JP2018082066A - Wafer polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer polishing method which can reduce the fluctuation of a pH value of a polishing liquid resulting from the use of a polishing pad including alkali particles.SOLUTION: A wafer polishing method is arranged to polish a wafer W, using a polishing pad 78b having abrasive grains and alkali particles mixed in a base material. The wafer polishing method comprises: a polishing step of turning around a wafer W with the polishing pad 78b remaining abutting against the rotating wafer W and in parallel, supplying water to the polishing pad 78b to produce an alkali polishing liquid and causing the alkali polishing liquid to act on the wafer W for polishing; a determination step of measuring a pH value of the polishing liquid, and determining whether or not the measured pH value is within a predetermined polishing liquid range; and a dressing step of dressing the polishing pad 78b to adjust the pH value of the polishing liquid so that the pH value is made larger than a lower limit threshold value of the polishing liquid range and is included in the polishing liquid range when it is determined in the determination step that the pH value is smaller than the lower limit threshold, and the measured pH value is out of the polishing liquid range.SELECTED DRAWING: Figure 6

Description

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

  In general, in a semiconductor device manufacturing process, a plurality of rectangular areas are defined on a surface of a substantially disk-shaped substrate (for example, a silicon substrate) by division lines arranged in a grid pattern, and an IC is formed in each rectangular area. A device such as an LSI is formed. Individual device chips are formed by dividing a semiconductor wafer on which a plurality of devices are formed (hereinafter simply referred to as a wafer) along a predetermined division line. The demand for smaller and lighter device chips is increasing, and prior to dividing the wafer into individual rectangular regions, the back surface of the wafer is ground to form a wafer having a predetermined thickness (for example, 100 μm) or less. Is required.

After grinding, the wafer made of a silicon substrate is subjected to CMP (Chemical Mechanical Polishing) in which polishing is performed while supplying an alkaline polishing liquid using a polishing pad. In this type of chemical mechanical polishing, for example, a polishing pad in which abrasive grains such as silica (SiO ₂ ) are fixed to a substrate made of urethane resin or the like is used, and an alkaline polishing liquid is supplied to the wafer from a polishing liquid supply source. The structure which performs is known (for example, refer patent document 1).

JP2015-46550A

  By the way, in the conventional structure, since it is necessary to provide the polishing liquid supply source which supplies alkaline polishing liquid, there exists a problem which a manufacturing apparatus and a manufacturing process become complicated. For this reason, development of a polishing pad in which water-soluble alkali particles are mixed with a base material together with abrasive grains is being sought. In this type of polishing pad, the alkali particles mixed in the base material are dissolved by water (pure water) supplied to the wafer to generate an alkaline polishing liquid.

  However, since the alkali particles mixed in the polishing pad are dissolved and consumed when the wafer is polished, the amount of alkali particles exposed on the polishing surface of the polishing pad changes with time, and thus generated polishing. The pH (hydrogen ion concentration) value of the liquid may fluctuate.

  The present invention has been made in view of the above, and an object of the present invention is to provide a wafer polishing method capable of suppressing fluctuations in the pH value of a generated polishing liquid when a polishing pad containing alkali particles is used. And

  In order to solve the above-described problems and achieve the object, the present invention provides a wafer polishing method for polishing a wafer using a polishing pad in which abrasive grains and alkali particles are mixed in a base material, the rotating method A polishing step in which a polishing pad is rotated against a wafer to be supplied, water is supplied to the polishing pad to generate an alkaline polishing liquid, and the wafer is polished by acting on the wafer, and the pH value of the polishing liquid is measured. And a determination step for determining whether the measured pH value is within a predetermined polishing liquid range, and in the determination step, the pH value is determined to be smaller than a lower limit threshold value of the polishing liquid range and not within the polishing liquid range. If so, a dressing step of dressing the polishing pad and adjusting the pH value of the polishing liquid to be within the polishing liquid range by making the pH value of the polishing liquid larger than the lower limit threshold value is included.

  According to this configuration, since the polishing pad contains alkali particles in the base material, an alkaline polishing liquid can be generated simply by supplying water to the polishing pad, and this polishing liquid can be easily supplied to the wafer. Can act. In addition, since the pH value is adjusted by dressing the polishing pad in a timely manner based on the pH value of the polishing liquid, fluctuations in the pH value of the generated polishing liquid can be suppressed, and variations in the polishing state of the wafer can be reduced. Can do.

  Further, when it is impossible to adjust the pH value to the polishing liquid range, the polishing pad may be replaced.

  According to the present invention, since the polishing pad contains alkali particles in the base material, an alkaline polishing liquid can be generated simply by supplying water to the polishing pad. This polishing liquid can be easily supplied to the wafer. Can act. In addition, since the pH value is adjusted by dressing the polishing pad in a timely manner based on the pH value of the polishing liquid, fluctuations in the pH value of the generated polishing liquid can be suppressed, and variations in the polishing state of the wafer can be reduced. Can do.

FIG. 1 is a perspective view showing a device wafer to be polished by the wafer polishing method according to the present embodiment. FIG. 2 is a perspective view showing an example of a grinding and polishing apparatus for executing the wafer polishing method according to the present embodiment. FIG. 3 is a perspective view of a polishing unit provided in the grinding and polishing apparatus. FIG. 4 is a schematic diagram showing a peripheral configuration of the polishing unit. FIG. 5 is a schematic cross-sectional view showing the configuration of the polishing pad. FIG. 6 is a schematic diagram showing a state of dressing the polishing pad.

  DESCRIPTION OF EMBODIMENTS Embodiments (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the structures described below can be combined as appropriate. Various omissions, substitutions, or changes in the configuration can be made without departing from the scope of the present invention.

  FIG. 1 is a perspective view showing a device wafer to be polished by the wafer polishing method according to the present embodiment. The wafer polishing method according to the present embodiment is performed by polishing a device wafer (hereinafter referred to as a wafer) W. As shown in FIG. 1, the wafer W is a disk-shaped semiconductor wafer or optical device wafer having silicon as a base material. The wafer W includes a region partitioned by a plurality of streets (division planned lines) S formed in a lattice shape on the surface WS, and a device DB is formed in each region. The wafer W is ground to the back surface WR on the back side of the front surface WS and thinned to a predetermined thickness (for example, 50 μm), and then polished to remove grinding distortion.

  FIG. 2 is a perspective view showing an example of a grinding and polishing apparatus for executing the wafer polishing method according to the present embodiment. The grinding and polishing apparatus 2 is a fully automatic processing apparatus, and is a series of carry-in processing, rough grinding processing, finish grinding processing, polishing processing, cleaning processing, and carry-out processing with respect to the wafer W under the control of the control unit 100. This operation is configured to be fully automatic.

  As shown in FIG. 2, the grinding and polishing apparatus 2 includes a base 4 that supports each component. An opening 4 a is formed on the front end side of the upper surface of the base 4, and a first transport unit 6 that transports the wafer W is provided in the opening 4 a. Further, in the region on the further front end side of the opening 4a, mounting tables 10a and 10b for mounting cassettes 8a and 8b capable of accommodating a plurality of wafers W are formed. The wafer W is carried into the grinding and polishing apparatus 2 while being accommodated in the cassettes 8a and 8b.

  Further, the base 4 is provided with an alignment mechanism 12 for aligning the wafer W. The alignment mechanism 12 includes a temporary placement table 14 on which the wafer W is temporarily placed. For example, the alignment mechanism 12 is positioned at the center of the wafer W that is transported from the cassette 8a by the first transport unit 6 and temporarily placed on the temporary placement table 14. Match.

  A gate-type support structure 16 that straddles the alignment mechanism 12 is disposed on the base 4. The support structure 16 is provided with a second transport unit 18 for transporting the wafer W. The second transport unit 18 is movable in the left-right direction (X-axis direction), the front-rear direction (Y-axis direction), and the up-down direction (Z-axis direction). For example, the wafer W aligned by the alignment mechanism 12 Is conveyed backward (in the + Y direction in FIG. 2).

  An opening 4 b is formed behind the opening 4 a and the alignment mechanism 12. A disc-shaped turntable 20 that rotates around a rotation axis extending in the vertical direction is disposed in the opening 4b. On the upper surface of the turntable 20, four chuck tables (holding portions) 22 for sucking and holding the wafer W are provided at substantially equal angular intervals.

  The wafer W carried out from the alignment mechanism 12 by the second carrying unit 18 is carried into the chuck table 22 positioned at the carry-in / carry-out position A on the front side so that the back side is exposed upward. The turntable 20 rotates in the clockwise direction R, and positions the chuck table 22 in the order of the carry-in / out position A, the rough grinding position B, the finish grinding position C, and the polishing position D.

  Each chuck table 22 is connected to a rotation drive source (not shown) such as a motor, and is configured to be rotatable around a rotation axis extending in the vertical direction. In this embodiment, each chuck table 22 is Rotation at a predetermined speed (for example, 300 to 1000 rpm) is possible under the control of the control unit 100. The upper surface of each chuck table 22 is a holding surface that holds the wafer W by suction. This holding surface is connected to a suction source (not shown) through a flow path (not shown) formed inside the chuck table 22. The wafer W carried into the chuck table 22 is sucked on the surface side by the negative pressure of the suction source acting on the holding surface.

  A wall-like support structure 24 that extends upward is erected on the rear side of the turntable 20. Two sets of lifting mechanisms 26 are provided on the front surface of the support structure 24. Each lifting mechanism 26 includes two lifting guide rails 28 extending in the vertical direction (Z-axis direction), and a lifting table 30 is slidably installed on the lifting guide rail 28.

  A nut portion (not shown) is fixed to the rear surface side of the lifting table 30, and a lifting ball screw 32 parallel to the lifting guide rail 28 is screwed to the nut portion. A lifting pulse motor 34 is connected to one end of the lifting ball screw 32. The lifting table 30 is moved up and down along the lifting guide rail 28 by rotating the lifting ball screw 32 by the lifting pulse motor 34.

  A fixture 36 is provided on the front surface of the lifting table 30. A grinding unit 38a for rough grinding for roughly grinding the wafer W is fixed to the fixture 36 of the lifting table 30 positioned above the rough grinding position B. On the other hand, a grinding unit 38b for finish grinding for finish grinding the wafer W is fixed to the fixture 36 of the lifting table 30 positioned above the finish grinding position C. Each of the spindle housings 40 of the grinding units 38a and 38b accommodates a spindle 42 that constitutes a rotating shaft, and a disk-like wheel mount 44 is fixed to the lower end portion (tip portion) of each spindle 42. Yes. 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. A grinding wheel 46b is mounted. A rotational drive source (not shown) such as a motor is connected to the upper end side of each spindle 42, and the grinding wheels 46a and 46b rotate with the rotational force transmitted from the rotational drive source.

  While rotating the chuck table 22 and the spindle 42, the grinding wheels 46 a and 46 b are lowered and brought into contact with the back surface WR side of the wafer W while supplying a grinding liquid such as pure water, whereby the wafer W is roughly ground or finish ground. it can. Further, in the vicinity of the polishing position D, a polishing unit 48 for polishing the back surface of the wafer W ground by the grinding units 38a and 38b is provided.

  A cleaning unit 52 for cleaning the wafer W is provided in front of the alignment mechanism 12, and the polished wafer W is transported from the chuck table 22 to the cleaning unit 52 by the second transport unit 18. The wafer W cleaned by the cleaning unit 52 is transported by the first transport unit 6 and stored in the cassette 8b.

  FIG. 3 is a perspective view of a polishing unit provided in the grinding and polishing apparatus, and FIG. 4 is a schematic diagram showing a peripheral configuration of the polishing unit. FIG. 5 is a schematic cross-sectional view showing the configuration of the polishing pad. FIG. 6 is a schematic diagram showing a state of dressing the polishing pad. As shown in FIG. 3, a block-like support structure 54 is erected on the upper surface of the base 4 (FIG. 2). A horizontal movement unit 56 that moves the polishing unit 48 in the horizontal direction (here, the X-axis direction) is provided on the rear surface of the support structure 54.

  The horizontal moving unit 56 includes a pair of horizontal guide rails 58 fixed to the rear surface of the support structure 54 and parallel to the horizontal direction (X-axis direction). A horizontal movement table 57 is slidably installed on the horizontal guide rail 58. A nut portion (not shown) is provided on the rear surface side of the horizontal movement table 57, and a horizontal ball screw (not shown) parallel to the horizontal guide rail 58 is screwed into the nut portion.

  A pulse motor 59 is connected to one end of the horizontal ball screw. By rotating the horizontal ball screw with the pulse motor 59, the horizontal movement table 57 moves in the horizontal direction (X-axis direction) along the horizontal guide rail 58. On the rear surface side of the horizontal movement table 57, a vertical movement unit 64 for moving the polishing unit 48 in the vertical direction (Z-axis direction) is provided. The vertical movement unit 64 includes a pair of vertical guide rails 66 fixed to the rear surface of the horizontal movement table 57 and parallel to the vertical direction (Z-axis direction). A vertical movement table 68 is slidably installed on the vertical guide rail 66. A nut portion (not shown) is provided on the front side (back side) of the vertical movement table 68, and a vertical ball screw (not shown) parallel to the vertical guide rail 66 is screwed into the nut portion. ing.

  A pulse motor 70 is connected to one end of the vertical ball screw. By rotating the vertical ball screw with the pulse motor 70, the vertical movement table 68 moves in the vertical direction (Z-axis direction) along the vertical guide rail 66. A polishing unit 48 for polishing the upper surface of the wafer W is fixed to the rear surface (front surface) of the vertical moving table 68. The spindle housing 72 of the polishing unit 48 accommodates a spindle 74 that constitutes a rotation shaft, and a disc-shaped wheel mount 76 is fixed to the lower end (tip) of the spindle 74. A polishing wheel 78 having substantially the same diameter as the wheel mount 76 is attached to the lower surface of the wheel mount 76. The polishing wheel 78 includes a wheel base 78a formed of a metal material such as stainless steel, and a disk-shaped polishing pad 78b attached to the lower surface of the wheel base 78a.

  In this embodiment, as shown in FIG. 4, the polishing pad 78 b is formed to have a large diameter (for example, wafer W; 300 mm, polishing pad; 450 mm) equal to or larger than the wafer W, and the polishing unit 48 is formed of the wafer W. It is eccentric with respect to the chuck table 22 while covering the entire back surface WR. In this embodiment, before grinding the back surface WR of the wafer W, a surface protection tape T is applied to the front surface WS of the wafer W in order to protect a device (not shown) formed on the front surface WS. Worn. For this reason, the front surface WS of the wafer W held by the chuck table 22 is protected and ground by the surface protection tape T and is ground and polished in a form in which the back surface WR is exposed.

  As shown in FIG. 4, the polishing unit 48 includes a fluid supply path 79 that penetrates the spindle 74, the wheel mount 76, and the polishing wheel 78. The fluid supply path 79 is a flow path for supplying water (pure water) to the back surface WR of the wafer W held on the chuck table 22. The fluid supply path 79 is connected to a pure water supply source via an electromagnetic valve 61. 62 is connected. Water is a liquid supplied when the back surface WR of the wafer W is polished. When alkali particles (described later) contained in the polishing pad 78b are dissolved, a chemical reaction with the silicon wafer occurs and CMP ( An alkaline polishing liquid for performing chemical mechanical polishing (chemical mechanical polishing) is generated. Further, the water supplied through the fluid supply path 79 is composed of only a substance that does not substantially cause a chemical reaction with the wafer W, and pure water, for example, is used. In the present embodiment, the electromagnetic valve 61 is a flow rate adjustment valve that can adjust the flow rate through the fluid supply path 79 by adjusting the opening degree under the control of the control unit 100.

  Further, around the chuck table 22, there are provided an annular receiving portion 63 that receives the polishing liquid that flows down during polishing, and a drain pipe 65 that is connected to the receiving portion 63. The drain pipe 65 is provided with a pH measuring unit 67 that measures the pH (hydrogen ion concentration) value of the drainage (polishing liquid) flowing through the drain pipe 65. The pH measurement unit 67 measures the pH value of the polishing liquid flowing through the drain pipe 65 every predetermined time (for example, 10 seconds) under the control of the control unit 100, and outputs the measured pH value to the control unit 100. In addition, the measurement interval of pH value can be changed suitably, and pH value may be measured continuously.

  Further, a dress unit 80 is arranged in the vicinity of the chuck table 22 along with the chuck table 22. The dress unit 80 includes a rotation drive source 81, a spindle 82 connected to the rotation drive source 81, and a disk-shaped wheel mount 83 fixed to the upper end portion (tip portion) of the spindle 82. A dressing pad 84 in which particles such as diamond are bonded to the surface is attached to the upper surface of the wheel mount 83. The dressing unit 80 performs dressing by bringing the dressing pad 84 into contact (pressing) with the polishing pad 78b and scraping the surface of the polishing pad 78b. By this dressing, the surface roughness of the polishing pad 78b is adjusted, and the polishing ability of the polishing pad 78b is set to an appropriate value. Further, the alkali particles contained in the polishing pad 78b are exposed on the surface of the polishing pad 78b. The polishing unit 48 is movable in the horizontal direction (X direction) by the horizontal moving unit 56 described above. Therefore, when the wafer W is not being polished, the polishing pad 48 b of the polishing unit 48 can be opposed to the dress unit 80 by moving the polishing unit 48 in the horizontal direction.

  The dress unit 80 is provided with a lifting mechanism 85 that lifts and lowers the dress unit 80 in the vertical direction (Z-axis direction). The elevating mechanism 85 elevates and lowers the dress unit 80 until the dressing pad 84 contacts the polishing pad 78b during dressing, and lowers and retracts the dress unit 80 otherwise.

  Next, the polishing pad will be described. As shown in FIG. 5, the polishing pad 78 b includes, for example, a base material 90 made of a resin material such as polyurethane resin and a nonwoven fabric, and abrasive grains 91 and alkali particles 92 dispersed in the base material 90. Is done. The polishing pad 78b is a fixed abrasive type polishing pad in which abrasive grains 91 and alkali particles 92 are dispersed in a base material 90 and fixed with an appropriate liquid binder. The shapes of the abrasive grains 91 and the alkali particles 92 in FIG. 5 are different from each other in order to distinguish them, and the abrasive grains 91 and the alkali particles 92 do not have the shapes described in FIG.

  The resin material which comprises the base material 90 is comprised from 1 or several resin material selected from polyurethane type, polyethylene type, a polystyrene type, a polyvinyl chloride type, or an acrylic resin, for example. Dispersed abrasive grains 91 and alkali particles 92 are exposed on the polishing surface 90a (the lower surface in FIG. 5) of the substrate 90, and the exposed abrasive grains 91 polish the back surface WR (FIG. 4) of the wafer W. . Although not shown, a groove for taking in foreign matter generated during polishing is formed on the polishing surface 90a of the substrate 90. The groove is preferably formed by connecting the central portion and the edge portion of the substrate 90, and is formed, for example, radially from the central portion toward the edge portion, or in a lattice shape or a spiral shape. As a result, the foreign matter taken into the groove is discharged to the outside through the groove. The groove also has a function as a flow path for uniformly supplying the supplied water (polishing liquid) over the polishing surface 90a.

The abrasive grains 91 only need to have Mohs hardness higher than that of the wafer W and can polish the wafer W. For example, when the wafer W is a silicon wafer, an abrasive mainly composed of a material having a Mohs hardness of 5 or more is preferable, and silica (SiO ₂ ) particles that are solid phase reaction fine particles are used. In the present embodiment, the silica particles as the abrasive grains 91 are adjusted to have an average particle size of 0.05 μm or more and less than 50 μm.

The alkali particles 92 are gradually dissolved in the supplied water to generate an alkaline polishing liquid. The alkali particle 92 is preferably a substance that exhibits strong alkalinity (for example, a pH value of 11 or more) when dissolved in water. For example, calcium hydroxide particles are used. In addition, if the alkali particles 92 exposed from the polishing surface 90a of the substrate 90 are dissolved and consumed immediately in water, the pH value of the polishing liquid is not stable. In the present embodiment, a substance having a solubility in water (pure water) at 25 ° C. of 0.17% by weight (0.17 g / 100 g H ₂ O) or less is preferable. By using a material in this range for the alkali particles 92, the alkali particles 92 exposed from the polishing surface 90a of the substrate 90 are gradually dissolved in water, so that consumption is suppressed and the pH value of the polishing liquid is stabilized. Can do. In addition, as the alkali particles 92, as long as the solubility in water (pure water) at 25 ° C. is 0.17% by weight (0.17 g / 100 g H ₂ O) or less, in addition to calcium hydroxide, carbonic acid Potassium, sodium bicarbonate, calcium oxide, magnesium oxide, barium carbonate, magnesium hydroxide, barium hydroxide, or calcium carbonate can be used.

  The pH value of the polishing liquid is adjusted to a predetermined polishing liquid range (for example, the pH value is 8.5 or more and 10 or less). Specifically, based on the pH value measured by the pH measurement unit 67, the control unit 100 controls the opening degree of the electromagnetic valve 61 and adjusts the amount of water supplied through the fluid supply path 79. That is, when the measured pH value is higher than the predetermined polishing liquid range, the amount of water supplied through the fluid supply path 79 is increased to lower the pH value. If the measured pH value is lower than the predetermined polishing liquid range, the amount of water supplied through the fluid supply path 79 is decreased to improve the pH value.

  As described above, the polishing pad 78b includes the alkali particles 92 dispersed in the base material 90, and the alkali particles 92 exposed from the polishing surface 90a of the base material 90 are dissolved in water to generate a polishing liquid. For this reason, when the number of wafers W polished increases, the alkali particles 92 exposed from the polishing surface 90a are consumed. Therefore, even if the amount of supplied water is adjusted (decreased), the pH value of the polishing liquid is within the polishing liquid range. It is assumed that the value falls below a lower threshold (for example, the pH value is 8.5). In this case, the horizontal movement unit 56 (FIG. 3) is operated, and the polishing unit 48 is moved in the horizontal direction (X direction) as shown in FIG. Further, while the polishing unit 48 is rotated, the dress unit 80 is raised, and the dressing pad 84 is brought into contact with the polishing pad 78b while the dressing pad 84 is rotated. At this time, the lifting mechanism 85 controls the pressing force so that the dressing pad 84 presses the polishing pad 78b with a predetermined pressure. Further, by operating the horizontal movement unit 56 and swinging the polishing unit 48 in the horizontal direction (X direction), the dressing pad 84 is brought into contact with the entire area of the polishing pad 78b. 90 polishing surfaces 90a are shaved. Therefore, the polishing ability of the polishing pad 78b is adjusted to an appropriate value, and the alkali particles 92 are exposed on the polishing surface 90a of the base material 90 of the polishing pad 78b. Thereby, the pH value of the polishing liquid exceeds the lower limit threshold (for example, the pH value is 8.5) of the polishing liquid range and is included in the polishing liquid range.

  Next, a wafer polishing method will be described. As shown in FIG. 2, the wafer W accommodated in the cassette 8 a is pulled out from the cassette 8 a by the first transport unit 6 and transported to the temporary placement table 14, and the center of the wafer W is aligned by the temporary placement table 14. To do.

  Subsequently, the second transport unit 18 transports the wafer W positioned on the temporary placement table 14 to the chuck table 22 positioned at the loading / unloading position A, with the surface protection tape T (FIG. 4) on the lower side. Is sucked and held by the chuck table 22. As a result, the wafer W is held by the chuck table 22 and the back surface WR is exposed. After the wafer W is sucked and held by the chuck table 22, the turntable 20 is rotated 90 degrees in the clockwise direction indicated by the arrow R. As a result, the wafer W held on the chuck table 22 is positioned at the rough grinding position B facing the grinding unit 38a for rough grinding.

  In the rough grinding of the wafer W, while rotating the chuck table 22 at, for example, 300 rpm with respect to the wafer W positioned at the rough grinding position B, the grinding wheel 46a is rotated in the same direction as the chuck table 22 at, for example, 6000 rpm, While supplying the grinding liquid, the up-and-down pulse motor 34 is operated to bring the grinding wheel for rough grinding into contact with the back surface WR of the wafer W. Then, the grinding wheel 46a is fed downward by a predetermined amount at a predetermined grinding feed speed, and rough grinding of the back surface WR of the wafer W is performed. By this rough grinding, the wafer W is ground to a desired thickness.

  When the rough grinding is finished, the turntable 20 is further rotated 90 degrees in the clockwise direction, and the wafer W after the rough grinding is positioned at the finish grinding position C. In this finish grinding, while rotating the chuck table 22 at, for example, 300 rpm, the grinding wheel 46b is rotated in the same direction as the chuck table 22 at, for example, 6000 rpm, and the lift pulse motor 34 is operated while supplying the grinding liquid to finish grinding. The grinding wheel for use is brought into contact with the back surface WR of the wafer W. Then, the grinding wheel 46b is fed downward by a predetermined amount at a predetermined grinding feed speed, and finish grinding of the back surface WR of the wafer W is performed. By this finish grinding, the wafer W is finished to a desired thickness (for example, 50 μm).

  The chuck table 22 holding the wafer W after finish grinding is positioned at the polishing position D facing the polishing unit 48 by further rotating the turntable 20 by 90 degrees in the clockwise direction, and the polishing process is performed. .

  In the polishing step, as shown in FIG. 4, polishing is performed with the polishing pad 78 b of the polishing unit 48 covering the entire back surface WR of the wafer W. In this polishing step, the electromagnetic valve 61 is opened, and water (pure water) adjusted to a predetermined flow rate (for example, 1 liter / min) from the pure water supply source 62 through the fluid supply path 79 is polished with the back surface WR of the wafer W. It is supplied to the pad 78b. This water dissolves the alkali particles 92 exposed from the polishing surface 90a of the substrate 90 of the polishing pad 78b, and a polishing liquid adjusted to a pH value within a predetermined polishing liquid range is generated. Then, a predetermined polishing condition, that is, the chuck table 22 is rotated in the direction of arrow α, for example, at 505 rpm, and the polishing pad 78b is rotated in the direction of arrow α, for example, at 500 rpm, while the polishing pad is applied to the back surface WR of the wafer W. Polishing of the back surface WR of the wafer W is performed under the polishing conditions for pressing 78b with a predetermined load (for example, 25 kPa). The above-described water supply flow rate is also included in the polishing conditions. By this polishing process, the grinding distortion generated when the back surface WR of the wafer W is ground is removed. In the polishing process, the elevating mechanism 85 lowers and retracts the dress unit 80 so that the dressing pad 84 does not come into contact with the polishing pad 78b.

  Further, during the polishing process, the polishing liquid flowing down from the chuck table 22 flows through the receiving part 63 and the drain pipe 65, and the pH value is measured by the pH measuring part 67 (pH measuring process). Here, the control unit 100 may change (correct) the polishing conditions in accordance with the measured pH value, and perform polishing under the changed polishing conditions. Specifically, the control unit 100 changes at least the polishing time of the wafer W and the amount of water supplied to the polishing pad 78b according to the pH value (polishing condition changing step, correction step). When the measured pH value is higher than a predetermined reference value, the water supply amount is increased and the polishing time of the wafer W is shortened from the predetermined reference time. When the measured pH value is lower than a predetermined reference value, the water supply amount is reduced and the polishing time of the wafer W is extended beyond the predetermined reference time. Thereby, the fluctuation | variation of the pH value of polishing liquid can be suppressed, the grinding | polishing state of the wafer W can be equalized, and the dispersion | variation in this grinding | polishing state can be reduced.

  Further, the control unit 100 determines whether or not the pH value measured during the polishing process is included in the predetermined polishing liquid range (determination process). In this determination step, when it is determined that the measured pH value is smaller than the lower limit threshold of the predetermined polishing liquid range and is not included in the polishing liquid range, the polishing unit 48 is raised when the polishing step is finished. At the same time, the rotation of the polishing unit 48 and the chuck table 22 is stopped. Then, as shown in FIG. 6, the polishing unit 48 is moved in the horizontal direction (X direction), and the polishing pad 78 b of the polishing unit 48 is disposed above the dress unit 80. With the polishing unit 48 rotated, the dress unit 80 is raised and the dressing pad 84 is brought into contact with the polishing pad 78b while the dressing pad 84 is rotated in the direction of arrow β (dressing step). Here, by swinging the polishing unit 48 in the horizontal direction (X direction), the dressing pad 84 is brought into contact with the entire area of the polishing pad 78b, so that the polishing surface 90a of the substrate 90 of the polishing pad 78b is scraped. . Therefore, the polishing ability of the polishing pad 78b is adjusted to an appropriate value, the alkali particles 92 are exposed on the polishing surface 90a of the base material 90 of the polishing pad 78b, and the pH value of the polishing liquid is the lower limit of the polishing liquid range. It exceeds the threshold (for example, pH value is 8.5) and is included in the polishing liquid range.

  When the pH value of the polishing liquid is included in the polishing liquid range, the polishing process is restarted. On the other hand, even when dressing the polishing pad 78b of the polishing unit 48, if the pH value of the polishing liquid is below the lower limit threshold of the polishing liquid range (not included in the polishing liquid range), the control unit 100 It is determined that it is impossible to adjust the pH value within the polishing liquid range. For example, an error is reported to prompt replacement of the polishing pad 78b. Thereby, since the polishing pad 78b can be replaced with a new one at an appropriate timing, the wafer W can be continuously polished appropriately. It should be noted that the determination that the pH value cannot be adjusted to the polishing liquid range can be made even when dressing is performed a plurality of times (for example, three times) or when the pH value is not included in the polishing liquid range. Good.

  The above-described embodiment includes the following wafer polishing method.

(Appendix 1)
A wafer polishing method for polishing a wafer using a polishing pad in which abrasive grains and alkali particles are mixed,
A polishing step of rotating the wafer while rotating the polishing pad in contact with the rotating wafer based on the set polishing conditions, supplying pure water to the polishing pad to generate an alkaline polishing liquid, and acting on the wafer for polishing;
A measuring step for measuring the pH value of the polishing liquid during the polishing step;
A correction step of correcting the polishing conditions based on the measured pH value,
A wafer polishing method for maintaining a constant polishing state of a wafer by polishing under a corrected new polishing condition.

  As described above, the polishing pad 78b of the present embodiment includes the abrasive grains 91 made of silica particles and the alkali particles 92 in the base material 90 made of polyurethane and non-woven fabric. Therefore, the alkaline polishing can be performed only by supplying water to the polishing pad 78b. A liquid can be produced. For this reason, it is not necessary to separately provide a polishing liquid supply source, and an alkaline polishing liquid can be easily supplied to the wafer W.

Further, according to the present embodiment, the solubility of the alkali particles 92 in water is 0.17% by weight (0.17 g / 100 g H ₂ O) or less at 25 ° C., and thus is exposed from the polishing surface 90a of the substrate 90. The alkali particles 92 are gradually dissolved in water, so that consumption of the alkali particles 92 is suppressed and the pH value of the polishing liquid can be stabilized.

  Further, in the polishing method of the wafer W of the present embodiment, since the polishing pad 78b contains the alkali particles 92 in the base material 90, an alkaline polishing liquid can be generated simply by supplying water to the polishing pad 78b. This polishing liquid can be easily supplied to the wafer W for polishing. Further, in the method for polishing the wafer W according to the present embodiment, the polishing pad 78b is rotated while contacting the rotating wafer W, and water is supplied to the polishing pad 78b to generate an alkaline polishing liquid. A polishing step of acting on the surface, a pH value of the polishing liquid, a determination step of determining whether the measured pH value is within a predetermined polishing liquid range, and the determination step, the pH value Is determined to be smaller than the lower limit threshold of the polishing liquid range and not within the polishing liquid range, the polishing pad 78b is dressed, and the pH value of the polishing liquid is set higher than the lower limit threshold and included in the polishing liquid range. And a dressing step for adjusting the pH value of the polishing liquid so that the pH value can be adjusted by dressing the polishing pad 78b in a timely manner based on the pH value of the polishing liquid. The ability to suppress the dynamic, it is possible to reduce variations in the polishing state of the wafer W.

  In addition, according to the present embodiment, when it is impossible to adjust the pH value to the polishing liquid range, the polishing pad 78b can be replaced with a new one at an appropriate timing. Can be polished.

  In the polishing method according to this embodiment, an alkaline polishing liquid is generated by supplying pure water to the polishing pad 78b, and the wafer W is polished by bringing the polishing pad 78b into contact with the wafer W. A pH measurement step for measuring the pH value of the polishing liquid during the polishing step, and at least the polishing time of the wafer W and the purity of the polishing pad 78b based on the pH value measured in the pH measurement step. And a polishing condition changing step for changing the amount of water supplied, so that fluctuations in the pH value of the polishing liquid can be suppressed, the polishing state of the wafer W can be equalized, and variations in the polishing state can be reduced. .

  As mentioned above, although one Embodiment of this invention was described, the said embodiment was shown as an example and is not intending limiting the range of invention. For example, the polishing conditions in the polishing step may include dressing conditions performed between the polishing process for the previous wafer W and the polishing process for the next wafer W. That is, when the pH value measured during the polishing process on the previous wafer W becomes smaller than the predetermined first threshold value, the notch at the time of dressing is polished before polishing the next wafer W. Dressing may be performed by increasing the amount (shaving amount) or increasing the pressing force of the dressing pad 84.

  In this embodiment, even if the polishing pad 78b is dressed, if the pH value of the polishing liquid is lower than the lower limit threshold value of the polishing liquid range (not included in the polishing liquid range), the pH value is set within the polishing liquid range. However, for example, a predetermined second threshold value that is smaller than the lower threshold value and cannot change the pH value even when the polishing conditions (such as the amount of water supplied) are changed is set. When the value falls below the second threshold value, it may be determined that the pH value cannot be adjusted to the polishing liquid range, and the polishing pad 78b may be replaced.

  In this embodiment, when the measured pH value is lower than the lower limit threshold of the polishing liquid range, the flow rate of the supplied water is changed (decreased). However, the solubility of the alkali particles depends on the temperature. Therefore, the temperature of the supplied water may be adjusted (for example, heated).

  Further, in this embodiment, when the polishing process is completed, the process is completed after being accommodated in the cassette 8b. However, after the polishing process, a gettering layer generation for the purpose of generating a gettering layer on the back surface WR of the wafer W You may implement a process. The gettering layer captures impurity atoms mainly composed of metals such as copper (Cu) contained in the wafer W to protect the device DB from contamination by impurities. For this reason, when the device DB is, for example, a memory (such as a flash memory or a DRAM (Dynamic Random Access Memory)), contamination by impurities is prevented by providing a gettering layer on the back surface WR of the wafer W. Can do. In the gettering layer generation step, since an alkaline polishing liquid is unnecessary, for example, the supply amount of water is increased to keep the pH value close to 7. When the gettering layer generation step is performed, the base material 90 of the polishing pad 78b further includes green carborundum (GC) abrasive grains (not shown) having an average particle diameter of 0.35 to 1.5 μm. You may use things. Further, the above-described green carborundum (GC) abrasive grains may be mixed into water during the gettering layer generation step. Since this gettering layer generation step is an additional step that is performed following the polishing step, the gettering layer generation step may be terminated without performing the gettering layer generation step.

  In the present embodiment, the fixed abrasive polishing pad in which the abrasive grains 91 are fixed to the base material 90 is exemplified as the polishing pad 78b. However, the abrasive grains 91 are supplied in a state where the abrasive grains 91 are dispersed in water. You may use the polishing pad which consists of a base material which is not fixing.

2 Grinding and polishing apparatus 38a, 38b Grinding unit 48 Polishing unit 56 Horizontal moving unit 61 Solenoid valve 62 Pure water supply source 63 Receiving part 65 Drain pipe 67 pH measuring part 78b Polishing pad 79 Fluid supply path 80 Dressing unit 84 Dressing pad 85 Elevating mechanism 90 Substrate 90a Polishing surface 91 Abrasive grain 92 Alkali particle 100 Control unit W Wafer WR Back surface WS Surface

Claims (2)

A method for polishing a wafer by polishing a wafer using a polishing pad in which abrasive grains and alkali particles are mixed in a substrate,
A polishing step of rotating while bringing the polishing pad into contact with the rotating wafer, supplying water to the polishing pad to generate an alkaline polishing liquid and acting on the wafer for polishing;
A determination step of measuring the pH value of the polishing liquid and determining whether the measured pH value is within a predetermined polishing liquid range;
In the determination step, when it is determined that the pH value is smaller than the lower threshold value of the polishing liquid range and not in the polishing liquid range, the polishing pad is dressed, and the pH value of the polishing liquid is set larger than the lower threshold value. Dressing step for adjusting to be included in the polishing liquid range,
A method for polishing a wafer, comprising:   The wafer polishing method according to claim 1, wherein when the pH value cannot be adjusted to the polishing liquid range, the polishing pad is replaced.

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