Wafer polishing method

Abstract

To provide a wafer polishing method which enables efficient improvement of flatness of a surface of a wafer.SOLUTION: In a wafer polishing method, a wafer is polished with a polishing pad. The wafer polishing method includes: a first polishing step in which a surface of the wafer is polished with a first polishing pad having a first polishing layer; and a second polishing step in which the surface of the wafer is polished with a second polishing pad having a second polishing layer. A glass-transition temperature of the second polishing layer is lower than a glass-transition temperature of the first polishing layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for polishing a wafer by using a polishing pad. [Background technology]

[0002] The device chip manufacturing process uses a wafer in which devices are formed in multiple areas defined by multiple streets (planned division lines) arranged in a grid pattern. By dividing this wafer along the streets, multiple device chips, each equipped with a device, are obtained. The device chips are incorporated into various electronic devices, such as mobile phones and personal computers.

[0003] Wafers are manufactured by slicing a cylindrical ingot. For example, single crystal silicon wafers of a predetermined thickness can be obtained by cutting a single crystal silicon ingot in the radial direction. The wafers cut from the ingot are subjected to various processes such as chamfering, lapping, and etching. The wafers are then polished to flatten and mirror-finish the surfaces (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-135164 Summary of the Invention [Problem to be solved by the invention]

[0005] By polishing a wafer, irregularities formed on the surface of the wafer during the wafer manufacturing process (ingot slicing, lapping, etching, etc.) are removed. For example, a polishing pad with a polishing layer made of nonwoven fabric or the like is used to polish a wafer. The surface of the wafer is polished by rotating the polishing pad and bringing the polishing layer into contact with the surface of the wafer.

[0006] The unevenness of a wafer includes a periodic wave-like waviness component (long-period waviness) and a fine roughness component (short-period waviness) with a shorter period than the waviness. Therefore, in order to improve the flatness of the wafer surface, it is desirable to efficiently reduce both the waviness component and the roughness component contained in the unevenness.

[0007] The present invention has been made in view of the above problems, and has as its object to provide a wafer polishing method that can efficiently improve the flatness of the wafer surface. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided a method for polishing a wafer with a polishing pad, comprising: a first polishing step of polishing a surface of the wafer with a first polishing pad having a first polishing layer; and a second polishing step of polishing the surface of the wafer with a second polishing pad having a second polishing layer, The glass transition temperature of the first polishing layer is 90°C or higher and 100°C or lower, and the glass transition temperature of the second polishing layer is 30°C or higher and 40°C or lower. A method for polishing a wafer is provided.

[0009] Preferably, , applicable First polishing layer and Applicable The second polishing layer contains abrasive grains, and in the first polishing step and the second polishing step, the surface of the wafer is polished while supplying a polishing liquid that does not contain abrasive grains to the wafer. Preferably, in the first polishing step, the surface of the wafer is polished with the first polishing pad to reduce the waviness of the surface of the wafer, and in the second polishing step, the surface of the wafer is polished with the second polishing pad to reduce the roughness of the surface of the wafer. [Effects of the Invention]

[0010] In one aspect of the present invention, a wafer polishing method includes polishing a wafer surface with a first polishing pad having a first polishing layer, and then polishing the wafer surface with a second polishing pad having a second polishing layer having a glass transition temperature lower than that of the first polishing layer, thereby efficiently reducing both the waviness and roughness components of the unevenness formed on the wafer surface and improving the flatness of the wafer surface. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing a polishing apparatus. [Figure 2] FIG. 2 is a perspective view showing a wafer. [Figure 3] FIG. 2 is an enlarged cross-sectional view showing a portion of the wafer. [Figure 4] FIG. 4(A) is a graph showing the cross-sectional curve of the wafer surface, FIG. 4(B) is a graph showing the roughness curve of the wafer surface, and FIG. 4(C) is a graph showing the waviness curve of the wafer surface. [Figure 5] FIG. 2 is a cross-sectional view showing a wafer held by a chuck table. [Figure 6] FIG. 6(A) is a cross-sectional view showing a wafer in a first polishing step, and FIG. 6(B) is an enlarged cross-sectional view showing a part of the wafer after the first polishing step. [Figure 7] FIG. 7(A) is a cross-sectional view showing the wafer in the second polishing step, and FIG. 7(B) is an enlarged cross-sectional view showing a part of the wafer after the second polishing step. [Figure 8] FIG. 10 is a perspective view showing a polishing apparatus according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment according to one aspect of the present invention will be described below with reference to the accompanying drawings. First, an example of the configuration of a polishing apparatus that can be used to implement the wafer polishing method according to this embodiment will be described. FIG. 1 is a perspective view showing a polishing apparatus 2. In FIG. 1, the X-axis direction (first horizontal direction, front-to-back direction) and the Y-axis direction (second horizontal direction, left-to-right direction) are perpendicular to each other. Furthermore, the Z-axis direction (vertical direction, up-down direction, height direction) is perpendicular to the X-axis direction and the Y-axis direction.

[0013] The polishing apparatus 2 includes a rectangular parallelepiped base 4 that supports or houses each of the components constituting the polishing apparatus 2. At the front end of the base 4, cassette placement areas (cassette placement stages) 6a and 6b on which cassettes 8a and 8b are placed are provided. The cassettes 8a and 8b are containers that can hold a plurality of wafers 11, and are placed on the cassette placement areas 6a and 6b, respectively. For example, the cassette 8a contains wafers 11 before polishing, and the cassette 8b contains wafers 11 after polishing.

[0014] 2 is a perspective view showing the wafer 11. For example, the wafer 11 is a disk-shaped single crystal wafer made of a semiconductor material, and has a pair of surfaces (a first surface 11a and a second surface 11b) that are generally parallel to each other.

[0015] The wafers 11 are manufactured by slicing a cylindrical ingot. Specifically, a cylindrical single crystal ingot made of a semiconductor material such as silicon (Si), silicon carbide (SiC), gallium nitride (GaN), or gallium arsenide (GaAs) is cut with a cutting tool such as a wire saw to obtain wafers 11 of a desired thickness.

[0016] Wafers 11 cut from an ingot are subjected to various processes such as chamfering, lapping, and etching. Then, the wafers 11 are polished by a polishing device 2 to flatten and mirror-finish one or both of a first surface 11a and a second surface 11b of the wafer 11. The following describes, as an example, the case where the first surface 11a of the wafer 11 is polished.

[0017] When polishing the first surface 11a of the wafer 11, a protective member 13 is attached to the second surface 11b of the wafer 11. The protective member 13 may be a tape (protective tape) including a flexible film-like substrate and an adhesive layer (glue layer) provided on the substrate. For example, the substrate may be made of a resin such as polyolefin, polyvinyl chloride, or polyethylene terephthalate, and the adhesive layer may be made of an epoxy-, acrylic-, or rubber-based adhesive. The adhesive layer may be an ultraviolet-curable resin that is cured by irradiation with ultraviolet light.

[0018] The wafers 11 are accommodated in a cassette 8a shown in Fig. 1 with the protective member 13 attached thereto. Then, the cassette 8a accommodating the plurality of wafers 11 is placed on the cassette placement area 6a.

[0019] An opening 4a is provided in an area located between the cassette placement areas 6a and 6b on the upper surface of the base 4. A first transport mechanism 10 for transporting wafers 11 is provided inside the opening 4a. An operation panel 12 for inputting various information (processing conditions, etc.) to the polishing apparatus 2 is also provided in the area in front of the opening 4a.

[0020] A position adjustment mechanism 14 that adjusts the position of the wafer 11 is provided diagonally behind the first transport mechanism 10. The wafer 11 stored in the cassette 8a is transported onto the position adjustment mechanism 14 by the first transport mechanism 10. The position adjustment mechanism 14 then adjusts the position of the wafer 11 by clamping the wafer 11. In addition, a second transport mechanism (loading arm) 16 that holds and rotates the wafer 11 is provided near the position adjustment mechanism 14.

[0021] A rectangular opening 4b, whose longitudinal direction is aligned with the X-axis direction, is provided in an area of ​​the upper surface of the base 4 behind the second transfer mechanism 16. A ball screw-type first movement mechanism 18 is provided inside the opening 4b. The first movement mechanism 18 includes a ball screw (not shown) arranged along the X-axis direction, a pulse motor (not shown) for rotating the ball screw, and the like. The first movement mechanism 18 also includes a flat plate-shaped movement table 20, which moves the movement table 20 along the X-axis direction. Furthermore, accordion-shaped dust-proof and drip-proof covers 22 that can expand and contract along the X-axis direction are provided in front and behind the movement table 20. The dust-proof and drip-proof covers 22 cover the components of the first movement mechanism 18 (the ball screw, the pulse motor, etc.).

[0022] A chuck table (holding table) 24 that holds the wafer 11 is provided on the moving table 20. The upper surface of the chuck table 24 is a flat surface that is roughly parallel to the horizontal direction (XY plane direction) and constitutes a holding surface 24a that holds the wafer 11. The holding surface 24a is connected to a suction source (not shown) such as an ejector via a suction path 24b (see FIG. 5) formed inside the chuck table 24, a valve (not shown), etc. The wafer 11 that has been aligned by the position adjustment mechanism 14 is transported onto the holding surface 24a of the chuck table 24 by the second transport mechanism 16 and is held by the chuck table 24.

[0023] When the moving table 20 is moved by the first moving mechanism 18, the chuck table 24 moves along the X-axis direction together with the moving table 20. In addition, the chuck table 24 is connected to a rotation drive source (not shown) such as a motor that rotates the chuck table 24 around a rotation axis that is approximately perpendicular to the holding surface 24a (a rotation axis that is approximately parallel to the Z-axis direction).

[0024] A rectangular parallelepiped support structure 26 is provided at the rear end of the base 4. A second movement mechanism 28 is provided on the front side of the support structure 26. The second movement mechanism 28 includes a pair of guide rails 30 fixed along the Z-axis direction on the front side of the support structure 26. A movement plate 32 is attached to the pair of guide rails 30 so as to be slidable along the guide rails 30.

[0025] A nut portion (not shown) is provided on the rear surface side (back surface side) of the moving plate 32. A ball screw 34, which is disposed along the Z-axis direction between a pair of guide rails 30, is threadedly engaged with this nut portion. A pulse motor 36 is connected to one end of the ball screw 34. When the ball screw 34 is rotated by the pulse motor 36, the moving plate 32 moves along the guide rails 30 in the Z-axis direction.

[0026] A support member 38 is provided on the front side (surface side) of the moving plate 32. The support member 38 supports a polishing unit 40 that polishes the wafer 11.

[0027] The polishing unit 40 includes a hollow, cylindrical housing 42 supported by a support member 38. A cylindrical spindle 44 is rotatably housed in the housing 42. The tip end (lower end) of the spindle 44 is exposed to the outside of the housing 42, and a base end (upper end) of the spindle 44 is connected to a rotation drive source (not shown), such as a motor.

[0028] A disk-shaped mount 46 made of metal or the like is fixed to the tip of the spindle 44. A disk-shaped polishing pad 48 for polishing the wafer 11 is attached to the mount 46. For example, the polishing pad 48 is fixed to the underside of the mount 46 by a fastener 50 such as a bolt. The polishing pad 48 rotates around a rotation axis that is approximately perpendicular to the holding surface 24a (a rotation axis that is approximately parallel to the Z-axis direction) by power transmitted from a rotation drive source via the spindle 44 and the mount 46.

[0029] When polishing the wafer 11, first, the chuck table 24 is moved by the first moving mechanism 18, and the wafer 11 is positioned below the polishing unit 40. Then, the polishing unit 40 is lowered at a predetermined speed by the second moving mechanism 28 while rotating the chuck table 24 and the spindle 44. As a result, the rotating polishing pad 48 comes into contact with the surface of the wafer 11 to be polished, and the wafer 11 is polished.

[0030] A polishing liquid supply path 52 is formed inside the polishing unit 40 along the Z-axis direction. One end (upper end) of the polishing liquid supply path 52 is connected to a polishing liquid supply source 56 via a valve 54. The other end (lower end) of the polishing liquid supply path 52 opens at the lower surface of the mount 46. When the wafer 11 is polished with the polishing pad 48, the polishing liquid is supplied from the polishing liquid supply source 56 to the wafer 11 and the polishing pad 48 via the valve 54 and the polishing liquid supply path 52.

[0031] A third transfer mechanism (unloading arm) 58 that holds and rotates the wafer 11 is disposed adjacent to the second transfer mechanism 16. A cleaning mechanism 60 that cleans the wafer 11 is disposed in front of the third transfer mechanism 58. The wafer 11 polished by the polishing unit 40 is transported by the third transfer mechanism 58 to the cleaning mechanism 60, where it is cleaned. The cleaned wafer 11 is then transported by the first transfer mechanism 10 and stored in the cassette 8b.

[0032] The first surface 11a of the wafer 11 is polished by the polishing apparatus 2, thereby flattening the first surface 11a. Thereafter, a plurality of devices (not shown), such as ICs (Integrated Circuits), LSIs (Large Scale Integration), LEDs (Light Emitting Diodes), and MEMS (Micro Electro Mechanical Systems) devices, are formed on the first surface 11a of the wafer 11. The wafer 11 on which the plurality of devices are formed is divided to manufacture a plurality of device chips, each including a device.

[0033] 3 is an enlarged cross-sectional view showing a portion of the wafer 11. Before the wafer 11 is polished by the polishing apparatus 2, unevenness exists on the first surface 11a of the wafer 11. The unevenness is formed on the first surface 11a of the wafer 11, for example, during the manufacturing process of the wafer 11 (ingot slicing, lapping, etching, etc.). By polishing the first surface 11a of the wafer 11 by the polishing apparatus 2, the unevenness is removed and the first surface 11a is flattened.

[0034] 4(A) is a graph showing a profile curve 15 of the first surface 11a of the wafer 11. The profile curve 15 is obtained by applying a low-pass filter with a cutoff value λs to a measured profile curve that indicates the cross-sectional shape of the first surface 11a of the wafer 11. In other words, the profile curve 15 represents the unevenness of the first surface 11a of the wafer 11.

[0035] Applying a high-pass filter with a cutoff value λc (>λs) to the profile curve 15 results in a roughness curve of the first surface 11a of the wafer 11. Furthermore, applying a band-pass filter with cutoff values ​​λc, λf (>λc) to the profile curve 15 results in a waviness curve of the first surface 11a of the wafer 11. Figure 4(B) is a graph showing a roughness curve 17 of the first surface 11a of the wafer 11, and Figure 4(C) is a graph showing a waviness curve 19 of the first surface 11a of the wafer 11.

[0036] The unevenness of the first surface 11a of the wafer 11 shown in Fig. 3 includes a periodic wave-like undulation (long-period undulation) component corresponding to the undulation curve 19 (see Fig. 4(C)) and a fine roughness component (short-period undulation) having a shorter period than the undulation and corresponding to the roughness curve 17 (see Fig. 4(B)). Therefore, in order to improve the flatness of the first surface 11a of the wafer 11, it is preferable to efficiently reduce both the undulation component and the roughness component included in the unevenness of the first surface 11a of the wafer 11.

[0037] Therefore, in this embodiment, the wafer 11 is polished using two types of polishing pads having polishing layers with different glass transition temperatures. This effectively reduces both the waviness and roughness components of the unevenness formed on the first surface 11a of the wafer 11. A specific example of the wafer polishing method according to this embodiment will be described below.

[0038] First, the wafer 11 is held by the chuck table 24. FIG.

[0039] The wafer 11 is placed on the chuck table 24 so that the first surface 11a (surface to be polished) is exposed upward and the second surface 11b (protective member 13 side) faces the holding surface 24a. In this state, when the suction force (negative pressure) of the suction source is applied to the holding surface 24a, the wafer 11 is sucked and held by the chuck table 24 via the protective member 13.

[0040] Next, the first surface 11a of the wafer 11 is polished with a first polishing pad (first polishing step). Fig. 6(A) is a cross-sectional view showing the wafer 11 in the first polishing step. In the first polishing step, a polishing pad 70A (first polishing pad) is attached to the mount 46 as the polishing pad 48 (see Fig. 1).

[0041] The polishing pad 70A includes a disk-shaped base 72A made of metal such as stainless steel or aluminum, or resin such as PPS (polyphenylene sulfide). A polishing layer 74A (first polishing layer) for polishing the wafer 11 is fixed to the lower surface of the base 72A. The polishing layer 74A is formed in a disk shape with roughly the same diameter as the base 72A, and is fixed to the lower surface of the base 72A by, for example, an adhesive. The lower surface of the polishing layer 74A forms a flat polishing surface 76A for polishing the wafer 11.

[0042] The polishing layer 74A contains abrasive grains (fixed abrasive grains). Specifically, the polishing layer 74A includes a polishing member as a base material and abrasive grains dispersed in the polishing member. The polishing member is, for example, a disk-shaped member made of a resin such as polyurethane or a nonwoven fabric such as felt. The abrasive grains are, for example, silica (SiO2) with a grain size of 1 μm to 10 μm. However, the material of the polishing member and the grain size and material of the abrasive grains can be selected appropriately depending on the material of the wafer 11, etc.

[0043] A cylindrical through-hole that penetrates the polishing pad 70 A in the thickness direction is formed in the center of the polishing pad 70 A. When the polishing pad 70 A is attached to the mount 46, the through-hole of the polishing pad 70 A is connected to the polishing liquid supply path 52.

[0044] The chuck table 24 holding the wafer 11 is positioned below the polishing unit 40 by the first moving mechanism 18 (see FIG. 1). At this time, the wafer 11 is positioned so that the entire first surface 11a of the wafer 11 overlaps the polishing surface 76A of the polishing pad 70A. Then, while rotating the chuck table 24 and the spindle 44, the polishing unit 40 is lowered by the second moving mechanism 28 (see FIG. 1). As a result, the polishing surface 76A of the rotating polishing pad 70A is pressed against the first surface 11a of the wafer 11, polishing the first surface 11a.

[0045] During polishing of the wafer 11, a polishing liquid is supplied from the polishing liquid supply source 56 to the wafer 11 and polishing pad 70A via the valve 54 and the polishing liquid supply path 52. If the polishing layer 74A contains abrasive grains, a polishing liquid that does not contain abrasive grains is supplied. Examples of polishing liquids that can be used include alkaline solutions containing sodium hydroxide, potassium hydroxide, etc., acidic solutions containing permanganate, etc., and pure water. The polishing layer 74A does not necessarily contain abrasive grains. In this case, a chemical solution (slurry) in which abrasive grains (loose abrasive grains) are dispersed is supplied as the polishing liquid.

[0046] The glass transition temperature of polishing layer 74A is higher than that of polishing layer 74B (see FIG. 7A) of polishing pad 70B (described later). Therefore, even if frictional heat is generated by contact between wafer 11 and polishing layer 74A during polishing of wafer 11, the shape of polishing layer 74A is unlikely to change, and polishing surface 76A is maintained flat.

[0047] 6(B) is an enlarged cross-sectional view showing a portion of wafer 11 after the first polishing step. When first surface 11a of wafer 11 is polished with polishing pad 70A having polishing layer 74A with a high glass transition temperature, upwardly protruding regions of first surface 11a, i.e., convex portions of waviness (see FIG. 4(C)), are preferentially polished by polishing surface 76A maintained in a flat state, thereby reducing the height difference of first surface 11a of wafer 11. As a result, waviness included in first surface 11a of wafer 11 is efficiently reduced.

[0048] Next, the first surface 11a of the wafer 11 is polished with a second polishing pad (second polishing step). Fig. 7(A) is a cross-sectional view showing the wafer 11 in the second polishing step. In the second polishing step, the polishing pad 70A is removed from the polishing unit 40, and a polishing pad 70B (second polishing pad) is attached instead.

[0049] The polishing pad 70B includes a disk-shaped base 72B and a polishing layer (second polishing layer) 74B that polishes the wafer 11. The polishing layer 74B is formed in a disk shape with approximately the same diameter as the base 72B and is fixed to the lower surface of the base 72B, for example, with an adhesive. The lower surface of the polishing layer 74B forms a flat polishing surface 76B that polishes the wafer 11. The polishing layer 74B also contains abrasive grains (fixed abrasive grains).

[0050] Examples of the material, shape, structure, etc. of base 72B and polishing layer 74B of polishing pad 70B are the same as those of base 72A and polishing layer 74A of polishing pad 70A (see FIG. 6(A)). Note that the material of polishing layer 74A and the material of polishing layer 74B may be the same or different.

[0051] In the second polishing step, similarly to the first polishing step, the polishing unit 40 is lowered by the second moving mechanism 28 (see FIG. 1) while the chuck table 24 and the spindle 44 are rotated. As a result, the polishing surface 76B of the rotating polishing pad 70B is pressed against the first surface 11a of the wafer 11, polishing the first surface 11a. During polishing of the wafer 11, a polishing liquid is supplied from the polishing liquid supply source 56 to the wafer 11 and the polishing pad 70B via the valve 54 and the polishing liquid supply path 52.

[0052] The glass transition temperature of the polishing layer 74B is lower than that of the polishing layer 74A of the polishing pad 70A (see FIG. 6A). Therefore, when frictional heat is generated by contact between the wafer 11 and the polishing layer 74B during polishing of the wafer 11, the temperature of the polishing layer 74B rises and approaches the glass transition temperature, softening the polishing layer 74A and making it more susceptible to deformation. As a result, the polishing surface 76B deforms to conform to the irregularities of the first surface 11a of the wafer 11.

[0053] 7(B) is an enlarged cross-sectional view showing a portion of wafer 11 after the second polishing step. When first surface 11a of wafer 11 is polished with polishing pad 70B having polishing layer 74B with a low glass transition temperature, polishing surface 76B deforms along first surface 11a of wafer 11 and enters into the concave portions of the minute irregularities formed on first surface 11a. As a result, the entire first surface 11a of wafer 11 is polished uniformly, and the roughness (see FIG. 4(B)) contained in first surface 11a of wafer 11 is efficiently reduced.

[0054] The glass transition temperature of polishing layer 74A is preferably at least 30°C higher than the glass transition temperature of polishing layer 74B, and more preferably at least 50°C higher. This prevents softening and deformation of polishing layer 74A due to frictional heat, and maintains polishing surface 76A flat. As a result, a high polishing rate is achieved in the first polishing step.

[0055] However, if the glass transition temperature of polishing layer 74A is extremely high, scratches are likely to remain on first surface 11a of wafer 11 after polishing. Therefore, the glass transition temperature of polishing layer 74A is preferably not more than 90°C higher than the glass transition temperature of polishing layer 74B, and more preferably not more than 60°C higher than the glass transition temperature of polishing layer 74B. This makes it possible to efficiently remove waviness on first surface 11a of wafer 11 while suppressing the remaining scratches.

[0056] Furthermore, the glass transition temperature of the polishing layer 74B is preferably approximately the same as the temperature at the contact area between the wafer 11 and the polishing layer 74B when the wafer 11 is polished in the second polishing step. Generally, the temperature at the contact area between the wafer 11 and the polishing layer 74B during polishing is approximately 30°C to 40°C. Therefore, the glass transition temperature of the polishing layer 74B is preferably also approximately 30°C to 40°C. This promotes appropriate deformation of the polishing layer 74B due to frictional heat generated during polishing, and the polishing surface 76B easily penetrates into the recesses of the fine irregularities formed on the first surface 11a of the wafer 11 while maintaining a certain degree of rigidity. As a result, it is possible to effectively remove roughness from the first surface 11a of the wafer 11 without significantly reducing the polishing rate.

[0057] Considering the above effects, the glass transition temperature of polishing layer 74A is preferably 90° C. or higher and 100° C. or lower, and the glass transition temperature of polishing layer 74B is preferably 30° C. or higher and 40° C. or lower. The glass transition temperatures of polishing layers 74A and 74B can be adjusted by the material, composition, etc. of polishing layers 74A and 74B.

[0058] For example, when both polishing layers 74A and 74B are made of polyurethane, the glass transition temperature of the polyurethane can be adjusted by appropriately selecting the type, number of functional groups, molecular weight, etc. of the polyol used as a raw material, and the difference in glass transition temperature between polishing layers 74A and 74B can be set to a desired value. When polishing layers 74A and 74B are formed using a commercially available product, for example, Sannix GP-600 (manufactured by Sanyo Chemical Industries, Ltd.) can be used to form polishing layer 74A with a glass transition temperature of 90°C to 100°C. Furthermore, for example, by using a polyol obtained by mixing Sannix GP-600 and Sannix GP-1000 (manufactured by Sanyo Chemical Industries, Ltd.) in a 1:1 ratio, polishing layer 74B with a glass transition temperature of 30°C to 40°C can be formed.

[0059] As described above, in this embodiment, the first surface 11a of the wafer 11 is polished with the polishing pad 70A having the polishing layer 74A, and then the first surface 11a of the wafer 11 is polished with the polishing pad 70B having the polishing layer 74B having a lower glass transition temperature than the polishing layer 74A. As a result, the polishing layer 74A, which is resistant to deformation due to frictional heat, reduces the height difference on the first surface 11a of the wafer 11, and then the polishing layer 74B, which is resistant to deformation due to frictional heat, uniformly polishes the entire first surface 11a of the wafer 11. As a result, both the waviness and roughness components of the unevenness formed on the first surface 11a of the wafer 11 are efficiently reduced, and the flatness of the first surface 11a of the wafer 11 is improved.

[0060] In the above embodiment, the case where polishing pad 70A (see FIG. 6A) is replaced with polishing pad 70B (see FIG. 7A) between the first and second polishing steps has been described. However, the polishing apparatus 2 may be equipped with two polishing units 40. In this case, the first polishing step is performed by one polishing unit 40 equipped with polishing pad 70A, and the second polishing step is performed by the other polishing unit 40 equipped with polishing pad 70B. This eliminates the need to replace the polishing pads.

[0061] Alternatively, the wafer 11 may be processed by two polishing apparatuses 2. In this case, a polishing pad 70A (see FIG. 6(A)) is attached to the polishing unit 40 of one polishing apparatus 2, and a polishing pad 70B (see FIG. 7(A)) is attached to the polishing unit 40 of the other polishing apparatus 2. Then, a first polishing step is performed by one polishing apparatus 2, and a second polishing step is performed by the other polishing apparatus 2.

[0062] Furthermore, in the above embodiment, the polishing apparatus 2 is described as supporting the underside of the wafer 11 and polishing the upper side, but a polishing apparatus that polishes the underside of the wafer 11 can also be used. FIG. 8 is a perspective view showing a polishing apparatus 80 corresponding to a modified example of the polishing apparatus 2 (see FIG. 1). In FIG. 8, the X-axis direction (first horizontal direction) and the Y-axis direction (second horizontal direction) are perpendicular to each other. The Z-axis direction (vertical direction, up-down direction, height direction) is perpendicular to the X-axis direction and the Y-axis direction.

[0063] The polishing apparatus 80 includes a support unit 82 that supports a polishing pad 90, and a holding unit 94 that holds the wafer 11. The wafer 11 held by the holding unit 94 is pressed against the polishing pad 90, thereby polishing the wafer 11.

[0064] The support unit 82 includes a disk-shaped support base (surface plate) 84 made of metal, ceramics, resin, etc. The upper surface of the support base 84 is a flat surface that is roughly parallel to the horizontal direction (XY plane direction) and forms a circular support surface 84a that supports the polishing pad 90.

[0065] A cylindrical spindle 86 arranged along the Z-axis direction is connected to the underside of the support base 84. The upper end of the spindle 86 is fixed to the center of the underside of the support base 84. A rotational drive source 88 such as a motor that rotates the spindle 86 is connected to the lower end of the spindle 86. The support base 84 rotates around a rotation axis that is approximately parallel to the Z-axis direction by power transmitted from the rotational drive source 88 via the spindle 86.

[0066] A polishing pad 90 for polishing the wafer 11 is fixed to the support surface 84a of the support table 84. The polishing pad 90 has a disk-shaped polishing layer 92 with a diameter larger than that of the wafer 11. The upper surface of the polishing layer 92 is a flat surface that is roughly parallel to the horizontal direction (XY plane direction) and forms a polishing surface for polishing the wafer 11. An example of the material of the polishing layer 92 is the same as that of the polishing layer 74A of the polishing pad 70A (see FIG. 6(A)) and the polishing layer 74B of the polishing pad 70B (see FIG. 7(A)).

[0067] A holding unit 94 is provided above the support unit 82. The holding unit 94 includes a disk-shaped holding portion 96 that holds the wafer 11. The holding portion 96 is disposed so as to overlap the region between the center and the outer periphery of the polishing layer 92.

[0068] A holding member (not shown) that holds the wafer 11 is provided on the underside of the holding unit 96. For example, the holding member includes a circular base material having a diameter larger than the wafer 11 and a holding film (backing film) provided on the surface (underside) of the base material. For example, the base material is made of a resin such as polyethylene terephthalate (PET), and the holding film is made of suede-like urethane foam or the like. The holding member is arranged so that the holding film is exposed on the underside of the holding unit 96. When the wafer 11 is wetted with a liquid such as water and brought into close contact with the holding film, the wafer 11 is adsorbed to the holding film by surface tension and is held by the holding unit 96. However, there are no limitations on the method for holding the wafer 11 by the holding unit 96.

[0069] A cylindrical spindle 98 arranged along the Z-axis direction is connected to the upper surface of the holding part 96. The lower end of the spindle 98 is fixed to the center of the holding part 96. A drive mechanism 100 that drives the spindle 98 is connected to the upper end of the spindle 98. The drive mechanism 100 includes a rotational drive source such as a motor that rotates the spindle 98, and an elevation mechanism such as an air cylinder that moves (lifts and lowers) the spindle 98 along the Z-axis direction.

[0070] The holder 96 rotates around a rotation axis that is roughly parallel to the Z-axis direction by power transmitted from the rotation drive source of the drive mechanism 100 via the spindle 98. Furthermore, by raising and lowering the spindle 98 using the lifting mechanism of the drive mechanism 100, the holder 96 rises and falls along the Z-axis direction, moving closer to and away from the polishing pad 90.

[0071] Furthermore, a polishing liquid supply unit 102 is provided in an area above the support unit 82 where the holding unit 94 is not provided, to supply a polishing liquid to the polishing pad 90. The polishing liquid supply unit 102 includes a nozzle 104 connected to a polishing liquid supply source (not shown), and the nozzle 104 supplies a polishing liquid 106 toward the upper surface (polishing surface) of the polishing pad 90 at a predetermined flow rate.

[0072] When polishing the wafer 11 with the polishing apparatus 80, the wafer 11 is first held by the holding unit 94. At this time, the wafer 11 is held so that the surface to be polished (first surface 11a) is exposed downward. Then, the polishing pad 90 is rotated in a predetermined direction (the direction indicated by arrow A) by the rotary drive source 88, and the holding part 96 is rotated in a predetermined direction (the direction indicated by arrow B) by the drive mechanism 100, and the holding part 96 is lowered by the drive mechanism 100. As a result, the first surface 11a of the wafer 11 comes into contact with the upper surface (polishing surface) of the polishing layer 92, and the first surface 11a of the wafer 11 is polished.

[0073] When the wafer polishing method according to this embodiment is carried out using the polishing apparatus 80, first, a polishing pad 90 (first polishing pad) having a polishing layer 92 with a high glass transition temperature (for example, a glass transition temperature of 90°C or more and 100°C or less) is supported by the support unit 82, and the first surface 11a of the wafer 11 is polished by the first polishing pad (first polishing step). Then, a polishing pad 90 (second polishing pad) having a polishing layer 92 with a low glass transition temperature (for example, a glass transition temperature of 30°C or more and 40°C or less) is supported by the support unit 82, and the first surface 11a of the wafer 11 is polished by the second polishing pad (second polishing step).

[0074] In addition, the structures, methods, etc. according to the above-described embodiments can be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of symbols]

[0075] 11 wafers 11a 1st side (front) 11b 2nd side (front) 13 Protective materials 15 Section curve 17 Roughness curve 19 Swell curve 2 Polishing equipment 4 Foundation 4a,4b opening 6a, 6b Cassette placement area (cassette placement table) 8a,8b cassette 10 First conveying mechanism 12 Operation panel 14 Position adjustment mechanism 16 Second transport mechanism (loading arm) 18 1st movement mechanism 20 Mobile Table 22 Dustproof and water-resistant cover 24 Chuck table (holding table) 24a Holding surface 24b Suction path 26 Support structure 28 Second movement mechanism 30 guide rail 32 Moving Plate 34 Ball screw 36 Pulse motor 38 Support member 40 Polishing Unit 42 Housing 44 Spindle 46 Mount 48 Polishing Pads 50 Fixtures 52 Polishing liquid supply path 54 Valve 56 Polishing fluid supply source 58 Third transport mechanism (unloading arm) 60 Cleaning mechanism 70A, 70B Polishing Pads 72A,72B base 74A,74B Polishing layer 76A,76B Polished surface 80 Polishing equipment 82 Support unit 84 Support table (surface plate) 84a Support surface 86 Spindle 88 Rotational drive source 90 polishing pads 92 Polishing layer 94 Holding Unit 96 Holding part 98 Spindle 100 Drive mechanism 102 Polishing liquid supply unit 104 nozzle 106 Polishing liquid

Claims

1. A method for polishing a wafer by using a polishing pad, comprising: a first polishing step of polishing the surface of the wafer with a first polishing pad having a first polishing layer; a second polishing step of polishing the surface of the wafer with a second polishing pad having a second polishing layer; the glass transition temperature of the first abrasive layer is 90°C or higher and 100°C or lower; A method for polishing a wafer, wherein the second polishing layer has a glass transition temperature of 30°C or higher and 40°C or lower.

2. the first abrasive layer and the second abrasive layer contain abrasive grains; 2. The method for polishing a wafer according to claim 1, wherein in the first polishing step and the second polishing step, the surface of the wafer is polished while a polishing liquid containing no abrasive grains is supplied to the wafer.

3. In the first polishing step, the surface of the wafer is polished with the first polishing pad to reduce waviness of the surface of the wafer; 3. The method for polishing a wafer according to claim 1, wherein in the second polishing step, the surface of the wafer is polished with the second polishing pad to reduce the roughness of the surface of the wafer.

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