JP7542404B2 - Wafer grinding method - Google Patents

Description

The present invention relates to a method for grinding wafers.

In order to grind plate-shaped workpieces such as semiconductor wafers and reduce their overall thickness, a grinding device is used that holds the wafer on a conical holding surface and brings the grinding wheel into contact with a radial area parallel to the wafer to reduce its thickness (see, for example, Patent Document 1).

JP 2019-130637 A

In conventional grinding devices, the center of the wafer held at the center of the holding surface is always in contact with the grinding wheel, so there is a tendency for the center of the wafer to be thinner than other parts. For this reason, the grinding device shown in the aforementioned Patent Document 1 forms a flat recess in the center of the holding surface when grinding the holding surface, thereby preventing the center of the wafer from being thinner than other parts. However, because the shape of the holding surface to be formed is complex, there was a problem in that grinding the holding surface took a long time.

The present invention was made in consideration of these points, and its purpose is to provide a wafer grinding method that can prevent the center of the wafer from becoming thin and minimize thickness variation.

In order to solve the above-mentioned problems and achieve the object, the present invention provides a method for grinding a wafer, comprising: a holding table having a conical holding surface with an apex at the center and rotatable about an axis at the center of the holding surface; a grinding unit having a ring-shaped grinding wheel rotatably attached thereto and grinding the wafer held on the holding surface with the grinding wheel; a horizontal movement unit for relatively moving the holding table and the grinding unit in a horizontal direction parallel to the bottom surface of the grinding wheel; and a grinding feed unit for moving the grinding unit away from or toward the holding surface. The method includes a holding step of holding a wafer on the holding surface; and a grinding step of moving the grinding wheel by the horizontal movement unit. The method includes a first positioning step of positioning the holding table at a first position relative to the grinding unit so that the rotational trajectory of the grinding wheel passes through the center of the holding surface, a first grinding step of grinding the wafer to a predetermined thickness after the first positioning step, a second positioning step of positioning the holding table relative to the grinding unit using the horizontal movement unit after the first grinding step so that the rotational trajectory of the grinding wheel does not pass through the center of the holding surface, and a second grinding step of grinding the wafer to a finishing thickness using the horizontal movement unit after the second positioning step while moving the holding table back and forth radially relative to the grinding unit in an area where the rotational trajectory of the grinding wheel does not pass through the center of the holding surface.

In addition, in the wafer grinding method, in the second positioning step, the holding table may be moved relative to the grinding unit in the radial direction of the holding surface by at least a distance equivalent to the blade width of the grinding wheel from the first positioning step.

The present invention has the effect of preventing the center of the wafer from becoming thin and minimizing thickness variation.

FIG. 1 is a side view, partially in section, illustrating a main part of a grinding apparatus used in a wafer grinding method according to a first embodiment. FIG. 2 is a perspective view showing an example of a workpiece to be processed by the grinding apparatus shown in FIG. FIG. 3 is a flowchart showing the flow of the wafer grinding method according to the first embodiment. FIG. 4 is a cross-sectional view showing a holding step of the wafer grinding method shown in FIG. FIG. 5 is a diagram showing the position of the holding table in the wafer grinding method shown in FIG. FIG. 6 is a diagram showing the relative moving speed in the X-axis direction of the holding table and the grinding unit in the wafer grinding method shown in FIG. FIG. 7 is a side view, partly in section, showing the first positioning step of the wafer grinding method shown in FIG. FIG. 8 is a plan view showing the rotation path of the grinding wheel, the holding table and the relative positions of the wafer after the first positioning step of the wafer grinding method shown in FIG. FIG. 9 is a diagram showing the relative moving speed in the Z-axis direction of the holding table and the grinding unit in the wafer grinding method shown in FIG. FIG. 10 is a side view, partly in section, showing the first grinding step of the wafer grinding method shown in FIG. FIG. 11 is a side view, partially in section, showing the second positioning step of the wafer grinding method shown in FIG. FIG. 12 is a plan view showing the relative positions of the rotation path of the grinding wheel, the holding table and the wafer after the second positioning step of the wafer grinding method shown in FIG. FIG. 13 is a side view, partially in section, showing the second grinding step of the wafer grinding method shown in FIG. FIG. 14 is a plan view showing the rotation path of the grinding wheel, the holding table and the relative positions of the wafer in the second grinding step of the wafer grinding method shown in FIG. FIG. 15 is a diagram showing the relative moving speed in the Z-axis direction of the holding table and the grinding unit in the wafer grinding method according to the modified example of the first embodiment. FIG. 16 is a diagram showing the variation in thickness of a wafer thinned to a finish thickness by the wafer grinding method of the present invention. FIG. 17 is a diagram showing the variation in thickness of wafers thinned to the finish thickness by the wafer grinding method of Comparative Example 1. FIG. 18 is a diagram showing the variation in thickness of wafers thinned to the finish thickness by the wafer grinding method of Comparative Example 2.

The following describes in detail the form (embodiment) for carrying out the present invention with reference to the drawings. The present invention is not limited to the contents described in the following embodiment. The components described below include those that a person skilled in the art can easily imagine and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Various omissions, substitutions, or modifications of the configuration can be made without departing from the spirit of the present invention.

[Embodiment 1]
A wafer grinding method according to a first embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a side view, partly in section, showing a schematic view of a main part of a grinding device used in the wafer grinding method according to the first embodiment. Fig. 2 is a perspective view showing an example of a workpiece to be processed by the grinding device shown in Fig. 1. Fig. 3 is a flow chart showing a flow of the wafer grinding method according to the first embodiment.

The wafer grinding method according to the first embodiment is a method of thinning the wafer 200, which is the object of processing, to a finishing thickness 206 (shown in FIG. 2), using the grinding device 1 shown in FIG. 1. The grinding device 1 shown in FIG. 1 is a processing device that grinds the wafer 200 shown in FIG. 2. First, the wafer 200, which is the object of processing by the grinding device 1, will be described.

(Wafer)
1 is a disk-shaped semiconductor wafer or optical device wafer having a substrate 201 made of silicon, sapphire, gallium arsenide, or the like. As shown in FIG. 2, the wafer 200 has devices 204 formed in each of a plurality of regions partitioned by a plurality of planned dividing lines 203 that intersect (orthogonal in the first embodiment) on a surface 202 of the substrate 201.

The device 204 is, for example, an integrated circuit such as an IC (Integrated Circuit) or an LSI (Large Scale Integration), an image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), or a MEMS (Micro Electro Mechanical System). The wafer 200 has a protective member 210 attached to the surface 202 side of the substrate 201, and the surface 202 side is suction-held to the holding surface 11 via the protective member 210, and the back surface 205 behind the surface 202 is ground. Next, a grinding device 1 that grinds the wafer 200 will be described.

(Grinding equipment)
1, the grinding apparatus 1 is a processing apparatus that grinds a back surface 205 side of a substrate 201 of a wafer 200 to thin the wafer 200 to a predetermined finish thickness 206. As shown in FIG. 1, the grinding apparatus 1 includes an apparatus main body 2, a holding table 10, a grinding unit 20, a horizontal movement unit 50, a grinding feed unit 30, an inclination adjustment unit 40, and a control unit 100.

The holding table 10 has a holding surface 11 that holds the front surface 202 side of the wafer 200, and is rotatable around an axis 112 shown by a dashed line in FIG. 1 that passes through the center 111 of the holding surface 11. In the first embodiment, the holding surface 11 of the holding table 10 is made of porous ceramics or the like, and the holding surface 11 is connected to a vacuum suction source (not shown) via a vacuum suction path (not shown). The front surface 202 side of the wafer 200 is placed on the holding surface 11 of the holding table 10 via a protective member 210, and the holding surface 11 is sucked by the vacuum suction source, thereby sucking and holding the wafer 200 placed on the holding surface 11.

In addition, in the first embodiment, the holding table 10 is provided on a moving table 3 that is moved in the X-axis direction parallel to the horizontal direction by a horizontal moving unit 50. The holding table 10 is rotated around an axis 112 by a rotary drive source 4 installed on the moving table 3. The moving table 3 is moved in the X-axis direction by the horizontal moving unit 50 so as to be located at a processing position 5 where the wafer 200 held on the holding table 10 is ground by a grinding unit 20, and at a carry-in/out position 6 where the wafer 200 is carried in to or out of the holding table 10.

The holding surface 11 has a circular planar shape and is formed into a cone shape with the outer edge 113 slightly lower than the center 111. That is, the holding surface 11 is formed into a cone shape with the center 111 as the apex, and an inclined surface is formed that is inclined with respect to the axis 112 and has a downward inclination from the center 111 to the outer edge 113. The holding table 10 holds the wafer 200 to be processed along the cone-shaped holding surface 11. Note that FIG. 1 shows the inclination of the cone-shaped holding surface 11 in an exaggerated manner, but the inclination of the cone-shaped holding surface 11 is actually so slight that it cannot be seen with the naked eye.

The axis 112, which is the center of rotation of the holding table 10, is arranged at a slight incline with respect to the vertical direction, i.e., the parallel Z-axis direction. In the first embodiment, the axis 112 of the holding table 10 is arranged at a horizontal distance from the axis 221 of the grinding unit 20. The radial region 114 of the holding surface 11 of the holding table 10 at the processing position 5, which includes the center 111 and is closer to the grinding unit 20 than the center 111, faces the grinding wheel 25 of the grinding unit 20 along the Z-axis direction. The radial region 114 of the holding surface 11 is parallel to both the horizontal direction and the underside of the grinding wheel 25 of the grinding unit 20.

In addition, in embodiment 1, the non-machined region 115 of the holding surface 11 of the holding table 10 at the processing position 5 that does not vertically face the grinding wheel 25 of the grinding unit 20 is lower than the radial region 114 when the grinding device 1 makes the thickness of the wafer 200 after grinding uniform, and is positioned gradually lower toward the outer edge 113. Note that FIG. 1 shows an exaggerated inclination 120 of the axis 112 with respect to the vertical direction, but the inclination 120 of the axis 112 with respect to the vertical direction is actually so slight that it cannot be detected by the naked eye.

The grinding unit 20 has a spindle 22 with a grinding wheel 21 attached to its lower end and rotatable around an axis 221 perpendicular to the X-axis direction and parallel to the vertical direction, and grinds the back surface 205 side of the substrate 201 of the wafer 200 held on the holding table 10 with the grinding stone 25 of the grinding wheel 21. The grinding unit 20 is supported by the device body 2 via the grinding feed unit 30. The grinding unit 20 includes the grinding wheel 21, the spindle 22, and a spindle motor 23.

The grinding wheel 21 grinds the wafer 200 held on the holding table 10. The grinding wheel 21 includes a disk-shaped wheel base 24 and a grinding stone 25 arranged in a ring shape on the outer edge of the lower surface of the wheel base 24.

The grinding wheels 25 are arranged at equal intervals in the circumferential direction on the underside of the wheel base 24 facing the holding table 10. In the first embodiment, the grinding wheels 25 are configured as a single so-called segmented grinding wheel formed into a single lump by mixing abrasive grains such as diamond or CBN (Cubic Boron Nitride) with a bonding material (also called a bond material) made of metal, ceramic, resin, etc.

The grinding wheel 21 is driven by a spindle motor 23 that rotates the spindle 22 around the axis 221, causing the grinding stone 25 to grind the back surface 205 of the wafer 200 held on the holding table 10.

The spindle 22 has the grinding wheel 21 attached to its lower end. In other words, the spindle 22 rotatably mounts an annular grinding stone 25. The spindle 22 is rotatably housed in a spindle housing 26 that is supported by the grinding feed unit 30 so as to be movable vertically. The axis 221 of the spindle 22 of the grinding unit 20 is parallel to the Z-axis direction. The spindle motor 23 rotates the spindle 22 around the axis 221.

In the first embodiment, the axis 221 of the grinding unit 20 is horizontally separated from the axis 112 of the holding table 10, and the rotation trajectory 251 (shown in FIG. 8) of the grinding wheel 25 of the grinding wheel 21 when the spindle 22 rotates is located on the center 111 of the holding table 10. Also, in the first embodiment, when the grinding device 1 makes the thickness of the wafer 200 after grinding uniform (suppressing the variation in thickness as much as possible), the lower surface of the grinding wheel 25 is parallel to the radial region 114 of the holding surface 11 of the holding table 10.

The horizontal movement unit 50 moves the holding table 10 and the grinding unit 20 relatively in the X-axis direction, which is the horizontal direction parallel to the underside of the grinding wheel 25. The horizontal movement unit 50 is installed on the device body 2, and moves the holding table 10 in the X-axis direction by moving the moving table 3 on which the holding table 10 and the rotary drive source 4 are installed in the X-axis direction. The horizontal movement unit 50 includes a well-known ball screw arranged parallel to the X-axis direction and rotatable about its axis, a motor that rotates the ball screw about its axis to move the moving table 3 in the X-axis direction, and a well-known guide rail that supports the moving table 3 so that it can be moved in the X-axis direction.

The grinding feed unit 30 is installed in the device body 2 and moves the spindle 22 of the grinding unit 20 in the Z-axis direction to move the grinding unit 20 away from or toward the holding surface 11 of the holding table 10 at the processing position 5. The grinding feed unit 30 lowers the spindle 22 of the grinding unit 20 to move the grinding unit 20 toward the holding table 10 at the processing position 5. The grinding feed unit 30 raises the spindle 22 of the grinding unit 20 to move the grinding unit 20 away from the holding table 10 at the processing position 5.

The grinding feed unit 30 is equipped with a well-known ball screw arranged parallel to the Z-axis direction and rotatable about its axis, a motor that rotates the ball screw about its axis to move the spindle 22 in the Z-axis direction via the spindle housing 26, and a well-known guide rail that supports the grinding unit 20 so that it can move in the Z-axis direction.

The tilt adjustment unit 40 adjusts the tilt 120 between the axis 112 of the holding table 10 and the axis 221 of the grinding unit 20 relative to each other. In the first embodiment, the tilt adjustment unit 40 is attached to the holding table 10 and adjusts (changes) the orientation of the axis 112 of the holding table 10. As shown in FIG. 1, the tilt adjustment unit 40 includes a support base 41 and a height fine adjustment unit 42. The support base 41 includes a cylindrical support tube portion 411 that supports the holding table 10 rotatably around the axis 112 via a bearing (not shown), and a flange portion 412 that expands in diameter from the lower end of the support tube portion 411. The tilt adjustment unit 40 adjusts the tilt 120 of the axis 112 by the height fine adjustment unit 42 adjusting the tilt of the flange portion 412.

Two or more height fine adjustment units 42 are provided at intervals in the radial direction of the flange portion 412. In the first embodiment, the tilt adjustment unit 40 has three height fine adjustment units 42 provided at intervals in the radial direction on the underside of the flange portion 412.

As shown in FIG. 1, the height fine adjustment unit 42 includes a cylindrical portion 421 fixed to the moving table 3, a shaft 422 that passes through the cylindrical portion 421, a drive portion 423 that is connected to the lower end of the shaft 422 and moves the shaft 422 in the Z-axis direction, and a fixed portion 424 that is fixed to the flange portion 412 at the upper end of the shaft 422.

The fixing part 424 is screwed into a male screw (not shown) formed on the upper end of the shaft 422. The height fine adjustment unit 42 changes the height of the fixing part 424 fixed to the flange part 412 by moving the shaft 422 in the Z-axis direction by the driving part 423, thereby adjusting the inclination 120 of the axis 112.

The grinding device 1 also includes a thickness gauge 60, as shown in FIG. 1. The thickness gauge 60 measures the thickness of the wafer 200 held on the holding surface 11 of the holding table 10. The thickness gauge 60 outputs the measured thickness of the wafer 200 to the control unit 100. In the first embodiment, the device includes a contactor 61 that contacts the back surface 205 of the wafer 200 and a contactor 62 that contacts the holding surface 11 of the holding table 10.

The control unit 100 processes multiple types of signals from each of the above-mentioned mechanisms constituting the grinding device 1 and controls each of the mechanisms. In other words, the control unit 100 causes the grinding device 1 to execute processing operations on the wafer 200. The control unit 100 is a computer that has an arithmetic processing device having a microprocessor such as a CPU (Central Processing Unit), a storage device having memory such as a ROM (Read Only Memory) or RAM (Random Access Memory), and an input/output interface device, and is capable of executing computer programs.

The arithmetic processing unit of the control unit 100 executes a computer program stored in the ROM on the RAM to generate control signals for controlling the grinding device 1. The arithmetic processing unit of the control unit 100 outputs the generated control signals to each component of the grinding device 1 via the input/output interface device.

The control unit 100 is also connected to a display means (not shown) configured with a liquid crystal display device or the like that displays the status of the processing operation and images, and to an input means used by the operator to register processing content information, etc. The input means is configured with at least one of a touch panel provided on the display means and a keyboard, etc.

The grinding device 1 described above holds the front surface 202 side of the wafer 200 on the holding surface 11 of the holding table 10 by suction via the protective member 210, positions the holding table 10 at the processing position 5, and rotates the grinding wheel 21 around the axis 221 and the holding table 10 around the axis 112 while supplying grinding fluid to the wafer 200. The grinding device 1 brings the grinding wheel 25 of the grinding wheel 21 into contact with the back surface 205 of the substrate 201 of the wafer 200, and moves the grinding unit 20 closer to the holding table 10 at a predetermined grinding feed rate using the grinding wheel 25 in the radial region 114 of the holding surface 11 of the holding table 10, thereby thinning the wafer 200 to the finishing thickness 206. Next, a method for grinding the wafer will be described.

(Wafer Grinding Method)
The wafer grinding method according to the first embodiment is a method for thinning the wafer 200 to a finishing thickness 206 using the grinding apparatus 1, and is also a processing operation of the grinding apparatus 1. As shown in Fig. 3, the wafer grinding method includes a holding step 1001, a first positioning step 1002, a first grinding step 1003, a second positioning step 1004, and a second grinding step 1005.

(holding step)
4 is a cross-sectional view showing a holding step of the wafer grinding method shown in FIG. 3. The holding step 1001 is a step of holding the wafer 200 on the holding surface 11 of the holding table 10. In the holding step 1001, an operator or the like registers processing content information in the control unit 100, and when the control unit 100 receives an instruction to start the processing operation from the operator or the like, the processing operation is started. When the processing operation is started, the grinding device 1 carries the wafer 200 into the holding surface 11 of the holding table 10 positioned at the carry-in/out position 6 by a carry-in/out unit (not shown). In the holding step 1001, the grinding device 1 suction-holds the wafer 200 on the holding surface 11, rotates the spindle 22 around the axis 221, and supplies grinding fluid, as shown in FIG.

(First positioning step)
Fig. 5 is a diagram showing the position of the holding table in the wafer grinding method shown in Fig. 3. Fig. 6 is a diagram showing the relative moving speed in the X-axis direction of the holding table and the grinding unit in the wafer grinding method shown in Fig. 3. Fig. 7 is a side view, partially in cross section, showing a first positioning step in the wafer grinding method shown in Fig. 3. Fig. 8 is a plan view showing the rotation trajectory of the grinding wheel, the holding table, and the relative positions of the wafer after the first positioning step in the wafer grinding method shown in Fig. 3.

The first positioning step 1002 is a step of positioning the holding table 10 at a first position 301 (shown in FIG. 5) relative to the grinding unit 20 using the horizontal movement unit 50 so that the rotational trajectory 251 (shown in FIG. 8) having the cutting width of the grinding wheel 25 passes through the center 111 of the holding surface 11. In the first positioning step 1002, the grinding device 1 moves the holding table 10 from the loading/unloading position 6 toward the processing position 5 at a first moving speed 401 (shown in FIG. 6) by the horizontal movement unit 50 as shown in FIG. 5. In the first positioning step 1002, the grinding device 1 positions the holding table 10 at the first position 301 of the processing position 5 by the horizontal movement unit 50 as shown in FIG. 7, and stops the movement of the holding table 10 in the X-axis direction.

The horizontal axis in Fig. 5 and Fig. 6 indicates the elapsed time from when the grinding apparatus 1 starts the wafer grinding method according to the first embodiment. The vertical axis in Fig. 5 indicates the horizontal position of the holding table 10. The vertical axis in Fig. 6 indicates the horizontal movement speed of the holding table 10. In addition, in the first positioning step 1002, the grinding apparatus 1 stops the movement of the grinding unit 20 in the Z-axis direction.

In the first embodiment, in the first positioning step 1002, the grinding device 1 positions the holding table 10 at a first position 301 where a rotational trajectory 251 including the inner edge, outer edge, and the space between the inner edge and the outer edge of the grinding wheel 25 of the grinding unit 20 shown in FIG. 8 passes above the center 111 of the holding surface 11 of the holding table 10 in the Z-axis direction. The rotational trajectory 251 refers to a position where the inner edge, outer edge, and the space between the inner edge and the outer edge of the grinding wheel 25 pass in a plane parallel to both the X-axis direction and the Y-axis direction that is perpendicular to the X-axis direction and parallel to the horizontal direction when the grinding wheel 21 of the grinding unit 20 rotates around the axis 221. In the first position 301, the center 111 of the holding surface 11 of the holding table 10 is aligned in the Z-axis direction with the center of the width of the rotational trajectory 251, i.e., the center of the blade thickness of the grinding wheel 25.

(First grinding step)
Fig. 9 is a diagram showing the relative moving speed in the Z-axis direction between the holding table and the grinding unit in the wafer grinding method shown in Fig. 3. Fig. 10 is a side view, partially in cross section, showing the first grinding step in the wafer grinding method shown in Fig. 3. The first grinding step 1003 is a step of grinding the wafer 200 to a predetermined thickness after the first positioning step 1002.

In the first embodiment, in the first grinding step 1003, the grinding device 1 rotates the holding table 10 around the axis 112, and the grinding feed unit 30 lowers the grinding wheel 21 of the grinding unit 20 at a first grinding feed speed 501 (shown in FIG. 9). The horizontal axis of FIG. 9 indicates the elapsed time since the grinding device 1 starts the wafer grinding method according to the first embodiment. The vertical axis of FIG. 9 indicates the moving speed of the grinding unit 20 in the Z-axis direction.

In the first embodiment, in the first grinding step 1003, as shown in FIG. 10, the grinding device 1 brings the grinding stone 25 of the grinding wheel 21 into contact with the back surface 205 of the substrate 201 of the wafer 200, and the grinding feed unit 30 further lowers the grinding unit 20 to the holding table 10 at a constant first grinding feed speed 501, grinding the back surface 205 of the wafer 200 in the radial region 114 of the holding surface 11 of the holding table 10 with the grinding stone 25, thinning the wafer 200 to a predetermined thickness while measuring the thickness of the wafer 200 with the thickness gauge 60.

The predetermined thickness is slightly thicker than the finishing thickness 206, and in the first embodiment, the predetermined thickness is 10 μm thicker than the finishing thickness 206. In the first embodiment, in the first grinding step 1003, the center 111 of the holding surface 11 of the holding table 10 is aligned with the center of the blade thickness of the grinding wheel 25 in the Z-axis direction at the first position 301 where the holding table 10 is positioned in the first positioning step 1002, so that the grinding wheel 25 always comes into contact with the circular central region 205-1 (shown by a dotted circle in FIG. 8) of the back surface 205 of the wafer 200, the diameter of which is centered on the center 111 of the holding surface 11 and is equal to the blade thickness of the grinding wheel 25. The central region 205-1 refers to the region of the back surface 205 of the wafer 200 that is always in contact with the grinding wheel 25, and because there is a slight inclination 120, the diameter centered on the center 111 of the holding surface 11 is slightly different from the circular region whose diameter is the blade thickness of the grinding wheel 25.

(Second positioning step)
Fig. 11 is a side view partially in section showing the second positioning step of the wafer grinding method shown in Fig. 3. Fig. 12 is a plan view showing the relative positions of the rotational trajectory of the grinding wheel, the holding table and the wafer after the second positioning step of the wafer grinding method shown in Fig. 3. The second positioning step 1004 is a step of positioning the holding table 10 relative to the grinding unit 20 using the horizontal movement unit 50 after the first grinding step 1003 so that the rotational trajectory 251 of the grinding wheel 25 does not pass through the center 111 of the holding surface 11.

In the first embodiment, in the second positioning step 1004, as shown in FIG. 5, the grinding device 1 moves the holding table 10 by the horizontal movement unit 50 toward the loading/unloading position 6 shown in FIG. 1 at the first movement speed 401 (shown in FIG. 6), and as shown in FIG. 11, the horizontal movement unit 50 positions the holding table 10 at the second position 302 of the processing position 5, and stops the movement of the holding table 10 in the X-axis direction.

In the first embodiment, in the second positioning step 1004, the grinding device 1 uses the horizontal movement unit 50 to position the holding table 10 at least the width of the grinding wheel 25 on the side of the loading/unloading position 6 after the first grinding step 1003. Thus, in the first embodiment, the holding table 10 at the second position 302 is positioned at least the width of the grinding wheel 25 on the side of the loading/unloading position 6 shown in FIG. 1 from the holding table 10 at the first position 301. Thus, in the present invention, in the second positioning step 1004, the holding table 10 is moved relative to the grinding unit 20 in the radial direction of the holding surface 11 by at least a distance equivalent to the width of the grinding wheel 25 from the first positioning step 1002 to position it.

In embodiment 1, in the second positioning step 1004, after the first grinding step 1003, the grinding device 1 positions the holding table 10 at a second position 302 at least the blade width of the grinding wheel 25 toward the loading/unloading position 6, thereby positioning the holding table 10 at the second position 302 where the rotational trajectory 251 of the inner and outer edges of the grinding wheel 25 of the grinding unit 20 shown in FIG. 12 (hereinafter, referred to as the rotational trajectory 251-2 at the second position 302) does not pass through the center 111 of the holding table 10. Also, in the first embodiment, in the second positioning step 1004, the grinding device 1 positions the holding table 10 at the second position 302 on the side of the carry-in/out position 6 by at least the blade width of the grinding wheel 25 after the first grinding step 1003, so that the grinding wheel 25 is shifted from the central region 205-1 of the back surface 205 of the wafer 200 by at least the blade width, as shown in FIG. 12, and the grinding wheel 25 does not come into contact with the central region 205-1.

(Second grinding step)
Fig. 13 is a side view partially in section showing the second grinding step of the wafer grinding method shown in Fig. 3. Fig. 14 is a plan view showing the relative positions of the grinding wheel rotation trajectory, the holding table, and the wafer in the second grinding step of the wafer grinding method shown in Fig. 3. The second grinding step 1005 is a step of grinding the wafer 200 to the finishing thickness 206 by using the horizontal movement unit 50 to move the holding table 10 back and forth in the radial direction relative to the grinding unit 20 in the region where the rotation trajectories 251, 251-2 of the grinding wheel 25 do not pass through the center of the holding surface 11 after the second positioning step 1004.

In the first embodiment, in the second grinding step 1005, as shown in FIG. 5, the grinding device 1 uses the horizontal movement unit 50 to move the holding table 10 back and forth a predetermined number of times between the second position 302 and the third position 303 at the second movement speed 402 (shown in FIG. 6) while the grinding feed unit 30 lowers the grinding wheel 21 of the grinding unit 20 at the second grinding feed speed 502 (shown in FIG. 9). Note that the second movement speed 402 is preferable to be slower than the first movement speed 401 because grinding is performed while moving the holding table 10 back and forth in a direction parallel to the holding surface 11, and therefore there is a risk of load being applied to the grinding wheel 25 and the grinding surface of the wafer 200 held by the holding table 10.

On the other hand, the first moving speed 401 is preferably high within a range that does not deteriorate the processing quality, in order to quickly move the grinding wheel 25 away from the central region 205-1. Also, in the first embodiment, between the second positioning step 1004 and the second grinding step 1005, the grinding device 1 lowers the grinding wheel 21 of the grinding unit 20 at the second grinding feed speed 502 by the grinding feed unit 30 as shown in FIG. 9, and grinds the back surface 205 of the wafer 200 as shown in FIG. 13. Note that the second grinding feed speed 502 is slower than the first grinding feed speed 501. This is because in the conventional grinding method, the grinding feed speed is slowed down at the end of the grinding process to prepare the grinding surface of the wafer 200, and the second grinding step 1005 is performed at the end of the grinding process.

In the second grinding step 1005, the amount of movement of the holding table 10 from the first position 301 to the loading/unloading position 6 is preferably a distance of 1/5 or less of the diameter of the holding table 10. In the second grinding step 1005, if the amount of movement of the holding table 10 from the first position 301 to the loading/unloading position 6 exceeds 1/5 of the diameter of the holding table 10, the variation in the thickness of the wafer 200 after grinding will increase (that is, the shape of the wafer 200 after grinding cannot be controlled, and the thickness distribution will spread undesirably). In the present invention, in order to further suppress the variation in the thickness of the wafer 200 after grinding, it is desirable that the holding table 10 is located at the loading/unloading position 6 side at a distance of 1/10 or less of the diameter of the holding table 10 from the first position 301 at most in the second grinding step 1005.

For this reason, in embodiment 1, in the second grinding step 1005, the grinding stone 25 of the grinding wheel 21 moves back and forth relative to the holding table 10 and the wafer 200 between the rotational locus 251-2 of the second position 302 shown by the dashed dotted line in FIG. 14 and the rotational locus 251 of the third position 303 shown by the dashed dotted line in FIG. 14 (hereinafter, at the third position 303, this will be referred to as the rotational locus 251-3), thereby grinding the back surface 205 of the wafer 200. In the first embodiment, in the second grinding step 1005, the grinding device 1 brings the grinding stone 25 of the grinding wheel 21 into contact with the back surface 205 of the substrate 201 of the wafer 200, and the grinding unit 20 is lowered to the holding table 10 by the grinding feed unit 30 at a constant second grinding feed speed 502, and the holding table 10 is moved back and forth between the second position 302 and the third position 303, while the grinding stone 25 grinds the back surface 205 of the wafer 200 in the radial region 114 of the holding surface 11 of the holding table 10, and the wafer 200 is thinned to the finishing thickness 206 while the thickness gauge 60 measures the thickness of the wafer 200.

In the second grinding step 1005, when the grinding device 1 thins the wafer 200 to the finishing thickness 206, the grinding feed unit 30 raises the grinding wheel 21 of the grinding unit 20 to separate the grinding stone 25 from the wafer 200, and then stops the rotation of the holding table 10 around the axis 112. In the second grinding step 1005, the grinding device 1 moves the holding table 10 to the loading/unloading position 6 using the horizontal movement unit 50, stops suction holding of the holding surface 11 of the wafer 200, and unloads the wafer 200 from the holding surface 11 of the holding table 10 positioned at the loading/unloading position 6 by a loading/unloading unit not shown, thus completing the processing operation, i.e., the wafer grinding method according to the first embodiment.

As described above, the wafer grinding method according to the first embodiment includes a first grinding step 1003 in which the grinding wheel 25 is brought into contact with the central region 205-1 of the back surface 205 of the wafer 200 to grind the region including the central region 205-1, and then a second positioning step 1004 in which the holding table 10 is positioned at the second position 302 relative to the grinding unit 20 so that the rotation trajectory 251-2 of the grinding wheel 25 does not pass through the center 111 and the central region 205-1, thereby reducing the frequency with which the central region 205-1 of the back surface 205 of the wafer 200 is ground.

In addition, in the wafer grinding method according to the first embodiment, the wafer 200 is ground to the finishing thickness 206 while the holding table 10 is moved back and forth between the second position 302 and the third position 303 relative to the grinding unit 20 in an area that does not pass through the center 111 in the second grinding step 1005, so that the variation in the thickness of the wafer 200 after grinding can be suppressed. In addition, in the first embodiment, the third position 303 is set closer to the loading/unloading position 6 than the second position 302, but the second position 302 may be located closer to the loading/unloading position 6 than the third position 303.

As a result, the wafer grinding method according to embodiment 1 has the effect of preventing the center of the wafer 200 from becoming thin and minimizing thickness variation.

In addition, in the wafer grinding method according to the first embodiment, the grinding wheel 25 is brought into contact with the central region 205-1 of the back surface 205 of the wafer 200 in the first grinding step 1003 to grind the region including the central region 205-1, and then in the second grinding step 1005, the wafer 200 is ground to the finishing thickness 206 in the region not passing through the center 111 while the holding table 10 is moved back and forth between the second position 302 and the third position 303 relative to the grinding unit 20, so that it is not necessary to form the holding surface 11 into a complex shape such as a cone shape with the center 111 as the apex. As a result, the wafer grinding method according to the first embodiment can prevent the time required for grinding the holding surface 11 from becoming too long.

[Modifications]
A wafer grinding method according to a modified example of the first embodiment of the present invention will be described with reference to the drawings. Fig. 15 is a diagram showing the relative moving speed in the Z-axis direction between the holding table and the grinding unit in the wafer grinding method according to the modified example of the first embodiment. In Fig. 15, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

The wafer grinding method according to the second embodiment is the same as that according to the first embodiment, except that, as shown in FIG. 15, in the second positioning step 1004 and the second grinding step 1005, the moving speed in the Z-axis direction of the grinding unit 20 is set to zero, and in the second positioning step 1004 and the second grinding step 1005, the movement in the Z-axis direction by the grinding feed unit 30 of the grinding unit 20 is stopped. Note that the horizontal axis of FIG. 15 indicates the elapsed time from when the grinding device 1 starts the wafer grinding method according to the modified example of the first embodiment. The vertical axis of FIG. 15 indicates the moving speed of the grinding unit 20.

In the wafer grinding method according to the modified embodiment 1, an area including the central area 205-1 of the back surface 205 of the wafer 200 is ground in a first grinding step 1003, and then the holding table 10 is positioned at a second position 302 relative to the grinding unit 20 in a second positioning step 1004. In addition, in the wafer grinding method according to the modified embodiment 1, the wafer 200 is ground to the finishing thickness 206 while the holding table 10 is moved back and forth between the second position 302 and the third position 303 relative to the grinding unit 20 in a second grinding step 1005, so that, as in the first embodiment, it is possible to prevent the center of the wafer 200 from becoming thin and to suppress thickness variations to a small value.

Next, the inventor of the present invention confirmed the effect of the wafer grinding method according to embodiment 1. The results are shown in Figures 16, 17, and 18. Figure 16 is a diagram showing the variation in thickness of a wafer thinned to a finishing thickness by the wafer grinding method of the present invention. Figure 17 is a diagram showing the variation in thickness of a wafer thinned to a finishing thickness by the wafer grinding method of Comparative Example 1. Figure 18 is a diagram showing the variation in thickness of a wafer thinned to a finishing thickness by the wafer grinding method of Comparative Example 2.

The horizontal axis in Figures 16, 17, and 18 indicates the measurement position of the wafer where the thickness was measured, with the center being the center of the wafer 200, the right edge being one edge of the wafer, and the left edge being the other edge with the center located between the one edge of the wafer. The vertical axis in Figures 16, 17, and 18 indicates the thickness of the wafer 200 measured at each measurement position. In the wafer grinding methods of the present invention, Comparative Example 1, and Comparative Example 2, a grinding wheel 25 with a blade width of 2 mm was used.

In the wafer grinding method of the present invention shown in FIG. 16, the wafer 200 was ground by the wafer grinding method according to the first embodiment. In the wafer grinding method of Comparative Example 1 shown in FIG. 17, the wafer 200 was ground by constantly bringing the grinding wheel 25 into contact with the central region 205-1 of the back surface 205 of the wafer 200, i.e., the wafer 200 was ground only by the first grinding step 1003 of the wafer grinding method according to the first embodiment. In the wafer grinding method of Comparative Example 2 shown in FIG. 18, the wafer 200 was ground by constantly bringing the grinding wheel 25 into contact with the outer periphery side of the central region 205-1 of the back surface 205 of the wafer 200, i.e., the wafer 200 was ground only by the second grinding step 1005 of the wafer grinding method according to the first embodiment.

In Comparative Example 1 shown in Figure 17, a circular recess 601 with a diameter equivalent to the blade width of the grinding wheel 25 was formed in the central region 205-1 of the back surface 205 of the wafer 200. The difference 602 between the bottom of the recess 601 and the finished thickness 206 of the wafer 200 was 2 μm. In Comparative Example 2 shown in Figure 18, the thickness of the central region 205-1 of the back surface 205 of the wafer 200 was the finished thickness 206, but a ring-shaped recess 603 with a width equivalent to the blade width of the grinding wheel 25 was formed on the outer periphery of the central region 205-1. The difference 604 between the bottom of the recess 603 and the finished thickness 206 of the wafer 200 was 3 μm. In contrast to these Comparative Examples 1 and 2, in the present invention shown in FIG. 16, a circular recess 605 with a diameter of 15 mm was formed in the center of the back surface 205 of the wafer 200, but the difference 606 between the bottom of the recess 605 and the finished thickness 206 of the wafer 200 was 0.5 μm, which was much smaller than the differences 602 and 604 in Comparative Examples 1 and 2.

Therefore, according to Figures 16, 17 and 18, it has become clear that by grinding an area including the central area 205-1 of the back surface 205 of the wafer 200 in the first grinding step 1003, and then positioning the holding table 10 at the second position 302 relative to the grinding unit 20 in the second positioning step 1004, and grinding the back surface 205 of the wafer 200 in the second grinding step 1005, it is possible to prevent the center of the wafer 200 from becoming thin and to keep thickness variations small.

The present invention is not limited to the above embodiment. In other words, the present invention can be implemented in various modifications without departing from the gist of the invention.

REFERENCE SIGNS LIST 1 Grinding device 10 Holding table 11 Holding surface 20 Grinding unit 25 Grinding wheel 30 Grinding feed unit 50 Horizontal movement unit 111 Center 112 Shaft 114 Radial area 200 Wafer 206 Finishing thickness 251, 251-2, 251-3 Rotation trajectory 301 First position 1001 Holding step 1002 First positioning step 1003 First grinding step 1004 Second positioning step 1005 Second grinding step

Claims (2)

a holding table having a conical holding surface with a vertex at the center and rotatable about an axis of the center of the holding surface;
a grinding unit having an annular grinding wheel rotatably mounted thereon and configured to grind the wafer held on the holding surface with the grinding wheel;
a horizontal movement unit that moves the holding table and the grinding unit relatively in a horizontal direction parallel to a lower surface of the grinding wheel;
a grinding feed unit for moving the grinding unit away from or toward the holding surface,
A method for grinding a wafer, comprising the steps of: thinning the wafer to a finish thickness in a radial region of the holding surface parallel to a lower surface of the grinding wheel, the method comprising the steps of:
a holding step of holding the wafer on the holding surface;
a first positioning step of positioning the holding table at a first position relative to the grinding unit by using the horizontal movement unit so that a rotational locus having a cutting edge width of the grinding wheel passes through a center of the holding surface;
a first grinding step of grinding the wafer to a predetermined thickness after the first positioning step;
a second positioning step of positioning the holding table relative to the grinding unit using the horizontal movement unit after the first grinding step such that a rotation locus of the second grinding wheel does not pass through a center of the holding surface;
a second grinding step of grinding the wafer to a finishing thickness by using the horizontal movement unit to reciprocate the holding table in a radial direction relative to the grinding unit in an area where a rotational trajectory of the grinding wheel does not pass through a center of the holding surface, using the horizontal movement unit;
A method for grinding a wafer comprising the steps of: In the second positioning step,
The holding table is moved relative to the grinding unit.
2. The method for grinding a wafer according to claim 1, further comprising the step of relatively moving said holding surface in a radial direction thereof from said first positioning step by a distance at least equivalent to the width of the cutting edge of said grinding wheel.

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