JP4906445B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a method for processing a wafer that is easy to handle even if formed thin.

  A wafer in which a device region in which a plurality of devices such as IC and LSI are formed and an outer peripheral surplus region surrounding the device region is formed on the surface is divided into individual devices by a dividing device such as a dicing device. Used for various electronic devices such as personal computers. In order to reduce the weight and size of the electronic device, the back surface of the wafer is ground by a grinding device, and the thickness of the wafer is reduced to 100 μm or less, and further to about 50 μm or less.

  Here, if the wafer is thinly ground, it becomes difficult to handle and may be damaged during transportation. Therefore, only the back surface corresponding to the device area of the wafer is ground, and the back surface corresponding to the outer peripheral surplus area surrounding the device area is ground. A technique for forming a ring-shaped reinforcing portion on the outer periphery has been proposed (see, for example, Patent Document 1 and Japanese Patent Application No. 2006-069118).

JP-A-5-121384

  By the way, this type of wafer grinding uses a grinding wheel provided with an annular grinding wheel positioned inside a ring-shaped reinforcing portion to be formed through the rotation center of the wafer held by the chuck table. Therefore, the grinding wheel has a relatively small outer diameter that is equal to or smaller than the radius of the chuck table (wafer) as compared with a simple surface grinding wheel. For this reason, the entire grinding wheel always overlaps with the holding surface (wafer) of the chuck table, and if the grinding is performed with the wheel rotation axis orthogonal to the wafer surface, the in-wafer thickness can be made uniform. Not only the semi-arc-shaped grinding line to be brought into contact with but also the opposite semi-arc-shaped non-grinding line is in contact with the wafer, resulting in a wrinkle-shaped streak (cross-grinding mark) on the ground surface of the wafer, There is a problem that it takes time to remove the streak by etching or the like in the next step.

  On the other hand, when grinding is performed by tilting the wheel rotation axis from the perpendicular direction to the wafer surface and bringing only the semicircular arc grinding line side into contact with the wafer, the non-grinding line side opposite to the grinding line is on the wafer side. Although it is possible to eliminate the occurrence of wrinkle-shaped streaks that float from the surface, the gap between the grinding line of the relatively small-diameter annular grinding wheel constituting the grinding wheel and the wafer surface held by the chuck table is uneven. Therefore, there is a problem that the thickness in the wafer surface on the back surface corresponding to the device region varies, and the thickness in the wafer surface cannot be made uniform.

  The greater the inclination of the wheel rotation axis, the greater the variation in the in-plane thickness of the wafer. The smaller the inclination of the wheel rotation axis, the more serious the occurrence of wrinkle-shaped streaks and the intermediate inclination of the wheel rotation axis. As a result, the wafer in-plane thickness varies, and the wrinkle-shaped streaks are partially generated.

  The present invention has been made in view of the above, and when grinding only the back surface corresponding to the device region so as to form a ring-shaped reinforcing portion on the outer periphery of the wafer, a streak of a candy shape is generated. It is another object of the present invention to provide a method for processing a wafer that can make the in-plane thickness uniform.

In order to solve the above-described problems and achieve the object, a wafer processing method according to the present invention includes a rotatable chuck table having a holding surface for holding a wafer, and grinding the wafer held on the holding surface. A grinding device including a grinding means for rotatably supporting a grinding wheel in which a grinding wheel to be rotated is arranged in an annular shape, and a device region in which a plurality of devices are formed and an outer peripheral heel region surrounding the device region A wafer processing method in which a back surface corresponding to the device region of a wafer formed on a front surface is ground to form a ring-shaped reinforcing portion on the back surface corresponding to the outer peripheral ridge region. An annular holding surface grinding wheel disposed on a holding surface grinding wheel having a wheel rotation axis that is slightly inclined relative to the wheel passes through the center of rotation of the holding surface. A holding surface grinding step in which the holding surface is ground with the holding surface grinding wheel and the region from the rotation center to the outer peripheral portion of the holding surface is ground into a slightly concave shape, and the holding surface grinding. A step of performing the step after the step is performed at least once with respect to the chuck table, wherein a wafer grinding wheel disposed on a wafer grinding wheel having the wheel rotation shaft that is relatively slightly inclined is The holding surface that passes through the center of rotation of the wafer held on the holding surface and the outer peripheral portion of the wafer grinding wheel is positioned at the boundary between the device region and the outer peripheral excess region of the wafer held on the holding surface. A wafer grinding step of grinding the back surface of the wafer held on the wafer, and an outer diameter D1 of the holding surface grinding wheel used in the holding surface grinding step is: When the outer diameter and D2, the outer diameter of the wafer grinding wheel was D3,
D3 ≦ D1 <D2
It is characterized by satisfying the following relationship.

  The wafer processing method according to the present invention is characterized in that, in the above invention, the depth of the concave shape formed in the holding surface grinding step is 1 μm to 20 μm.

  The wafer processing method according to the present invention is characterized in that, in the above-described invention, a protective tape is attached to the surface of the wafer and held on the holding surface in the wafer grinding step.

  According to the wafer processing method of the present invention, the chucking is performed in the holding surface grinding process using the holding surface grinding wheel having a wheel diameter substantially the same as the wheel diameter for actually grinding the wafer using the wafer grinding wheel in the wafer grinding process. By grinding the holding surface of the table and grinding the area from the rotation center to the outer periphery of the holding surface to a slightly concave shape, when grinding the wafer with the wafer grinding wheel, the annular wafer grinding The distance between the processing line of the grinding wheel and the holding surface can be made almost equal, the wafer surface can be ground uniformly, and the rotation axis of the chuck table and the wheel rotation axis are relative to each other. Is slightly inclined to the wafer surface on the non-grinding line side opposite to the grinding line of the wafer grinding wheel that actually grinds the wafer. This makes it possible to increase the amount of relief and make it difficult to touch, so that only the grinding line has a grinding action. There is an effect that a semicircular arc can be formed radially.

  Hereinafter, a wafer processing method which is the best mode for carrying out the present invention will be described with reference to the drawings.

  First, a wafer that is an object to be ground in the present embodiment will be described. The surface Wa of the wafer W shown in FIG. 1 has a device region W1 and an outer peripheral surplus region W2. A plurality of devices D partitioned by streets S are formed in the device region W1, and an outer peripheral surplus region W2 in which no device D is formed is formed on the outer peripheral side of the device region W1. This device region W1 is surrounded by the outer peripheral surplus region W2. As shown in FIG. 2, a protective tape T is attached to the front surface Wa of the wafer W to protect the device D when the rear surface Wb of the wafer W is ground into a concave shape.

  Thereafter, the portion corresponding to the device region W1 in the back surface Wb of the wafer W, that is, the back side of the device region W1, is ground to a desired thickness. For this grinding, for example, a grinding apparatus 1 shown in FIG. 3 can be used.

  FIG. 3 is an external perspective view showing an example of a grinding apparatus for carrying out the wafer processing method of the present embodiment. The grinding apparatus 1 of the present embodiment includes a rotatable chuck table 20 having a holding surface 21 for holding a wafer W, and a wafer grinding wheel 31 for grinding the back surface Wb of the wafer W held on the chuck table 20. Grinding means 30 for rotatably supporting a wafer grinding wheel 32 arranged in an annular shape, and a grinding feed means 40 for grinding and feeding the grinding means 30 in the Z-axis direction are provided.

  First, the chuck table 20 is rotatable with a rotation shaft connected to a drive source (not shown). The chuck table 20 is provided so as to be movable in the X-axis direction by a feed mechanism such as a ball screw, nut, pulse motor or the like. The holding surface 21 is for sucking and holding the wafer W by a suction force from a suction source (not shown).

  The grinding means 30 includes a wafer grinding wheel 32 in which a plurality of wafer grinding wheels 31 are annularly divided at the lower end, a housing 33, and a wafer grinding wheel rotatably attached to the lower end of the housing 33. A mount 34 that supports the wheel 32, a wheel rotation shaft 35 that supports and rotates the mount 34, a motor 36 that rotationally drives the wheel rotation shaft 35, and a moving base 37 on which a housing 33 is mounted. The movable base 37 has a guided rail 37a. The guided rail 37a is movably fitted to a guide rail 9a provided on the support plate 9 of the housing 8 so that the grinding means 30 can move in the vertical direction (Z It is supported so as to be movable in the axial direction).

  Here, the wafer grinding wheel 31 (wafer grinding wheel 32) used in the present embodiment has an outermost diameter of the rotation locus larger than the radius of the device region W1 and smaller than the diameter of the device region W1, and is rotated. The diameter of the innermost circumference of the locus is formed to be smaller than the radius of the device region W1. For this reason, when the outer diameter of the wafer W, which is a workpiece, is D2, and the outer diameter of the wafer grinding wheel 31 (wafer grinding wheel 32) is D3, it is set so as to satisfy the relationship of D3 <D2. Yes. For example, when the outer diameter D2 of the wafer W is 200 mm, the outer diameter D3 of the wafer grinding wheel 31 (wafer grinding wheel 32) is set such that D3 = 100 mm.

  The grinding feed means 40 is for grinding and feeding the grinding wheel 32 in the Z-axis direction by moving the moving base 37 of the grinding means 30 along the guide rail 9a. The grinding feed means 40 includes a male screw rod 41 which is disposed on the support plate 9 in parallel with the guide rail 9a in the vertical direction and is rotatably supported, a pulse motor 42 for rotationally driving the male screw rod 41, a moving base 37 and a female screw block (not shown) that is fitted to the male screw rod 41.

  Furthermore, as is well known, the grinding apparatus 1 according to the present embodiment has cassettes 51 and 52 for accommodating the wafer W on the front side of the housing 8, and the wafer W before being ground from the cassette 51 or the wafer W after being ground. Loading / unloading means 53 for loading the wafer W into the cassette 52, positioning means 54 for aligning the center of the wafer W, loading means 55 for loading the wafer W before grinding to the chuck table 20, and grinding from the chuck table 20 An unloading means 56 for unloading the finished wafer W and a cleaning means 57 for cleaning the wafer W after grinding are provided. Further, in the vicinity of the chuck table 20, there is provided a grinding water supply means 58 that supplies grinding water toward a processing point of the wafer W and the grinding wheel 31 during grinding by the grinding wheel 32.

  Next, a basic grinding method of the back surface Wb corresponding to the device region W1 of the wafer W using such a grinding apparatus 1 will be described. When grinding the back surface Wb of the wafer W, the wafer W is in a state where the protective tape T side of the front surface Wa is sucked and held by the holding surface 21 of the chuck table 20 and the back surface Wb is exposed. Then, while the chuck table 20 is rotated counterclockwise at a rotational speed of, for example, 300 rpm, the grinding means 30 is rotated by the grinding feed of the grinding feed means 40 while the grinding wheel 32 is rotated counterclockwise at a rotational speed of, for example, 6000 rpm. By descending, the rotating grinding wheel 31 is pressed against the back surface Wb of the wafer W to perform grinding.

  At this time, the annular grinding wheel 31 for grinding the wafer passes through the center of rotation of the back surface Wb of the wafer W and is inside the ring-shaped reinforcing portion to be formed (boundary portion between the device region W1 and the excess outer region W2). By positioning, the grinding wheel 31 for wafer grinding is controlled so that it always contacts the rotation center of the back surface Wb of the wafer W and does not contact the back surface of the outer peripheral surplus area W2. Specifically, as shown in FIG. 4, the rotation center Wo of the wafer W is always located inside the outermost circumference 31o of the rotation locus of the wafer grinding wheel 31 and outside the inner circumference 31i of the rotation locus. In this way, the wafer grinding wheel 31 is always brought into contact with the rotation center Wo. Furthermore, control is performed so that the outermost periphery 31o of the rotation locus does not contact the back side of the outer peripheral surplus region W2.

  By such control, only the region corresponding to the device region W1 of the back surface Wb of the wafer W is ground, and as shown in FIGS. 5 and 6, a concave portion W3 is formed on the back surface Wb and corresponds to the outer peripheral surplus region W2. The ring-shaped reinforcing portion W4 having the same thickness as that before grinding remains in the portion to be ground.

  Here, the malfunction which arises at the time of this kind of wafer grinding is demonstrated with reference to FIGS. FIG. 7A shows that a wafer grinding wheel 31 ′ disposed on a wafer grinding wheel 32 ′ having a wheel rotation shaft 35 ′ parallel to the rotation axis of the chuck table 20 ′ is simply replaced with the chuck table 20 ′. And the outer periphery of the wafer grinding wheel 31 'is positioned at the boundary between the device region W1' and the excess outer region W2 'of the wafer W' to grind the back surface Wb 'of the wafer W'. It is a principle schematic diagram which shows the mode in the case of doing. In this case, since the distance between the grinding surface of the wafer grinding wheel 31 'and the wafer surface is uniform over the entire circumference, the wafer W' obtained as a result of grinding is shown in FIG. Although the inner thickness (TTV) can be made uniform, the entire wafer grinding wheel 31 ′ always overlaps the wafer W ′ surface held by the chuck table 20 ′ and is in contact with the entire circumference. For this reason, a wrinkle-shaped streak (cross grinding trace) as shown in FIG. 7A is generated on the ground surface of the wafer W ′, and it takes time to remove the streak by etching or the like in the next step. The problem occurs.

  On the other hand, as shown in FIG. 7-2, the semicircular grinding line 31a ′ that the wheel rotation shaft 35 ′ of the grinding wheel 32 ′ is inclined from the orthogonal state to the front downward direction to contact the wafer W ′. When grinding is performed with only the side in contact, the non-grinding line 31b 'side opposite to the grinding line 31a' is lifted from the wafer surface, the occurrence of wrinkle-shaped streaks is eliminated, and the saw mark is moved from the rotation center toward the outer periphery A semicircular arc can be formed radially. However, since the distance between the semi-arc-shaped grinding line 31a 'of the relatively small-diameter wafer grinding wheel 32' and the wafer surface held by the chuck table 20 'is not uniform, the thickness of the wafer W' in this state. Even if the back surface Wb ′ corresponding to the device region W1 ′ is ground so that the thickness becomes a predetermined thickness, the wafer W ′ obtained as a result of grinding has a wafer in-plane thickness (TTV) as shown in FIG. This causes a problem that the wafer in-plane thickness cannot be made uniform.

  As the inclination of the wheel rotation shaft 35 ′ of the wafer grinding wheel 32 ′ increases, the variation in the wafer in-plane thickness increases, and as the inclination of the wheel rotation shaft 35 ′ of the wafer grinding wheel 32 ′ decreases, The occurrence of wrinkle-shaped streaks becomes significant, and when the inclination of the wheel rotation shaft 35 'of the wafer grinding wheel 32' is set to the middle, the thickness in the wafer surface varies and a part of the wrinkle-shaped streaks is generated. Resulting in.

  Therefore, in the present embodiment, when only the back surface corresponding to the device region W1 is ground so as to form the ring-shaped reinforcing portion W4 on the outer periphery of the wafer W, the wafer surface is not produced without generating a streak-shaped streak. The present invention provides a wafer processing method capable of making the inner thickness uniform. In carrying out this processing method, first, the wheel rotation shaft 35 is lowered forward in the chuck table rotation direction (circumferential direction) with respect to the rotation shaft of the chuck table 20 in order to eliminate the wrinkle-shaped streak. It shall be inclined slightly. Further, when grinding the wafer W with the wafer grinding wheel 32 having the inclined wheel rotation shaft 35, in order to prevent variation in the wafer in-plane thickness, the wheel diameter for actually grinding the wafer W A holding surface grinding step is performed in advance, in which the holding surface 21 of the chuck table 20 is ground with a grinding wheel having substantially the same wheel diameter, and a region from the rotation center of the holding surface 21 to the outer peripheral portion is ground into a slightly concave shape. To do. Here, the holding surface grinding step is performed using a holding surface grinding wheel 32A in which a holding surface grinding wheel 31A is arranged in an annular shape, as shown in FIG. 9 and the like, instead of the wafer grinding wheel 32. For this purpose, the wafer grinding wheel 32 and the holding surface grinding wheel 32A can be attached to and detached from the mount 34 of the inclined wheel rotation shaft 35. Here, since the grinding object is different between the wafer grinding wheel 32 and the holding surface grinding wheel 32A, the bond material, the abrasive grain size, and the like are completely different. Further, when the outer diameter of the grinding wheel 31A for holding surface grinding (the holding surface grinding wheel 32A) is D1, D1 = D3 (the outer diameter of the wafer grinding wheel 32) = 100 mm.

  Hereinafter, a method for processing the wafer W according to the present embodiment will be described. The method for processing the wafer W according to the present embodiment includes a holding surface grinding process as shown in FIG. 9A and a wafer grinding process as shown in FIG. 9B.

  First, the holding surface grinding process will be described. 9A is a perspective view of the vicinity of the grinding portion showing the holding surface grinding step, FIG. 10 is a longitudinal front view thereof, and FIG. 11 is a longitudinal side view in the direction of arrow A in FIG. . In the holding surface grinding step, the holding surface grinding wheel 32A having the wheel rotation shaft 35 inclined so as to be forwardly lowered in the chuck table rotation direction (circumferential direction) with respect to the rotation axis φc of the chuck table 20 is disposed. The annular holding surface grinding wheel 31A is positioned so as to pass through the rotation center Co of the holding surface 21, and the holding surface 21 is ground by the holding surface grinding wheel 32A, and the outer peripheral portion from the rotation center Co of the holding surface 21 is obtained. The region leading to is slightly ground into a concave shape. Here, both the chuck table 20 and the holding surface grinding wheel 32A rotate counterclockwise. Further, the inclination angle α of the wheel rotation shaft 35 with respect to the rotation axis φc of the chuck table 20 shown in FIG. 11 is set to a slight inclination angle of about α = 0.001 ° to 0.02 °, for example. Reference numeral 22 denotes a concave shape portion formed on the surface of the holding surface 21 by a semi-arc-shaped grinding line that contacts the holding surface 21 with a downward slope of the holding surface grinding wheel 32A. The depth h of the concave surface portion 22 is, for example, about 1 μm to 20 μm, and is a slight concave surface shape.

  Next, the wafer grinding process will be described. FIG. 9B is a perspective view of the vicinity of the grinding portion showing the wafer grinding process, and FIG. 12 is a longitudinal front view thereof. In the wafer grinding step, the back surface Wb of the wafer W sucked and held so as to follow the shape of the concave shape portion 22 on the holding surface 21 of the chuck table 20 on which the concave shape portion 22 was previously formed in the holding surface grinding step. Then, grinding is performed using the wafer grinding wheel 32. That is, the wafer grinding disposed on the wafer grinding wheel 32 having the wheel rotation shaft 35 slightly inclined so as to be lowered forward in the chuck table rotation direction (circumferential direction) with respect to the rotation axis φc of the chuck table 20. The grinding wheel 31 passes through the rotation center Wo of the wafer W held on the holding surface 21 and the outer peripheral portion of the wafer grinding wheel 31 is held on the holding surface 21 between the device region W1 and the outer peripheral surplus region W2. The back surface Wb of the wafer W positioned at the boundary portion and held on the holding surface 21 is ground. Here, both the chuck table 20 and the wafer grinding wheel 32 rotate counterclockwise. Further, the chuck table 20 rotates at a rotational speed of 300 rpm, for example, and the grinding wheel 32 rotates at a rotational speed of 6000 rpm, for example.

  FIG. 13 is a schematic flowchart showing the relationship between the holding surface forming step and the wafer forming step in the wafer processing method of the present embodiment. First, when performing wafer grinding (step S1: Yes), it is determined whether or not the chuck table 20 is a new one (step S2). If the chuck table 20 is a new one that is newly mounted by replacement or the like (step S2: Yes), the holding surface grinding process is performed on the holding surface 21 of the chuck table 20 using the holding surface grinding wheel 32A. It implements and forms the concave shape part 22 in the holding surface 21 (step S3). Then, the wafer W to be ground is sucked and held on the concave shape portion 22 of the holding surface 21 (step S4), and the wafer grinding process is performed using the wafer grinding wheel 32 to form the reinforcing portion W4 (step). S5). In addition, when performing wafer grinding (step S1), if the chuck table 20 is not a new one (step S2: No), the holding surface grinding process has already been performed on the holding surface 21 of the chuck table 20. Therefore, the wafer W to be ground is sucked and held on the concave surface portion 22 of the holding surface 21 without going through the holding surface forming step of step S3 (step S4), and wafer grinding is performed using the wafer grinding wheel 32. A process is implemented and the reinforcement part W4 is formed (step S5).

  That is, the wafer grinding process of the present embodiment is performed after the holding surface grinding process is performed at least once on the new chuck table 20 to form the concave shape portion 22. The holding surface grinding step is not limited to once when the chuck table 20 is replaced with a new one, but may be performed a plurality of times at an appropriate timing as necessary to correct the shape of the concave surface portion 22. Good.

  According to the processing method of the wafer W of the present embodiment, the holding using the holding surface grinding wheel 32A having the same wheel diameter as the wheel diameter for actually grinding the wafer W using the wafer grinding wheel 32 in the wafer grinding step. Since the holding surface 21 of the chuck table 20 is ground in the surface grinding process and the region from the rotation center Co to the outer peripheral portion of the holding surface 21 is slightly ground into a concave shape, the concave shape portion 22 is formed. Is actually ground by the wafer grinding wheel 32, the distance between the semicircular grinding line 31a of the annular wafer grinding wheel 31 and the holding surface 21 (wafer surface) can be made substantially equal. It can grind so that in-plane thickness may become uniform.

  Further, since the wheel rotation shaft 35 is inclined with respect to the rotation shaft φc of the chuck table 20 so as to be lowered forward in the chuck table rotation direction (circumferential direction), a wafer grinding wheel for actually grinding the wafer W. The non-grinding line 31b side opposite to the grinding line 31a of 31 can be made difficult to come into contact with the wafer surface by increasing the escape amount with respect to the wafer surface as a rearward rising slope, and only the grinding line 31a can have a grinding action, Therefore, on the back surface (grinding surface) of the wafer W, saw marks formed by the grinding line are formed radially from the center of rotation toward the outer periphery as shown in FIG. be able to.

  FIG. 14 shows the result of carrying out the holding surface forming step on the wafer W having an outer diameter D2 = 200 mm with the holding surface grinding wheel 32A having the same outer diameter D1 as the outer diameter D3 = 100 mm of the wafer grinding wheel 32. It is a figure which shows an example of the cross-sectional shape of the holding surface 21 of the obtained chuck table 20. FIG. In this case, the depth h of the concave shaped portion 22 is set to about h = 10 μm. Further, FIG. 15 shows the in-wafer thickness when the wafer W held by suction on the holding surface 21 of the chuck table 20 shown in FIG. 14 is ground using the wafer grinding wheel 32 having an outer diameter D3 = 100 mm. It is explanatory drawing which shows the characteristic of dispersion | variation GBIR (TTV), and the escape amount of a non-grinding line. According to the present embodiment, it can be seen that the wafer surface thickness variation GBIR (TTV) is 0 μm, the uniformity is excellent, and the maximum grinding amount of the non-grinding line 31 can be increased to, for example, 20 μm. Here, even if the inclination angle α is changed within a range of α = 0.001 ° to 0.02 °, for example, or the depth h of the concave-shaped portion 22 is changed within a range of 1 μm to 20 μm, for example, The size is not particularly changed and can be made uniform so that TTV = 0 μm.

  FIG. 16 shows the holding surface 21 of the chuck table 20 obtained as a result of carrying out the holding surface forming step with the holding surface grinding wheel 32A having the outer diameter D1 = 120 mm for the wafer W having the outer diameter D2 = 200 mm. It is a figure which shows the other example of a cross-sectional shape. FIG. 17 shows the in-wafer thickness when the wafer W is sucked and held on the holding surface 21 of the chuck table 20 shown in FIG. 16 using the wafer grinding wheel 32 having an outer diameter D3 = 100 mm. It is explanatory drawing which shows the characteristic of dispersion | variation GBIR (TTV), and the escape amount of a non-grinding line. In this case, the variation in wafer in-plane thickness (TTV) was about 0.99 μm, and the maximum clearance of the non-grinding line was about 9.50 μm, for example.

  14 to 17, it is preferable to set the outer diameter D1 of the holding surface grinding wheel 32A used in the holding surface forming step to a value as close as possible to the outer diameter D3 of the wafer grinding wheel 32. However, even if the holding surface grinding step is performed under the condition satisfying the relationship of D3 ≦ D1 <D2 as in the case of D1 = 120 mm, the generation of wrinkle-shaped streak is suppressed, and the in-plane thickness of the wafer is within an allowable range. It can be made uniform in the interior.

  In the present embodiment, the wheel rotation shaft 35 is slightly tilted in the forward and downward direction in the rotation direction of the chuck table 20 with respect to the rotation shaft φc of the chuck table 20. Alternatively, the rotation axis φc side of the chuck table 20 may be inclined. Further, although the rotation direction of the chuck table 20 and the grinding wheels 32 and 32A is counterclockwise, it may be rotated clockwise.

  In the present embodiment, the rotation axis φc of the chuck table 20 and the wheel rotation axis 35 are parallel to each other in the radial direction, and the concave shape portion 22 is formed with respect to the planar holding surface 21. The rotation axis φc of the chuck table 20 and the wheel rotation axis 35 have a relatively slight inclination even in the radial direction, and are formed in a conical shape (umbrella shape) having a slight inclination with the rotation center Co as an apex. The concave surface portion may be formed by a holding surface grinding wheel slightly inclined in the forward downward direction with respect to the holding surface. According to this, since the non-grinding line side of the wafer grinding wheel can be easily lifted from the wafer surface during wafer grinding, the depth h of the concave-shaped portion 22 to be formed is reduced or the inclination angle α is reduced. be able to.

It is a perspective view which shows the wafer and protective tape of a process target. It is a perspective view which shows the state by which the protective tape was stuck on the surface of the wafer. It is an external appearance perspective view which shows an example of the grinding device for enforcing the processing method of the wafer of this Embodiment. It is explanatory drawing like the top view which shows the positional relationship with the rotation locus | trajectory of a grinding wheel and a wafer. It is the perspective view which looked at the wafer in which the ring-shaped reinforcement part was formed from the back surface side. It is sectional drawing of the wafer in which the ring-shaped reinforcement part was formed. It is a perspective view which shows typically a mode that a wafer is ground in the state without an inclination. It is a perspective view which shows typically a mode that a wafer is ground in the state which gave the front downward inclination. It is a TTV characteristic figure which shows the grinding result of the wafer in the case of FIGS. It is a TTV characteristic figure which shows the grinding result of the wafer in the case of FIGS. 7-2. It is a schematic perspective view which shows the holding surface grinding process and wafer grinding process of this Embodiment in order. It is a vertical front view of Fig.9 (a). It is a vertical side view of the arrow A direction of FIG. It is a vertical front view of FIG.9 (b). It is a schematic flowchart which shows the relationship between the holding surface formation process and wafer formation process in the processing method of the wafer of this Embodiment. It is a figure which shows an example of the cross-sectional shape of the holding surface formed at the holding surface formation process of this Embodiment. FIG. 15 is a characteristic diagram of a result of wafer grinding using the holding surface of FIG. 14. It is a figure which shows the other example of the cross-sectional shape of the holding surface formed at the holding surface formation process of this Embodiment. FIG. 17 is a characteristic diagram such as a wafer grinding result using the holding surface of FIG. 16.

Explanation of symbols

20 chuck table 21 holding surface 22 concave surface portion 30 grinding means 31 wafer grinding wheel 31A holding surface grinding wheel 32 wafer grinding wheel 32A holding surface grinding wheel 35 wheel rotating shaft D device T protective tape W wafer W1 device region W2 Outer peripheral area W4 Reinforcement part Wa Front surface Wb Rear surface Wo Wafer center of rotation Co Center of rotation of holding surface

Claims (3)

A rotatable chuck table having a holding surface for holding a wafer, and a grinding means for rotatably supporting a grinding wheel in which a grinding wheel for grinding the wafer held on the holding surface is arranged in an annular shape. Using a grinding apparatus, the back surface corresponding to the device area of the wafer formed on the surface of the device area where a plurality of devices are formed and the outer peripheral edge area surrounding the device area is ground to correspond to the outer peripheral edge area. A wafer processing method for forming a ring-shaped reinforcing portion on the back surface,
An annular holding surface grinding wheel disposed on a holding surface grinding wheel having a wheel rotating shaft that is slightly inclined relative to the rotating shaft of the chuck table passes through the center of rotation of the holding surface. A holding surface grinding step in which the holding surface is ground by the holding surface grinding wheel and the region from the rotation center of the holding surface to the outer peripheral portion is ground into a slightly concave shape,
Wafer grinding that is performed after the holding surface grinding step is performed at least once on the chuck table, and is disposed on a wafer grinding wheel having the wheel rotation shaft that is relatively slightly inclined. The grinding wheel passes through the center of rotation of the wafer held on the holding surface, and the outer peripheral portion of the wafer grinding wheel is positioned at the boundary between the device region and the outer peripheral surplus region of the wafer held on the holding surface. A wafer grinding step for grinding the back surface of the wafer held by the holding surface;
With
When the outer diameter D1 of the holding surface grinding wheel used in the holding surface grinding step is D2 as the outer diameter of the wafer and D3 as the outer diameter of the wafer grinding wheel,
D3 ≦ D1 <D2
A wafer processing method characterized by satisfying the following relationship:   2. The wafer processing method according to claim 1, wherein a depth of the concave shape formed in the holding surface grinding step is 1 μm to 20 μm.   The wafer processing method according to claim 1 or 2, wherein, in the wafer grinding step, a protective tape is attached to the surface of the wafer and held on the holding surface.

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