JP7301472B2 - Wafer processing method - Google Patents

Description

The present invention relates to a wafer processing method.

A wafer having devices such as IC (Integrated Circuit) and LSI (Large Scale Integration) formed on the front side is divided along planned dividing lines (street) to manufacture a plurality of device chips each containing a device. be. Device chips are incorporated in 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 of thinning the wafer by grinding it with a grinding wheel is used before splitting. A grinding apparatus including a chuck table for holding the wafer and a grinding unit to which a grinding wheel for grinding the wafer is mounted is used for grinding the wafer (see Patent Document 1). The wafer is ground by rotating the grinding wheel and bringing it into contact with the back side of the wafer.

When the back side of the wafer is ground with a grinding wheel, minute irregularities (grinding marks, saw marks) are formed in the ground area along the track of the grinding wheel. If this grinding mark remains, the bending strength of the device chip manufactured by dividing the wafer is lowered. Therefore, it is desired that the grinding marks be removed.

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

JP-A-2000-288881 JP-A-8-99265

As described above, when removing unevenness (grinding marks, etc.) formed on the back side of the wafer by polishing, it is necessary to polish the back side of the wafer with a polishing pad and remove a considerable amount of the back 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.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wafer processing method capable of suppressing a decrease in wafer productivity.

According to one aspect of the present invention, there is provided a wafer processing method in which a wafer having a first surface and a second surface is held and processed by a holding surface of a chuck table, the first surface side facing the holding surface. a holding step of holding the wafer by the chuck table so that the second surface side is exposed upward; a grinding step of grinding the second surface side of the wafer with a grinding wheel; a polishing step of polishing the surface side to remove grinding marks formed on the second surface side of the wafer in the grinding step, and in the polishing step, the hardness measured by durometer type D is 30. A method of processing a wafer is provided that polishes the wafer with a polishing pad that is greater than or equal to less than 65. Preferably, in the polishing step, the wafer is polished with the polishing pad having a hardness of 44 or more and 50 or less 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 of 30 or more and less than 65 as measured by durometer type D. As a result, the amount of polishing required to remove irregularities is reduced, and the time required to remove irregularities is reduced. As a result, a decrease in wafer productivity is suppressed.

It is a perspective view showing a wafer. It is a perspective view which shows a processing apparatus. 3 is a perspective view showing a polishing unit; FIG. FIG. 4 is a perspective view showing how a protective member is attached to a wafer; FIG. 4 is a partial cross-sectional front view showing a wafer held by a chuck table; FIG. 4 is a perspective view showing a wafer ground by a grinding unit; It is a perspective view showing a wafer after grinding. FIG. 4 is a partial cross-sectional front view showing a wafer to be polished by a polishing unit; 4 is a graph showing the relationship between the hardness of a polishing pad and the polishing amount of a wafer;

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 wafer that can be processed using the wafer processing method according to the present embodiment will be described. FIG. 1 is a perspective view showing a wafer 11. FIG.

The wafer 11 is made of a material such as silicon and has a disc shape, and has a front surface 11a and a back surface 11b. The wafer 11 is partitioned into a plurality of regions by a plurality of dividing lines (streets) 13 arranged in a grid pattern so as to intersect with each other. ), LSI (Large Scale Integration), or the like.

The material, shape, structure, size, etc. of the wafer 11 are not limited. For example, the wafer 11 may be made of a material such as a semiconductor other than silicon (GaAs, InP, GaN, SiC, etc.), glass, ceramics, resin, metal, or the like. Moreover, there are no restrictions on the type, number, shape, structure, size, arrangement, etc. of the device 15 .

A plurality of device chips each including a device 15 are obtained by dividing the wafer 11 along the dividing line 13 . For the purpose of thinning the device chips, the wafer 11 before splitting is subjected to a grinding process. Specifically, the wafer 11 is thinned by grinding the back surface 11b side of the wafer 11 with a grinding wheel.

However, when the back surface 11b side of the wafer 11 is ground by the grinding wheel, unevenness (grinding marks, saw marks) is formed in the ground region along the track of the grinding wheel. If the unevenness remains on the wafer 11, the bending strength of the device chips manufactured by dividing the wafer 11 is lowered. 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.

A processing apparatus capable of grinding and polishing the wafer 11 is used for the above grinding and polishing. FIG. 2 is a perspective view showing the processing device 2. As shown in FIG. Although an example in which both grinding and polishing of the wafer 11 are performed by the processing device 2 will be described below, grinding and polishing may be performed by separate 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 transferring the wafer 11 is provided in the opening 4a. Mounting tables 10a and 10b on which cassettes 8a and 8b capable of accommodating a plurality of wafers 11 are mounted are provided in front of the opening 4a.

An alignment mechanism 12 for positioning the wafer 11 is provided obliquely behind the opening 4a. The alignment mechanism 12 has a temporary placement table 14 on which the wafer 11 is temporarily placed. For example, the alignment mechanism 12 aligns the center position of the wafer 11 transferred from the cassette 8 a to the temporary placement table 14 by the first transfer unit 6 .

A gate-shaped support structure 16 is provided on the side surface of the base 4 so as to straddle the alignment mechanism 12 . A second transport unit 18 for transporting the wafer 11 is attached to 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-rear direction, second horizontal direction), and Z-axis direction (vertical direction, up-down direction). For example, the wafer 11 aligned by the alignment mechanism 12 is transported backward.

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. As shown in FIG. A disk-shaped turntable 20 that rotates around a rotation axis substantially parallel to the Z-axis direction is arranged in the opening 4b. Four chuck tables (holding tables) 22 for holding the wafer 11 are installed on the upper surface of the turntable 20 at approximately equal angular intervals.

The turntable 20 rotates clockwise (in the direction indicated by the arrow R in FIG. 2) in plan view, and positions the chuck table 22 in the order of the transfer position A, the rough grinding position B, the finish grinding position C, and the polishing position D. The wafer 11 aligned by the alignment mechanism 12 is transferred 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 rotational drive source (not shown) such as a motor, and rotates around a rotation axis generally parallel to the Z-axis direction. The upper surface of the chuck table 22 forms a holding surface 22a (see FIG. 5) that holds the wafer 11. As shown in FIG. The holding surface 22 a is connected to a suction source (not shown) through a channel (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 moving unit 26 has a pair of guide rails 28 arranged along the Z-axis direction, and a moving table 30 is slidably mounted on the pair of guide rails 28 .

A nut portion (not shown) is fixed to the rear side (rear 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 fixture 36 positioned above the rough grinding position B is fixed with a grinding unit 38 a for rough grinding of the wafer 11 . On the other hand, the fixture 36 positioned above the finish grinding position C is fixed with a grinding unit 38b for finish grinding that performs finish grinding of the wafer 11 .

Grinding units 38 a , 38 b each include a cylindrical housing 40 . The housing 40 accommodates a cylindrical spindle 42 that forms a rotating shaft. A 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 having a grinding wheel for rough grinding is attached to the lower surface of the wheel mount 44 of the grinding unit 38a, and a grinding wheel for finish grinding is attached to the lower surface of the wheel mount 44 of the grinding unit 38b. A grinding wheel 46b is mounted. A rotational drive source (not shown) such as a motor is connected to the upper end of the spindle 42 . Grinding wheels 46a and 46b each rotate about a rotation axis generally parallel to the Z-axis direction by power (rotational force) transmitted from a rotation drive source via spindle 42. As shown in FIG.

The wafer 11 is roughly ground by placing the chuck table 22 holding the wafer 11 at the rough grinding position B and bringing it into contact with the wafer 11 while rotating the grindstone of the grinding wheel 46a. Further, the chuck table 22 holding the wafer 11 is placed at the finish grinding position C, and the grinding wheel 46b of the grinding wheel 46b is rotated and brought into contact with the wafer 11, thereby performing finish grinding of the wafer 11.

A polishing unit 52 for polishing the wafer 11 is provided near the polishing position D. As shown in FIG. The wafer 11 ground by the grinding units 38 a and 38 b is positioned at the polishing position D and polished by the polishing unit 52 . 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 ground by the grinding units 38 a and 38 b 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 . After the wafers 11 are cleaned by the cleaning unit 54, they are accommodated in the cassette 8b by the first transfer unit 6, for example.

FIG. 3 is a perspective view showing the polishing unit 52. As shown in FIG. 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 (the X-axis direction in FIG. 3) is provided on the rear surface of the support structure 60 .

The horizontal movement unit 62 comprises 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 movement 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 this nut portion. .

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

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 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 movement table 74 is slidably mounted on the pair of vertical guide rails 72 .

A nut portion (not shown) is fixed to the front side (rear side) of the vertical movement table 74, and a vertical ball screw (not shown) arranged substantially parallel to the vertical guide rail 72 is attached to the nut portion. screwed together. 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 vertically (Z-axis direction) along the vertical guide rail 72 .

A polishing unit 52 for polishing the wafer 11 is fixed on the rear surface (front surface) side of the vertical movement table 74 . The polishing unit 52 has a cylindrical housing 78, and the housing 78 accommodates a columnar spindle 80 forming a rotating shaft. A 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 attached to the lower surface of the wheel mount 82 . The polishing wheel 84 has a disk-shaped wheel base 86 made of a metal material such as stainless steel. A disk-shaped polishing pad 88 is fixed to the lower surface of the wheel base 86 . The wafer 11 is polished by placing the chuck table 22 (see FIG. 2) holding the wafer 11 at the polishing position D and rotating the polishing pad 88 to contact the wafer 11 .

Next, a specific example of a method for processing the wafer 11 using the processing apparatus 2 will be described. In this embodiment, first, the wafer 11 is thinned by grinding the rear surface 11b side of the wafer 11 by grinding units 38a and 38b. After that, the back surface 11 b of the wafer 11 is polished by the polishing unit 52 to remove the grinding marks formed on the back surface 11 b 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. As shown in FIG. The protective member 17 is formed in a circular shape having approximately the same diameter as the wafer 11 and is attached to the front surface 11a side of the wafer 11 . A plurality of devices 15 formed on the front surface 11a side of the wafer 11 are covered by the protective member 17 . This protects multiple devices 15 .

As the protective member 17, for example, a film tape made of resin or the like is used. If it is not necessary to protect the front surface 11a of the wafer 11 (such as when the device 15 is not formed on the front surface 11a 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 transferred 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. As shown in FIG. In the holding step, the wafer 11 is transferred from the alignment mechanism 12 (see FIG. 2) to the chuck table 22 arranged at the transfer position A. As shown in FIG.

The wafer 11 is placed on the chuck table 22 so that the front surface 11a side (first surface side), that is, the protection 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 above. In this state, when a negative pressure of a suction source is applied to the holding surface 22a, the wafer 11 is suction-held by the chuck table 22 via the protective member 17. As shown in FIG. 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 grinding units 38a and 38b. FIG. 6 is a perspective view showing the wafer 11 ground by the grinding unit 38a.

A grinding wheel 46a attached to the grinding unit 38a has an annular wheel base 48 made of a metal material such as stainless steel. A plurality of rectangular parallelepiped grinding wheels 50 are fixed along the outer circumference of the wheel base 48 on the lower surface side 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 bonding material such as metal bond, resin bond or vitrified bond. However, the material, shape, structure, size, etc. of the grinding wheel 50 are not limited. Also, any number of grinding wheels 50 can be fixed to the wheel base 48 .

When the wafer 11 is ground, the chuck table 22 and the grinding wheel 46a are rotated, and the grinding wheel 46a is lowered while supplying a grinding fluid (pure water, etc.) toward the back surface 11b of the wafer 11, to obtain a plurality of grinding surfaces. A 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 arrow a at a predetermined number of revolutions (eg 300 rpm), and the grinding wheel 46a is rotated in the direction indicated by arrow b at a predetermined number of revolutions (eg 6000 rpm). Further, the descending 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 continues until the wafer 11 reaches the desired thickness. When the wafer 11 is thinned to the desired thickness, rough grinding of the wafer 11 is completed.

After the rough grinding is completed, the chuck table 22 moves to the finish grinding position C (see FIG. 2). Then, the rear surface 11b side of the wafer 11 is ground by the grinding unit 38b in the same procedure. Thereby, 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 of the grinding wheel 46b is smaller than the average particle size of the grinding wheel 50 of the grinding wheel 46a.

Although an 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. . In this case, the processing device 2 may be provided with one set of grinding units. When the grinding of the wafer 11 is completed, the chuck table 22 moves to the grinding 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, irregularities 19 are radially formed on the back surface 11b of the wafer 11 along the trajectory of the grinding wheel. The irregularities 19 are grinding marks (saw marks) formed by grinding.

Next, the unevenness 19 is removed by polishing the rear surface 11b side of the wafer 11 (polishing step). FIG. 8 is a partial cross-sectional front view showing the wafer 11 to be polished by the polishing unit 52. As shown in FIG. In the polishing process, the rear surface 11b side of the wafer 11 is polished by pressing the polishing pad 88 of the polishing wheel 84 attached to the polishing unit 52 against the rear surface 11b side of the wafer 11 while rotating. The lower surface of the polishing pad 88 constitutes a polishing surface 88a for polishing the wafer 11. As shown in FIG.

The polishing pad 88 is made of, for example, polyurethane, and contains abrasive grains (fixed abrasive grains). As 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 grain size, material, etc. of the abrasive grains can be appropriately changed according to the material, etc. of the wafer 11 .

Further, inside the polishing unit 52, a polishing liquid supply path 90 is formed that penetrates the polishing unit 52 along the Z-axis direction. 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 88 a of the polishing pad 88 . It is open downwards.

When polishing the wafer 11 sucked and held by the chuck table 22 with the polishing pad 88 , the polishing liquid is supplied to the wafer 11 and the polishing pad 88 through the polishing liquid supply path 90 . If the polishing pad 88 contains abrasive grains, a polishing liquid that does not contain abrasive grains is used. As the polishing liquid, for example, an alkaline solution in which sodium hydroxide, potassium hydroxide, or the like is dissolved, or an acidic liquid such as permanganate can be used. Pure water can also be used as the polishing liquid.

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

In the polishing process, the chuck table 22 and the polishing wheel 84 are rotated, and the polishing wheel 84 is lowered while supplying the polishing liquid to the polishing liquid supply path 90 to bring the polishing pad 88 into contact with the rear surface 11b side of the wafer 11 . For example, the chuck table 22 is rotated at a predetermined number of revolutions (eg, 95 rpm) in the direction indicated by arrow c, and the polishing wheel 84 is rotated at a predetermined number of revolutions (eg, 90 rpm) in the direction indicated by arrow d. Further, the descending 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 contacts the wafer 11, the rear surface 11b side of the wafer 11 is polished. By this polishing, the irregularities 19 (see FIG. 7) formed on the back surface 11b side of the wafer 11 are removed. The polishing amount of the wafer 11 (corresponding to the difference in thickness of the wafer 11 before and after polishing) is set so that the irregularities 19 are appropriately removed.

When removing the unevenness 19 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, the polishing process takes a long time, and the productivity of the wafer 11 may decrease.

Here, as a result of diligent research by the present inventors on the removal of the unevenness 19 by polishing, it has been confirmed that the polishing amount of the wafer 11 required for removing the unevenness 19 decreases as the hardness of the polishing pad 88 increases. rice field. This phenomenon is presumed to be due to the fact that the ease with which the polishing pad 88 enters the irregularities 19 depends on the hardness of the polishing pad 88 .

Specifically, when the hardness of the polishing pad 88 is low, the polishing pad 88 tends to deform along the shape of the back surface 11b side of the wafer 11 . Therefore, when the polishing pad 88 is pressed against the back surface 11 b of the wafer 11 , the polishing pad 88 tends to enter the recesses of the unevenness 19 and polish the inside of the recesses together with the back surface 11 b of the wafer 11 . As a result, it is considered that the height difference between the projections and recesses of the unevenness 19 is less likely to be eliminated, and the polishing amount of the wafer 11 necessary 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 rear surface 11 b of the wafer 11 , the polishing pad 88 is less likely to be deformed and less likely to enter the recesses of the unevenness 19 . Therefore, it is considered that the phenomenon in which the inside of the concave portion is polished is unlikely to occur, and the polishing amount of the wafer 11 necessary for removing the unevenness 19 is unlikely to increase.

Therefore, in this embodiment, the unevenness 19 is removed by polishing the wafer 11 using a 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 durometer type D. As a result, the polishing amount 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 wafers 11 is improved.

However, if the hardness of the polishing pad 88 is too high, scratches are likely to be formed on the rear 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 are more likely to be pressed against the wafer 11 during polishing. be.

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

Next, the results 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, and D) with different hardness were used. Polishing pads A, B, C, and D were each formed using polyurethane.

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

As the wafer, a silicon wafer having unevenness (grinding marks) formed on the back side was used. The unevenness was formed by finish-grinding the back surface of the wafer using a grinding wheel containing diamond abrasive grains (grain size #2000). After polishing the back side of the wafer with a polishing pad until the unevenness is removed, the amount of polishing of the wafer (difference in thickness of the wafer before and after polishing) is measured using polishing pads A, B, C, and D respectively. followed.

When polishing the wafer, the rotation speed of the chuck table (the rotation 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 of the wafer by the polishing pad was 250 g/cm ³ or more and 300 g/cm ³ or less. Silica was used as 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, polishing pad A (conventional product, hardness 23) is used. By comparison, it was confirmed that the polishing amount of the wafer necessary 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 a durometer type D for removing irregularities.

In particular, when using polishing pad C (hardness 44) or polishing pad D (hardness 50), compared with the case of using polishing pad A (conventional product, hardness 23), the wafer polishing necessary for removing unevenness is reduced. 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 a durometer type D for removing irregularities.

Observation of the back side of the wafer polished by the polishing pads B, C, and D confirmed that the unevenness was removed and the back side of the wafer was flattened. On the other hand, a polishing pad having a hardness of 65 as measured with a durometer type D was separately prepared, and the back side of the wafer was polished using this polishing pad. confirmed to be formed. Therefore, it is preferable to use a polishing pad having a hardness of less than 65, and more preferably a polishing pad having a hardness of 50 or less, as measured by a durometer type D, to remove irregularities.

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

In the above-described embodiment, a case has been described in which unevenness (grinding marks) formed on the wafer 11 by grinding is removed by polishing. However, there is no limitation on the mode of 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. In some cases, process conditions are selected for In this case, unevenness is formed on the surface side of the test wafer due to electrodes, wiring, and the like.

After the test is completed, the pattern formed on the test wafer is removed so that the test wafer can be reclaimed and used for testing again. The polishing process according to the present embodiment can be used for reclaiming the test wafer.

Specifically, the rear surface side (first surface side) faces the holding surface 22a of the chuck table 22 (see FIG. 8), and the surface side (second surface side) on which unevenness is formed is exposed upward. , a test wafer is held by the chuck table 22 . 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.

Thus, the polishing process according to this embodiment can also be used for the reprocessing of test wafers. 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 durometer type D, the amount of polishing required to remove unevenness is reduced, and the time required for reprocessing the test wafer is reduced. reduced.

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.

REFERENCE SIGNS LIST 11 Wafer 11a Front surface 11b Back surface 13 Scheduled division line (street)
REFERENCE SIGNS LIST 15 device 17 protective member 19 unevenness 2 processing device 4 base 4a, 4b opening 6 first transfer unit 8a, 8b cassette 10a, 10b mounting table 12 alignment mechanism 14 temporary placement table 16 support structure 18 second transfer unit 20 turn 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 polishing 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 (2)

A wafer processing method for holding and processing a wafer having a first surface and a second surface on a holding surface of a chuck table, comprising:
a holding step of holding the wafer by the chuck table such that the first surface side faces the holding surface and the second surface side is exposed upward;
a grinding step of grinding the second surface side of the wafer with a grinding wheel;
a polishing step of polishing the second surface side of the wafer to remove grinding marks formed on the second surface side of the wafer in the grinding step ;
A method of processing a wafer, wherein, in the polishing step, the wafer is polished with a polishing pad having a hardness of 30 or more and less than 65 as measured by durometer type D. 2. The method of processing a wafer according to claim 1, wherein in the polishing step, the wafer is polished with the polishing pad having a hardness of 44 or more and 50 or less as measured by a durometer type D.

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