Polishing apparatus and pressing pad for pressing polishing tool

A polishing apparatus which can keep a width of a polishing tool constant when a peripheral portion of a substrate is polished by the polishing tool is disclosed. The polishing apparatus includes a substrate holder 3 configured to hold a substrate W and to rotate the substrate W, and a pressing pad 50 configured to press a polishing tool 23 against a peripheral portion of the substrate W held by the substrate holder 3. The pressing pad 50 includes an elastic member 55 having a pressing surface 55a configured to press the polishing tool 23 against the peripheral portion of the substrate W and a support member 56 configured to support the elastic member 55. The support member 56 has a recess 57 formed in a front surface 56a of the support member 56, the elastic member 55 being capable of entering the recess 57.

CROSS REFERENCE TO RELATED APPLICATIONS

This document claims priority to Japanese Patent Application No. 2016-243295, filed Dec. 15, 2016 and Japanese Patent Application No. 2017-210426, filed Oct. 31, 2017, the entire contents of which are hereby incorporated by reference.

BACKGROUND

From a viewpoint of improving yield in fabrication of semiconductor devices, management of surface conditions of a peripheral portion of a substrate has been attracting attention in recent years. In the fabrication process of the semiconductor devices, various materials are deposited on a silicon wafer to form a multilayer structure. As a result, unwanted films and roughened surface are formed on a peripheral portion of the substrate. It has been a recent trend to transport the substrate by holding only its peripheral portion using arms. Under such circumstances, the unwanted films remaining on the peripheral portion would be peeled off during various processes and could adhere to devices, causing lowered yield. Thus, in order to remove the unwanted films formed on the peripheral portion of the substrate, the peripheral portion of the substrate is polished using a polishing apparatus. In this specification, the peripheral portion of the substrate is defined as a region including a bevel portion which is the outermost portion of the substrate, and a top edge portion and a bottom edge portion located radially inwardly of the bevel portion.

FIG. 23AandFIG. 23Bare enlarged cross-sectional views each showing a peripheral portion of a wafer as an example of a substrate. More specifically,FIG. 23Ais a cross-sectional view of a so-called straight-type wafer, andFIG. 23Bis a cross-sectional view of a so-called round-type wafer. In the wafer W shown inFIG. 23A, the bevel portion is an outermost circumferential surface of the wafer W (indicated by a letter B) that is constituted by an upper slope portion (an upper bevel portion) P, a lower slope portion (a lower bevel portion) Q, and a side portion (an apex) R. In the wafer W shown inFIG. 23B, the bevel portion is a portion (indicated by a letter B) having a curved cross section and forming an outermost circumferential surface of the wafer W. A top edge portion is a flat portion E1located radially inwardly of the bevel portion B. A bottom edge portion is a flat portion E2located on the opposite side of the top edge portion and located radially inwardly of the bevel portion B. The top edge portion may also include a region where the devices are formed.

As an apparatus for removing such films formed on the peripheral portion of the wafer W, there has been known a polishing apparatus using a polishing tool such as a polishing tape (for example, see Japanese Patent No. 5254575). This type of polishing apparatus has a substrate holder for holding a wafer W and rotating the wafer W, and a polishing head for bringing the polishing tape (polishing tool) into contact with the peripheral portion of the wafer W. The polishing head has a pressing pad for pressing the polishing tape against the peripheral portion of the wafer W. The pressing pad disposed on the reverse side of the polishing tape presses a polishing surface of the polishing tape against the peripheral portion of the wafer W, thereby polishing the peripheral portion of the wafer W. As the polishing tool, a strip-shaped polishing cloth may be used in place of the polishing tape.

FIG. 24is a perspective view showing an example of a conventional pressing pad. As shown inFIG. 24, a pressing pad150has an elastic member155having a rectangular pressing surface155a, and a pad body154to which the elastic member155is secured. The elastic member155is fixed to the pad body154in a state where an entire rear surface on an opposite side of the pressing surface155ais brought in contact with the pad body154. The pressing pad150is disposed on the reverse side of the polishing tape and presses the front surface (polishing surface) of the polishing tape against the bevel portion B of the wafer W by the pressing surface155aof the elastic member155. The elastic member155of the pressing pad150is made of a material such as rubber or sponge. For example, urethane rubber or silicon sponge with a hardness (e.g., 20 to 40 degrees) suitable for polishing a substrate is selected as a material of the elastic member155.

FIG. 25is a schematic view showing the state where the bevel portion B of the wafer W is polished by a polishing head130having the pressing pad150shown inFIG. 24. As shown inFIG. 25, the polishing head130has the pressing pad150for pressing a polishing tape123against the peripheral portion of the wafer W, an air cylinder (driving mechanism)152for moving the pressing pad150toward the peripheral portion of the wafer W, and a tape feed mechanism142for feeding the polishing tape123in a predetermined direction. The force of the pressing pad150that presses the polishing tape123against the wafer W is regulated by controlling air pressure supplied to the air cylinder152. During polishing of the bevel portion B of the wafer W, the polishing head130(i.e., the pressing pad150) is inclined with respect to the wafer W by a tilting mechanism (not shown). While the polishing head130is inclined with respect to the wafer W, the pressing surface155aof the elastic member155of the pressing pad150presses the polishing tape123against the bevel portion B of the wafer W, thereby polishing the entire bevel portion B by the polishing tape123.

When the polishing head130(i.e., the pressing pad150) is inclined with respect to the wafer W to polish the entire bevel portion B, the width of the polishing tape123which is brought into contact with the bevel portion B of the wafer W is changed.FIG. 26is a schematic view showing the width of the pressing surface155aof the elastic member155which is brought into contact with the bevel portion B of the wafer W through the polishing tape123when the pressing surface155aof the elastic member155of the pressing pad150shown inFIG. 24is perpendicular to a flat surface of the wafer W.FIG. 27is a schematic view showing the width of the pressing surface155aof the elastic member155which is brought into contact with the bevel portion B of the wafer W through the polishing tape123when the pressing surface155aof the elastic member155of the pressing pad150shown inFIG. 24is inclined with respect to the flat surface of the wafer W. InFIGS. 26 and 27, although the polishing tape123is not shown for the sake of simplifying the explanation, the width of the polishing tape123which is brought into contact with the bevel portion B of the wafer W during polishing corresponds to the width of the pressing surface155aof the elastic member155which is brought into contact with the bevel portion B of the wafer W through the polishing tape123.

As shown inFIGS. 26 and 27, the width Wa of the polishing tape which is brought into contact with the bevel portion B of the wafer W when the pressing surface155ais perpendicular to the flat surface of the wafer W is smaller than the width Wb of the polishing tape which is brought into contact with the bevel portion B of the wafer W when the pressing surface155ais inclined with respect to the flat surface of the wafer W. As the inclination angle of the pressing surface155awith respect to the flat surface of the wafer W becomes larger, the width of the polishing tape which is brought into contact with the bevel portion B of the wafer W becomes larger.

FIG. 28is a photograph showing polishing impressions formed in the polishing tape123when the bevel portion B is polished by pressing the polishing tape123against the bevel portion B of the wafer W with the conventional pressing pad150.FIG. 28shows a plurality of polishing impressions when the bevel portion B of the wafer W has been polished by changing the inclination angle θ of the pressing surface155awith respect to the flat surface of the wafer W every 10 degrees.FIGS. 29A, 29B and 29Care schematic views showing the inclination angle θ of the pressing surface155awith respect to the flat surface of the wafer W. InFIGS. 29A, 29B and 29C, the polishing tape123is shown as a vertical cross section along a center of the pressing surface155a. As shown inFIG. 29A, this inclination angle θ is zero degree when the pressing surface155aof the elastic membrane155of the pressing pad150is perpendicular to the flat surface of the wafer W. This inclination angle θ becomes a value of plus when the pressing surface155ais inclined in a direction where the upper end of the pressing surface155aapproaches the flat surface of the wafer W as shown inFIG. 29B, and becomes a value of minus when the pressing surface155ais inclined in a direction where the upper end of the pressing surface155amoves away from the flat surface of the wafer W as shown inFIG. 29C.

As can be seen from the photograph shown inFIG. 28, as an absolute value of the inclination angle θ becomes larger, the polishing impression becomes larger in length. For example, the length La of the polishing impression when the inclination angle θ is 0° is smaller than the length Lb of the polishing impression when the inclination angle θ is 70°. The difference in length between the polishing impressions corresponds to the difference in width between the polishing tapes123which are brought into contact with the bevel portion B of the wafer W. As the width of the polishing tape123which is brought into contact with the bevel portion B of the wafer W is smaller, the polishing tape123which contributes to polishing of the bevel portion B is smaller in amount. As a result, the polishing rate when the absolute value of the inclination angle θ of the pressing surface155ais small is lower than the polishing rate when the absolute value of the inclination angle θ of the pressing surface155ais large.

Further, as can be seen from the photograph shown inFIG. 28, when the absolute value of the inclination angle θ is small, brightness of color at a central region of the polishing impression is higher than brightness of color at an outer region of the polishing impression. As shown inFIG. 30, the difference in brightness of color of the polishing impression means that a pressing force Fa at a central part of a contact area between the polishing tape123and the bevel portion B of the wafer W is larger than a pressing force Fb at an outer part of the contact area between the polishing tape123and the bevel portion B of the wafer W. In this case, the polishing tape123is liable to be clogged at the central part of the contact area of the polishing tape, thus lowering the polishing rate.

SUMMARY OF THE INVENTION

According to an embodiment, there is provided a polishing apparatus which can keep a width of a polishing tool, which is brought into contact with a peripheral portion of a substrate, constant when the peripheral portion of the substrate is polished by the polishing tool while the polishing tool is inclined with respect to the substrate. Further, according to an embodiment, there is provided a pressing pad for pressing the polishing tool used in such polishing apparatus.

Embodiments, which will be described below, relate to a polishing apparatus for polishing a substrate such as a wafer, and more particularly to a polishing apparatus for polishing a peripheral portion of a substrate using a polishing tool such as a polishing tape. Further, the below-described embodiments relate to a pressing pad for pressing the polishing tool against the peripheral portion of the substrate.

In an embodiment, there is provided a polishing apparatus comprising: a substrate holder configured to hold a substrate and to rotate the substrate; and a pressing pad configured to press a polishing tool against a peripheral portion of the substrate held by the substrate holder; wherein the pressing pad comprises: an elastic member having a pressing surface configured to press the polishing tool against the peripheral portion of the substrate; and a support member configured to support the elastic member; wherein the support member has a recess formed in a front surface of the support member, the elastic member being capable of entering the recess.

In an embodiment, the pressing pad further comprises a fixing means configured to fix both end portions of the elastic member to the support member.

In an embodiment, a bottom surface of the recess is curved.

In an embodiment, a sheet is attached to a rear surface on the opposite side of the pressing surface of the elastic member.

In an embodiment, the polishing tool comprises a polishing tape.

In an embodiment, a groove extending toward a rear surface on the opposite side of the pressing surface is formed in the pressing surface of the elastic member, and the elastic member has block bodies divided by the groove.

In an embodiment, the polishing tool comprises a whetstone attached to a front surface of the block body.

In an embodiment, there is provided a pressing pad for pressing a polishing tool configured to polish a peripheral portion of a substrate against the peripheral portion of the substrate, comprising: an elastic member having a pressing surface configured to press the polishing tool against the peripheral portion of the substrate; and a support member configured to support the elastic member; wherein the support member has a recess formed in a front surface of the support member, the elastic member being capable of entering the recess.

In an embodiment, the pressing pad further comprises a fixing means configured to fix both end portions of the elastic member to the support member.

In an embodiment, a bottom surface of the recess is curved.

In an embodiment, a sheet is attached to a rear surface on the opposite side of the pressing surface of the elastic member.

In an embodiment, the polishing tool comprises a polishing tape.

In an embodiment, a groove extending toward a rear surface on the opposite side of the pressing surface is formed in the pressing surface of the elastic member; and the elastic member has block bodies divided by the groove.

in an embodiment, a whetstone used as the polishing tool is attached to the front surface of the block body.

According to the above-described embodiments, when the pressing pad presses the polishing tool against the peripheral portion of the substrate which is rotating, the elastic member of the pressing pad enters the recess of the support member, and the elastic member is deformed in a shape along the peripheral portion of the substrate. As a result, the width of the polishing tool which is brought into contact with the substrate can be kept constant when the peripheral portion of the substrate is polished by the polishing tool while the polishing tool is inclined with respect to the substrate.

DESCRIPTION OF EMBODIMENTS

FIG. 1is a plan view showing a polishing apparatus according to an embodiment.FIG. 2is a vertical cross-sectional view of the polishing apparatus shown inFIG. 1. As shown inFIG. 1andFIG. 2, the polishing apparatus includes a rotary holding mechanism (a substrate holder)3configured to hold a wafer W as an example of a substrate horizontally and to rotate the wafer W. The rotary holding mechanism3is located in the center of the polishing apparatus.FIG. 1shows a state in which the rotary holding mechanism3holds the wafer W. This rotary holding mechanism3has a dish-shaped holding stage4configured to hold a rear surface of the wafer W by a vacuum suction, a hollow shaft5coupled to a central portion of the holding stage4, and a motor M1for rotating the hollow shaft5. The wafer W is placed onto the holding stage4by hands of a transporting mechanism (not shown) such that a center of the wafer W is aligned with a central axis of the hollow shaft5.

The hollow shaft5is supported by ball spline bearings (i.e., linear motion bearings)6which allow the hollow shaft5to move vertically. The holding stage4has an upper surface having grooves4a. These grooves4acommunicate with a communication passage7extending through the hollow shaft5. According to an embodiment, a sheet in which grooves4acommunicating with the communication passage7extending through the hollow shaft5are formed may be attached to the upper surface of the holding stage4. For example, the grooves4aare formed by blanking of the sheet. The communication passage7is coupled to a vacuum line9via a rotary joint8provided on a lower end of the hollow shaft5. The communication passage7is also coupled to a nitrogen-gas supply line10for use in releasing the wafer W from the holding stage4after processing. By selectively coupling the vacuum line9and the nitrogen-gas supply line10to the communication passage7, the wafer W can be held on the upper surface of the holding stage4by the vacuum suction and can be released from the upper surface of the holding stage4.

A pulley p1is coupled to the hollow shaft5, and a pulley p2is mounted on a rotational shaft of the motor M1. The hollow shaft5is rotated by the motor M1through the pulley p1, the pulley p2, and a belt b1riding on these pulleys p1and p2. With these structures, the wafer W, held on the upper surface of the holding stage4, is rotated by the motor M1.

The ball spline bearing6is a bearing that allows the hollow shaft5to move freely in its longitudinal direction. The ball spline bearings6are secured to a cylindrical casing12. Therefore, in the resent embodiment, the hollow shaft5can move linearly up and down relative to the casing12, and the hollow shaft5and the casing12rotate in unison. The hollow shaft5is coupled to an air cylinder (elevating mechanism)15, so that the hollow shaft5and the holding stage4are elevated and lowered by the air cylinder15.

A cylindrical casing14is provided so as to surround the casing12in a coaxial arrangement. Radial bearings18are provided between the casing12and the cylindrical casing14, so that the casing12is rotatably supported by the radial bearings18. With these structures, the rotary holding mechanism3can rotate the wafer W about its central axis Cr and can elevate and lower the wafer W along the central axis Cr.

As shown inFIG. 1, tour polishing head assemblies (polishing units)1A,1B,1C, and1D are arranged around the wafer W held by the rotary holding mechanism3. Polishing-tape supply mechanisms2A,2B,2C, and2D are provided radially outwardly of the polishing head assemblies1A,1B,1C, and1D, respectively. The polishing head assemblies1A,1B,1C, and1D are isolated from the polishing-tape supply mechanisms2A,2B,2C, and2D by a partition20. An interior space of the partition20provides a polishing room21. The four polishing head assemblies1A,1B,1C, and1D and the holding stage4are located in the polishing room21. On the other hand, the polishing-tape supply mechanisms2A,2B,2C, and2D are located outside the partition20(i.e., outside the polishing room21). The polishing head assemblies1A,1B,1C, and1D have the same structure, and the polishing-tape supply mechanisms2A,2B,2C, and2D also have the same structure. Hereinafter, the polishing head assembly1A and the polishing-tape supply mechanism2A will be described.

The polishing-tape supply mechanism2A has a supply reel24for supplying a polishing tape23as an example of a polishing tool to the polishing head assembly1A, and a recovery reel25for recovering the polishing tape23that has been used in polishing of the wafer W. The supply reel24is arranged above the recovery reel25. Motors M2are coupled to the supply reel24and the recovery reel25, respectively, via couplings27(FIG. 1shows only the coupling27and the motor M2coupled to the supply reel24). Each of the motors M2is configured to exert a constant torque in a predetermined rotational direction so as to apply a predetermined tension to the polishing tape23.

The polishing tape23is a long strip-shaped polishing tool, and one of surfaces of the polishing tape23provides a polishing surface. The polishing tape23includes a base tape made from PET sheet or the like and a polishing layer formed on the base tape. The polishing layer comprises a binder (e.g., resin) covering one surface of the base tape, and abrasive grains bound by the binder. A surface of the polishing layer provides the polishing surface. Instead of the polishing tape23, a strip-shaped polishing cloth may be used as the polishing tool.

The polishing tape23is mounted on the polishing-tape supply mechanism2A in a state where the polishing tape23is wound on the supply reel24. Side surfaces of the wound polishing tape23are supported by reel plates so that the wound polishing tape23does not collapse. One end of the polishing tape23is attached to the recovery reel25. The recovery reel25takes up the polishing tape23that has been supplied to the polishing head assembly1A to thereby recover the polishing tape23. The polishing head assembly1A has a polishing head30for pressing the polishing tape23, supplied from the polishing-tape supply mechanism2A, against a peripheral portion of the wafer W. The polishing tape23is supplied to the polishing head30such that the polishing surface (front surface) of the polishing tape23faces the wafer W.

The polishing-tape supply mechanism2A has plural guide rollers31,32,33, and34. The polishing tape23, to be supplied to and recovered from the polishing head assembly1A, is guided by these guide rollers31,32,33, and34. The polishing tape23is supplied to the polishing head30from the supply reel24through an opening20aformed in the partition20, and the polishing tape23that has been used is recovered by the recovery reel25through the opening20a.

As shown inFIG. 2, an upper supply nozzle36is provided above the wafer W. This upper supply nozzle36is configured to supply a polishing liquid onto a center of an upper surface of the wafer W held by the rotary holding mechanism3. Further, a lower supply nozzle37is provided for supplying a polishing liquid onto a boundary between the rear surface of the wafer W and the holding stage4of the rotary holding mechanism3(i.e., onto a peripheral portion of the holding stage4). Typically, pure water is used as the polishing liquid. In a case of using silica as the abrasive grains of the polishing tape23, ammonia may be used as the polishing liquid. The polishing apparatus further includes a cleaning nozzle38for cleaning the polishing head30after the polishing process. The wafer W is elevated by the rotary holding mechanism3after the polishing process, and then the cleaning nozzle38ejects cleaning water toward the polishing head30, whereby the polishing head30is cleaned after the polishing process.

In order to isolate mechanical devices, such as the ball spline bearings6and the radial bearings18, from the polishing room21when the hollow shaft5is elevated and lowered relative to the casing12, the hollow shaft5and an upper end of the casing12are coupled to each other by a bellows19that is extensible and contractible in a vertical direction, as shown inFIG. 2.FIG. 2shows a state in which the hollow shaft5is in a lowered position and the holding stage4is in a polishing position. After the polishing process, the air cylinder15elevates the wafer W, together with the holding stage4and the hollow shaft5, to a transport position, where the wafer W is released from the holding stage4.

The partition20has an entrance20bthrough which the wafer W is transported into and removed from the polishing room21. The entrance20bis a horizontally extending cutout. Therefore, the wafer W, held by the transporting mechanism, can travel horizontally across the polishing room21through the entrance20b. An upper surface of the partition20has an aperture20cand louvers40, and a lower surface of the partition20has a gas-discharge opening (not shown in the drawing). During the polishing process, the entrance20bis closed by a non-illustrated shutter. Therefore, as a fan mechanism (not shown in the drawing) is driven to evacuate an air through the gas-discharge opening, downward flow of clean air is formed in the polishing room21. Because the polishing process is performed under such conditions, the polishing liquid is prevented from scattering upwardly. Therefore, the polishing process can be performed while an upper space of the polishing room21is kept clean.

As shown inFIG. 1, the polishing head30is secured to one end of an arm60, which is rotatable about an axis Ct extending parallel to a tangential direction of the wafer W. The other end of the arm60is coupled to a motor M4via pulleys p3and p4and a belt b2. As the motor M4rotates in a clockwise direction and a counterclockwise direction through a certain angle, the arm60rotates about the axis Ct through a certain angle. In this embodiment, the motor M4, the arm60, the pulleys p3and p4, and the belt b2constitute a tilting mechanism for tilting the polishing head30with respect to the surface of the wafer W.

The tilting mechanism is mounted on a movable base61. This movable base61is movably coupled to a base plate65via guides62and rails63. The rails63extend linearly in a radial direction of the wafer W held on the rotary holding mechanism3, so that the movable base61can move linearly in the radial direction of the wafer W. A connection plate66, extending through the base plate65, is secured to the movable base61. A linear actuator67is coupled to the connection plate66via a joint68. This linear actuator67is secured to the base plate65directly or indirectly.

The linear actuator67may comprise an air cylinder or a combination of a positioning motor and a ball screw. The linear actuator67, the rails63, and the guides62constitute a moving mechanism for linearly moving the polishing head30in the radial direction of the wafer W. Specifically, the moving mechanism is operable to move the polishing head30closer to and away from the wafer W along the rails63. On the other hand, the polishing-tape supply mechanism2A is fixed to the base plate65.

FIG. 3is an enlarged view of the polishing head30. As shown inFIG. 3, the polishing head30has a pressing mechanism41configured to press the polishing surface of the polishing tape23against the wafer W at predetermined force. The polishing head30further has a tape feed mechanism42configured to feed the polishing tape23from the supply reel24to the recovery reel25. The polishing head30has plural guide rollers43,44,45,46,47,48, and49, which guide the polishing tape23such that the polishing tape23travels in a direction perpendicular to the tangential direction of the wafer W.

The tape feed mechanism42provided in the polishing head30includes a tape feed roller42a, a tape-holding roller42b, and a motor M3configured to rotate the tape feed roller42a. The motor M3is mounted on a side surface of the polishing head30. The tape feed roller42ais mounted to a rotational shaft of the motor M3. The tape-holding roller42bis arranged adjacent to the tape feed roller42a. The tape-holding roller42bis supported by a non-illustrated mechanism, which biases the tape-holding roller42bin a direction indicated by arrow NF inFIG. 3(i.e., in a direction toward the tape feed roller42a) so as to press the tape-holding roller42bagainst the tape feed roller42a.

As the motor M3rotates in a direction indicated by arrow inFIG. 3, the tape feed roller42ais rotated to feed the polishing tape23from the supply reel24to the recovery reel25via the polishing head30. The tape-holding roller42bis configured to be rotatable freely about its own axis and is rotated as the polishing tape23is fed.

The pressing mechanism41includes a pressing pad50located at the rear side of the polishing tape23, and an air cylinder (an actuator)52configured to move the pressing pad50toward the peripheral portion of the wafer W. The air cylinder52is a so-called single rod cylinder. The force of the pressing pad50that presses the polishing tape23against the wafer W is regulated by controlling air pressure supplied to the air cylinder52. The four polishing head assemblies1A,1B,1C, and1D arranged around the wafer W have the tilting mechanisms, the pressing mechanisms41, the tape feed mechanisms42, and the polishing-head moving mechanisms, which are capable of operating independently.

FIG. 4is a perspective view showing the pressing pad50schematically according to an embodiment,FIG. 5is a schematic front view of the pressing pad50shown inFIG. 4, andFIG. 6is a schematic side view of the pressing pad50shown inFIG. 4.

As shown inFIGS. 4 to 6, the pressing pad50includes an elastic member55having a flat pressing surface55afor directly pressing the polishing tape23against the peripheral portion of the wafer W, and a plate-like support member56for supporting the elastic member55. Specific structures of the elastic member55and the support member56will be described later. In the present embodiment, the pressing pad50further includes a pad body54, and the support member56is sandwiched between the elastic member55and the pad body54.

The elastic member55is made of a material such as sponge or rubber. For example, silicon sponge with a hardness (e.g., 20 to 40 degrees) suitable for polishing the wafer W is selected as a material of the elastic member55. The elastic member55may be made of rubber (e.g., urethane rubber) with a hardness (e.g., 20 to 40 degrees) suitable for polishing the wafer W. The support member56is made of a material harder than the elastic member55. In the embodiments described below, the elastic member55is made of silicon sponge, and the elastic member55is referred to as a silicon sponge55.

The pressing surface55aof the silicon sponge55for directly pressing a rear surface (i.e., opposite surface of the polishing surface) of the polishing tape23is rectangular, and the width (dimension along a circumferential direction of the wafer W) D1of the pressing surface55ais larger than the height (dimension along a direction perpendicular to the surface of the wafer W) D2of the pressing surface55a.

In the present embodiment, the pressing pad50has two protrusions54aand54bformed on a front surface thereof. These protrusions54aand54bare in a shape of rail and are arranged in parallel. The protrusions54aand54bare curved along the circumferential direction of the wafer W. More specifically, the protrusions54aand54bhave a circular arc shape whose curvature is substantially the same as a curvature of the wafer W.

The two protrusions54aand54bare symmetrical about the rotational axis Ct (seeFIG. 1). As shown inFIG. 5, the protrusions54aand54bare curved inwardly toward the rotational axis Ct as viewed from a front of the pressing pad50. The polishing head30is disposed such that a center line (i.e., the rotational axis Ct) extending between tip ends of the protrusions54aand54bcoincides with a center of a thickness of the wafer W. The protrusions54aand54bare arranged such that the protrusions54aand54bare closer to the wafer W than the guide rollers46and47(seeFIG. 3) that are disposed at the front of the polishing head30, so that the polishing tape23is supported from the rear side thereof by the protrusions54aand54b. The pad body54including the protrusions54aand54bare made from resin, such as PEEK (polyetheretherketone).

As shown inFIGS. 4 and 5, the silicon sponge55is arranged between the two protrusions54aand54b. A height of the silicon sponge55is slightly lower than a height of the protrusions54aand54b. When the pressing pad50is moved toward the wafer W by the air cylinder52in a state where the polishing head30is kept horizontal, the silicon sponge55presses the polishing tape23from the rear side thereof against the bevel portion B of the wafer W.

FIG. 7is a cross-sectional view taken along line A-A ofFIG. 5,FIG. 8Ais a schematic perspective view of the silicon sponge55shown inFIG. 4, andFIG. 8Bis a schematic front view of the silicon sponge55shown inFIG. 8A.FIG. 9Ais a front view of the support member56shown inFIG. 4, andFIG. 9Bis a cross-sectional view taken along line B-B ofFIG. 9A. InFIG. 9B, the silicon sponge55supported by the support member56is shown by imaginary lines (dotted lines).FIG. 10is a cross-sectional view taken along line C-C ofFIG. 7.

As shown inFIG. 7, both end portions55c,55dof the silicon sponge55are supported by the support member56, and the both end portions55c,55dof the silicon sponge55are fixed to the support member56by a fixing means70(described later).

As shown inFIGS. 8A and 8B, the silicon sponge55has fixing projections55e,55fprojecting from both side surfaces of the silicon sponge55, respectively. The fixing projections55e,55fextend in a longitudinal direction of the silicon sponge55. The fixing projection55econstitutes a part of one end portion55cof the silicon sponge55and the fixing projection55fconstitutes a part of the other end portion55dof the silicon sponge55.

As shown inFIGS. 9A and 9B, a recess57is formed in the front surface56aof the support member56. The recess57is formed between both end portions58,59of the support member56. Specifically, the support member56includes a recess area where the recess57is formed, and two end areas located outwardly of the recess area, respectively and forming the both end portions58,59of the support member56, respectively. One end portion55cof the silicon sponge55is a part of the silicon sponge55facing one end portion58(i.e., one end area) of the support member56. In the present embodiment, the end portion55cof the silicon sponge55including the fixing projection55eis brought in contact with the end portion58of the support member56. One end area of the support member56comprises a fixing area facing the fixing projection55e, and a support area facing the end portion55cof the silicon sponge55except for the fixing projection55e. Similarly, the other end portion55dof the silicon sponge55is a part of the silicon sponge55facing the other end portion59(i.e., the other end area) of the support member56. In the present embodiment, the end portion55dof the silicon sponge55including the fixing projection55fis brought in contact with the end portion59of the support member56. The other end area of the support member56comprises a fixing area facing the fixing projection55f, and a support area facing the end portion55dof the silicon sponge55except for the fixing projection55f. The support areas are areas formed on the support member56to support the silicon sponge55reliably, and the fixing areas are areas formed to fix the both end portions55c,55dof the silicon sponge55to the support member56by the fixing means70(described later).

By forming the recess57in the support member56, the front surface56aof the support member56is divided into a bottom surface57aof the recess57, a front surface58aof the end portion58, and a front surface59aof the end portion59. Specifically, the front surface58aof the end portion58corresponds to a front surface of the support member56in one end area, and the front surface59aof the end portion59corresponds to a front surface of the support member56in the other end area. In the present embodiment, the bottom surface57aof the recess57is connected to the front surface58aof one end portion58of the support member56through one side surface57bof the recess57, and is connected to the front surface59aof the other end portion59of the support member56through the other side surface57cof the recess57.

As shown inFIG. 7, the front surfaces58a,59aof the both end portions58,59of the support member56are brought in contact with the rear surface55bat the opposite side of the pressing surface55aof the silicon sponge55. More specifically, the front surfaces58a,59aof the both end portions58,59of the support member56are brought in contact with the rear surface of the end portion55cof the silicon sponge55including the fixing projection55eand the rear surface of the end portion55dof the silicon sponge55including the fixing projection55f, respectively. The rear surface (i.e., the opposite surface of the front surface56aof the support member56)56bis brought in contact with the pad body54.

Next, the fixing means70for fixing the both end portions55c,55dof the silicon sponge55to the support member56will be described with reference toFIGS. 7 and 10. The fixing means70is provided on each of the end portions of the pressing pad50and has a fixing block71and a screw72screwed into the fixing block71. As shown inFIG. 10, the fixing block71of the fixing means70has a step portion71a, and has an L-shaped cross-sectional shape. The step portion71ahas a shape corresponding to the fixing projection55e(or55f) of the silicon sponge55shownFIGS. 8A and 8B, and the fixing projection55e(or55f) is fitted with the step portion71a. A threaded hole71binto which the screw72is screwed is formed in the fixing block71, and a through-hole56cinto which the screw72is inserted is formed in the fixing area (seeFIG. 9B) of each end area of the support member56. The through-hole56cis formed at a position corresponding to the threaded hole71b. Through-holes54cinto which the screws72are inserted are formed in the both end portions of the pad body54, respectively, and these through-holes54care formed at positions corresponding to the threaded holes71b.

The step portions71aof the fixing blocks71are fitted with the fixing projections55e,55fof the silicon sponge55, respectively in a state where the both end portions55c,55dof the silicon sponge55are supported on the both end portions58,59of the support member56. In this state, the screw72is inserted into the through-hole54cof the pad body54and the through-hole56cof the support member56, and is further screwed into the threaded hole71bof the fixing block71. By this fixing operation, the both end portions55c,55dof the silicon sponge55is fixed to the support member56, and the support member56to which the silicon sponge55is fixed is fixed to the pad body54.

The fixing means for fixing the silicon sponge55and the support member56to the pad body54is not limited to the above-described embodiment including the fixing block71and the screw72. For example, the silicon sponge55may be fixed to the support member56by a clip for clipping the both end portions55c,55dof the silicon sponge55, the support member56, and the pad body54, and simultaneously, the silicon sponge55and the support member56may be fixed to the pad body54. Alternatively, the both end portions55c,55dof the silicon sponge55may be attached (i.e., fixed) to the both end portions58,59of the support member56with an adhesive, and the support member56to which the silicon sponge55is fixed may be fixed to the pad body54with an adhesive or screws.

FIG. 11is a view showing the manner in which the polishing head30polishes the bevel portion B of the wafer W. When polishing the bevel portion of the wafer W, as shown inFIG. 11, the polishing tape23is pressed against the bevel portion of the wafer W by the pressing pad50while the inclination angle of the polishing head30is changed intermittently or continuously by the above-described tilting mechanism. During polishing, the polishing tape may be fed at a predetermined speed by the tape feed mechanisms42.

Further, the polishing head30having the pressing pad50according to the present embodiment is capable of polishing the top edge portion and the bottom edge portion of the wafer W. Specifically, as shown inFIG. 12, the polishing head30is inclined upward by the above-described tilting mechanism to allow the protrusion54ato press the polishing tape23against the top edge portion of the wafer W, thereby polishing the top edge portion of the wafer W. Further, as shown inFIG. 13, the polishing head30is inclined downward to allow the protrusion54bto press the polishing tape23against the bottom edge portion of the wafer W, thereby polishing the bottom edge portion of the wafer W.

As described above, the polishing head30according to the present embodiment can polish the entire peripheral portion of the wafer W including the top edge portion E1, the bevel portion B and the bottom edge portion E2. Each of the polishing head assemblies1A to1D (seeFIG. 1) has the polishing head30. Therefore, in order to improve the throughput of the polishing apparatus, all of the polishing head assemblies1A to1D may polish the entire peripheral portion of the wafer W including the top edge portion E1, the bevel portion B and the bottom edge portion E2. Alternatively, the polishing head assembly1A may polish the top edge portion E1, the polishing head assembly1B may polish the bevel portion B, and the polishing head assembly1C may polish the bottom edge portion E2.

When the silicon sponge55of the pressing pad50is pressed against the bevel portion B of the wafer W through the polishing tape23under a predetermined force by the air cylinder52to polish the bevel portion B of the wafer W, the silicon sponge55is pushed back by the bevel portion B of the wafer W and is thus deformed. At this time, the silicon sponge55can easily enter the recess57of the support member56because the recess57is formed in the front surface56aof the support member56and the silicon sponge55is supported at its end portions55c,55dby the support member56.

FIG. 14is a schematic view showing the state where the silicon sponge55enters the recess57of the support member56.FIG. 15Ais a schematic view showing the silicon sponge55which has been pushed back by the bevel portion B of the wafer W and thus deformed when the pressing surface55aof the silicon sponge55of the pressing pad50is perpendicular to the flat surface of the wafer W.FIG. 15Bis a schematic view showing pressing forces in a contact area between the bevel portion B of the wafer W and the polishing tape23pressed by the pressing pad50shown inFIG. 15A.FIG. 16Ais a schematic view showing the silicon sponge55which has been pushed back by the bevel portion B of the wafer W and thus deformed when the pressing surface55aof the silicon sponge55of the pressing pad50is inclined with respect to the flat surface of the wafer W.FIG. 16Bis a schematic view showing pressing forces in a contact area between the bevel portion B of the wafer W and the polishing tape23pressed by the pressing pad50shown inFIG. 16A.

InFIGS. 14 to 16B, the pressing pad50is schematically shown for the sake of facilitating understanding of the invention. More specifically, only the silicon sponge55, the support member56, the pad body54and the fixing blocks71of the fixing means70are schematically shown. Further, although the polishing tape23is not shown for the sake of simplifying the explanation inFIGS. 15A, 15B, 16A and 16B, during polishing of the bevel portion B of the wafer W, the pressing pad50presses the polishing tape23against the bevel portion B of the wafer W as shown inFIG. 14. More specifically, the pressing surface55aof the silicon sponge55of the pressing pad50is brought into direct contact with the rear surface of the polishing tape23, and in this state, the pressing pad50presses the front surface (polishing surface) of the polishing tape23against the bevel portion B of the wafer W. The width of the polishing tape23which is brought into contact with the bevel portion B of the wafer W during polishing corresponds to the width of the pressing surface55aof the silicon sponge55which is brought into contact with the bevel portion B of the wafer W through the polishing tape23.

As shown inFIG. 14, when the silicon sponge55of the pressing pad50is pressed against the bevel portion B of the wafer W through the polishing tape23under a predetermined force, the silicon sponge55is deformed so as to enter the recess57of the support member56. The rear surface55bof the silicon sponge55which has entered the recess57of the support member56is brought into contact with the bottom surface57aof the recess57, and the silicon sponge55is deformed in a shape along the bevel portion B of the wafer W as shown inFIGS. 15A and 16A. In this manner, by forming the recess57in the support member56so as to allow the silicon sponge55to enter the recess57, the silicon sponge55can be deformed in a shape along the bevel portion B of the wafer W. As a result, even if the pressing surface55aof the silicon sponge55is inclined with respect to the wafer W, the width of the polishing tape23which is brought into contact with the bevel portion B of the wafer W can be kept constant. Specifically, the width W1(seeFIG. 15A) of the polishing tape23which is brought into contact with the bevel portion B of the wafer W when the pressing surface55ais perpendicular to the flat surface of the wafer W is equal to the width W2(seeFIG. 16A) of the polishing tape23which is brought into contact with the bevel portion B of the wafer W when the pressing surface55ais inclined with respect to the flat surface of the wafer W.

The silicon sponge55comprises a foam containing a plurality of fine voids therein. For example, the silicon sponge55is formed by foaming silicon in a forming die. The surface of the silicon sponge55immediately after removing the silicon sponge55from the forming die is a smooth flat surface having no concavity and convexity. However, when this flat surface is cut off, voids in the silicon sponge55are exposed. Specifically, the concavity and convexity emerge on the surface of the silicon sponge55which has been cut off. For example, when the pressing surface55aand/or the rear surface55bof the silicon sponge55is cut off to adjust the height of the silicon sponge55, the concavity and convexity emerge on the pressing surface55aand/or the rear surface55bwhich has been cut off.

When the silicon sponge55having the concavity and convexity on the pressing surface55aand/or the rear surface55bis pressed against the bevel portion B of the wafer W, the concavity and convexity of the pressing surface55aand/or the rear surface55bare crushed, and thus the silicon sponge55cannot be deformed in a desired shape along the bevel portion B of the wafer W in some cases. Therefore, it is preferable that the pressing surface55aand/or the rear surface55bof the silicon sponge55is configured to be a smooth flat surface without applying processing treatment such as cutting work to the pressing surface55aand/or the rear surface55b.

FIG. 17is a photograph showing polishing impressions formed in the polishing tape23when the bevel portion B is polished by pressing the polishing tape23against the bevel portion B of the wafer W with the pressing pad50according to the present embodiment.FIG. 17shows a plurality of polishing impressions when the bevel portion B of the wafer W has been polished by changing the inclination angle θ of the pressing surface55awith respect to the flat surface of the wafer W every 10 degrees. This inclination angle θ is 0 degree when the pressing surface55aof the silicon sponge55of the pressing pad50is perpendicular to the flat surface of the wafer W. This inclination angle θ becomes a value of plus when the pressing surface55ais inclined in a direction where the upper end of the pressing surface55aapproaches the flat surface of the wafer W, and becomes a value of minus when the pressing surface55ais inclined in a direction where the upper end of the pressing surface55amoves away from the flat surface of the wafer W.

As can be seen from the photograph shown inFIG. 17, the lengths of the polishing impressions are substantially the same in all of the inclination angles. For example, the length L1of the polishing impression when the inclination angle θ is 0° is substantially equal to the length L2of the polishing impression when the inclination angle θ is 70°. Thus, by using the pressing pad50according to the present embodiment, when the bevel portion B of the wafer W is polished by the polishing tape23while the polishing tape23is inclined with respect to the wafer W, the width of the polishing tape23which is brought into contact with the wafer W can be kept constant. As a result, even if the inclination angle θ of the pressing surface55ais changed, the polishing rate is not changed, and thus the throughput of the polishing apparatus can be increased compared to the case where the bevel portion B of the wafer W is polished using the conventional pressing pad150(seeFIG. 24).

Further, as can be seen from the photograph shown inFIG. 17, brightness of color at a central region of the polishing impression is substantially equal to brightness of color at an outer region of the polishing impression in all of the inclination angles θ. This means that as shown inFIGS. 15B and 16B, the central pressing force F1in the contact area between the polishing tape23and the bevel portion B of the wafer W is substantially equal to the outer pressing force F2in the contact area between the polishing tape23and the bevel portion B of the wafer W. Therefore, clogging of the polishing tape23at the central area of the polishing tape23hardly occurs compared to the case where the bevel portion B of the wafer W is polished using the conventional pressing pad150(seeFIG. 24). As a result, the polishing rate of the bevel portion B of the wafer W is not lowered, and thus the throughput of the polishing apparatus can be increased.

The silicon sponge (elastic member)55according to the present embodiment has a plurality of fine voids therein, but has a solid structure in which the pressing surface55aand the rear surface55bof the silicon sponge55are integrally deformed. Specifically, an internal space configured to allow a deformation of only the pressing surface55aof the silicon sponge55is not formed in the silicon sponge55. Also in the case where the silicon sponge55has a hollow structure in which such internal space is formed, when the pressing pad50is pressed against the bevel portion B of the wafer W, the pressing surface55aof the silicon sponge55can be curved along the circumferential direction of the wafer W. However, in this case, it is difficult to control the deformation amount of the pressing surface55aof the silicon sponge55. If the pressing surface55aof the silicon sponge55is greatly deformed, the polishing tape23is brought into contact with the top edge portion E1and/or the bottom edge portion E2of the wafer W to damage the wafer W in some cases. Further, the central pressing force in the contact area between the polishing tape23and the bevel portion B of the wafer W becomes larger than the outer pressing force in the contact area between the polishing tape23and the bevel portion B of the wafer W, thus being liable to cause clogging of the polishing tape23at the central area of the polishing tape.

In the present embodiment, the both end portions55c,55dof the silicon sponge55having the solid structure are supported by the both end portions58,59of the support member56having the recess57. With this configuration, when the pressing pad50is pressed against the bevel portion B of the wafer W, the pressing surface55aand the rear surface55bof the silicon sponge55are integrally deformed, and thus the silicon sponge55can easily enter the recess57. The silicon sponge55which has entered the recess57is deformed along the shape of the bevel portion B of the wafer W in a state where the rear surface55bof the silicon sponge55is supported by the bottom surface57aof the recess57. Therefore, the deformation amount of the silicon sponge55can be controlled to a desired value by optimizing the shape of the recess57(e.g., the width of the recess57, the depth of the recess57, and the like) and the width Wd (seeFIG. 9B) of the support area in the support member56based on the shape of the bevel portion of the wafer W, the width of the polishing tape23, the force for pressing the polishing tape23against the wafer W, and the like. Further, as shown inFIGS. 15B and 16B, the central pressing force F1in the contact area between the polishing tape23and the bevel portion B of the wafer W can be substantially equal to the outer pressing force F2in the contact area between the polishing tape23and the bevel portion B of the wafer W.

Experiments for polishing bevel portions B of bare silicon wafers using the polishing head30having the above-described pressing pad50have been conducted. In the experiments, when the inclination angles of the polishing head30(i.e., inclination angles θ of the pressing surface55aof the silicon sponge55) were 0°, 70°, and −70°, polishing areas (μm2) when the polishing tape23was pressed against the bevel portion B of the bare silicon wafer for predetermined time by the pressing pad50were measured. Further, plural experiments were conducted by changing the width Wd (seeFIG. 9B) of the support area and the depth Dp (seeFIG. 9B) of the recess57in the support member56. Further, as comparative examples, polishing areas (μm2) when the polishing tape23was pressed against the bevel portion B of the bare silicon wafer by the conventional pressing pad150(seeFIG. 24) were measured under the same conditions. TABLE 1 shows experimental results when the inclination angle of the polishing head30was 0°, TABLE 2 shows experimental results when the inclination angle of the polishing head30was 70°, and TABLE 3 shows experimental results when the inclination angle of the polishing head30was −70°.

As can be seen from TABLE 1 to TABLE 3, the polishing area of the bare silicon wafer which has been polished using the above-described pressing pad50is larger than the polishing area of the bare silicon wafer which has been polished using the conventional pressing pad150. Therefore, the bare silicon wafer W can be polished efficiently by using the pressing pad50according to the present embodiments. Further, TABLE 1 to TABLE 3 show that when the width Wd of the support area in the support member56is 3 mm or 5 mm and the depth Dp of the recess57is 0.5 mm, the polishing area increases greatly.

Further, other experiments for polishing the entire bevel portions of the wafers having silicon nitride films deposited on the bare silicon wafers using the polishing head30having the above-described pressing pad50have been conducted. For the purpose of the explanation, the wafer W having a silicon nitride film deposited on the bare silicon wafer is referred to as an SiN wafer. In other experiments, the polishing head30having the pressing pad50was intermittently tilted, the time required for polishing the silicon nitride film of the SiN wafer by 200 nm in each angle was measured. Further, plural other experiments were conducted by changing the width Wd of the support area and the depth Dp of the recess57(seeFIG. 9B) in the support member56. Furthermore, as comparative examples, the polishing head30having the conventional pressing pad150(seeFIG. 24) was intermittently tilted, and the time required for polishing the silicon nitride film of the SiN wafer by 200 nm in each angle was measured.

Other experimental results are shown in a graph ofFIG. 18. In the graph shown inFIG. 18, the vertical axis represents the time required for polishing the silicon nitride film by 200 nm, and the horizontal axis represents inclination angles of the polishing head30. In the graph shown inFIG. 18, the results obtained by the polishing head30having the conventional pressing pad150as comparative examples are shown by a bold solid line.

As can be seen from the graph shown inFIG. 18, the polishing time of the silicon nitride film by the polishing head30having the pressing pad50according to the present embodiment is shorter than the polishing time of the silicon nitride film by the polishing head30having the conventional pressing pad150. In particular, when the pressing pad50in which the depth Dp of the recess57of the support member56is 0.5 mm is used, the polishing time of the silicon nitride film can be reduced greatly. More specifically, when the polishing head30having the conventional pressing pad150is used, the polishing time of the silicon nitride film in the entire bevel portion of the SiN wafer is 69 seconds. In contrast, when the polishing head30having the pressing pad50in which the depth Dp of the recess57of the support member56is 0.5 mm is used, the polishing time of the silicon nitride film in the entire bevel portion of the SiN wafer is 52 seconds. Therefore, the polishing time when the silicon nitride film is polished by the polishing head30having the above-described pressing pad50is shorter than the polishing time when the silicon nitride film is polished by the polishing head130having the conventional pressing pad150by about 25%.

FIG. 19is a cross-sectional view showing a pressing pad50according to another embodiment. The configuration of the present embodiment which will not be particularly described is the same as that of the embodiment described with reference toFIGS. 4 to 10, and will not be described in duplication. The recess57of the pressing pad50shown inFIG. 19has a curved bottom surface57a. More specifically, the bottom surface57aof the recess57has a shape curved into a circular arc. In the present embodiment, the bottom surface57aof the recess57is directly coupled to the front surfaces58a,59aof the both end portions58,59of the support member56. Specifically, the recess57according to the present embodiment has no side surfaces57b,57cof the recess57shown inFIGS. 9A and 9B. In one embodiment, the curved bottom surface58amay be coupled to the front surfaces58a,59aof the both end portions58,59of the support member56through the side surfaces58b,58cof the recess57.

The silicon sponge55can enter the recess57having the curved bottom surface58a. The rear surface55bof the silicon sponge55which has entered the recess57of the support member56is brought into contact with the curved bottom surface57aof the recess57, and the silicon sponge55is deformed into a shape along the bevel portion B of the wafer W. Therefore, when the bevel portion B of the wafer W is polished while the polishing tape23is inclined with respect to the wafer W, the width of the polishing tape23which is brought into contact with the wafer W can be kept constant. Further, the pressing force in the contact area between the polishing tape23and the bevel portion B of the wafer W can be uniformized. It is preferable that the bottom surface57aof the recess57has a circular arc shape having a radius of curvature substantially equal to a radius of curvature of the bevel portion of the wafer W. In this case, when the rear surface55bof the silicon sponge55which has entered the recess57of the support member56is brought into contact with the curved bottom surface57aof the recess57, the silicon sponge55is deformed into the same shape as the bevel portion B along the circumferential direction of the wafer W.

FIG. 20is a cross-sectional view of a pressing pad50according to still another embodiment. The configuration of the present embodiment which will not be particularly described is the same as that of the embodiment described with reference toFIGS. 4 to 10, and will not be described in duplication. The pressing pad50shown inFIG. 20has a sheet73attached to the pressing surface55aof the silicon sponge55to reduce a friction against the rear surface of the polishing tape23. The sheet73has a surface to which treatment for reducing a friction coefficient such as Teflon (registered trademark) coating is applied, and this surface is brought into contact with the rear surface of the polishing tape23. Further, in the present embodiment, a sheet74having the same structure as the sheet73is attached to the rear surface55bof the silicon sponge55.

Because the sheets73,74having the same structure are attached to the pressing surface55aand the rear surface55bof the silicon sponge55, respectively, when the pressing surface55aof the silicon sponge55presses the bevel portion B of the wafer W and is thus deformed, the rear surface55bof the silicon sponge55can be deformed in response to the deformation of the pressing surface55aof the silicon sponge55. Specifically, the silicon sponge55can enter the recess57properly, and thus the silicon sponge55can be deformed in a shape along the bevel portion B of the wafer W. As a result, even if the sheet73is attached to the pressing surface55aof the silicon sponge55, the width of the polishing tape23which is brought into contact with the wafer W can be kept constant when the bevel portion B of the wafer W is polished by the polishing tape23while the polishing tape23is inclined with respect to the wafer W. Further, the pressing force in the contact area between the polishing tape23and the bevel portion B of the wafer W can be uniformized.

FIG. 21is a cross-sectional view of a pressing pad50according to still another embodiment. The configuration of the present embodiment which will not be particularly described is the same as that of the embodiment described with reference toFIGS. 4 to 10, and will not be described in duplication. A plurality of grooves (two grooves inFIG. 21)78extending from the pressing surface55atoward the rear surface55bare formed in the pressing surface55aof the silicon sponge55of the pressing pad50shown inFIG. 21. These grooves78are parallel to each other and are arranged at a regular interval. Because the plural grooves78are formed in the pressing surface55aof the silicon sponge55, a plurality of block bodies (three block bodies inFIG. 21)80are formed in the silicon sponge55. In the present embodiment, the pressing surface55aof the silicon sponge55comprises front surfaces of the plural block bodies80.

By using the silicon sponge55in which the plural block bodies80are formed, the silicon sponge55is liable to be deformed into a shape along the bevel portion B of the wafer W. As a result, the width of the polishing tape23which is brought into contact with the wafer W can be kept constant when the bevel portion B of the wafer W is polished by the polishing tape23while the polishing tape23is inclined with respect to the wafer W. Further, the pressing force in the contact area between the polishing tape23and the bevel portion B of the wafer W can be uniformized.

FIG. 22is a cross-sectional view of a pressing pad50according to still another embodiment. The configuration of the present embodiment which will not be particularly described is the same as that of the embodiment described with reference toFIG. 21, and will not be described in duplication. A plurality of grooves78extending from the pressing surface55atoward the rear surface55bare formed also in the silicon sponge55of the pressing pad50shown inFIG. 22. Therefore, a plurality of block bodies80are formed in the silicon sponge55of the pressing pad50shown inFIG. 22.

Whetstones82are attached respectively to the front surfaces of the plural block bodies80of the silicon sponge55shown inFIG. 22. The whetstone82constitutes a polishing tool for polishing the bevel portion B of the wafer W. Specifically, in the present embodiment, the whetstone82is used as the polishing tool in place of the polishing tape23. Therefore, by using the pressing pad50shown inFIG. 22, the above-described polishing-tape supply mechanisms2A to2D become unnecessary, and thus the polishing apparatus can be compact and can be manufactured at a low cost.

Also in the case where the bevel portion B of the wafer W is polished using the polishing head30having the pressing pad50according to the present embodiment, the silicon sponge55is deformed into a shape along the bevel portion B of the wafer W. As a result, the width of the polishing tape23which is brought into contact with the wafer W can be kept constant when the bevel portion B of the wafer W is polished by the whetstones82while the whetstones82are inclined with respect to the wafer W. Further, the pressing force in the contact area between the whetstones82and the bevel portion B of the wafer W can be uniformized.

The present invention is not limited to the above-described embodiments. For example, in the embodiments shown inFIGS. 20 to 22, the bottom surface57aof the recess57may have a curved shape shown inFIG. 19. Further, the whetstone82shown inFIG. 22may be attached to the pressing surface55aof the silicon sponge55shown inFIG. 7orFIG. 19. In this case, the whetstone82may be attached to the entire pressing surface55aor only to a part of the pressing surface55a. For example, the whetstone82is attached only to a part of the pressing surface55adeformed when the pressing pad50is pressed against the bevel portion B of the substrate.