is more uniform. Specifically, the Von Mises stress applied between the wafer edge and the grinding pad can be better controlled to fine-tune the removal profile near the wafer edge.

[0069] As used herein, when used in conjunction with ranges of size, concentration, temperature or other physical or chemical properties or characteristics, the terms “about,” “substantially,” “basically,” and “approximately” are intended to cover variations that may exist within the upper and / or lower limits of the range of properties or characteristics, including, for example, variations arising from rounding, measurement methods, or other statistical variations.

[0070] When describing elements of the present invention or embodiments thereof, the articles "a" and "the" are intended to mean that one or more elements are present. The terms "comprising," "including," and "having" are intended to be inclusive and mean that additional elements may be present in addition to the listed elements. Terms indicating a particular orientation (e.g., "top," "bottom," "side," "lower," "upper," etc.) are used for ease of description and do not require any particular orientation of the described items.

[0071] Since various changes can be made to the above construction and methods without departing from the scope of the invention, all substances contained in the above description and shown in (some) figures should be interpreted as illustrative rather than restrictive.

[0072] 100: Grinding device 110: Backing film 120: Keeping ring 130: Grinding head assembly 140: Turntable 150: Grinding pad 200: Grinding head assembly 202: Chamber 210: Grinding head 212: Top 214: Bottom 216: Concave surface 220: Platform 222: Chamber access 230: Ring-shaped component 232: Outer surface 234: Inner surface 238: Side groove 240: Cover 242: Base Plate 244: Top surface 246: Bottom 248: protrusion 250: Annular wall 252: Outer surface 253: Inner surface 254: Part One 255: Notch 256: Part Two 257: Rounded corners 270: with 280: Part 282: Part 290: Connector 400: Grinding head assembly 500: Grinding head assembly 600: Grinding head assembly 602: Chamber 610: Grinding head 612: Top 614: Bottom 616: Concave surface 618: Kong 620: Platform 622: Chamber access 630: Ring-shaped component 632: Outer surface 634: Inner surface 638: Side Groove 639: Inner groove 640: Cover 642: Base Plate 644: Top surface 646: Bottom 648: protrusion 650: Annular wall 652: Outer surface 653: Inner surface 654: Part One 655: Notch 656: Part Two 657: Rounded corners 658: Kong 659: Part 670: with 672: Dovetail 690: Connector 692: Shoulder 694: Top Edge 696: Angle 700: Grinding head assembly 800: Grinding head assembly C: Center W: Wafer

Claims

1. A grinding head assembly for grinding semiconductor wafers, the grinding head assembly comprising: A grinding head having a groove along a bottom, the groove having a concave surface; The device includes a cover positioned within the recess, the cover comprising: an annular wall fixed to the grinding head, the annular wall including a first portion having a first thickness and a second portion extending from the first portion and having a second thickness; and a base plate engaged to the annular wall at a joint, the base plate extending across the annular wall and having an upper surface and a lower surface, the upper surface being spaced from the recess to form a chamber therebetween, wherein the first portion of the annular wall is engaged to the base plate, and the first thickness is less than the second thickness, such that a portion of the base plate near the joint has reduced deformation resistance relative to other portions of the base plate, allowing that portion of the base plate near the joint to be deflected relative to the grinding head by a pressure change in the chamber.

2. The grinding head assembly of claim 1, wherein the first thickness is from about 3 mm to about 5 mm.

3. The grinding head assembly of claim 2, wherein the first thickness is approximately 3 mm.

4. The grinding head assembly of claim 1, wherein the base plate has a continuous thickness of about 5 mm to about 6 mm.

5. The grinding head assembly as described in request item 1, wherein: The grinding head has a top and a hole extending from the top through the concave surface; the annular wall further includes a shoulder extending from the second portion, the shoulder having a diameter corresponding to the holes; and the holes and the corresponding diameter receive fasteners to secure the shoulder of the annular wall to the concave surface of the grinding head.

6. The grinding head assembly of claim 1, wherein the annular wall tapers inward toward the joint from the second thickness toward the first thickness, such that the first thickness of the annular wall approaches the joint, thereby reducing the deformation resistance of the portion of the base plate near the joint.

7. The grinding head assembly of claim 6, wherein the first thickness of the annular wall near the connector is from about 3 mm to about 5 mm.

8. The grinding head assembly of claim 6, wherein the first thickness of the annular wall near the connector is approximately 3 mm.

9. The grinding head assembly of claim 6, wherein the base plate has a continuous thickness of about 5 mm to about 6 mm.

10. The grinding head assembly of claim 1, wherein the thickness of one of the base plates tapers inward toward the joint such that the thickness of the base plate is minimized at the portion near the joint to reduce the deformation resistance of the portion of the base plate near the joint.

11. The grinding head assembly of claim 10, wherein the thickness of the base plate is greatest at one center of the base plate.

12. The grinding head assembly of claim 11, wherein the thickness of the base plate near the portion of the connector is about 3 mm and the thickness of the base plate at the center is from about 5 mm to about 6 mm.

13. The grinding head assembly of claim 1, wherein the cover is made of a metallic material.

14. The grinding head assembly of claim 1, wherein an adhesive is used to secure the annular wall to the grinding head.

15. A grinding head assembly for grinding semiconductor wafers, the grinding head assembly comprising: A grinding head having a top and a groove along a bottom having a concave surface, and a hole extending from the top through the concave surface; A cover body positioned within the recess, the cover body comprising: an annular wall having an aperture corresponding to the holes, wherein the holes and the corresponding aperture receive fasteners to secure the annular wall to the recess. A base plate is joined to the annular wall at a joint, the base plate extending across the annular wall, the base plate having an upper surface and a lower surface, the upper surface being spaced from the concave surface to form a chamber therebetween, the base plate being deflectable relative to the grinding head by a pressure change in the chamber; wherein a portion of the base plate near the joint has reduced deformation resistance compared to other portions of the base plate, allowing that portion of the base plate near the joint to deflect relative to the grinding head.

16. The grinding head assembly of claim 15, wherein the thickness of one of the base plates tapers inward toward the joint such that the thickness of the base plate is minimized at the portion near the joint to reduce the deformation resistance of the portion of the base plate near the joint.

17. The grinding head assembly of claim 16, wherein the thickness of the base plate at the portion near the connector is about 3 mm and the thickness of the base plate at one center of the base plate is from about 5 mm to about 6 mm.

18. The grinding head assembly of claim 15, wherein the cover is made of a metallic material.

19. A grinding head assembly for grinding semiconductor wafers, the grinding head assembly comprising: A grinding head having a platform and a hole extending through the platform; A cover having an annular wall fixed to the grinding head and a base plate joined to the annular wall at a joint, the annular wall having an aperture corresponding to the holes, wherein the holes and the corresponding aperture receive fasteners to secure the annular wall to the platform of the grinding head; wherein the grinding head and the cover define a chamber between the grinding head and the base plate of the cover; wherein the base plate is made of a metallic material capable of responding to a pressure change in the chamber relative to the deflection of the grinding head; and wherein the thickness of at least one of the annular wall and the base plate decreases near the joint, such that the deformation resistance of the base plate near the joint is weakened compared to other portions of the base plate.

Images