JP2020189345A - Wafer processing method - Google Patents

Abstract

To provide a wafer processing method that can restrain reduction in productivity of wafers.SOLUTION: A wafer processing method is for processing a wafer having a first surface and a second surface with asperities formed on the second surface side by holding the wafter with a holding surface of a chuck table 22. The method includes a holding step of holding the wafer with the chuck table so that the first surface side faces the holding surface and the second surface side is exposed upward, and a polishing step of removing the asperities by polishing the second surface side of the wafer. In the polishing step, the wafer is polished with a polishing pad having a hardness of 30-65 as measured by durometer type D.SELECTED DRAWING: Figure 2

Description

The present invention relates to a wafer processing method.

By dividing a wafer in which a device made of IC (Integrated Circuit), LSI (Large Scale Integration), etc. is formed on the surface side along a planned division line (street), a plurality of device chips including the device are manufactured. To. Device chips are built into various electronic devices such as mobile phones and personal computers. In recent years, as electronic devices have become smaller and thinner, device chips are also required to be smaller and thinner.

Therefore, a method is used in which the wafer before division is ground with a grinding wheel to make it thinner. For grinding a wafer, a grinding device including a chuck table for holding the wafer and a grinding unit on which a grinding wheel for grinding the wafer is mounted is used (see Patent Document 1). The wafer is ground by bringing the grinding wheel into contact with the back surface side of the wafer while rotating it.

When the back surface side of the wafer is ground with a grinding wheel, fine irregularities (grinding marks, saw marks) are formed in the ground area along the trajectory of the grinding wheel. If the grinding marks remain, the bending strength of the device chip manufactured by dividing the wafer decreases. Therefore, it is desirable that the grinding marks be removed.

Therefore, a method has been proposed in which the wafer is ground with a grinding wheel and then the back surface side of the wafer on which the grinding marks are formed is polished to remove the grinding marks. For polishing a wafer, for example, a polishing apparatus including a chuck table for holding the wafer and a polishing unit on which a polishing pad for polishing the wafer is mounted is used (see Patent Document 2). By pressing the polishing pad against the back surface side of the wafer while rotating it, the back surface side of the wafer is polished and grinding marks are removed.

Japanese Unexamined Patent Publication No. 2000-288881 Japanese Unexamined Patent Publication No. 8-99265

As described above, when removing irregularities (grinding marks, etc.) formed on the back surface side of the wafer by polishing, it is necessary to polish the back surface side of the wafer with a polishing pad and remove a considerable amount of the back surface side of the wafer. .. Therefore, there is a problem that a long time is spent in the process of removing the unevenness and the productivity of the wafer is lowered.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a wafer processing method capable of suppressing a decrease in wafer productivity.

According to one aspect of the present invention, it is a wafer processing method for processing a wafer having a first surface and a second surface and having irregularities formed on the second surface side by holding the wafer on a holding surface of a chuck table. The holding step of holding the wafer by the chuck table and polishing the second surface side of the wafer so that the first surface side faces the holding surface and the second surface side is exposed upward. The polishing step includes a polishing step for removing the unevenness, and the polishing step provides a method for processing a wafer in which the wafer is polished with a polishing pad having a hardness of 30 or more and less than 65 as measured by a durometer type D.

In the wafer processing method according to one aspect of the present invention, the unevenness formed on the wafer is removed by polishing the wafer with a polishing pad having a hardness measured by a durometer type D of 30 or more and less than 65. As a result, the amount of polishing required to remove the unevenness is reduced, and the time required to remove the unevenness is reduced. As a result, the decrease in wafer productivity is suppressed.

It is a perspective view which shows the wafer. It is a perspective view which shows the processing apparatus. It is a perspective view which shows the polishing unit. It is a perspective view which shows the state in which a protective member is attached to a wafer. It is a partial cross-sectional front view which shows the wafer held by a chuck table. It is a perspective view which shows the wafer which is ground by a grinding unit. It is a perspective view which shows the wafer after grinding. It is a partial cross-sectional front view which shows the wafer which is polished by a polishing unit. It is a graph which shows the relationship between the hardness of a polishing pad and the polishing amount of a wafer.

Hereinafter, embodiments according to one aspect of the present invention will be described with reference to the accompanying drawings. First, a configuration example of a wafer that can be processed by using the wafer processing method according to the present embodiment will be described. FIG. 1 is a perspective view showing the wafer 11.

The wafer 11 is formed in a disk shape by a material such as silicon, and includes a front surface 11a and a back surface 11b. The wafer 11 is divided into a plurality of regions by a plurality of scheduled division lines (streets) 13 arranged in a grid pattern so as to intersect each other, and ICs (Integrated Circuits) are provided on the surface 11a side of the plurality of regions, respectively. ), LSI (Large Scale Integration), and the like.

There are no restrictions on the material, shape, structure, size, etc. of the wafer 11. For example, the wafer 11 may be formed of a material other than silicon (GaAs, InP, GaN, SiC, etc.), glass, ceramics, resin, metal, or the like. Further, there are no restrictions on the type, quantity, shape, structure, size, arrangement, etc. of the device 15.

By dividing the wafer 11 along the scheduled division line 13, a plurality of device chips including the device 15 can be obtained. For the purpose of reducing the thickness of the device chip, the wafer 11 before division is ground. Specifically, the back surface 11b side of the wafer 11 is ground with a grinding wheel to thin the wafer 11.

However, when the back surface 11b side of the wafer 11 is ground with a grinding wheel, irregularities (grinding marks, saw marks) are formed in the ground area along the trajectory of the grinding wheel. If this unevenness remains on the wafer 11, the bending strength of the device chip manufactured by dividing the wafer 11 decreases. Therefore, after grinding the wafer 11, a step of removing the unevenness is performed by polishing the back surface 11b side of the wafer 11 on which the unevenness is formed.

For the above grinding and polishing, a processing device capable of grinding and polishing the wafer 11 is used. FIG. 2 is a perspective view showing the processing apparatus 2. In the following, an example in which both grinding and polishing of the wafer 11 are performed by the processing device 2 will be described, but grinding and polishing may be performed by different processing devices (grinding device and polishing device).

The processing device 2 includes a base 4 that supports each component included in the processing device 2. An opening 4a is formed on the front end side of the upper surface of the base 4, and a first transfer unit 6 for conveying the wafer 11 is provided in the opening 4a. Further, in front of the opening 4a, mounting tables 10a and 10b on which cassettes 8a and 8b capable of accommodating a plurality of wafers 11 are placed are provided.

An alignment mechanism 12 for aligning the wafer 11 is provided diagonally behind the opening 4a. The alignment mechanism 12 includes a temporary placement table 14 on which the wafer 11 is temporarily placed. For example, the alignment mechanism 12 aligns the center of the wafer 11 transported from the cassette 8a to the temporary storage table 14 by the first transport unit 6.

On the side surface side of the base 4, a gate-shaped support structure 16 arranged so as to straddle the alignment mechanism 12 is provided. A second transfer unit 18 for transporting the wafer 11 is mounted on the support structure 16. The second transport unit 18 is configured to be movable in the X-axis direction (horizontal direction, first horizontal direction), Y-axis direction (front-back direction, second horizontal direction), and Z-axis direction (vertical direction, vertical direction). For example, the wafer 11 aligned by the alignment mechanism 12 is conveyed rearward.

An opening 4b is formed in a region located behind the opening 4a and the alignment mechanism 12 on the upper surface side of the base 4. In the opening 4b, a disk-shaped turntable 20 that rotates around a rotation axis that is substantially parallel to the Z-axis direction is arranged. Further, on the upper surface of the turntable 20, four chuck tables (holding tables) 22 for holding the wafer 11 are installed at substantially equal angular intervals.

The turntable 20 rotates clockwise in a plan view (direction indicated by the arrow R in FIG. 2), and positions the chuck table 22 in the order of transport position A, rough grinding position B, finish grinding position C, and polishing position D. The wafer 11 aligned by the alignment mechanism 12 is conveyed to the chuck table 22 positioned at the transfer position A by the second transfer unit 18.

Each of the chuck tables 22 is connected to a rotation drive source (not shown) such as a motor, and rotates around a rotation axis substantially parallel to the Z-axis direction. Further, the upper surface of the chuck table 22 constitutes a holding surface 22a (see FIG. 5) for holding the wafer 11. The holding surface 22a is connected to a suction source (not shown) via a flow path (not shown) formed inside the chuck table 22.

A rectangular parallelepiped support structure 24 is arranged behind the turntable 20 along the Z-axis direction. Two sets of moving units (moving mechanisms) 26 are provided on the front surface of the support structure 24. Each of the moving units 26 includes a pair of guide rails 28 arranged along the Z-axis direction, and the moving table 30 is slidably mounted on the pair of guide rails 28.

A nut portion (not shown) is fixed to the rear surface side (rear surface side) of the moving table 30, and a ball screw 32 arranged substantially parallel to the guide rail 28 is screwed into the nut portion. A pulse motor 34 is connected to one end of the ball screw 32. When the ball screw 32 is rotated by the pulse motor 34, the moving table 30 moves along the guide rail 28 in the Z-axis direction.

A fixture 36 is provided on the front surface (surface) of the moving table 30. A grinding unit 38a for rough grinding for rough grinding the wafer 11 is fixed to the fixture 36 positioned above the rough grinding position B. On the other hand, a grinding unit 38b for finish grinding that performs finish grinding of the wafer 11 is fixed to the fixture 36 positioned above the finish grinding position C.

The grinding units 38a and 38b each include a cylindrical housing 40. The housing 40 houses a columnar spindle 42 that constitutes a rotating shaft. The lower end (tip) of the spindle 42 is exposed from the housing 40, and a disk-shaped wheel mount 44 is fixed to the lower end.

A grinding wheel 46a provided with a grinding wheel for rough grinding is mounted on the lower surface of the wheel mount 44 of the grinding unit 38a, and a grinding wheel for finish grinding is provided on the lower surface of the wheel mount 44 of the grinding unit 38b. The grinding wheel 46b is mounted. A rotary drive source (not shown) such as a motor is connected to the upper end side of the spindle 42. The grinding wheels 46a and 46b rotate around a rotation axis substantially parallel to the Z-axis direction by the power (rotational force) transmitted from the rotation drive source via the spindle 42, respectively.

Rough grinding of the wafer 11 is performed by arranging the chuck table 22 holding the wafer 11 at the rough grinding position B and bringing the grinding wheel provided on the grinding wheel 46a into contact with the wafer 11 while rotating it. Further, the chuck table 22 holding the wafer 11 is arranged at the finish grinding position C, and the grinding wheel provided in the grinding wheel 46b is rotated and brought into contact with the wafer 11, so that the wafer 11 is finished and ground.

A polishing unit 52 for polishing the wafer 11 is provided in the vicinity of the polishing position D. The wafer 11 ground by the grinding units 38a and 38b is positioned at the polishing position D and is polished by the polishing unit 52. The details of the structure and function of the polishing unit 52 will be described later.

A cleaning unit 54 for cleaning the wafer 11 is provided in front of the alignment mechanism 12. The wafer 11 that has been ground by the grinding units 38a and 38b and polished by the polishing unit 52 is transferred from the chuck table 22 positioned at the transfer position A to the cleaning unit 54 by the second transfer unit 18. Then, after the wafer 11 is cleaned by the cleaning unit 54, it is housed in the cassette 8b by, for example, the first transfer unit 6.

FIG. 3 is a perspective view showing the polishing unit 52. A rectangular parallelepiped support structure 60 is arranged along the Z-axis direction on the upper surface of the base 4 (see FIG. 2). A horizontal movement unit (horizontal movement mechanism) 62 for moving the polishing unit 52 in the horizontal direction (X-axis direction in FIG. 3) is provided on the rear surface of the support structure 60.

The horizontal movement unit 62 includes a pair of horizontal guide rails 64 fixed to the rear surface of the support structure 60 and arranged along the X-axis direction. A horizontal moving table 66 is slidably mounted on the pair of horizontal guide rails 64. A nut portion (not shown) is fixed to the front side of the horizontal movement table 66, and a horizontal ball screw (not shown) arranged substantially parallel to the horizontal guide rail 64 is screwed into the nut portion. ..

A pulse motor 68 is connected to one end of the horizontal ball screw. When the horizontal ball screw is rotated by the pulse motor 68, the horizontal movement table 66 moves in the X-axis direction along the horizontal guide rail 64.

A vertical movement unit (vertical movement mechanism) 70 for moving the polishing unit 52 in the vertical direction (Z-axis direction) is provided on the rear surface side of the horizontal movement table 66. The vertical movement unit 70 includes a pair of vertical guide rails 72 fixed to the rear surface of the horizontal movement table 66 and arranged along the vertical direction (Z-axis direction). A vertical moving table 74 is slidably mounted on the pair of vertical guide rails 72.

A nut portion (not shown) is fixed to the front side (back surface side) of the vertical movement table 74, and a vertical ball screw (not shown) arranged substantially parallel to the vertical guide rail 72 is fixed to this nut portion. It is screwed. A pulse motor 76 is connected to one end of the vertical ball screw. When the vertical ball screw is rotated by the pulse motor 76, the vertical movement table 74 moves in the vertical direction (Z-axis direction) along the vertical guide rail 72.

A polishing unit 52 for polishing the wafer 11 is fixed on the rear surface (surface) side of the vertical moving table 74. The polishing unit 52 includes a cylindrical housing 78, and the housing 78 houses a cylindrical spindle 80 that constitutes a rotation shaft. The lower end (tip) of the spindle 80 is exposed from the housing 78, and a disk-shaped wheel mount 82 is fixed to the lower end.

A polishing wheel 84 having substantially the same diameter as the wheel mount 82 is mounted on the lower surface of the wheel mount 82. The polishing wheel 84 includes a disc-shaped wheel base 86 made of a metal material such as stainless steel. Further, a disk-shaped polishing pad 88 is fixed to the lower surface side of the wheel base 86. The wafer 11 is polished by arranging the chuck table 22 (see FIG. 2) holding the wafer 11 at the polishing position D and bringing the polishing pad 88 into contact with the wafer 11 while rotating it.

Next, a specific example of the processing method of the wafer 11 using the processing apparatus 2 will be described. In the present embodiment, first, the back surface 11b side of the wafer 11 is ground by the grinding units 38a and 38b to thin the wafer 11. After that, the back surface 11b side of the wafer 11 is polished by the polishing unit 52 to remove the grinding marks formed on the back surface 11b of the wafer 11.

When processing the wafer 11 with the processing apparatus 2, first, the protective member 17 is attached to the wafer 11. FIG. 4 is a perspective view showing how the protective member 17 is attached to the wafer 11. The protective member 17 is formed in a circular shape having substantially the same diameter as the wafer 11, and is attached to the surface 11a side of the wafer 11. The protective member 17 covers a plurality of devices 15 formed on the surface 11a side of the wafer 11. As a result, the plurality of devices 15 are protected.

As the protective member 17, for example, a film-shaped tape made of resin or the like is used. When it is not necessary to protect the surface 11a side of the wafer 11 (for example, when the device 15 is not formed on the surface 11a side of the wafer 11), the attachment of the protective member 17 can be omitted.

After that, the wafer 11 to which the protective member 17 is attached is housed in the cassette 8a (see FIG. 2), and the cassette 8a is arranged on the mounting table 10a. Then, the wafer 11 is conveyed from the cassette 8a to the alignment mechanism 12 by the first transfer unit 6, and the wafer 11 is aligned.

Next, the wafer 11 is held by the chuck table 22 (holding step). FIG. 5 is a partial cross-sectional front view showing the wafer 11 held by the chuck table 22. In the holding step, the wafer 11 is conveyed from the alignment mechanism 12 (see FIG. 2) to the chuck table 22 arranged at the transfer position A.

The wafer 11 has a chuck table 22 such that the front surface 11a side (first surface side), that is, the protective member 17 side faces the holding surface 22a of the chuck table 22, and the back surface 11b side (second surface side) is exposed upward. Placed on top. When the negative pressure of the suction source is applied to the holding surface 22a in this state, the wafer 11 is sucked and held by the chuck table 22 via the protective member 17. Then, the chuck table 22 holding the wafer 11 moves to the rough grinding position B (see FIG. 2).

Next, the back surface 11b side of the wafer 11 is ground until the wafer 11 has a predetermined thickness. Grinding of the wafer 11 is performed by the grinding units 38a and 38b. FIG. 6 is a perspective view showing the wafer 11 ground by the grinding unit 38a.

The grinding wheel 46a mounted on the grinding unit 38a includes an annular wheel base 48 made of a metal material such as stainless steel. On the lower surface side of the wheel base 48, a plurality of grinding wheels 50 formed in a rectangular parallelepiped shape are fixed along the outer circumference of the wheel base 48.

For example, the grinding wheel 50 is formed by fixing abrasive grains made of diamond, CBN (Cubic Boron Nitride) or the like with a binder such as a metal bond, a resin bond or a vitrified bond. However, there are no restrictions on the material, shape, structure, size, etc. of the grinding wheel 50. Further, an arbitrary number of grinding wheels 50 can be fixed to the wheel base 48.

When grinding the wafer 11, the chuck table 22 and the grinding wheel 46a are rotated, respectively, and the grinding wheel 46a is lowered while supplying the grinding liquid (pure water or the like) toward the back surface 11b side of the wafer 11, and a plurality of grinding wheels 46a are lowered. The grinding wheel 50 is brought into contact with the back surface 11b side of the wafer 11. For example, the chuck table 22 is rotated in the direction indicated by the arrow a at a predetermined rotation speed (for example, 300 rpm), and the grinding wheel 46a is rotated in the direction indicated by the arrow b at a predetermined rotation speed (for example, 6000 rpm). Further, the lowering speed of the grinding wheel 46a is adjusted so that the grinding wheel 50 is pressed against the back surface 11b side of the wafer 11 with an appropriate force.

When the plurality of grinding wheels 50 come into contact with the wafer 11, the back surface 11b side of the wafer 11 is ground. This grinding is continued until the wafer 11 has a desired thickness. When the wafer 11 is thinned to a desired thickness, rough grinding of the wafer 11 is completed.

When the rough grinding is completed, the chuck table 22 moves to the finish grinding position C (see FIG. 2). Then, the back surface 11b side of the wafer 11 is ground by the grinding unit 38b in the same procedure. As a result, the finish grinding of the wafer 11 is performed. The structure and function of the grinding wheel 46b included in the grinding unit 38b are the same as those of the grinding wheel 46a shown in FIG. However, the average particle size of the abrasive grains contained in the grinding wheel included in the grinding wheel 46b is smaller than the average particle size of the grinding wheel 50 included in the grinding wheel 46a.

Although the example in which the wafer 11 is ground by two sets of grinding units 38a and 38b has been described above, the wafer 11 may be ground by one set of grinding units depending on the processing conditions of the wafer 11 and the like. .. In this case, the processing device 2 may include a set of grinding units. Then, when the grinding of the wafer 11 is completed, the chuck table 22 moves to the polishing position D (see FIG. 2).

FIG. 7 is a perspective view showing the wafer 11 after grinding. When the back surface 11b side of the wafer 11 is ground, unevenness 19 is formed radially on the back surface 11b of the wafer 11 along the trajectory of the grinding wheel. The unevenness 19 is a grinding mark (saw mark) formed by grinding.

Next, the back surface 11b side of the wafer 11 is polished to remove the unevenness 19 (polishing step). FIG. 8 is a partial cross-sectional front view showing the wafer 11 polished by the polishing unit 52. In the polishing step, the polishing pad 88 of the polishing wheel 84 mounted on the polishing unit 52 is pressed against the back surface 11b side of the wafer 11 while rotating, thereby polishing the back surface 11b side of the wafer 11. The lower surface of the polishing pad 88 constitutes a polishing surface 88a for polishing the wafer 11.

The polishing pad 88 is formed of, for example, polyurethane or the like, and contains abrasive grains (fixed abrasive grains). As the abrasive grains, for example, silica having a particle size of 0.5 μm or more and 10 μm or less can be used. However, the particle size and material of the abrasive grains can be appropriately changed according to the material of the wafer 11.

Further, inside the polishing unit 52, a polishing liquid supply path 90 that penetrates the polishing unit 52 along the Z-axis direction is formed. One end side (upper end side) of the polishing liquid supply path 90 is connected to a polishing liquid supply source (not shown), and the other end side (lower end side) of the polishing liquid supply path 90 is the central portion of the polishing surface 88a of the polishing pad 88. It opens downward.

When the wafer 11 sucked and held by the chuck table 22 is polished by the polishing pad 88, the polishing liquid is supplied to the wafer 11 and the polishing pad 88 via the polishing liquid supply path 90. When the polishing pad 88 contains abrasive grains, a polishing liquid containing no abrasive grains is used. As the polishing solution, for example, an alkaline solution in which sodium hydroxide, potassium hydroxide or the like is dissolved, or an acidic solution such as permanganate can be used. Further, pure water can be used as the polishing liquid.

However, the polishing pad 88 may not contain abrasive grains. In this case, as the polishing liquid supplied from the polishing liquid supply path 90, a chemical solution (slurry) in which abrasive grains (free abrasive grains) are dispersed is used. The material of the chemical solution, the material of the abrasive grains, the particle size of the abrasive grains, and the like are appropriately selected according to the material of the wafer 11.

In the polishing step, the chuck table 22 and the polishing wheel 84 are rotated respectively, the polishing wheel 84 is lowered while supplying the polishing liquid to the polishing liquid supply path 90, and the polishing pad 88 is brought into contact with the back surface 11b side of the wafer 11. For example, the chuck table 22 is rotated at a predetermined rotation speed (for example, 95 rpm) in the direction indicated by the arrow c, and the polishing wheel 84 is rotated at a predetermined rotation speed (for example, 90 rpm) in the direction indicated by the arrow d. Further, the lowering speed of the polishing wheel 84 is adjusted so that the polishing pad 88 is pressed against the back surface 11b side of the wafer 11 with an appropriate force.

When the polishing surface 88a of the polishing pad 88 comes into contact with the wafer 11, the back surface 11b side of the wafer 11 is polished. By this polishing, the unevenness 19 (see FIG. 7) formed on the back surface 11b side of the wafer 11 is removed. The polishing amount of the wafer 11 (corresponding to the difference in the thickness of the wafer 11 before and after polishing) is set so that the unevenness 19 is appropriately removed.

When the unevenness 19 is removed by polishing as described above, it is necessary to remove a considerable amount of the back surface 11b side of the wafer 11 with the polishing pad 88. As a result, a long time is spent in the polishing process, and the productivity of the wafer 11 may decrease.

Here, as a result of diligent research by the present inventor on the removal of the unevenness 19 by the polishing process, it was confirmed that as the hardness of the polishing pad 88 increases, the amount of polishing of the wafer 11 required for removing the unevenness 19 decreases. It was. It is presumed that this phenomenon is caused by the ease with which the polishing pad 88 penetrates into the unevenness 19 depending on the hardness of the polishing pad 88.

Specifically, when the hardness of the polishing pad 88 is low, the polishing pad 88 is likely to be deformed along the shape of the back surface 11b of the wafer 11. Therefore, when the polishing pad 88 is pressed against the back surface 11b of the wafer 11, the polishing pad 88 enters the inside of the concave portion of the unevenness 19, and the inside of the concave portion is easily polished together with the back surface 11b of the wafer 11. As a result, it is considered that the height difference between the convex portion and the concave portion of the unevenness 19 becomes difficult to disappear, and the amount of polishing of the wafer 11 required for removing the unevenness 19 increases.

On the other hand, when the hardness of the polishing pad 88 is high, even if the polishing pad 88 is pressed against the back surface 11b side of the wafer 11, the polishing pad 88 is less likely to be deformed, and the polishing pad 88 is less likely to enter the inside of the concave portion of the unevenness 19. Therefore, it is considered that the phenomenon that the inside of the concave portion is polished is unlikely to occur, and the amount of polishing of the wafer 11 required for removing the unevenness 19 is unlikely to increase.

Therefore, in the present embodiment, the unevenness 19 is removed by polishing the wafer 11 using the polishing pad 88 having a higher hardness than the conventional one. Specifically, the back surface 11b side of the wafer 11 is polished using a polishing pad 88 having a hardness of 30 or more, preferably 44 or more as measured by the durometer type D. As a result, the amount of polishing of the wafer 11 required for removing the unevenness 19 is reduced, and the processing time is shortened. As a result, the production efficiency of the wafer 11 is improved.

However, if the hardness of the polishing pad 88 is too high, scratches are likely to be formed on the back surface 11b side of the wafer 11 by the polishing process. It is presumed that this is because when the hardness of the polishing pad 88 increases, the abrasive grains (fixed abrasive grains or free abrasive grains) existing between the polishing pad 88 and the wafer 11 during the polishing process are likely to be pressed against the wafer 11. To.

Therefore, for removing the unevenness 19, it is preferable to use a polishing pad 88 having a hardness of less than 65 as measured by the durometer type D, and more preferably to use a polishing pad 88 having a hardness of 50 or less. As a result, the formation of scratches due to polishing can be suppressed.

Next, the result of evaluating the relationship between the hardness of the polishing pad 88 and the polishing amount of the wafer 11 will be described. For the evaluation, four types of polishing pads (polishing pads A, B, C, D) having different hardness were used. The polishing pads A, B, C, and D were each formed using polyurethane.

When the hardnesses of the polishing pads A, B, C and D were measured by the durometer type D, the hardnesses were 23, 30, 44 and 50, respectively. The polishing pad A (hardness 23) corresponds to a polishing pad (conventional product) conventionally used for removing grinding marks. The wafer was polished using each of these polishing pads A, B, C, and D.

As the wafer, a silicon wafer having irregularities (grinding marks) formed on the back surface side was used. These irregularities are formed by performing finish grinding on the back surface side of the wafer using a grinding wheel containing abrasive grains made of diamond (particle size # 2000). After polishing the back surface side of the wafer with a polishing pad until this unevenness is removed, the work of measuring the polishing amount of the wafer (difference in the thickness of the wafer before and after polishing) is performed for each of the polishing pads A, B, C, and D. I went about.

When polishing the wafer, the rotation speed of the chuck table (rotational speed of the wafer) was set to 95 rpm, and the rotation speed of the polishing pad was set to 90 rpm. The lowering speed of the polishing pad was adjusted so that the pressure applied to the back surface side of the wafer by the polishing pad was 250 g / cm ³ or more and 300 g / cm ³ or less. Further, silica was used as the abrasive grains.

FIG. 9 is a graph showing the relationship between the hardness of the polishing pad and the polishing amount of the wafer. As shown in FIG. 9, when polishing pad B (hardness 30), polishing pad C (hardness 44), or polishing pad D (hardness 50) is used, there is a case where polishing pad A (conventional product, hardness 23) is used. In comparison, it was confirmed that the amount of polishing of the wafer required for removing the unevenness was reduced to 2/3 or less. Therefore, it is preferable to use a polishing pad having a hardness of 30 or more as measured by the durometer type D for removing the unevenness.

Further, particularly when the polishing pad C (hardness 44) or the polishing pad D (hardness 50) is used, the wafer polishing required for removing the unevenness is required as compared with the case where the polishing pad A (conventional product, hardness 23) is used. The amount was reduced to less than 1/3. Therefore, it is more preferable to use a polishing pad having a hardness of 44 or more as measured by the durometer type D for removing the unevenness.

Further, when the back surface side of the wafer polished by the polishing pads B, C, and D was observed, it was confirmed that the unevenness was removed and the back surface side of the wafer was flattened. On the other hand, when a polishing pad having a hardness of 65 measured by the durometer type D was separately prepared and the back surface side of the wafer was polished using this polishing pad, scratches were found on the back surface side of the wafer although the unevenness was removed. It was confirmed that it was formed. Therefore, for removing the unevenness, it is preferable to use a polishing pad having a hardness of less than 65 as measured by the durometer type D, and it is more preferable to use a polishing pad having a hardness of 50 or less.

As described above, by appropriately selecting the hardness of the polishing pad, it is possible to reduce the amount of polishing required for removing the unevenness formed on the back surface side of the wafer. As a result, the time required for the step of removing the unevenness can be reduced, and the decrease in the productivity of the wafer 11 can be suppressed.

In the above embodiment, the case where the unevenness (grinding mark) formed on the wafer 11 by the grinding process is removed by the polishing process has been described. However, there is no limitation on the mode of the unevenness removed by the polishing process according to the present embodiment.

For example, when forming the device 15 on the wafer 11 as shown in FIG. 1, first, electrodes, wiring, and the like are experimentally formed on the surface side of the test wafer (test wafer) to form the device 15. The process conditions for this may be selected. In this case, irregularities due to electrodes, wiring, etc. are formed on the surface side of the test wafer.

After the test is completed, the pattern formed on the test wafer can be removed so that the test wafer can be regenerated and used for the test again. Then, the polishing process according to the present embodiment can be used for the regeneration of the test wafer.

Specifically, the back surface side (first surface side) faces the holding surface 22a of the chuck table 22 (see FIG. 8), and the front surface side (second surface side) on which the unevenness is formed is exposed upward. , The test wafer is held by the chuck table 22. Then, by polishing the surface side of the test wafer with the polishing pad 88, the unevenness (electrodes, wiring, etc.) formed on the surface side of the test wafer can be removed.

As described above, the polishing process according to the present embodiment can also be used for the regeneration process of the test wafer. In this case, by polishing the test wafer with a polishing pad having a hardness of 30 or more and less than 65 as measured by the durometer type D, the amount of polishing required for removing unevenness is reduced, and the time required for the regeneration process of the test wafer is reduced. It will be reduced.

In addition, the structure, method, etc. according to the above-described embodiment can be appropriately modified and implemented as long as they do not deviate from the scope of the object of the present invention.

11 Wafer 11a Front surface 11b Back surface 13 Scheduled division line (street)
15 Device 17 Protective member 19 Concavo-convex 2 Processing device 4 Base 4a, 4b Opening 6 First transfer unit 8a, 8b Cassette 10a, 10b Mounting table 12 Alignment mechanism 14 Temporary table 16 Support structure 18 Second transfer unit 20 turns Table 22 Chuck table (holding table)
22a Holding surface 24 Support structure 26 Moving unit (moving mechanism)
28 Guide rail 30 Moving table 32 Ball screw 34 Pulse motor 36 Fixture 38a, 38b Grinding unit 40 Housing 42 Spindle 44 Wheel mount 46a, 46b Grinding wheel 48 Wheel base 50 Grinding wheel 52 Grinding unit 54 Cleaning unit 60 Support structure 62 Horizontal movement Unit (horizontal movement mechanism)
64 Horizontal guide rail 66 Horizontal movement table 68 Pulse motor 70 Vertical movement unit (vertical movement mechanism)
72 Vertical guide rail 74 Vertical movement table 76 Pulse motor 78 Housing 80 Spindle 82 Wheel mount 84 Polishing wheel 86 Wheel base 88 Polishing pad 88a Polishing surface 90 Polishing liquid supply path

Claims (1)

A wafer processing method in which a wafer having a first surface and a second surface and having irregularities formed on the second surface side is held by a holding surface of a chuck table for processing.
A holding step of holding the wafer by the chuck table so that the first surface side faces the holding surface and the second surface side is exposed upward.
A polishing step of polishing the second surface side of the wafer to remove the unevenness is provided.
A method for processing a wafer, which comprises polishing the wafer with a polishing pad having a hardness of 30 or more and less than 65 as measured by a durometer type D in the polishing step.