TWI869541B - Wafer processing method - Google Patents

Abstract

[Topic] To stably implement the so-called TAIKO grinding, which forms a circular concave portion corresponding to the device area and an annular convex portion corresponding to the peripheral remaining area on the back side of the wafer. [Solution] The wafer processing method comprises: a processing preparation step 1001, in which a wafer is held by a chuck table, a rough grinding wheel is fixed at the lower end of a main shaft, and the diameter of the rough grinding wheel is equivalent to the radius of the wafer; a limited grinding step 1002, in which the back side of the wafer corresponding to the component area after excluding the central part of the wafer held by the chuck table is ground with the rough grinding wheel to form an annular concave portion and a central convex portion; a position adjustment step 1003, in which the rough grinding wheel is separated from the wafer and moved toward the outer periphery of the wafer; and a circular grinding step 1004, in which the back side of the wafer corresponding to the component area including the central convex portion is ground, the central convex portion is removed to form a circular concave portion, and an annular convex portion is formed on the back side of the wafer corresponding to the remaining peripheral area.

Description

Wafer processing method

The present invention relates to a method for processing a wafer, and in particular to a method for processing a wafer by so-called TAIKO (registered trademark) grinding.

Semiconductor wafers are becoming thinner and shorter, and wafers with semiconductor components are ground to a thickness of less than 100µm. After grinding, the wafer will warp due to grinding deformation on the ground surface. Since it is very difficult to form a film of metal, etc. on the back of a warped wafer, only the area excluding the outer periphery of the wafer is ground, and the so-called TAIKO grinding technology (for example, see Patent Documents 1 and 2) is used, which forms a circular concave portion corresponding to the component area and an annular convex portion corresponding to the remaining area on the periphery on the back of the wafer. [Known Technical Documents] [Patent Documents]

[Patent document 1] Japanese Patent No. 5390740 [Patent document 2] Japanese Patent No. 4758222

[Problem to be solved by the invention] In TAIKO grinding, since a grinding wheel with a smaller diameter than the wafer is used, the amount of material removed by each grinding wheel is relatively large compared to a general grinding wheel with a diameter equal to or larger than the wafer, and sometimes TAIKO grinding cannot be performed stably. In addition, even if the rotation speed is the same, it is difficult to increase the rotation speed due to the small diameter, which is also the reason for the same tendency.

In particular, oxide films and nitride films formed on the back surface are difficult to grind, and sometimes the spindle motor load current value exceeds the specified value, making it impossible to perform stable Taiko grinding. And the so-called highly doped wafers also have the same tendency.

The object of the present invention is to provide a wafer processing method which can stably implement the so-called TAIKO grinding for forming a circular concave portion corresponding to a device region and an annular convex portion corresponding to a peripheral residual region on the back side of the wafer.

[Technical means for solving the problem] In order to solve the above-mentioned problem and achieve the purpose, the wafer processing method of the present invention has: a component area on the front side of the wafer, in which components are formed in each area divided by a plurality of predetermined dividing lines intersecting each other; and a peripheral residual area, which surrounds the component area. The wafer processing method is characterized in that it has: a processing preparation step, which has a holding surface for holding the wafer and holds the wafer with a rotatable chuck table, and a grinding wheel is fixed at the lower end of the main shaft of the rotating axis perpendicular to the holding surface, and the diameter of the grinding wheel is equivalent to the radius of the wafer; a limited grinding step, which uses the grinding wheel to grind the wafer held by the chuck table to exclude A central part is formed on the back of the wafer corresponding to the component area, and a central convex part surrounded by the annular concave part is formed on the back of the wafer; a position adjustment step, after the limited grinding step is performed, the grinding wheel is separated from the wafer and the grinding wheel is moved relatively toward the outer periphery of the wafer; and a circular grinding step, after the position adjustment step is performed, the grinding wheel is used to grind the back of the wafer corresponding to the component area including the central convex part, the central convex part of the back of the wafer corresponding to the component area is removed to form a circular concave part, and an annular convex part is formed on the back of the wafer corresponding to the peripheral residual area.

The wafer processing method may also include a fine grinding step, in which after the circular grinding step, the circular recess is ground more deeply with a fine grinding wheel having a grinding stone, wherein the grinding stone is formed by fixing abrasive grains finer than the grinding wheel with a binder.

In the wafer processing method, the circular recess formed in the circular grinding step is formed deeper than the annular recess formed in the limiting grinding step.

[Effect of the invention] The wafer processing method of the present invention has the following effects: it can stably implement the so-called TAIKO grinding on the back side of the wafer to form a circular concave portion corresponding to the device area and an annular convex portion corresponding to the peripheral remaining area.

Refer to the drawings for detailed description of the methods (implementations) for implementing the present invention. The present invention is not limited to the contents described in the following implementations. Furthermore, the constituent elements described below include those that are easily conceivable by a person having ordinary knowledge in the technical field to which the present invention belongs and are substantially the same. Furthermore, the constituent elements described below can be appropriately combined. Furthermore, various omissions, substitutions, or changes in the constituent elements can be made without departing from the gist of the present invention.

[Implementation method 1] The wafer processing method of implementation method 1 of the present invention is described based on the drawings. FIG. 1 is a three-dimensional view of a wafer to be processed by the wafer processing method of implementation method 1. FIG. 2 is a three-dimensional view showing a configuration example of a grinding device used in the wafer processing method of implementation method 1. FIG. 3 is a three-dimensional view showing the rough grinding unit and the fine grinding unit of the grinding device shown in FIG. 2 from below. FIG. 4 is a flow chart showing the process of the wafer processing method of implementation method 1.

The wafer processing method of the embodiment 1 is a method for processing the wafer 200 shown in FIG. The wafer 200 to be processed by the wafer processing method of the embodiment 1 is a disk-shaped semiconductor wafer with silicon as a base material or an optical element wafer with sapphire, SiC (silicon carbide) or the like as a base material. In the embodiment 1, the disk-shaped base material of the wafer 200 is made of silicon, and a film 202 such as an oxide film or a nitride film is formed on at least the back side 201.

In Embodiment 1, a film 202 is formed on the back side 201 of the wafer 200. Since the wafer 200 has more film 202 formed thereon than a wafer without film 202 formed thereon, the back side 201 is more difficult to grind than a wafer whose base material is made of silicon and without film 202 formed thereon (i.e., it is a difficult-to-grind wafer).

As shown in FIG. 1 , the wafer 200 has a device region 203 and a peripheral residual region 204 surrounding the device region 203 on the front side 205. The device region 203 has devices 207 formed in each region divided by a plurality of predetermined dividing lines 206 that are orthogonal to each other. The device 207 is an integrated circuit such as an IC (Integrated Circuit) or an LSI (Large Scale Integration). In addition, the peripheral residual region 204 is a region surrounding the device region 203 in the front side 205 of the wafer 200 and where the device 207 is not formed.

Next, the grinding device 1 shown in FIG. 2 used in the wafer processing method of embodiment 1 is described. The grinding device 1 is a processing device for grinding (equivalent to processing) the back side 201 of the wafer 200. As shown in FIG. 2, the grinding device 1 mainly includes: a device body 2; a rough grinding unit 3 (equivalent to a grinding unit); a fine grinding unit 4 (equivalent to a grinding unit); a grinding feed unit 5; a turntable 6; a plurality of (three in embodiment 1) chuck tables 7 arranged on the turntable 6; cassettes 8 and 9; an alignment unit 10; a conveying unit 11; a cleaning unit 12; a carry-in and carry-out unit 13; and a control unit 100.

The turntable 6 is a disk-shaped worktable provided on the upper surface of the device body 2, and is configured to be rotatable in a horizontal plane and to be rotationally driven at a predetermined time point. On this turntable 6, three chuck tables 7 are arranged at intervals of, for example, a phase angle of 120 degrees. These three chuck tables 7 are chuck table structures having a vacuum chuck on a holding surface 71, and the wafer 200 is placed on the holding surface 71 and is held by suction. During grinding, these chuck tables 7 are rotationally driven in a horizontal plane by a rotation drive mechanism around an axis parallel to the lead vertical direction, i.e., the Z-axis direction. In this way, the chuck table 7 has a holding surface 71 for holding the wafer 200 and can rotate around the axis.

The chuck table 7 is moved to the loading/unloading area 301, the rough grinding area 302, the fine grinding area 303, and the loading/unloading area 301 in sequence by the rotation of the turntable 6.

In addition, the loading and unloading area 301 is an area for loading and unloading the wafer 200 on and off the chuck table 7, the rough grinding area 302 is an area where the rough grinding unit 3 performs rough grinding (equivalent to grinding) on the wafer 200 held on the chuck table 7, and the fine grinding area 303 is an area where the fine grinding unit 4 performs fine grinding (equivalent to grinding) on the wafer 200 held on the chuck table 7.

The rough grinding unit 3 is equipped with a rough grinding wheel 32 for rough grinding having a grinding stone 31 for rough grinding, and is a grinding unit that performs rough grinding on the back side 201 of the wafer 200 held on the holding surface 71 of the chuck table 7 in the rough grinding area 302. The fine grinding unit 4 is equipped with a fine grinding wheel 42 for fine grinding having a grinding stone 41 for fine grinding, and is a grinding unit that performs fine grinding on the back side 201 of the wafer 200 held on the holding surface 71 of the chuck table 7 in the fine grinding area 303. In addition, since the grinding units 3 and 4 have substantially the same structure, the same symbols are assigned to the same parts and are explained below.

As shown in FIG3 , the rough grinding unit 3 and the fine grinding unit 4 are formed by mounting grinding wheels 32 and 42 on the lower end of the main shaft 33. The grinding wheels 32 and 42 have: an annular base 34 in the shape of an annulus, and a plurality of grinding stones 31 and 41 fixed to the lower surface 341 of the annular base 34. The grinding stones 31 and 41 are arranged in the circumferential direction at the outer edge of the lower surface 341 of the annular base 34. The lower surfaces 311 and 411 of the plurality of grinding stones 31 and 41 form an annular shape. The grinding stones 31 and 41 are formed by fixing abrasive grains with a binder. The abrasive grains of the grinding stone 41 of the fine grinding wheel 42 are finer than the abrasive grains of the grinding stone 31 of the rough grinding wheel 32.

In the first embodiment, the outer diameter 35 (equivalent to the diameter of the grinding wheel 32, 42) of the ring-shaped ring formed by the lower surfaces 311, 411 of the plurality of grinding stones 31, 41 of the grinding wheel 32, 42 is equal to the radius 208 of the wafer 200. In the present invention, the outer diameter 35 of the ring-shaped ring formed by the lower surfaces 311, 411 of the plurality of grinding stones 31, 41 of the grinding wheel 32, 42 is equal to the radius 208 of the wafer 200, which means that the diameter, i.e., the outer diameter, of the grinding wheel 32, 42 is equal to the radius 208 of the wafer 200.

The spindle 33 is housed in a spindle housing 36 (shown in FIG. 2 ) so as to be rotatable about a rotation axis 38 parallel to the Z-axis direction perpendicular to the holding surface 71, and is rotated about the axis by a spindle motor 37 (shown in FIG. 2 ) mounted on the spindle housing 36. The spindle 33 is formed in a cylindrical shape, and a wheel frame 39 for mounting the grinding wheels 32 and 42 is provided at the lower end. The wheel frame 39 protrudes from the lower end of the spindle 33 over the entire circumference in the outer circumferential direction, and the plane shape of the outer circumferential surface is formed in a circular shape. The wheel frame 39 overlaps the upper surface of the annular base 34 at the lower surface 391, and the grinding wheels 32 and 42 are fixed by bolts (not shown). The main shaft 33 and the carrier 39 are arranged at coaxial positions with each other.

The grinding units 3 and 4 rotate the spindle 33 and the grinding wheels 32 and 42 around the rotating shaft 38 through the spindle motor 37, and supply grinding water to the back side 201 of the wafer 200 held on the chuck table 7 in the grinding areas 302 and 303. At the same time, the grinding feed unit 5 brings the grinding stones 31 and 41 close to the chuck table 7 at a predetermined feed speed, thereby performing rough grinding or fine grinding on the back side 201 of the wafer 200.

The grinding feed unit 5 is a unit that moves the grinding units 3 and 4 in the Z-axis direction. In the first embodiment, the grinding feed unit 5 is provided with a vertical column 21, and the vertical column 21 is vertically provided from one end of the device body 2 in the Y-axis direction parallel to the horizontal direction. The grinding feed unit 5 has: a known ball screw that is set to rotate freely around the axis; a known motor that rotates the ball screw around the axis; and a known guide rail that supports the spindle housing 36 of each grinding unit 3 and 4 so that it can move freely in the Z-axis direction.

Furthermore, in embodiment 1, the rotation centers of the grinding wheels 32 and 42 of the rough grinding unit 3 and the fine grinding unit 4, i.e., the rotation axis 38, and the rotation center of the chuck table 7, i.e., the axis, are spaced apart and arranged in parallel with each other in the horizontal direction, and the grinding stones 31 and 41 are held at the center 210 or near the center 210 of the back side 201 of the wafer 200 of the chuck table 7, and the wheel frame 39 and the chuck table 7 of the grinding areas 302 and 303 are coaxially positioned, and each grinding feed unit 5 and each vertical column 21 are moved in the horizontal direction by the sliding movement mechanism 16. The sliding movement unit 16 includes: a conventional ball screw which is rotatable around an axis; a conventional motor which rotates the ball screw around the axis; and a conventional guide rail which supports the vertical column 21 supporting each grinding unit 3, 4 so as to be movable in the horizontal direction.

The cassettes 8 and 9 are containers with multiple slots for accommodating wafers 200. The cassette 8 accommodates wafers 200 before grinding, and the cassette 9 accommodates wafers 200 after grinding. In addition, the alignment unit 10 is a workbench for temporarily placing the wafers 200 taken out of the cassette 8 and performing center alignment.

There are two conveying units 11. The two conveying units 11 have adsorption pads for adsorbing the wafers 200. One of the conveying units 11 adsorbs and holds the wafer 200 before grinding that has been aligned by the alignment unit 10 and moves it onto the chuck table 7 located in the carry-in/out area 301. The other conveying unit 11 adsorbs and holds the wafer 200 after grinding that is held on the chuck table 7 located in the carry-in/out area 301 and moves it out to the cleaning unit 12.

The loading and unloading unit 13 is, for example, a pick-up robot having a U-shaped hand 131, and the U-shaped hand 131 sucks, holds, and transports the wafer 200. Specifically, the loading and unloading unit 13 takes out the wafer 200 before grinding from the cassette 8 and carries it out to the alignment unit 10, and takes out the wafer 200 after grinding from the cleaning unit 12 and carries it into the cassette 9. The cleaning unit 12 cleans the wafer 200 after grinding to remove contaminants such as grinding chips attached to the ground back surface 201.

The control unit 100 is a unit that controls the above-mentioned components constituting the grinding device 1. That is, the control unit 100 is a unit that causes the grinding device 1 to perform grinding operations on the wafer 200. The control unit 100 is a computer having the following devices: an operation processing device having a microprocessor such as a CPU (central processing unit); a memory device having a memory such as a ROM (read only memory) or a RAM (random access memory); and an input-output interface device.

The operation processor of the control unit 100 performs operation processing according to the computer program stored in the memory device, and outputs the control signal used to control the grinding device 1 to the above-mentioned components of the grinding device 1 through the input and output interface device. In addition, the control device 100 is connected to: a display unit, which is composed of a liquid crystal display device that displays the state or image of the processing action, etc.; and an input unit, which is used when the operator logs in the processing content information, etc. The input unit is composed of at least one of a touch panel and a keyboard provided in the display unit.

The wafer processing method of implementation method 1 is to use grinding wheels 32, 42 to grind the back side 201 of the wafer 200 corresponding to the component area 203, forming a circular recess 211 (as shown in Figures 15 and 16) on the back side 201 of the wafer 200 corresponding to the component area 203, and forming an annular protrusion 212 (as shown in Figures 15 and 16) on the back side 201 of the wafer 200 corresponding to the peripheral residual area 204, that is, the wafer 200 is subjected to the so-called TAIKO grinding processing method. In addition, the back side 201 of the wafer 200 corresponding to the component area 203 refers to the area on the back side 201 of the wafer 200 that overlaps with the component area 203 in the thickness direction of the wafer 200, and the back side 201 of the wafer 200 corresponding to the peripheral remaining area 204 refers to the area on the back side 201 of the wafer 200 that overlaps with the peripheral remaining area 204 in the thickness direction of the wafer 200.

As shown in FIG. 4 , the wafer processing method of the first embodiment includes: a processing preparation step 1001 , a limited grinding step 1002 , a position adjustment step 1003 , a circular grinding step 1004 , a fine grinding step 1005 , and a cleaning and accommodating step 1006 .

(Processing preparation step) FIG. 5 is a perspective view showing a state in which the front surface of the wafer and the protective member are facing each other in the processing preparation step of the processing method of the wafer shown in FIG. 4. FIG. 6 is a perspective view showing a state in which the protective member is attached to the front surface of the wafer in the processing preparation step of the processing method of the wafer shown in FIG. 4.

The processing preparation step 1001 is a step of holding the wafer 200 on the chuck table 7 of the grinding device 1 and fixing the grinding wheels 32 and 42 at the lower end of the spindle 33. In the first embodiment, in the processing preparation step 1001, as shown in FIG5, the protective member 213 is made to face the front surface 205 of the wafer 200, and as shown in FIG6, the protective member 213 is pasted on the front surface 205 of the wafer 200. In the first embodiment, the protective member 213 is formed into a circular plate of the same size as the wafer 200, and is composed of a flexible synthetic resin or a rigid substrate.

In the first embodiment, in the processing preparation step 1001, the operator fixes the grinding wheels 32 and 42 to the lower ends of the spindles 33 of the grinding units 3 and 4 of the grinding device 1, and stores the wafer 200 with the protective member 213 attached to the front surface 205 in the cassette 8 with the protective member 213 facing downward. In the processing preparation step 1001, the operator registers the processing conditions in the control unit 100, and sets the cassette 8 containing the wafer 200 with the protective member 213 attached before grinding and the cassette 9 not containing the wafer 200 in the device body 2. In the processing preparation step 1001, if the control unit 100 of the grinding device 1 receives the processing action start instruction from the operator, the processing action is started.

During the processing operation, the control unit 100 of the grinding device 1 rotates the spindles 33 of each grinding unit 3, 4 around the rotation axis 38, takes out a wafer 200 from the cassette 8 in the loading and unloading unit 13, and unloads it to the alignment unit 10. The control unit 100 performs center alignment of the wafer 200 in the alignment unit 10, and loads the front side 205 of the wafer 200 aligned with the transport unit 11 onto the chuck table 7 located in the loading and unloading area 301. At this time, the wafer 200 that has been loaded into the chuck table 7 is positioned at a position coaxial with the chuck table 7.

In the processing preparation step 1001 , the control unit 100 of the grinding device 1 attracts and holds the front side 205 of the wafer 200 on the chuck table 7 of the loading/unloading area 301 through the protection member 213 , and enters the limited grinding step 1002 .

(Limited grinding step) FIG. 7 is a schematic top view of the rough grinding wheel and the wafer immediately after the limited grinding step of the wafer processing method shown in FIG. 4 begins. FIG. 8 is a schematic side view of a state in which the rough grinding wheel shown in FIG. 7 is brought into contact with the wafer in a partial cross-section. FIG. 9 is a schematic cross-sectional view of the rough grinding wheel and the wafer at the end of the limited grinding step of the wafer processing method shown in FIG. 4. FIG. 10 is a schematic top view of the rough grinding wheel and the wafer shown in FIG. 9.

The limited grinding step 1002 is the following step: the back side 201 of the wafer 200 corresponding to the device area 203 is ground with the rough grinding wheel 32, excluding the central part of the wafer 200 held by the chuck table 7, to form an annular concave portion 214 (shown in FIGS. 9 and 10), and a central convex portion 215 surrounded by the annular concave portion 214 is formed on the back side 201 of the wafer 200 (shown in FIGS. 9 and 10). In the limited grinding step 1002, the control unit 100 of the grinding device 1 rotates the turntable 6, moves the chuck table 7 holding the wafer 200 in the loading and unloading area 301 to the rough grinding area 302, exposes the back side 201, and transports the wafer 200 to the rough grinding area 302 with the turntable 6.

In the limited grinding step 1002, the control unit 100 of the grinding device 1 moves the rough grinding unit 3 in the horizontal direction through the sliding movement mechanism 16, and as shown in FIG7, the rotation axis 38 of the main axis 33 of the rough grinding unit 3 and the axis of the turntable 6, that is, the center 210 of the wafer 200 held on the chuck table 7 are arranged to be spaced apart in the horizontal direction (that is, the wafer 200 and the rough grinding wheel 32 are positioned to be non-coaxial). In addition, in the limited grinding step 1002, the control unit 100 of the grinding device 1 positions the center 210 of the wafer 200 held on the chuck table 7 on the inner circumference of the grinding stone 31 of the rough grinding wheel 32 in a top view, and rotates the chuck table 7 around the axis. Furthermore, in the first embodiment, in the limited grinding step 1002, the control unit 100 of the grinding device 1 rotates the chuck table 7 and the rough grinding wheel 32 of the rough grinding unit 3 in the same direction in a plan view.

In the limited grinding step 1002, the control unit 100 of the grinding device 1 makes the rough grinding unit 3 descend to the grinding feed unit 5, as shown in FIG8, so that the lower surface 311 of the grinding stone 31 of the rough grinding wheel 32 of the rough grinding unit 3 abuts against the back side 201 of the wafer 200, and the rough grinding unit 3 is lowered at the grinding feed speed determined by the processing content information. Then, the grinding stone 31 grinds the back side 201 of the wafer 200 corresponding to the device area 203 after excluding the central part of the back side 201, and grinds the film 202 and the base material of the back side 201 of the wafer 200 corresponding to the device area 203 in sequence. In the limited grinding step 1002, as shown in FIG. 9, if the control unit 100 of the grinding device 1 grinds from the back side 201 to the depth 216 specified by the processing content information using the rough grinding unit 3, the position adjustment step 1003 is entered.

In addition, in the limited grinding step 1002, the wafer 200 and the rough grinding wheel 32 are positioned at a non-coaxial position. Since the center 210 of the wafer 200 held on the chuck table 7 is positioned on the inner peripheral side of the grinding stone 31 of the rough grinding wheel 32 in a top view, the back side 201 of the wafer 200 after the limited grinding step 1002 is formed with an annular recess 214 recessed from the back side 201 as shown in FIG9 and FIG10, and a central protrusion 215 surrounded by the annular recess 214 is formed. The planar shape of the annular recess 214 is formed into a circular ring, and the planar shape of the central protrusion 215 is formed into a circular shape. The annular recess 214 and the central protrusion 215 are formed at a position coaxial with the wafer 200. In addition, in the present invention, since the base material of the wafer 200 is made of silicon, in the limited grinding step 1002, it is sufficient to grind the rough grinding wheel 32 until at least the base material is exposed at the bottom surface of the annular recess 214, that is, it is sufficient to at least remove the film 202 contacting the lower surface 311 of the grinding stone 31.

(Position adjustment step) FIG. 11 is a side view showing a state in which the rough grinding unit is raised and the rough grinding wheel is separated from the wafer in the position adjustment step of the wafer processing method shown in FIG. 4, with a partial section. FIG. 12 is a side view showing a state in which the rough grinding wheel shown in FIG. 11 is relatively moved toward the outer periphery of the wafer, with a partial section. FIG. 13 is a top view showing the rough grinding wheel shown in FIG. 12 and the wafer, with a schematic diagram.

The position adjustment step 1003 is a step of separating the rough grinding wheel 32 from the wafer 200 after the limited grinding step 1002 is performed, and then relatively moving the rough grinding wheel 32 toward the outer periphery of the wafer 200. In the position adjustment step 1003, as shown in FIG. 11 , the control unit 100 of the grinding device 1 raises the rough grinding unit 3 to the grinding feed unit 5, and separates the grinding stone 31 of the rough grinding wheel 32 from the wafer 200 held on the chuck table 7.

In the position adjustment step 1003, the control unit 100 of the grinding device 1 moves the rough grinding wheel 32 of the rough grinding unit 3 toward the outer periphery of the wafer 200 held on the chuck table 7 in the rough grinding area 302 through the sliding movement mechanism 16. In the embodiment 1, in the position adjustment step 1003, as shown in FIG. 12 and FIG. 13, the control unit 100 of the grinding device 1 positions the outer edge of the grinding stone 31 of a part of the rough grinding wheel 32 at the boundary between the device area 203 and the peripheral residual area 204 of the wafer 200, and positions the lower surface 311 of the other part of the grinding stone 31 at the center 210 of the wafer 200, and enters the circular grinding step 1004.

(Circular grinding step) FIG. 14 is a side view schematically showing a state in which the rough grinding wheel and the wafer are in contact with each other just after the circular grinding step of the processing method of the wafer shown in FIG. 4 has just started, with a partial cross section. FIG. 15 is a side view schematically showing a rough grinding wheel and the wafer at the end of the circular grinding step of the processing method of the wafer shown in FIG. 4, with a partial cross section. FIG. 16 is a top view schematically showing the rough grinding wheel and the wafer shown in FIG. 15.

The circular grinding step 1004 is the following step: after the position adjustment step 1003 is implemented, the back side 201 of the wafer 200 corresponding to the component area 203 including the central protrusion 215 is ground using the rough grinding wheel 32, the central protrusion 215 of the back side 201 of the wafer 200 corresponding to the component area 203 is removed and a circular recess 211 is formed, and an annular protrusion 212 is formed on the back side 201 of the wafer 200 corresponding to the peripheral residual area 204.

In the circular grinding step 1004, the control unit 100 of the grinding device 1 lowers the rough grinding unit 3 to the grinding feed unit 5, as shown in FIG14, so that the lower surface 311 of the grinding stone 31 of the rough grinding wheel 32 of the rough grinding unit 3 abuts against the outer peripheral area and the central convex area 215 of the annular concave portion 214 of the back side 201 of the wafer 200, and the rough grinding unit 3 is lowered at the grinding feed speed determined by the processing content information. Therefore, the grinding stone 31 grinds and removes the outer peripheral area and the central convex area 215 of the annular concave portion 214 of the back side 201 of the wafer 200 corresponding to the device area 203.

In the circular grinding step 1004, when grinding starts, the grinding stone 31 abuts against the corners of the central convex portion 215 and the corners of the annular concave portion 214 to trim the grinding stone 31. In the circular grinding step 1004, as shown in FIG. 15, if the control unit 100 of the grinding device 1 grinds from the back surface 201 to a depth 217 specified by the processing content information deeper than the depth 216 of the limited grinding step 1002 by the rough grinding unit 3, the fine grinding step 1005 is entered.

Furthermore, in the position adjustment step 1003, since the outer edge of the grinding stone 31 of a portion of the rough grinding wheel 32 is positioned on the boundary between the component area 203 and the peripheral residual area 204 of the wafer 200, and the lower surface 311 of the other portion of the grinding stone 31 is positioned on the center 210 of the wafer 200, in the back side 201 of the wafer 200 after the circular grinding step 1004, as shown in FIGS. 15 and 16 , a circular recess 211 is formed as a whole on the back side 201 of the wafer 200 corresponding to the component area 203, and an annular protrusion 212 is formed on the back side 201 of the wafer 200 corresponding to the peripheral residual area 204 because the back side 201 has not been ground. Thus, in the wafer processing method of the first embodiment, the circular concave portion 211 formed in the circular grinding step 1004 is formed deeper than the annular concave portion 214 formed in the limited grinding step 1002. Furthermore, in the first embodiment, during the limited grinding step 1002, the position adjustment step 1003, and the circular grinding step 1004, the chuck table 7 positioned in the rough grinding area 302 rotates in the same direction.

(Fine grinding step) The fine grinding step 1005 is the following step: after the circular grinding step 1004 is performed, the circular concave portion 211 is further ground with the fine grinding wheel 42. In the fine grinding step 1005, the control unit 100 of the grinding device 1 rotates the turntable 6, moves the chuck table 7 holding the wafer 200 that has been subjected to the circular grinding step 1004 in the rough grinding area 302 to the fine grinding area 303, exposes the back side 201, and transports the wafer 200 to the fine grinding area 303 with the turntable 6.

In implementation method 1, in the fine grinding step 1005, the control unit 100 of the grinding device 1 moves the fine grinding unit 4 in the horizontal direction through the sliding movement mechanism 16, and positions the outer edge of the grinding stone 41 of a part of the fine grinding wheel 42 on the boundary between the component area 203 and the peripheral residual area 204 of the wafer 200, and positions the lower surface 411 of the other part of the grinding stone 41 on the center 210 of the wafer 200. While the chuck table 7 positioned in the fine grinding area 303 is rotated in the same direction as the grinding wheel 42, the fine grinding unit 4 is lowered to the grinding feed unit 5.

In the fine grinding step 1005, the control unit 100 of the grinding device 1 uses the fine grinding unit 4 to grind the bottom surface of the circular recess 211 to the depth specified by the processing content information, and then raises the grinding unit 4 to the grinding feed unit 5 and enters the cleaning and accommodating step 1006.

(Cleaning and accommodating step) The cleaning and accommodating step 1006 is the following step: after the fine grinding step 1005 is performed, the wafer 200 is cleaned and accommodated in the cassette 9. In the cleaning and accommodating step 1006, the control unit 100 of the grinding device 1 rotates the turntable 6, moves the chuck table 7 holding the wafer 200 that has been subjected to the fine grinding step 1005 in the fine grinding area 303 to the loading and unloading area 301, exposes the back side 201, and transports the wafer 200 to the loading and unloading area 301 by the turntable 6. Thus, the wafer processing method is to sequentially transport the wafer 200 to the rough grinding area 302, the fine grinding area 303, and the loading and unloading area 301, and sequentially implement the limited grinding step 1002, the position adjustment step 1003, the circular grinding step 1004, and the fine grinding step 1005. In addition, every time the turntable 6 rotates 120 degrees, the control unit 100 of the grinding device 1 will move the wafer 200 before grinding into the chuck table 7 of the loading and unloading area 301.

In the cleaning and accommodating step 1006, the control unit 100 of the grinding device 1 moves the ground wafer 200 into the cleaning unit 12 via the conveying unit 11, and the cleaning unit 12 cleans it. The conveying hand of the carrying unit 13 holds the cleaned wafer 200 from the protective component 213 side of the wafer 200 and moves it into the cassette 9. In addition, in the first embodiment, whenever the turntable 6 rotates 120 degrees, the control unit 100 of the grinding device 1 sequentially performs the limited grinding step 1002, the position adjustment step 1003, and the circular grinding step 1004 on the wafer 200 positioned in the rough grinding area 302, performs the fine grinding step 1005 on the wafer 200 positioned in the fine grinding area 303, transfers the ground wafer 200 from the chuck table 7 positioned in the loading and unloading area 301 to the cleaning unit 12, and transfers the wafer 200 before grinding to the chuck table 7. If the control unit 100 of the grinding device 1 performs grinding on all the wafers 200 in the cassette 8, the processing operation, that is, the wafer processing method, is terminated.

As described above, in the wafer processing method of the first embodiment, even for the difficult-to-grind wafer 200, in the grinding step 1002, the grinding area is limited to be narrower than the conventional TAIKO grinding and the grinding is performed with the central protrusion 215 remaining in the center, and then the back side 201 of the wafer 200 corresponding to the entire device region 203 including the central protrusion 215 is ground in the circular grinding step 1004. Therefore, the grinding ranges of the limited grinding step 1002 and the circular grinding step 1004 of the wafer processing method can be made narrower than the conventional TAIKO grinding, and the burden on the grinding grindstone 31 can be reduced. As a result, the wafer processing method has the following effects: the load current value of the spindle motor 37 can be suppressed from exceeding the specified value, and the so-called TAIKO grinding can be stably implemented to form a circular recess 211 corresponding to the device area 203 and an annular protrusion 212 corresponding to the peripheral residual area 204 on the back side 201 of the wafer 200.

Furthermore, in the circular grinding step 1004 of the wafer processing method, when grinding the central protrusion 215, the grinding grindstone 31 collides with the corners of the central protrusion 215 and the corners of the annular recess 214, so a trimming effect can be obtained, and the effect of maintaining a good grinding state can also be achieved.

[Variation] A wafer processing method of a variation of the first embodiment of the present invention is described based on the drawings. FIG. 17 is a cross-sectional view schematically showing a state in which an annular concave portion and a central convex portion are initially formed in a limited grinding step of the wafer processing method of the first embodiment. In addition, in FIG. 17, the same symbols are given to the same parts as those of the first embodiment and the description is omitted.

The wafer processing method of the modification of the first embodiment is to gradually change the relative position of the rough grinding wheel 32 with respect to the wafer 200 from the position close to the center 210 to the position of the outer periphery, and perform a plurality of limited grinding steps 1002 to form an annular concave portion 214 and a central convex portion 215 on the back surface 201. In addition, FIG. 17 shows an example in which the rough grinding wheel 32 and the wafer 200 are positioned at a coaxial position in the limited grinding step 1002 to initially form the annular concave portion 214 and the central convex portion 215. In addition, in the present invention, when the annular recess 214 and the central protrusion 215 are initially formed, the rough grinding wheel 32 and the wafer 200 are not limited to being positioned coaxially as shown in FIG. 17 . Instead, the relative position of the rough grinding wheel 32 with respect to the wafer 200 is gradually changed from a position close to the center 210 to a position at the outer periphery while performing multiple limited grinding steps 1002.

The wafer processing method of the variant example shown in Figure 17 is to gradually change the relative position of the rough grinding wheel 32 relative to the wafer 200 from a position close to the center 210 to a position at the outer periphery while performing multiple limited grinding steps 1002. Therefore, compared with the implementation method, the burden imposed on the grinding stone 31 can be further reduced.

In addition, the present invention is not limited to the above-mentioned embodiments. That is, various modifications can be made and implemented without departing from the scope of the backbone of the present invention. In the above-mentioned embodiment 1, the base material of the difficult-to-grind wafer 200 is composed of silicon, and the wafer 200 has a film 202 formed on the outer surface, but the present invention is not limited to this. For example, in the present invention, the base material of the difficult-to-grind wafer 200 can also be composed of sapphire or glass, etc., and the wafer 200 can also be a so-called highly doped wafer, which adjusts the resistivity to, for example, 0.001Ωcm or more and 0.1Ωcm or less by mixing in dopants (for example, boron: B, phosphorus: P, tin: Sn or arsenic: As). When a circular concave portion 211 and an annular convex portion 212 are formed on such a difficult-to-grind wafer 200, the wafer processing method of the present invention only needs to use at least one of the rough grinding unit 3 and the fine grinding unit 4 and implement the limited grinding step 1002, the position adjustment step 1003 and the circular grinding step 1004.

7: Chuck table 32: Rough grinding wheel (grinding wheel) 33: Spindle 35: Outer diameter (diameter) 38: Rotating axis 41: Grinding stone for fine grinding (grinding stone) 42: Fine grinding wheel (grinding wheel) 71: Holding surface 200: Wafer 201: Back surface 203: Component area 204: Peripheral remaining area 205: Front surface 206: Predetermined dividing line 207: Component 208: Radius 211: Circular concave part 212: Annular convex part 214: Annular concave part 215: Central convex part 1001: Processing preparation step 1002: Limited grinding step 1003: Position adjustment step 1004: Circular grinding step 1005: Fine grinding step 1006: Cleaning and accommodating step

FIG. 1 is a perspective view of a wafer to be processed by the wafer processing method of embodiment 1. FIG. 2 is a perspective view showing a configuration example of a grinding device used in the wafer processing method of embodiment 1. FIG. 3 is a perspective view showing a rough grinding unit and a fine grinding unit of the grinding device shown in FIG. 2 from below. FIG. 4 is a flow chart showing the flow of the wafer processing method of embodiment 1. FIG. 5 is a perspective view showing a state in which the front surface of the wafer and the protective member are facing each other in the processing preparation step of the wafer processing method shown in FIG. 4. FIG. 6 is a perspective view showing a state in which the protective member is attached to the front surface of the wafer in the processing preparation step of the wafer processing method shown in FIG. 4. FIG. 7 is a top view schematically showing a rough grinding wheel and a wafer just after the limited grinding step of the wafer processing method shown in FIG. 4 starts. FIG8 is a side view schematically showing a state in which the rough grinding wheel shown in FIG7 is brought into contact with the wafer in partial section. FIG9 is a cross-sectional view schematically showing the rough grinding wheel and the wafer at the end of the limited grinding step of the wafer processing method shown in FIG4. FIG10 is a top view schematically showing the rough grinding wheel and the wafer shown in FIG9. FIG11 is a side view schematically showing a state in which the rough grinding unit is raised and the rough grinding wheel is separated from the wafer in the position adjustment step of the wafer processing method shown in FIG4 in partial section. FIG12 is a side view schematically showing a state in which the rough grinding wheel shown in FIG11 is relatively moved toward the outer periphery of the wafer in partial section. FIG13 is a top view schematically showing the rough grinding wheel and the wafer shown in FIG12. FIG. 14 is a side view schematically showing a state in which the rough grinding wheel and the wafer are in contact with each other just after the circular grinding step of the wafer processing method shown in FIG. 4 has just started, with a partial cross section. FIG. 15 is a side view schematically showing a state in which the rough grinding wheel and the wafer are in contact with each other, with a partial cross section, at the end of the circular grinding step of the wafer processing method shown in FIG. 4. FIG. 16 is a top view schematically showing the rough grinding wheel and the wafer shown in FIG. 15. FIG. 17 is a cross-sectional view schematically showing a state in which the annular concave portion and the central convex portion are initially formed in the limited grinding step of the wafer processing method of the variant of the first embodiment.

1001: Processing preparation steps

1002: Limit grinding steps

1003: Position adjustment step

1004: Circular grinding step

1005: Fine grinding and sharpening steps

1006: Cleaning and storage steps

Claims (3)

A method for processing a wafer, the wafer having on the front side: a component area, in which components are formed in each area divided by a plurality of intersecting predetermined dividing lines; and a peripheral residual area, which surrounds the component area. The method for processing a wafer comprises: a processing preparation step, which has a holding surface for holding the wafer and holds the wafer with a rotatable chuck table, and a grinding wheel is fixed at the lower end of a main shaft of a rotating axis perpendicular to the holding surface, and the diameter of the grinding wheel is equivalent to the radius of the wafer; a limited grinding step, which grinds the wafer held by the chuck table with the grinding wheel, excluding the central part, corresponding to the component area. The back side of the wafer is provided with an annular concave portion and a central convex portion surrounded by the annular concave portion is formed on the back side of the wafer; a position adjustment step, after the limited grinding step is performed, the grinding wheel is separated from the wafer and the grinding wheel is moved relatively toward the outer periphery of the wafer; and a circular grinding step, after the position adjustment step is performed, the back side of the wafer corresponding to the component area including the central convex portion is ground using the grinding wheel, the central convex portion of the back side of the wafer corresponding to the component area is removed to form a circular concave portion, and an annular convex portion is formed on the back side of the wafer corresponding to the peripheral residual area. A wafer processing method as claimed in claim 1, wherein the method comprises: a fine grinding step, after implementing the circular grinding step, grinding the circular recess more deeply with a fine grinding wheel having a grinding stone, wherein the grinding stone is formed by fixing abrasive grains finer than the grinding wheel with a binder. A wafer processing method as claimed in claim 1 or 2, wherein the circular recess formed in the circular grinding step is formed deeper than the annular recess formed in the limiting grinding step.