JP7776339B2 - Wafer polishing method - Google Patents

Description

The present invention relates to a wafer polishing method in which a wafer is polished with a polishing pad.

The device chip manufacturing process uses a wafer on which devices are formed in multiple areas partitioned 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.

Wafer are manufactured by slicing a cylindrical ingot. For example, single crystal silicon wafers of a specified thickness can be obtained by cutting a single crystal silicon ingot radially. Wafers cut from the ingot undergo various processes such as chamfering, lapping, and etching. The wafers are then polished to flatten and mirror-finish the surface (see Patent Document 1).

Japanese Patent Application Publication No. 10-135164

By polishing a wafer, irregularities formed on the wafer surface 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 similar 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.

The unevenness of a wafer includes both 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, 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.

The present invention was made in consideration of these problems, and aims to provide a wafer polishing method that can efficiently improve the flatness of the wafer surface.

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 the 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, wherein 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 .

Preferably , the first polishing layer and the second polishing layer contain abrasive grains, and in the first polishing step and the second polishing step, the surface of the wafer is polished while an abrasive-free polishing liquid is supplied to the wafer. Also, preferably, in the first polishing step, the waviness of the wafer surface is reduced by polishing the wafer surface with the first polishing pad, and in the second polishing step, the roughness of the wafer surface is reduced by polishing the wafer surface with the second polishing pad.

In one aspect of the present invention, a wafer polishing method involves polishing the surface of a wafer with a first polishing pad having a first polishing layer, and then polishing the surface of the wafer with a second polishing pad having a second polishing layer that has a lower glass transition temperature than the first polishing layer. This effectively reduces both the waviness and roughness components of the irregularities formed on the wafer surface, improving the flatness of the wafer surface.

FIG. 1 is a perspective view showing a polishing apparatus. FIG. 2 is a perspective view showing a wafer. FIG. 2 is an enlarged cross-sectional view showing a portion of the wafer. FIG. 4A is a graph showing the cross-sectional curve of the wafer surface, FIG. 4B is a graph showing the roughness curve of the wafer surface, and FIG. 4C is a graph showing the waviness curve of the wafer surface. FIG. 2 is a cross-sectional view showing a wafer held by a chuck table. FIG. 6A is a cross-sectional view showing a wafer in a first polishing step, and FIG. 6B is an enlarged cross-sectional view showing a part of the wafer after the first polishing step. FIG. 7A is a cross-sectional view showing the wafer in the second polishing step, and FIG. 7B is an enlarged cross-sectional view showing a part of the wafer after the second polishing step. FIG. 10 is a perspective view showing a polishing apparatus according to a modified example.

An embodiment of the present invention will now be described 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. Figure 1 is a perspective view showing a polishing apparatus 2. Note that in Figure 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 mutually perpendicular. Furthermore, the Z-axis direction (vertical direction, up-down direction, height direction) is a direction perpendicular to the X-axis direction and the Y-axis direction.

The polishing apparatus 2 includes a rectangular parallelepiped base 4 that supports or houses each of the components that make up the polishing apparatus 2. At the front end of the base 4, there are provided cassette mounting areas (cassette mounting tables) 6a and 6b on which cassettes 8a and 8b are placed. Cassettes 8a and 8b are containers that can hold multiple wafers 11, and are placed on the cassette mounting areas 6a and 6b, respectively. For example, cassette 8a contains wafers 11 before polishing, and cassette 8b contains wafers 11 after polishing.

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

Wafer 11 is 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 the desired thickness.

Wafer 11 cut from the ingot undergoes various processes such as chamfering, lapping, and etching. The wafer 11 is then polished by polishing device 2 to flatten and mirror-finish one or both of the first surface 11a and 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.

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) that includes 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 also be made of an ultraviolet-curing resin that hardens when exposed to ultraviolet light.

The wafers 11, with the protective member 13 attached, are stored in the cassette 8a shown in Figure 1. Then, the cassette 8a containing multiple wafers 11 is placed on the cassette placement area 6a.

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

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 it. In addition, a second transport mechanism (loading arm) 16 that holds the wafer 11 and rotates is provided near the position adjustment mechanism 14.

A rectangular opening 4b is provided on the top surface of the base 4 in an area located behind the second transport mechanism 16, with its longitudinal direction aligned with the X-axis direction. 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 other components. The first movement mechanism 18 also includes a flat 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 (ball screw, pulse motor, etc.).

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 forms 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 Figure 5) formed inside the chuck table 24 and a valve (not shown). After the wafer 11 has been aligned by the position adjustment mechanism 14, it is transported by the second transport mechanism 16 onto the holding surface 24a of the chuck table 24 and held by the chuck table 24.

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. The chuck table 24 is also connected to a rotational drive source (not shown), such as a motor, that rotates the chuck table 24 around a rotation axis generally perpendicular to the holding surface 24a (a rotation axis generally parallel to the Z-axis direction).

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 has a pair of guide rails 30 fixed along the Z-axis direction on the front side of the support structure 26. In addition, a movement plate 32 is attached to the pair of guide rails 30 so that it can slide along the guide rails 30.

A nut portion (not shown) is provided on the rear side (back side) of the moving plate 32. A ball screw 34, which is arranged along the Z-axis direction between a pair of guide rails 30, is threadedly engaged with this nut portion. A pulse motor 36 is also 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 in the Z-axis direction along the guide rails 30.

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.

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 (lower end) of the spindle 44 is exposed to the outside of the housing 42, and a rotational drive source (not shown), such as a motor, is connected to the base (upper end) of the spindle 44.

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 roughly perpendicular to the holding surface 24a (a rotation axis roughly parallel to the Z-axis direction) by power transmitted from the rotation drive source via the spindle 44 and the mount 46.

When polishing the wafer 11, the chuck table 24 is first moved by the first movement mechanism 18, and the wafer 11 is positioned below the polishing unit 40. Then, while rotating the chuck table 24 and spindle 44, the polishing unit 40 is lowered at a predetermined speed by the second movement mechanism 28. This causes the rotating polishing pad 48 to come into contact with the surface of the wafer 11 to be polished, polishing the wafer 11.

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 underside of the mount 46. When polishing the wafer 11 with the polishing pad 48, polishing liquid is supplied from the polishing liquid supply source 56 to the wafer 11 and polishing pad 48 via the valve 54 and the polishing liquid supply path 52.

A third transfer mechanism (unloading arm) 58 is located adjacent to the second transfer mechanism 16 and rotates while holding the wafer 11. A cleaning mechanism 60 for cleaning the wafer 11 is located 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.

The first surface 11a of the wafer 11 is polished using the polishing device 2, thereby flattening the first surface 11a. Thereafter, a plurality of devices (not shown), such as integrated circuits (ICs), large-scale integration (LSIs), light-emitting diodes (LEDs), and microelectromechanical systems (MEMS) 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 produce a plurality of device chips, each equipped with a device.

Figure 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. These unevenness are formed on the first surface 11a of the wafer 11, for example, during the wafer 11 manufacturing process (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.

Figure 4(A) is a graph showing the 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.

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

The unevenness of the first surface 11a of the wafer 11 shown in Figure 3 includes a periodic wave-like waviness (long-period waviness) component corresponding to the waviness curve 19 (see Figure 4(C)), and a fine roughness component (short-period waviness) with a shorter period than the waviness, corresponding to the roughness curve 17 (see Figure 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 waviness component and the roughness component contained in the unevenness of the first surface 11a of the wafer 11.

In this embodiment, therefore, the wafer 11 is polished using two types of polishing pads equipped with polishing layers with different glass transition temperatures. This effectively reduces both the waviness and roughness components of the irregularities formed on the first surface 11a of the wafer 11. A specific example of the wafer polishing method according to this embodiment is described below.

First, the wafer 11 is held by the chuck table 24. Figure 5 is a cross-sectional view showing the wafer 11 held by the chuck table 24.

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. When the suction force (negative pressure) of the suction source is applied to the holding surface 24a in this state, the wafer 11 is suction-held by the chuck table 24 via the protective member 13.

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

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) that polishes the wafer 11 is fixed to the underside 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 underside of the base 72A with, for example, an adhesive. The underside of the polishing layer 74A forms a flat polishing surface 76A that polishes the wafer 11.

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 (SiO ₂ ) 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.

A cylindrical through-hole is formed in the center of the polishing pad 70A, penetrating the polishing pad 70A in the thickness direction. When the polishing pad 70A is attached to the mount 46, the through-hole of the polishing pad 70A is connected to the polishing liquid supply channel 52.

The chuck table 24 holding the wafer 11 is positioned below the polishing unit 40 by the first moving mechanism 18 (see Figure 1). 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 spindle 44, the polishing unit 40 is lowered by the second moving mechanism 28 (see Figure 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.

During polishing of the wafer 11, 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 liquid 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 have to 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.

The glass transition temperature of the polishing layer 74A is higher than the glass transition temperature of the polishing layer 74B of the polishing pad 70B (see Figure 7(A)), which will be described later. Therefore, even if frictional heat is generated by contact between the wafer 11 and the polishing layer 74A during polishing of the wafer 11, the shape of the polishing layer 74A is less likely to change, and the polishing surface 76A remains flat.

Figure 6(B) is an enlarged cross-sectional view showing a portion of the wafer 11 after the first polishing step. When the first surface 11a of the wafer 11 is polished with the polishing pad 70A having the polishing layer 74A with a high glass transition temperature, the polishing surface 76A, which is maintained in a flat state, preferentially polishes the upwardly protruding areas of the first surface 11a, i.e., the convex portions of the waviness (see Figure 4(C)), reducing the height difference of the first surface 11a of the wafer 11. This effectively reduces the waviness contained in the first surface 11a of the wafer 11.

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

The polishing pad 70B comprises 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 roughly the same diameter as the base 72B and is fixed to the underside of the base 72B, for example, with an adhesive. The underside 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).

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

In the second polishing process, as in the first polishing process, the polishing unit 40 is lowered by the second moving mechanism 28 (see Figure 1) while the chuck table 24 and spindle 44 are rotated. This causes the polishing surface 76B of the rotating polishing pad 70B to be pressed against the first surface 11a of the wafer 11, polishing the first surface 11a. During polishing of the wafer 11, polishing liquid is supplied from the polishing liquid supply source 56 to the wafer 11 and polishing pad 70B via the valve 54 and the polishing liquid supply path 52.

The glass transition temperature of the polishing layer 74B is lower than the glass transition temperature of the polishing layer 74A of the polishing pad 70A (see Figure 6(A)). 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.

Figure 7(B) is an enlarged cross-sectional view showing a portion of the wafer 11 after the second polishing step. When the first surface 11a of the wafer 11 is polished with the polishing pad 70B having the polishing layer 74B with a low glass transition temperature, the polishing surface 76B deforms along the first surface 11a of the wafer 11 and penetrates into the minute concave portions of the first surface 11a. This results in the entire first surface 11a of the wafer 11 being polished uniformly, effectively reducing the roughness (see Figure 4(B)) contained in the first surface 11a of the wafer 11.

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 the polishing surface 76A flat. As a result, a high polishing rate is achieved in the first polishing step.

However, if the glass transition temperature of the polishing layer 74A is extremely high, scratches are more likely to remain on the first surface 11a of the wafer 11 after polishing. Therefore, the glass transition temperature of the polishing layer 74A is preferably no more than 90°C higher than the glass transition temperature of the polishing layer 74B, and more preferably no more than 60°C higher than the glass transition temperature of the polishing layer 74B. This makes it possible to efficiently remove waviness on the first surface 11a of the wafer 11 while suppressing the formation of scratches.

Furthermore, it is preferable that the glass transition temperature of the polishing layer 74B be 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, it is preferable that the glass transition temperature of the polishing layer 74B be approximately 30°C to 40°C. This promotes appropriate deformation of the polishing layer 74B due to frictional heat generated during polishing, making it easier for the polishing surface 76B to penetrate 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.

Taking the above effects into consideration, 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.

For example, if 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 the raw material, and the difference in glass transition temperature between polishing layers 74A and 74B can be set to the desired value. When using a commercially available product to form polishing layers 74A and 74B, 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 or higher and 100°C or lower. Furthermore, for example, a polyol obtained by mixing Sannix GP-600 and Sannix GP-1000 (manufactured by Sanyo Chemical Industries, Ltd.) in a 1:1 ratio can be used to form polishing layer 74B with a glass transition temperature of 30°C or higher and 40°C or lower.

As described above, in this embodiment, the first surface 11a of the wafer 11 is polished with polishing pad 70A having polishing layer 74A, and then the first surface 11a of the wafer 11 is polished with polishing pad 70B having polishing layer 74B with a lower glass transition temperature than polishing layer 74A. As a result, the polishing layer 74A, which is less likely to deform due to frictional heat, reduces the elevation differences on the first surface 11a of the wafer 11, and then the polishing layer 74B, which is more likely to deform 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 irregularities formed on the first surface 11a of the wafer 11 are efficiently reduced, improving the flatness of the first surface 11a of the wafer 11.

In the above embodiment, the polishing pad 70A (see FIG. 6A) is replaced with polishing pad 70B (see FIG. 7A) between the first and second polishing steps. However, the polishing apparatus 2 may also 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.

The wafer 11 may also be processed by two polishing apparatuses 2. In this case, a polishing pad 70A (see FIG. 6A) is attached to the polishing unit 40 of one polishing apparatus 2, and a polishing pad 70B (see FIG. 7A) 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.

Furthermore, while the above embodiment describes a polishing apparatus 2 that supports the underside of the wafer 11 and polishes the upper side, it is also possible to use a polishing apparatus that polishes the underside of the wafer 11. Figure 8 is a perspective view showing a polishing apparatus 80, which is a modified version of the polishing apparatus 2 (see Figure 1). Note that in Figure 8, the X-axis direction (first horizontal direction) and the Y-axis direction (second horizontal direction) are mutually perpendicular. Furthermore, the Z-axis direction (vertical direction, up-down direction, height direction) is a direction perpendicular to the X-axis direction and the Y-axis direction.

The polishing apparatus 80 includes a support unit 82 that supports the 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.

The support unit 82 includes a disk-shaped support base (surface plate) 84 made of metal, ceramic, resin, or the like. The top 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.

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 rotational axis that is roughly parallel to the Z-axis direction due to the power transmitted from the rotational drive source 88 via the spindle 86.

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 the polishing surface for polishing the wafer 11. Examples of materials for the polishing layer 92 are the same as those for the polishing layer 74A of the polishing pad 70A (see Figure 6(A)) and the polishing layer 74B of the polishing pad 70B (see Figure 7(A)).

A holding unit 94 is provided above the support unit 82. The holding unit 94 has a disk-shaped holding portion 96 that holds the wafer 11. The holding portion 96 is positioned so as to overlap the area between the center and outer edge of the polishing layer 92.

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 with 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 positioned 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 due to surface tension and is held by the holding unit 96. However, there are no limitations on how the holding unit 96 holds the wafer 11.

A cylindrical spindle 98 arranged along the Z-axis direction is connected to the upper surface of the holding portion 96. The lower end of the spindle 98 is fixed to the center of the holding portion 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 elevating mechanism such as an air cylinder that moves (raises and lowers) the spindle 98 along the Z-axis direction.

The holding unit 96 rotates around a rotation axis roughly parallel to the Z-axis direction by power transmitted from the rotational 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 holding unit 96 rises and falls along the Z-axis direction, moving closer to and further away from the polishing pad 90.

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

When polishing a 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 (indicated by arrow A) by the rotary drive source 88, and the holding part 96 is rotated in a predetermined direction (indicated by arrow B) by the drive mechanism 100. With this in place, 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.

When the wafer polishing method according to this embodiment is performed using the polishing apparatus 80, first, a polishing pad 90 (first polishing pad) having a polishing layer 92 with a high glass transition temperature (e.g., a glass transition temperature of 90°C or higher and 100°C or lower) 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 (e.g., a glass transition temperature of 30°C or higher and 40°C or lower) 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).

In addition, the structures, methods, etc. related to the above embodiments can be modified as appropriate without departing from the scope of the present invention.

11 Wafer 11a First surface (front surface)
11b Second side (front)
13 Protective member 15 Profile curve 17 Roughness curve 19 Waviness curve 2 Polishing device 4 Base 4a, 4b Opening 6a, 6b Cassette placement area (cassette placement table)
8a, 8b cassette 10 first transport mechanism 12 operation panel 14 position adjustment mechanism 16 second transport mechanism (loading arm)
18 First moving mechanism 20 Moving table 22 Dust-proof and drip-proof cover 24 Chuck table (holding table)
24a Holding surface 24b Suction path 26 Support structure 28 Second moving 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 pad 50 Fixture 52 Polishing liquid supply path 54 Valve 56 Polishing liquid supply source 58 Third transport mechanism (unloading arm)
60 Cleaning mechanism 70A, 70B Polishing pad 72A, 72B Base 74A, 74B Polishing layer 76A, 76B Polishing surface 80 Polishing device 82 Support unit 84 Support table (surface plate)
84a Support surface 86 Spindle 88 Rotation drive source 90 Polishing pad 92 Polishing layer 94 Holding unit 96 Holding portion 98 Spindle 100 Drive mechanism 102 Polishing liquid supply unit 104 Nozzle 106 Polishing liquid

Claims (3)

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 . 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. 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.