JP2018060873A - Processing method for wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a processing method for a wafer, whereby productively and processability can be improved in polishing a recessed part of a wafer that has a ring-like reinforcement part on its rear surface.SOLUTION: A processing method for a wafer W having a device area W1 where a plurality of devices are formed and an outer peripheral margin area W2 surrounding the device area W1, comprises: a step in which a ring-like reinforcement part W4 including the outer peripheral margin area W2 is formed on an outer peripheral side of a recessed part W3 by holding a surface WS side of the wafer W on a chuck table 22, and grinding an area, corresponding to a device area, of a rear surface WR of the wafer W, thereby forming the recessed part W3; and a step in which the recessed part W3 is polished by, while supplying polishing liquid to the rear surface WR, rotating the chuck table 22 and a polishing pad 78b with a diameter equal to or larger than the wafer W, and pressing the polishing pad 78b against the rear face of the wafer W.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a wafer processing method.

  In general, in a device manufacturing process, after the back surface of a wafer is ground to process the wafer to a desired thickness, a polishing process is performed to increase the flatness and the strength of the chip. In particular, in a memory device or the like, it is necessary to form a gettering layer that captures metal after the device is formed. The wafer to be polished is being thinned and has a thickness of about several tens of μm. As a result, in the polishing process and the gettering layer forming process, the possibility that the wafer is damaged increases. On the other hand, so-called TAIKO (registered trademark) grinding is known as a process for improving handling properties while grinding a wafer extremely thin (see, for example, Patent Document 1). TAIKO grinding is a technique in which a central portion corresponding to a region where a device is provided is ground on the back surface of a wafer to form a concave portion and ground to a shape having a ring-shaped reinforcing portion on the outer peripheral portion.

JP 2009-176896 A

  In a wafer subjected to TAIKO grinding, it is necessary to remove grinding distortion generated on the back surface of the wafer by grinding after grinding. For example, when polishing the back surface of a wafer using a polishing pad having a diameter smaller than that of the recess, the polishing pad cannot cover the entire surface of the recess at the same time, resulting in poor productivity and the outer periphery of the recess along the ring-shaped reinforcing portion. Therefore, there is a problem that an area that cannot be polished sufficiently or cannot be polished sufficiently.

  Therefore, an object of the present invention is to provide a wafer processing method capable of improving productivity and workability when a concave portion of a wafer having a ring-shaped reinforcing portion on the back surface is polished.

  In order to solve the above-described problems and achieve the object, the present invention is a wafer processing method including a device region in which a plurality of devices are formed on a surface and an outer peripheral surplus region surrounding the device region, A ring shape including the outer peripheral surplus region on the outer peripheral side of the concave portion by holding the front surface side of the wafer on the chuck table and grinding a region corresponding to the device region on the rear surface of the wafer to form a concave portion. A ring-shaped reinforcing portion forming step for forming a reinforcing portion, and holding the front side of the wafer on the chuck table, exposing the concave portion and supplying a polishing liquid to the back surface, and at least equivalent to the chuck table and the wafer A polishing step of polishing the recess by rotating the polishing pad having a diameter and pressing the polishing pad against the back surface of the wafer.

  According to this configuration, by using a polishing pad having a diameter equal to or larger than that of the wafer, the concave portion and the ring-shaped reinforcing portion can be simultaneously polished, so that the vicinity of the outer peripheral edge of the concave portion along the ring-shaped reinforcing portion can be obtained. Polishing can be sufficiently performed, and the productivity of the wafer can be improved.

  Further, in this configuration, after performing the polishing step, the polishing pad is rotated and pressed while supplying a rinse liquid different from the polishing liquid to the back surface of the rotating wafer, and a gettering layer is formed in the recess. You may provide the gettering layer formation process to form.

  According to the present invention, since the recess and the ring-shaped reinforcing portion can be polished simultaneously by using a polishing pad having a diameter equal to or larger than that of the wafer, the outer periphery of the recess along the ring-shaped reinforcing portion is close to the vicinity. Polishing can be sufficiently performed, and the productivity of the wafer can be improved.

FIG. 1 is a perspective view showing a device wafer to be processed by the wafer processing method according to the present embodiment. FIG. 2 is a perspective view showing an example of a grinding and polishing apparatus that executes the wafer processing method according to the present embodiment. FIG. 3 is a perspective view showing a state in which the back surface of the wafer is ground by the grinding unit. FIG. 4 is a side sectional view showing the ground wafer. FIG. 5 is a perspective view showing the configuration of the polishing unit. FIG. 6 is a schematic diagram showing a peripheral configuration of the polishing unit. FIG. 7 is a schematic view showing a state where the back surface of the wafer is polished in the configuration of FIG. FIG. 8 is a schematic diagram showing a state of the polishing pad when the back surface side of the wafer is polished. FIG. 9 is a diagram illustrating an observation position of a grinding mark. FIG. 10 is a schematic diagram showing a modification of the wafer. FIG. 11 is a schematic diagram showing a modification of the wafer. FIG. 12 is a schematic diagram showing a peripheral configuration of a polishing unit according to another embodiment.

  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 processed by the wafer processing method according to the present embodiment. In the wafer processing method according to the present embodiment, so-called TAIKO grinding is performed on a device wafer (hereinafter referred to as a wafer) W, and grinding distortion is removed by polishing. 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 device area W1 in which a device DB is formed in an area partitioned by a plurality of streets (division lines) S formed in a lattice pattern on the surface WS, and an outer peripheral surplus area W2 that surrounds the device area W1. It has. In FIG. 1, the boundary between the device region W1 and the outer peripheral surplus region W2 is indicated by a one-dot chain line for convenience, but there is actually no line at the boundary. A notch WA indicating the crystal orientation of the wafer W is formed on the outer peripheral edge of the wafer W.

  The wafer W performs a polishing process after grinding a region corresponding to the device region W1 in the back surface WR on the back side of the front surface WS to a predetermined thickness. The wafer W may be a plate-like workpiece to be ground and polished, and may be a semiconductor substrate made of a material other than silicon (for example, gallium arsenide).

  FIG. 2 is a perspective view showing an example of a grinding and polishing apparatus that executes the wafer processing method according to the present embodiment. The grinding / polishing apparatus 2 is a fully automatic processing apparatus, and under the control of the control unit 100, the wafer W is brought into the carry-in process, rough grinding process, finish grinding process, polishing process, gettering layer process, cleaning process, A series of operations including carry-out processing is configured to be performed fully automatically.

  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 the wafer W can be rough ground or finish ground by contacting the back surface side of the wafer W while supplying a grinding liquid such as pure water. . 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 and generating the gettering layer G (FIG. 1) on the back surface is provided. .

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

  Next, the grinding unit will be described. FIG. 3 is a perspective view showing a state in which the back surface of the wafer is ground by the grinding unit, and FIG. 4 is a side sectional view showing the ground wafer. The grinding unit 38a (38b) grinds the back surface WR side of the wafer W as described above. As shown in FIG. 3, the wafer W has a surface protection tape T attached to the surface WS side to protect the device DB (FIG. 1), and is held by the chuck table 22 via the surface protection tape T. The The grinding unit 38a (38b) includes a grinding wheel 46a (46b) provided with a grinding wheel for rough grinding (for finish grinding). The grinding wheel 46a (46b) is formed so that the outer diameter is larger than the radius of the device region W1 of the wafer W and smaller than the diameter of the device region W1.

  In the present embodiment, while rotating the chuck table 22 and lowering the grinding wheel 46a while rotating, the rotating grinding wheel comes into contact with the back surface WR of the rotating wafer W to perform grinding. At this time, for example, control is performed so that the grinding wheel of the grinding wheel 46a is always brought into contact with the rotation center of the back surface WR of the wafer W and is not brought into contact with the back surface side of the outer peripheral surplus area W2 of the wafer W. By such control, only the central region corresponding to the device region W1 in the back surface WR is ground, and as shown in FIGS. 3 and 4, a recess W3 is formed on the back surface WR, and the outer peripheral surplus region W2 is formed. A ring-shaped reinforcing portion W4 having the same thickness as that before grinding is left and formed in the portion corresponding to. Although exaggerated in FIGS. 3 and 4, for example, when the diameter of the wafer W is 300 mm, the width of the ring-shaped reinforcing portion W4 may be about 2 to 3 mm. Further, the thickness of the ring-shaped reinforcing portion W4 is preferably several hundred μm. On the other hand, the thickness of the recess W3 can be reduced to about 10 to 100 μm.

  FIG. 5 is a perspective view showing a configuration of the polishing unit, and FIG. 6 is a schematic diagram showing a peripheral configuration of the polishing unit. FIG. 7 is a schematic view showing a state where the back surface of the wafer is polished in the configuration of FIG. As shown in FIG. 5, 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.

As the polishing pad 78b, for example, a fixed abrasive type polishing pad in which abrasive grains are dispersed in a base material made of urethane and / or nonwoven fabric and fixed with an appropriate liquid binder can be suitably used. As the fixed-abrasive polishing pad, for example, silica (SiO ₂ ) particles as solid-phase reaction fine particles or those containing GC (Green Carbide) abrasive grains in addition to silica particles in the above-described base material are preferable. . The solid-phase reaction fine particles are not limited to silica, and ceria (CeO ₂ ), zirconia (ZeO ₂ ), or the like may be used. The abrasive grains only need to have a 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. Preferably, for example, abrasive grains such as diamond, alumina, ceria, cBN (cubic boron nitride) may be included instead of the GC abrasive grains.

  As shown in FIG. 6, the polishing unit 48 includes a fluid supply path 79 that passes through the spindle 74, the wheel mount 76, and the wheel base 78a. The fluid supply path 79 is a flow path for supplying a polishing liquid or a rinse liquid to the back surface WR of the wafer W held and exposed by the chuck table 22. The fluid supply path 79 is connected to an unillustrated electromagnetic switching valve. The polishing liquid supply source and the rinse liquid supply source are selectively connected. The polishing liquid is a liquid that is supplied when polishing the back surface WR of the wafer W, and includes a substance that can cause chemical reaction with the wafer W and perform CMP (Chemical Mechanical Polishing). It is. In this embodiment, since the wafer W is a silicon wafer, for example, an alkaline polishing liquid is used. The rinsing liquid is a liquid that is supplied when the gettering layer G (FIG. 1) is generated on the back surface WR of the wafer W, and is composed of only a substance that does not substantially cause a chemical reaction with the wafer W. Pure water is used.

  In this embodiment, as shown in FIGS. 6 and 7, the polishing pad 78b 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. The wafer W is disposed eccentrically with respect to the chuck table 22 while covering the entire rear surface WR of the wafer W. Specifically, the polishing pad 78b is disposed so as to cover the ring-shaped reinforcing portion W4 and the concave portion W3 on the back surface WR of the wafer W, and the ring-shaped reinforcing portion W4 and the concave portion W3 are simultaneously polished by the single polishing pad 78b. To do. In the present embodiment, the gettering layer G (FIG. 1) is generated on the back surface WR of the wafer W with the same arrangement relationship between the polishing pad 78b and the wafer W.

  Next, a wafer processing 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 aligned with the temporary placement table 14 to the chuck table 22 positioned at the loading / unloading position A, and the chuck table 22 with the surface protection tape T on the lower side. Is held by suction. 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. At this time, for example, the grinding wheel 46a is controlled so that the grinding wheel of the grinding wheel 46a is always in contact with the rotation center of the back surface WR of the wafer W and is not brought into contact with the back surface side of the outer peripheral surplus area W2 of the wafer W. A predetermined amount is fed downward at a grinding feed rate, and rough grinding of the back surface WR of the wafer W is performed. By such control, as shown in FIG. 3, only the central region corresponding to the device region W1 in the back surface WR is ground to form the concave portion W3, and the outer peripheral surplus region W2 around the concave portion W3. The ring-shaped reinforcing portion W4 including the remaining portion is formed (ring-shaped reinforcing portion forming step). Since this ring-shaped reinforcing portion W4 is not ground, it has the same thickness as before grinding.

  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. Also in this case, for example, the grinding wheel 46b is controlled so that the grinding wheel of the grinding wheel 46b is always in contact with the rotation center of the back surface WR of the wafer W and is not brought into contact with the back surface side of the outer peripheral surplus area W2 of the wafer W. Is fed downward by a predetermined amount at a predetermined grinding feed rate, and finish grinding of the back surface WR of the wafer W is performed. By this finish grinding, the recess W3 of the wafer W is finished to a desired thickness (for example, 30 μm). In the present embodiment, the ring-shaped reinforcing portion forming step includes not only rough grinding but also finish grinding.

  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. 7, the polishing is performed in a state where the polishing pad 78b of the polishing unit 48 covers the entire back surface WR of the wafer W. In this polishing step, the fluid supply path 79 is connected to the polishing liquid supply source 62 via the electromagnetic switching valve 61, and supplies an alkaline polishing liquid to the back surface WR of the wafer W and the polishing pad 78b through the fluid supply path 79. 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 78b is applied to the back surface WR of the wafer W with a predetermined load (for example, 25 kPa). And the back surface WR of the wafer W is polished. By this polishing process, the grinding distortion generated when the back surface WR of the wafer W is ground in the above-described ring-shaped reinforcing portion forming process is removed. In this polishing step, since the base material of the polishing pad 78b elastically deforms following the shape of the back surface WR of the back surface WR of the wafer W, almost the entire surface of the concave portion W3 and the ring-shaped reinforcing portion W4 can be polished simultaneously. The polishing time can be shortened and the productivity of the polishing process can be improved.

  Further, in the wafer processing method according to the present embodiment, a gettering layer forming step of forming a gettering layer on the back surface WR can be executed following the polishing step of polishing the back surface WR of the wafer W. This gettering layer forming step can be performed using the polishing unit 48 as in the polishing step. 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 forming step, although not shown, the electromagnetic switching valve 61 is switched to connect the rinsing liquid supply source 63 to the fluid supply path 79, and the rinsing liquid (pure water) is passed through the fluid supply path 79 to the wafer. W is supplied to the back surface WR of W and the polishing pad 78b. As in the polishing step, the chuck table 22 is rotated in the direction of arrow α, for example, at 505 rpm, and the polishing pad 78 b is rotated on the back surface WR of the wafer W, while the polishing pad 78 b is rotated in the direction of arrow α, for example, 500 rpm. Then, the gettering layer is formed on the back surface WR (concave portion W3) of the wafer W by pressing with a predetermined load (for example, 5 kPa) smaller than the polishing step. Since this gettering layer forming step is an additional step that is performed following the polishing step, the gettering layer forming step may be terminated without performing the gettering layer forming step.

  Next, the hardness of the base material of the polishing pad 78b and the polishing region of the recess W3 of the wafer W will be described. FIG. 8 is a schematic diagram illustrating a state of the polishing pad when the back surface side of the wafer is polished, and FIG. 9 is a diagram illustrating an observation position of a grinding mark. As described above, the wafer W of the present embodiment is configured to include the concave portion W3 and the ring-shaped reinforcing portion W4 on the back surface WR. For this reason, as shown in FIG. 8, when simultaneously polishing the concave portion W3 and the ring-shaped reinforcing portion W4 of the wafer W, the polishing pad 78b elastically deforms following the shape of the wafer W. Here, since the ring-shaped reinforcing portion W4 is at a predetermined height H1 (for example, several hundred μm) higher than the concave portion W3, the outer peripheral portion W3A of the concave portion W3 along the ring-shaped reinforcing portion W4 is polished. It is assumed that the pad 78b does not come into contact and an area that cannot be polished or cannot be sufficiently polished is generated.

  In view of this problem, the inventor conducted sharp research on the hardness of the base material of the polishing pad 78b and the polishing region of the recess W3. Specifically, using a wafer W in which a ring-shaped reinforcing portion W4 is formed around the concave portion W3, a grinding mark (Saw Mark) at the time of finish grinding remaining on the outer peripheral portion W3A of the concave portion W3 is observed to form a ring shape. The distance L2 from the inner wall W4A of the reinforcing portion W4 to the position where the grinding mark remains was measured. In this embodiment, as an example of the wafer W, a silicon wafer having a diameter of 300 mm, a width L1 of the ring-shaped reinforcing portion W4 of 2.1 mm, and a height H1 of the ring-shaped reinforcing portion W4 from the concave portion W3 of 625 μm is used. . In this case, the ratio L1 / H1 between the width L1 and the height H1 is preferably 3 or more and 4 or less, and in this example, L1 / H1 = 3.36. As shown in FIG. 9, the grinding marks were observed at four locations every 90 degrees including the position corresponding to the notch WA of the wafer W. In addition, an optical microscope was used to observe the grinding marks.

  Here, in a conventional configuration using a wafer W having the same shape and a polishing pad having a smaller diameter (for example, 150 mm) than the wafer W, the distance from the inner wall W4A of the ring-shaped reinforcing portion W4 to the position where the grinding mark remains. L2 was about 0.6 mm (600 μm).

  In contrast, in the present embodiment, two polishing pads 78b having high hardness (49 in A hardness) and low hardness (46 in A hardness) are prepared, and the recess W3 of the wafer W is formed using each polishing pad. Polished. About the wafer W after grinding | polishing, the grinding trace was observed in the position of (1)-(4) of FIG. These observation results are shown in Table 1.

  As shown in Table 1, in the configuration in which the recess W3 and the ring-shaped reinforcing portion W4 of the wafer W are simultaneously polished using the polishing pad 78b having a diameter larger than that of the wafer W, the conventional configuration is used regardless of the hardness value. Further, the distance L2 (polishing distance in Table 1) to the position where the grinding mark remains is shortened, and is less than 1/4 of the conventional distance. In this example, a polishing pad with a low A hardness has a greater effect, and the distance L2 to the position where the grinding mark remains can be reduced to 1/8 or less as compared with the conventional configuration, and the recess W3 is polished. The area can be made larger. Further, since the concave portion W3 and the ring-shaped reinforcing portion W4 of the wafer W are polished at the same time, the polishing time is shortened and the polishing time in the conventional configuration is about 5 minutes. Then, it was shortened to about 90 seconds. In addition, the effect of reducing the variation in the removal amount (polishing rate) in the wafer W was also observed.

  In this embodiment, a wafer W having a width L1 of the ring-shaped reinforcing portion W4 of 2.1 mm and a height H1 of the ring-shaped reinforcing portion W4 from the concave portion W3 of 625 μm (L1 / H1 = 3.36) is used. It is not limited to. From the viewpoint of easy follow-up of the polishing pad, it is more preferable that the height H1 of the ring-shaped reinforcing portion W4 is low and / or the inner wall of the ring-shaped reinforcing portion W4 is formed in an inclined shape. FIG. 10 and FIG. 11 are schematic views showing modifications of the wafer W. FIG. As shown in FIG. 10, a wafer W in which the height H1 of the ring-shaped reinforcing portion W4 from the recess W3 is lower than that in the example of FIG. 8 may be used. Further, as shown in FIG. 11, the inner wall W4A of the ring-shaped reinforcing portion W4 may be formed as an inclined surface that is inclined from the ring-shaped reinforcing portion W4 toward the center.

  According to this embodiment, the polishing pad 78b having a diameter larger than that of the wafer W is used to cover the entire back surface WR of the wafer W, and the recess W3 and the ring-shaped reinforcing portion W4 are polished simultaneously. Time was shortened and the workability and productivity of the wafer W were improved. Further, by simultaneously polishing the concave portion W3 and the ring-shaped reinforcing portion W4, it is possible to sufficiently polish the vicinity of the outer peripheral portion of the concave portion W3 along the ring-shaped reinforcing portion W4. The number of can be increased. Further, by performing polishing using the polishing pad 78b, the flatness of the polished wafer W (recessed portion W3) can be improved as compared with, for example, a configuration in which grinding distortion is removed by wet etching (stress relief). .

  Further, according to the present embodiment, after performing the polishing step, the polishing pad 78 is rotated and pressed while supplying a rinse liquid different from the polishing liquid to the rotating back surface WR of the wafer W, and gettering is performed in the recess W3. Since the gettering layer forming step for forming the layer is provided, the gettering layer can be easily formed using the same polishing pad 78b as that in the polishing step.

  Next, another form of the polishing unit will be described. FIG. 12 is a schematic diagram showing a peripheral configuration of a polishing unit according to another embodiment. In another form, the polishing unit 148 performs polishing by partially covering the back surface WR of the wafer W with a polishing pad 178b, as shown in FIG. Since the spindle housing 172, the spindle 174, the wheel mount 176, the polishing wheel 78, and the wheel base 178a provided in the polishing unit 148 have the same configuration as each part of the polishing unit 48 described above, description thereof is omitted. The polishing pad 178b is formed to have a large diameter equal to or larger than that of the wafer W (for example, wafer W; 300 mm, polishing pad; 300 mm), and the polishing unit 148 is arranged to be greatly eccentric with respect to the chuck table 22. Specifically, the polishing pad 178b is arranged so that the outer peripheral portion of the polishing pad 178b covers the center of the back surface WR of the wafer W and extends (extends) in the radial direction from the back surface WR of the wafer W. In this state, by rotating the chuck table 22 and the polishing unit 148, the polishing pad 178b partially presses the back surface WR of the wafer W, and the concave portion W3 and the ring-shaped reinforcing portion W4 of the wafer W are simultaneously polished.

  Further, as shown in FIG. 12, a machining liquid supply nozzle 60 for supplying a polishing liquid or a rinsing liquid to the back surface WR of the wafer W held and exposed by the chuck table 22 is disposed in the vicinity of the polishing wheel 178. The machining liquid supply nozzle 60 is selectively connected to a polishing liquid supply source 62 and a rinsing liquid supply source 63 via an electromagnetic switching valve 61. Also in this configuration, the polishing pad 178b partially presses the back surface WR of the wafer W, and the concave portion W3 of the wafer W and the ring-shaped reinforcing portion W4 are simultaneously polished, so that the concave portion W3 along the ring-shaped reinforcing portion W4. Therefore, the number of chips cut out from the wafer W can be increased accordingly. Further, by polishing using the polishing pad 178b, for example, the polished wafer W can be compared with a configuration (stress relief) in which a small-diameter polishing pad is brought into contact with only the recess of the wafer W to remove grinding distortion. The flatness of (concave portion W3) can be improved.

  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, in this embodiment, the ring-shaped reinforcing portion forming step and the polishing step are performed using the grinding and polishing apparatus 2 including the grinding units 38a and 38b for rough grinding and finish grinding and the polishing unit 48. Of course, for example, the ring-shaped reinforcing portion forming step and the polishing step may be executed by separate apparatuses each having a grinding unit and a polishing unit.

  Moreover, in this embodiment, although the fixed abrasive polishing pad which fixed the abrasive grain in the base material which consists of urethane and / or a nonwoven fabric was illustrated as the polishing pad 78b, in the state which disperse | distributed the abrasive grain to polishing liquid. The wafer W may be polished using a polishing pad that is supplied and not fixed with abrasive grains.

2 Grinding and polishing equipment 22 Chuck table 38a and 38b Grinding unit 46a and 46b Grinding wheel 48 and 148 Polishing unit 78 and 178 Polishing wheel 78b and 178b Polishing pad W Wafer W1 Device area W2 Outer peripheral area W3 Recessed part W3A Outer part W4 Ring-shaped reinforcement Part W4A Inner wall WR Back side

Claims (2)

A wafer processing method comprising a device region in which a plurality of devices are formed on a surface and an outer peripheral surplus region surrounding the device region,
A ring shape including the outer peripheral surplus region on the outer peripheral side of the concave portion by holding the front surface side of the wafer on the chuck table and grinding a region corresponding to the device region on the rear surface of the wafer to form a concave portion. A ring-shaped reinforcing portion forming step for forming the reinforcing portion;
The front surface side of the wafer is held on a chuck table, the recess is exposed, and the polishing pad is rotated to rotate the chuck table and a polishing pad having a diameter equal to or larger than that of the wafer while supplying a polishing liquid to the back surface. A polishing step of polishing the recess by pressing against the back surface of the wafer;
A method for processing a wafer.   Forming a gettering layer that forms a gettering layer in the recess by rotating the polishing pad while supplying a rinsing liquid different from the polishing liquid to the back surface of the rotating wafer after performing the polishing step The wafer processing method according to claim 1, comprising a step.

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