JP2023108102A - Wafer polishing method - Google Patents

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

The present invention relates to a wafer polishing method for polishing a wafer with a polishing pad.

In the process of manufacturing device chips, a wafer is used in which devices are formed in a plurality of regions partitioned by a plurality of streets (dividing lines) arranged in a grid pattern. A plurality of device chips each having a device is obtained by dividing the wafer along the streets. Device chips are incorporated into various electronic devices such as mobile phones and personal computers.

Wafers are manufactured by slicing cylindrical ingots. For example, a monocrystalline silicon wafer having a predetermined thickness is obtained by radially cutting a monocrystalline silicon ingot. Wafers cut from ingots are subjected to various treatments such as chamfering, lapping, and etching. After that, the wafer is polished to flatten and mirror-finish the surface of the wafer (see Patent Document 1).

JP-A-10-135164

By subjecting the wafer to a polishing process, unevenness formed on the surface of the wafer during the wafer manufacturing process (ingot slicing, lapping, etching, etc.) is removed. For example, a polishing pad having a polishing layer made of nonwoven fabric or the like is used for polishing 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 the wafer includes a component of periodic wave-like waviness (long-period waviness) and a component of fine roughness having a shorter period than the waviness (short-period waviness). Therefore, in order to improve the flatness of the wafer surface, it is desired to efficiently reduce both the waviness component and the roughness component included in the unevenness.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wafer polishing method capable of efficiently improving the flatness of the surface of a wafer.

According to one aspect of the present invention, there is provided a wafer polishing 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 polishing layer, wherein the glass transition temperature of the second polishing layer is lower than the glass transition temperature of the first polishing layer. A polishing method is provided.

Preferably, 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, while supplying a polishing liquid containing no abrasive grains to the wafer, Polish the surface of the wafer. Preferably, in the first polishing step, waviness of the wafer surface is reduced by polishing the surface of the wafer with the first polishing pad, and in the second polishing step, the surface of the wafer is polished with the second polishing pad. Polishing the surface of the wafer reduces the roughness of the surface of the wafer.

In the method for polishing a wafer according to one aspect of the present invention, after polishing the surface of the wafer with a first polishing pad having a first polishing layer, the second polishing layer having a glass transition temperature lower than that of the first polishing layer is formed. Polish the surface of the wafer with a second polishing pad. As a result, both the waviness component and the roughness component of the unevenness formed on the surface of the wafer are efficiently reduced, and the flatness of the surface of the wafer is improved.

It is a perspective view which shows a polishing apparatus. It is a perspective view showing a wafer. It is an enlarged sectional view showing a part of wafer. 4A is a graph showing the cross-sectional curve of the surface of the wafer, FIG. 4B is a graph showing the roughness curve of the surface of the wafer, and FIG. 4C is a graph showing the waviness curve of the surface of the wafer. It is a graph showing. FIG. 4 is a cross-sectional view showing a wafer held by a chuck table; FIG. 6A is a cross-sectional view showing the wafer in the first polishing step, and FIG. 6B is an enlarged cross-sectional view showing 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. It is a perspective view which shows the polishing apparatus which concerns on a modification.

An embodiment according to one aspect of the present invention will be described below with reference to the accompanying drawings. First, a configuration example of a polishing apparatus that can be used for implementing the wafer polishing method according to the present embodiment will be described. FIG. 1 is a perspective view showing a polishing apparatus 2. FIG. In FIG. 1, the X-axis direction (first horizontal direction, front-rear direction) and the Y-axis direction (second horizontal direction, left-right direction) are perpendicular to each other. Also, the Z-axis direction (vertical direction, vertical 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 for supporting or housing each component constituting the polishing apparatus 2 . A front end portion of the base 4 is provided with cassette mounting areas (cassette mounting tables) 6a and 6b on which the cassettes 8a and 8b are mounted. Cassettes 8a and 8b are containers capable of accommodating a plurality of wafers 11, and are arranged on cassette mounting areas 6a and 6b, respectively. For example, the cassette 8a contains wafers 11 before polishing, and the cassette 8b contains wafers 11 after polishing.

FIG. 2 is a perspective view showing the wafer 11. FIG. 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 substantially parallel to each other.

The 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. By doing so, a wafer 11 having a desired thickness is obtained.

The wafers 11 cut out from the ingot are subjected to various treatments such as chamfering, lapping and etching. After that, the wafer 11 is polished by the polishing device 2, and one or both of the first surface 11a and the second surface 11b of the wafer 11 are flattened and mirror-finished. As an example, the case where the first surface 11a of the wafer 11 is polished will be described below.

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

The wafer 11 is accommodated in the cassette 8a shown in FIG. 1 with the protective member 13 attached. A cassette 8a containing a plurality of wafers 11 is mounted on the cassette mounting area 6a.

An opening 4a is provided in a region located between the cassette mounting regions 6a and 6b on the upper surface side of the base 4. As shown in FIG. A first transfer mechanism 10 for transferring the wafer 11 is provided inside the opening 4a. An operation panel 12 for inputting various kinds of information (processing conditions, etc.) to the polishing apparatus 2 is installed in the area in front of the opening 4a.

A position adjusting mechanism 14 for adjusting the position of the wafer 11 is provided obliquely behind the first transfer mechanism 10 . The wafers 11 accommodated in the cassette 8a are transferred onto the position adjusting mechanism 14 by the first transfer mechanism 10. As shown in FIG. The position adjusting mechanism 14 adjusts the position of the wafer 11 by sandwiching the wafer 11 therebetween. A second transfer mechanism (loading arm) 16 that holds the wafer 11 and rotates is provided in the vicinity of the position adjustment mechanism 14 .

A rectangular opening 4 b whose longitudinal direction is along the X-axis direction is provided in a region located behind the second transport mechanism 16 on the upper surface side of the base 4 . A ball screw type first moving mechanism 18 is provided inside the opening 4b. The first moving 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 moving mechanism 18 includes a flat plate-like moving table 20 and moves the moving table 20 along the X-axis direction. Further, accordion-shaped dust and splash proof covers 22 that are extendable along the X-axis direction are provided on the front and rear sides of the moving table 20 . The dust and drip proof cover 22 covers the constituent elements (ball screw, pulse motor, etc.) of the first moving mechanism 18 .

A chuck table (holding table) 24 for holding the wafer 11 is provided on the moving table 20 . The upper surface of the chuck table 24 is a flat surface substantially parallel to the horizontal direction (XY plane direction), and constitutes a holding surface 24a for holding 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) and the like. The wafer 11 aligned by the position adjusting mechanism 14 is transferred onto the holding surface 24 a of the chuck table 24 by the second transfer mechanism 16 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 together with the moving table 20 along the X-axis direction. Further, the chuck table 24 is connected to a rotary drive source (not shown) such as a motor that rotates the chuck table 24 around a rotation axis that is substantially perpendicular to the holding surface 24a (a rotation axis that is substantially parallel to the Z-axis direction). ing.

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

A nut portion (not shown) is provided on the rear surface side (rear surface side) of the moving plate 32 . A ball screw 34 arranged along the Z-axis direction between the pair of guide rails 30 is screwed into the 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 rail 30 in the Z-axis direction.

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 .

Polishing unit 40 includes a hollow cylindrical housing 42 supported by support member 38 . A cylindrical spindle 44 is rotatably accommodated in the housing 42 . A distal end (lower end) of the spindle 44 is exposed outside the housing 42 , and a base end (upper end) of the spindle 44 is connected to a rotational drive source (not shown) such as a motor.

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 lower surface side of the mount 46 with a fixture 50 such as a bolt. The polishing pad 48 rotates around a rotation axis generally perpendicular to the holding surface 24a (a rotation axis generally parallel to the Z-axis direction) by power transmitted from a rotation drive source via the spindle 44 and the mount 46 .

When polishing the wafer 11 , first, the chuck table 24 is moved by the first moving mechanism 18 to position the wafer 11 below the polishing unit 40 . Then, while rotating the chuck table 24 and the spindle 44, the second moving mechanism 28 lowers the polishing unit 40 at a predetermined speed. As a result, the rotating polishing pad 48 contacts the surface to be polished of the wafer 11, and the wafer 11 is polished.

Inside the polishing unit 40, a polishing liquid supply path 52 is formed along the Z-axis direction. One end side (upper end side) of the polishing liquid supply path 52 is connected to a polishing liquid supply source 56 via a valve 54 . The other end side (lower end side) of the polishing liquid supply path 52 is opened at the lower surface of the mount 46 . When polishing the wafer 11 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 through the valve 54 and the polishing liquid supply path 52 .

A third transport mechanism (unloading arm) 58 that holds the wafer 11 and rotates is arranged at a position adjacent to the second transport mechanism 16 . A cleaning mechanism 60 for cleaning the wafer 11 is arranged in front of the third transfer mechanism 58 . The wafer 11 polished by the polishing unit 40 is transferred to the cleaning mechanism 60 by the third transfer mechanism 58 and cleaned by the cleaning mechanism 60 . After cleaning, the wafer 11 is transported by the first transport mechanism 10 and accommodated in the cassette 8b.

By polishing the first surface 11a of the wafer 11 with the polishing apparatus 2, the first surface 11a is flattened. After that, for example, on the first surface 11a side of the wafer 11, a plurality of devices (not shown) such as IC (Integrated Circuit), LSI (Large Scale Integration), LED (Light Emitting Diode), MEMS (Micro Electro Mechanical Systems) devices, etc. It is formed. A plurality of device chips each having a device are manufactured by dividing the wafer 11 on which a plurality of devices are formed.

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

FIG. 4A is a graph showing a cross-sectional curve 15 of the first surface 11a of the wafer 11. FIG. The cross-sectional curve 15 is obtained by applying a low-pass filter with a cutoff value λs to the measured cross-sectional curve representing the cross-sectional shape of the first surface 11 a of the wafer 11 . That is, the cross-sectional curve 15 represents the unevenness of the first surface 11 a of the wafer 11 .

A roughness curve of the first surface 11a of the wafer 11 is obtained by applying a high-pass filter with a cutoff value λc (>λs) to the cross-sectional curve 15 . Further, by applying a band-pass filter with cutoff values λc and λf (>λc) to the cross-sectional curve 15, an undulating curve of the first surface 11a of the wafer 11 is obtained. 4B is a graph showing the roughness curve 17 of the first surface 11a of the wafer 11, and FIG. 4C is a graph showing the waviness curve 19 of the first surface 11a of the wafer 11. FIG.

The unevenness of the first surface 11a of the wafer 11 shown in FIG. (See FIG. 4(B)) and a component of finer roughness (short-period waviness) having a shorter period than the waviness corresponding to (see FIG. 4B). 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 included in the unevenness of the first surface 11a of the wafer 11.

Therefore, in this embodiment, the wafer 11 is polished using two types of polishing pads having polishing layers with different glass transition temperatures. As a result, both the waviness component and the roughness component of the unevenness formed on the first surface 11a of the wafer 11 are efficiently reduced. A specific example of the method for polishing a wafer according to this embodiment will be described below.

First, the wafer 11 is held by the chuck table 24 . FIG. 5 is a sectional view showing the wafer 11 held by the chuck table 24. As shown in FIG.

The wafer 11 is placed on the chuck table 24 such that the first surface 11a (surface to be polished) side is exposed upward and the second surface 11b side (protection member 13 side) faces the holding surface 24a. When the suction force (negative pressure) of the suction source is applied to the holding surface 24 a 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). FIG. 6A 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).

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 side of the base 72A. The polishing layer 74A is formed in a disc shape having approximately the same diameter as the base 72A, and is fixed to the lower surface side of the base 72A with an adhesive, for example. The lower surface of the polishing layer 74A constitutes a flat polishing surface 76A for polishing the wafer 11. As shown in FIG.

The polishing layer 74A contains abrasive grains (fixed abrasive grains). Specifically, the polishing layer 74A includes a polishing member serving as a base material and abrasive grains dispersed in the polishing member. As the polishing member, for example, a disk-shaped member made of resin such as polyurethane or non-woven fabric such as felt is used. As abrasive grains, for example, silica (SiO ₂ ) having a particle size of 1 μm or more and 10 μm or less is used. However, the material of the polishing member and the grain size and material of the abrasive grains can be appropriately selected according to the material of the wafer 11 and the like.

A cylindrical through-hole is formed in the central portion of the polishing pad 70A so as to pass through 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 path 52. As shown in FIG.

The chuck table 24 holding the wafer 11 is arranged below the polishing unit 40 by the first moving mechanism 18 (see FIG. 1). At this time, the wafer 11 is positioned such 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). Thereby, the polishing surface 76A of the rotating polishing pad 70A is pressed against the first surface 11a of the wafer 11, and the first surface 11a is polished.

During polishing of the wafer 11, the polishing liquid is supplied from the polishing liquid supply source 56 to the wafer 11 and the polishing pad 70A through the valve 54 and the polishing liquid supply path 52. FIG. When the polishing layer 74A contains abrasive grains, a polishing liquid containing no abrasive grains is supplied. As the polishing liquid, an alkaline solution containing sodium hydroxide, potassium hydroxide, etc., an acidic liquid containing permanganate, pure water, or the like can be used. Note that the polishing layer 74A may not 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.

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

FIG. 6B is an enlarged cross-sectional view showing part 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 including the polishing layer 74A having a high glass transition temperature, the polishing surface 76A maintained in a flat state causes a region of the first surface 11a protruding upward, That is, the convex portion of the undulation (see FIG. 4C) is preferentially polished, and the height difference of the first surface 11a of the wafer 11 is reduced. As a result, waviness included in the first surface 11a of the wafer 11 is efficiently reduced.

Next, the first surface 11a of the wafer 11 is polished with a second polishing pad (second polishing step). FIG. 7A 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 the polishing pad 70B (second polishing pad) is attached instead.

The polishing pad 70B includes a disk-shaped base 72B and a polishing layer (second polishing layer) 74B for polishing the wafer 11 . The polishing layer 74B is formed in a disc shape having approximately the same diameter as the base 72B, and is fixed to the lower surface side of the base 72B with an adhesive, for example. The lower surface of the polishing layer 74B constitutes a flat polishing surface 76B for polishing the wafer 11. As shown in FIG. Further, the polishing layer 74B contains abrasive grains (fixed abrasive grains).

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

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

Here, the glass transition temperature of the polishing layer 74B is lower than the glass transition temperature of the polishing layer 74A (see FIG. 6A) of the polishing pad 70A. Therefore, when frictional heat is generated due to 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, and the polishing layer 74A softens and becomes easily deformed. . As a result, the polished surface 76B deforms along the unevenness of the first surface 11a of the wafer 11 .

FIG. 7B 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 is deformed along the first surface 11a of the wafer 11 and formed on the first surface 11a. It gets into the recesses of fine unevenness. As a result, the entire first surface 11a of the wafer 11 is uniformly polished, and the roughness (see FIG. 4B) included in the first surface 11a of the wafer 11 is efficiently reduced.

The glass transition temperature of the polishing layer 74A is preferably 30° C. or higher, more preferably 50° C. or higher, than the glass transition temperature of the polishing layer 74B. As a result, softening and deformation of the polishing layer 74A due to frictional heat are suppressed, and the polishing surface 76A is maintained 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 tend 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 90° C. or lower than the glass transition temperature of the polishing layer 74B, more preferably 60° C. or lower than the glass transition temperature of the polishing layer 74B. preferable. Thereby, the waviness of the first surface 11a of the wafer 11 can be efficiently removed while suppressing the remaining scratches.

Further, the glass transition temperature of the polishing layer 74B is preferably approximately the same as the temperature in the contact area between the wafer 11 and the polishing layer 74B when polishing the wafer 11 in the second polishing step. Generally, the temperature of the contact area between the wafer 11 and the polishing layer 74B during the polishing process is about 30.degree. C. to 40.degree. Therefore, it is preferable that the glass transition temperature of the polishing layer 74B is also about 30.degree. As a result, moderate deformation of the polishing layer 74B is promoted by the frictional heat generated during the polishing process, and the polishing surface 76B maintains a certain degree of rigidity, while the fine recesses and protrusions formed on the first surface 11a of the wafer 11 are maintained. easier to get into. As a result, it becomes possible to effectively remove the roughness of the first surface 11a of the wafer 11 without significantly lowering the polishing rate.

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 temperature of the polishing layers 74A, 74B can be adjusted by the material, composition, etc. of the polishing layers 74A, 74B.

For example, when both the 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. The difference in glass transition temperature between 74B can be set to a desired value. When the polishing layers 74A and 74B are formed using a commercially available product, for example, SANNIX GP-600 (manufactured by Sanyo Chemical Industries, Ltd.) is used to form the polishing layer 74A having a glass transition temperature of 90° C. or higher and 100° C. or lower. can be formed. Further, for example, by using a polyol obtained by mixing Sannics GP-600 and Sannics GP-1000 (manufactured by Sanyo Chemical Industries, Ltd.) at a ratio of 1:1, the glass transition temperature is 30 ° C. or higher and 40 ° C. or less can be formed.

As described above, in the present embodiment, after polishing the first surface 11a of the wafer 11 with the polishing pad 70A having the polishing layer 74A, the first surface 11a of the wafer 11 is polished with the polishing pad 70B having the polishing layer 74B having a glass transition temperature lower than that of the polishing layer 74A. A first surface 11a of the wafer 11 is polished. As a result, after the height difference of the first surface 11a of the wafer 11 is reduced by the polishing layer 74A that is difficult to deform by frictional heat, the entire first surface 11a of the wafer 11 is made uniform by the polishing layer 74B that is easily deformable by frictional heat. polished to As a result, both the waviness component and the roughness component 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.

In the above embodiment, the case where the polishing pad 70A (see FIG. 6A) is replaced with the polishing pad 70B (see FIG. 7A) between the first polishing process and the second polishing process is described. bottom. However, the polishing apparatus 2 may have two sets of polishing units 40 . In this case, the first polishing step is performed by one of the polishing units 40 to which the polishing pad 70A is attached, and the second polishing step is performed by the other polishing unit 40 to which the polishing pad 70B is attached. Thereby, the replacement work of the polishing pad can be omitted.

Also, the wafer 11 may 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. ) is attached. Then, one polishing device 2 performs the first polishing process, and the other polishing device 2 performs the second polishing process.

Furthermore, in the above embodiment, the polishing apparatus 2 that supports the lower surface side of the wafer 11 and polishes the upper surface side has been described, but a polishing apparatus that polishes the lower surface side of the wafer 11 can also be used. FIG. 8 is a perspective view showing a polishing device 80 corresponding to a modification of the polishing device 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. Also, the Z-axis direction (vertical direction, vertical 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 . By pressing the wafer 11 held by the holding unit 94 against the polishing pad 90, the wafer 11 is polished.

The support unit 82 includes a disk-shaped support base (surface plate) 84 made of metal, ceramics, resin, or the like. The upper surface of the support base 84 is a flat surface substantially parallel to the horizontal direction (XY plane direction), and forms a circular support surface 84a that supports the polishing pad 90. As shown in FIG.

A cylindrical spindle 86 arranged along the Z-axis direction is connected to the lower surface side of the support base 84 . The upper end side of the spindle 86 is fixed to the center portion of the lower surface side of the support base 84 . A rotation driving source 88 such as a motor for rotating the spindle 86 is connected to the lower end of the spindle 86 . The support table 84 rotates around a rotation axis substantially parallel to the Z-axis direction by power transmitted from a rotation drive source 88 via a spindle 86 .

A polishing pad 90 for polishing the wafer 11 is fixed to the support surface 84 a of the support table 84 . The polishing pad 90 includes a disk-shaped polishing layer 92 having a diameter larger than that of the wafer 11 . The upper surface of the polishing layer 92 is a flat surface substantially parallel to the horizontal direction (XY plane direction), and constitutes a polishing surface for polishing the wafer 11 . Examples of the material of the polishing layer 92 are the same as those of the polishing layer 74A of the polishing pad 70A (see FIG. 6A) and the polishing layer 74B of the polishing pad 70B (see FIG. 7A).

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 part 96 is arranged so as to overlap the area between the center and the outer peripheral edge of the polishing layer 92 .

A holding member (not shown) for holding the wafer 11 is provided on the lower surface side of the holding portion 96 . For example, the holding member includes a circular substrate having a diameter larger than that of the wafer 11 and a holding film (backing film) provided on the surface (lower surface) side of the substrate. For example, the base material is made of 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 such that the holding film is exposed on the lower surface side of the holding portion 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 attracted to the holding film by surface tension and is held by the holding portion 96 . However, the method of holding the wafer 11 by the holding portion 96 is not limited.

A columnar spindle 98 arranged along the Z-axis direction is connected to the upper surface side of the holding portion 96 . The lower end side of the spindle 98 is fixed to the central portion of the holding portion 96 . A driving mechanism 100 for driving the spindle 98 is connected to the upper end side 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 (elevates) the spindle 98 along the Z-axis direction.

The holding portion 96 rotates around a rotation axis substantially parallel to the Z-axis direction by power transmitted from the rotation drive source of the drive mechanism 100 via the spindle 98 . Further, by raising and lowering the spindle 98 by the raising and lowering mechanism of the drive mechanism 100 , the holding portion 96 is raised and lowered along the Z-axis direction to relatively approach and separate from the polishing pad 90 .

A polishing liquid supply unit 102 that supplies polishing liquid to the polishing pad 90 is provided in a region above the support unit 82 where the holding unit 94 is not provided. The polishing liquid supply unit 102 includes 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. do.

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) side is exposed downward. Then, while the polishing pad 90 is rotated in a predetermined direction (direction indicated by arrow A) by the rotary drive source 88 and the holding portion 96 is rotated in a predetermined direction (direction indicated by arrow B) by the driving mechanism 100, The holding portion 96 is lowered by the drive mechanism 100 . Thereby, the first surface 11a of the wafer 11 contacts the upper surface (polishing surface) of the polishing layer 92, and the first surface 11a of the wafer 11 is polished.

When performing the wafer polishing method according to the present embodiment using the polishing apparatus 80, first, a polishing layer 92 having a high glass transition temperature (for example, a glass transition temperature of 90° C. or higher and 100° C. or lower) is provided. A pad 90 (first polishing pad) 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). Thereafter, 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 wafer is polished by the second polishing pad. The first surface 11a of 11 is polished (second polishing step).

In addition, the structures, methods, and the like according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention.

11 Wafer 11a First surface (front surface)
11b Second surface (surface)
REFERENCE SIGNS LIST 13 Protective member 15 Cross-sectional curve 17 Roughness curve 19 Waviness curve 2 Polishing device 4 Bases 4a, 4b Openings 6a, 6b Cassette mounting area (cassette mounting 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 and drip proof cover 24 chuck table (holding table)
24a holding surface 24b suction path 26 support structure 28 second movement mechanism 30 guide rail 32 movement 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 Supporting Unit 84 Supporting Base (Surface Plate)
84a support surface 86 spindle 88 rotation drive source 90 polishing pad 92 polishing layer 94 holding unit 96 holding section 98 spindle 100 drive mechanism 102 polishing liquid supply unit 104 nozzle 106 polishing liquid

Claims (4)

A wafer polishing 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;
a second polishing step of polishing the surface of the wafer with a second polishing pad having a second polishing layer;
A method of polishing a wafer, wherein the glass transition temperature of the second polishing layer is lower than the glass transition temperature of the first polishing layer. The glass transition temperature of the first polishing layer is 90° C. or higher and 100° C. or lower,
2. The method of polishing a wafer according to claim 1, wherein the second polishing layer has a glass transition temperature of 30[deg.] C. or higher and 40[deg.] C. or lower. The first polishing layer and the second polishing layer contain abrasive grains,
3. The 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. polishing method. In the first polishing step, waviness of the surface of the wafer is reduced by polishing the surface of the wafer with the first polishing pad,
4. The wafer according to any one of claims 1 to 3, wherein in the second polishing step, the surface roughness of the wafer is reduced by polishing the surface of the wafer with the second polishing pad. polishing method.

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