TW202408721A - Wafer grinding method for efficiently grinding a wafer to have a uniform thickness in a short time such that portions other than the central portion of the wafer are ground - Google Patents

Abstract

An object of the present invention is to provide a wafer grinding method that can efficiently grind a wafer to have a uniform thickness in a short time. A wafer grinding method is provided to grind a wafer W by enabling a rotating annular grindstone 26b to be in contact with a radius portion of the rotating wafer W held on a conical holding surface 11a of a chuck table 10, and the wafer W is ground by the following steps: a holding step in which the wafer W is held on the holding surface 11a; a first grinding step in which the lower surface of the annular grindstone 26b is enabled to be in contact with the radius portion of the wafer W held on the holding surface 11a to form a slight recess W1 in the central portion Wa of the wafer W so as to thickly grind the peripheral portion Wb of the wafer W at the same time; and a second grinding step, in which, after the first grinding step, the inclination of the chuck table 10 and the annular grindstone 26b is adjusted in such a way that the lower surface of the annular grindstone 26b does not come into touch with the center of the wafer W, such that portions other than the central portion Wa of the wafer W are ground.

Description

Wafer grinding method

The present invention relates to a wafer grinding method for grinding a wafer held on a holding surface of a chuck table using an annular grinding stone.

In the manufacturing process of semiconductor components such as IC and LSI used in various electronic devices, in order to reduce the size and weight of the semiconductor components, the back side of the wafer is ground and the wafer is thinned to a predetermined thickness. For example, if the grinding device disclosed in Patent Document 1 is used and the lower surface of the annular grindstone is used to grind the radial portion of the wafer held on the chuck table, as described in Patent Document 2, the ground surface of the wafer will be ground. A tiny depression forms in the central part of the circle. This dent is thought to be caused by the fact that the holding surface of the chuck table holding the wafer is formed in a cone shape, so that the central part of the wafer becomes convex at the center part of the holding surface, and the convex central part is more grinding.

Therefore, Patent Document 3 has proposed a method of forming a holding surface by removing the center of the holding surface of the chuck table, that is, the apex of the cone. According to this method, it is possible to prevent the central portion of the wafer from being dented due to excessive grinding. form. [Known technical documents] [Patent Document]

[Patent Document 1] Japanese Patent Application Publication No. 2018-114573 [Patent Document 2] Japanese Patent Application Publication No. 2021-146416 [Patent Document 3] Japanese Patent Application Publication No. 2020-175472

[Problem to be solved by the invention] However, according to the holding surface forming method proposed in Patent Document 3, it takes a long time to form the holding surface of the chuck table, which has the problem of poor working efficiency.

The present invention was made in view of the above problems, and an object thereof is to provide a grinding method that can efficiently grind a wafer into a wafer with a uniform thickness in a short time.

[Technical means to solve the problem] In order to achieve the above object, the present invention is a wafer grinding method in which a rotating annular grindstone is brought into contact with a conical holding surface held on a chuck table and the radial portion of the rotating wafer is ground to grind the wafer. And it is characterized in that it is provided with: a holding step of holding the wafer on the holding surface; and a first grinding step of making the lower surface of the annular grinding stone contact the radius portion of the wafer held on the holding surface, and while Forming a tiny depression in the central part of the wafer while grinding the outer peripheral part of the wafer slightly thickly; and a second grinding step in which, after the first grinding step, the lower surface of the annular grinding stone does not contact the wafer The inclination of the chuck table and the annular grinding stone is relatively changed in a manner such as the center of the wafer, so as to grind the wafer except the central part.

[Effect of the invention] According to the present invention, in the first grinding step, a small depression is formed in the central part of the wafer while the peripheral part of the wafer is ground slightly thicker. In the second grinding step, the inclination of the chuck table and the annular grindstone is relatively changed in such a way that the lower surface of the annular grindstone does not contact the center of the wafer, and the slightly thicker peripheral part other than the central part of the wafer is ground. Therefore, by grinding in the second grinding step, the thickness of the wafer can be uniformly finished to the thickness of the depression formed in the central part of the wafer in the first grinding step. Therefore, it is not necessary to remove the vertex of the holding surface of the chuck table in such a way that a depression is not generated in the central part of the wafer, and it does not take a long time to form the holding surface. Therefore, the effect of efficiently grinding the wafer to a uniform thickness in a short time is obtained.

The following describes the implementation of the present invention based on the accompanying drawings.

First, based on FIGS. 1 and 2 , the structure of a wafer grinding device for implementing the method of the present invention will be described below. In addition, in the following description, the arrow directions shown in FIG. 1 are respectively referred to as the X-axis direction (left-right direction), the Y-axis direction (front-back direction), and the Z-axis direction (up-down direction).

[Grinding device] The grinding device 1 shown in FIG. 1 grinds a workpiece, i.e., a disk-shaped wafer W, and has the following components.

That is, as main components, the grinding device 1 includes: a chuck table 10 that holds the wafer W and rotates around the axis CL1 of the wafer W (see FIGS. 3 and 4 ); and the grinding unit 20 . It grinds the wafer W attracted and held on the chuck table 10; a thickness measuring device 30 that measures the thickness of the wafer W during the grinding process; a grinding feed means 40 that makes the grinding unit 20 relative to the chuck. The holding surface 11 a of the table 10 rises and falls in the vertical direction (Z-axis direction); the nozzle 50 supplies grinding to the contact area (grinding area) R (refer to FIG. 2 ) between the annular grindstone 26 b of the grinding unit 20 and the wafer W. water; a tilt adjustment mechanism 70 that adjusts the tilt of the chuck table 10; and a horizontal movement mechanism 80 that moves the chuck table 10 in the horizontal direction (Y-axis direction) relative to the holding surface 11a.

Here, the wafer W is made of a single crystal silicon mother material, and in the state shown in FIG. 1 , a plurality of unillustrated components are formed on the front side facing downward, and these components are protected by a protective film T attached to the front side of the wafer W. Furthermore, the front side (the lower side in FIG. 1 ) of the wafer W is attracted and held on the holding surface 11 a of the chuck table 10 through the protective film T, and the back side (the upper side in FIG. 1 ) of the wafer W is ground by the grinding stone 26 b of the grinding unit 20 while receiving the supply of grinding water from the nozzle 50.

Next, the configurations of the chuck table 10, the grinding unit 20, the thickness measuring device 30, the grinding feed means 40, the nozzle 50, the tilt adjustment mechanism 70, and the horizontal movement mechanism 80, which are the main components of the grinding device 1, will be described respectively. .

(Chuck stage) The chuck stage 10 is a disk-shaped member, and is composed of a disk-shaped frame 10A and a porous member 11, and the porous member 11 is mounted in a circular recess 10a formed in the center of the frame 10A. Here, the porous member 11 is made of porous ceramics, etc., and its upper surface constitutes a holding surface 11a for attracting and holding the disk-shaped wafer W.

Furthermore, the chuck table 10 is rotationally driven in the arrow direction (counterclockwise direction) in FIG. 2 about the axis CL1 by a rotational drive mechanism (not shown). That is, the chuck table 10 has a rotation shaft 12 extending vertically and integrally from the center downward, and the rotation shaft 12 is rotationally driven at a predetermined speed by a rotation drive mechanism (not shown). In addition, although not shown in the figure, the porous member 11 of the chuck table 10 is selectively connected to a suction source not shown in the figure, such as a vacuum pump.

Furthermore, the grinding device 1 of the present embodiment has a rectangular box-shaped base 100 which is long in the Y-axis direction (front-rear direction), and the chuck table 10 faces a rectangular opening 100a which is long in the Y-axis direction and is opened in the base 100. Moreover, the periphery of the chuck table 10 of the opening 100a is covered by a rectangular plate-shaped cover 101, and the front and rear (-Y direction and +Y direction) parts of the cover 101 of the opening 100a are respectively covered by bellows-shaped retractable covers 102 and 103 which move and retract together with the cover 101. Therefore, no matter where the chuck table 10 is on the Y axis, the opening 100a is always closed by the cover 101 and the retractable covers 102 and 103, thereby preventing foreign matter from entering the base 100 through the opening 100a.

(Grinding unit) The grinding unit 20 includes: a spindle housing 22 fixed to a retaining seat 21; a spindle motor 23 accommodated in the spindle housing 22; a vertical spindle 24 driven by the spindle motor 23; a disk-shaped mounting member 25 mounted on the lower end of the spindle 24; and a grinding wheel 26 detachably mounted on the lower surface of the mounting member 25. Here, the grinding wheel 26 is composed of a disk-shaped base 26a and a plurality of annular grindstones 26b as a machining tool mounted in an annular shape on the lower surface of the base 26a. In addition, the annular grindstone 26b is a rectangular block-shaped tool used for grinding the wafer W, and its lower surface constitutes the grinding surface that contacts the upper surface (grinding surface) of the wafer W.

(Thickness gauge) The thickness gauge 30 is a height gauge for measuring the thickness of the wafer W held on the chuck table 10 during the grinding process, and has a first contactor 31 in contact with the upper surface of the wafer W and a second contactor 32 in contact with the upper surface of the frame 10A of the chuck table 10. Here, although the height of the upper surface of the wafer W during the grinding process is measured by the first contactor 31, the thickness of the wafer W is obtained by the difference between the height of the upper surface of the wafer W measured by the first contactor 31 and the height of the upper surface of the frame 10A measured by the second contactor 32.

(Grinding feed method) The grinding feed means 40 moves the grinding unit 20 up and down in the vertical direction (Z-axis direction) relative to the holding surface 11a of the chuck table 10, and is arranged on the -Y-axis direction end surface (front) of the rectangular box-shaped cylinder 41. surface), the rectangular box-shaped column 41 is vertically erected on the +Y-axis direction end (rear end) of the upper surface of the base 100 . This grinding feed means 40 moves a rectangular plate-shaped lifting plate 42 mounted on the back of the holder 21 along with the holder 21, the spindle 24 held by the holder 21, and the grinding wheel 26 along a pair of left and right guide rails 43. Raise and lower in the Z-axis direction. Here, a pair of left and right guide rails 43 are arranged perpendicularly and parallel to each other on the front surface of the column 41 .

In addition, between the pair of left and right guide rails 43, a rotatable ball screw 44 is vertically installed along the Z-axis direction (up and down direction). The upper end of the ball screw 44 is connected to the driving source, that is, the forward and reverse rotation. Electric motor 45 links. Here, the electric motor 45 is installed vertically on the column 41 through a rectangular plate-shaped bracket 46 installed on the upper surface of the column 41 . In addition, the lower end of the ball screw 44 is rotatably supported by the column 41, and the ball screw 44 is screwed with a nut member (not shown), and the nut member (not shown) faces rearward (+Y-axis direction). It is protrudingly provided on the back surface of the lifting plate 42 .

Therefore, if the electric motor 45 is started to rotate the ball screw 44 forward and reverse, the lifting plate 42 equipped with a nut component (not shown) threaded with the ball screw 44 will move up and down along a pair of guide rails 43 together with the grinding unit 20, so that the grinding unit 20 will rise and fall to set the grinding amount (grinding surplus) of the grinding stone 26b for the wafer W.

(Nozzle) The nozzle 50 supplies grinding water such as pure water to the contact portion between the grinding stone 26b and the wafer W during the grinding process, that is, the grinding area R (see FIG. 2), and sprays the grinding water from the inner side of the grinding stone 26b that covers the wafer W and rotates during the grinding process. More specifically, the nozzle 50 is a member bent into an inverted L shape, which sprays the grinding water in a radial straight line from the outer periphery of the wafer W toward the center.

(Tilt adjustment mechanism) The tilt adjustment mechanism 70 is a mechanism for adjusting the tilt of the chuck table 10. As shown in FIG. 1, it is provided between the flange 13 of the chuck table 10 and the slider 82 described below. Specifically, as shown in Figure 2, the tilt adjustment mechanism 70 is composed of two actuators 71 and a pivot 72. The actuators 71 and the pivot 72 are at equal angular intervals (120° spacing) arranged in the circumferential direction.

Here, each actuator 71 moves a rod (not shown) up and down to tilt the chuck table 10 around the pivot axis 72 to adjust the inclination of the holding surface 11a relative to the horizontal plane. In addition, each actuator 71 may also be provided with a vertical load measuring device such as a load cell, which is used to measure the vertical load acting on the wafer W in the vertical direction from the annular grindstone 26 b.

(horizontal moving mechanism) The horizontal moving mechanism 80 is a mechanism that moves the chuck table 10 in the horizontal direction (Y-axis direction) with respect to the holding surface 11a. As shown in FIG. 1, it is arranged inside the rectangular block-shaped interior of the base 100. on base 81. This horizontal movement mechanism 80 includes a block-shaped slider 82 that can slide in the Y-axis direction along a pair of left and right guide rails 83 arranged parallel to each other in the Y-axis direction (front-rear direction). Therefore, the chuck table 10 supported by the slider 82 and the rotation drive mechanism (not shown) can slide along the Y-axis direction together with the slider 82 .

Furthermore, a rotatable ball screw 84 extending in the Y-axis direction (forward and backward direction) is arranged between a pair of left and right guide rails 83 on the inner base 81, and one end of the ball screw 84 in the Y-axis direction (the left end in FIG. 1 ) is connected to a driving source, namely, an electric motor 85 that can rotate forward and backward. Furthermore, the other end of the ball screw 84 in the Y-axis direction (the right end in FIG. 1 ) is rotatably supported by the inner base 81 via a bearing 86 erected on the inner base 81. Furthermore, the ball screw 84 is screwed into a nut member (not shown) that is protruded downward from the slider 82.

Therefore, when the electric motor 85 is activated to rotate the ball screw 84 forward and reverse, the nut member (not shown) threadedly engaged with the ball screw 84 slides in the Y-axis direction (forward and backward direction) along the ball screw 84 together with the slider 82, so the chuck table 10 also moves in the Y-axis direction together with the slider 82. As a result, the wafer W attracted and held on the holding surface 11a of the chuck table 10 also moves in the Y-axis direction.

[Wafer grinding method] Next, the grinding method of the wafer W of the present invention performed by the grinding device 1 configured as above will be described below based on FIGS. 3 to 5 .

Before the grinding process of the wafer W, the holding surface 11a of the chuck table 10 holding the wafer W is formed into a conical surface with the center as the apex by self-grinding, that is, as shown in FIGS. 3 and 4 It is formed as a slope inclined downward from the center toward the radially outer side. In addition, although the conical shape of the holding surface 11a is exaggerated in FIGS. 3 and 4 , in fact, the inclination of the conical surface is so slight that it cannot be recognized by the naked eye.

The method of the present invention is a method for grinding a wafer W through 1) a holding step, 2) a first grinding step, and 3) a second grinding step. Hereinafter, the holding step, the first grinding step, and the second grinding step are described respectively.

1) Holding step: The holding step is a step of holding the wafer W to be ground on the holding surface 11a of the chuck table 10. In this holding step, the wafer W is placed on the holding surface 11a of the chuck table 10 with the protective film T (see Figure 1) facing downward. Then, the porous component 11 of the chuck table 10 is connected to a suction source (not shown) such as a vacuum pump, and the porous component 11 is evacuated. In this way, a negative pressure is generated in the porous component 11, and the wafer W is attracted by the negative pressure and held on the holding surface 11a of the chuck table 10.

2) The first grinding step: In the first grinding step, the horizontal moving mechanism 80 shown in FIG. 1 is driven to move the chuck table 10 in the +Y-axis direction (rearward), and the wafer W attracted and held by the chuck table 10 is positioned in the grinding unit. 20 below the grinding wheel 26. That is, when the electric motor 85 is started and the ball screw 84 is rotated, the slider 82 equipped with a nut member (not shown) screwed to the ball screw 84 will move along the left and right pairs together with the chuck table 10 and the like. The guide rail 83 slides in the +Y-axis direction, so that the wafer W held on the holding surface 11 a of the chuck table 10 is positioned below the grinding wheel 26 of the grinding unit 20 . In addition, at this time, the horizontal positional relationship between the two is adjusted so that the lower surface (processed surface) of the annular grindstone 26 b passes through the center of the wafer W (see FIG. 2 ).

Then, the rotation drive mechanism (not shown) is driven to rotate the chuck table 10, so that the wafer W held on the holding surface 11a of the chuck table 10 is rotated at a predetermined rotation speed (eg, 1,000 rpm), and the spindle motor 23 is driven in advance to rotate the grinding wheel 26.

Then, in this first grinding step, as shown in FIG. 3 , with the axis CL1 of the chuck table 10 tilted at a predetermined first angle α relative to the axis CL2 perpendicular to the spindle 24, the lower surface of the annular grindstone 26 b is brought into contact with the radial portion of the wafer W held on the holding surface 11 a of the chuck table 10, and the annular grindstone 26 b is lowered in the -Z axis direction (the direction approaching the holding surface) by the grinding feed means 40 until the thickness of the wafer W (the thickness measured by the thickness gauge 30) reaches a predetermined thickness.

That is, when the electric motor 45 of the grinding feed means 40 is driven and the ball screw 44 is rotated, the lifting plate 42 provided with a nut member (not shown) threadedly engaged with the ball screw 44 is lowered in the -Z axis direction together with the grinding wheel 26 and the like. In this way, the lower surface (grinding surface) of the annular grindstone 26b of the grinding wheel 26 contacts the upper surface (back surface) of the wafer W. In this way, if the grinding wheel 26 is further lowered in the -Z axis direction by only a predetermined amount from the state in which the lower surface of the annular grindstone 26b contacts the upper surface of the wafer W, the upper surface of the wafer W is only ground by the predetermined amount by the annular grindstone 26b. Furthermore, as described above, during the grinding of the wafer W, the grinding water is sprayed from the nozzle 50 in a radial straight line from the outer periphery of the wafer W toward the center.

As described above, as a result of the wafer W being ground by the annular grindstone 26b, as shown in FIG5(a), a tiny depression W1 with a thickness t1 is formed in the central portion Wa of the upper surface of the wafer W, and the peripheral portion Wb other than the central portion Wa having the depression W1 is ground to be slightly thicker than the thickness t1 of the central portion Wa. Here, the maximum thickness at the peripheral edge of the wafer W is set to t2. In addition, the processing area R of the wafer W performed by the annular grindstone 26b in this first grinding step becomes the arc-shaped portion shown in FIG2.

3) Second grinding step: In the second grinding step performed after the above-described first grinding step, as shown in FIG. 4 , the axis CL1 of the chuck table 10 is moved so that the lower surface of the annular grindstone 26 b does not contact the center of the wafer W. The vertical axis CL2 of the spindle 24 (annular grindstone 26b) is only inclined at the second angle β and the descent of the annular grindstone 26b by the grinding and feeding means 40 has stopped (in the direction approaching the holding surface 11a While moving), the outer peripheral portion Wb of the wafer W other than the central portion Wa where the recess W1 is formed is ground by the annular grindstone 26 b.

As a result of the above, the peripheral portion Wb (the shaded portion of FIG. 5 (a) ) of the wafer W shown in FIG. 5 (a) which has been ground in the first grinding step is ground by the second grinding step, and as shown in FIG. 5 (b), the thickness of the entire wafer W becomes equal to the thickness t1 of the central portion Wa where the recess W1 is formed.

As described above, in the wafer grinding method of the present invention, the grinding step is set as two stages of a first grinding step and a second grinding step. In the first grinding step, a tiny depression W1 is formed in the central portion Wa of the wafer W while the peripheral portion Wb of the wafer W is ground slightly thicker. In the second grinding step, the inclination of the chuck table 10 and the annular grindstone 26b is relatively changed in such a way that the lower surface of the annular grindstone 26b does not contact the center of the wafer W, and the slightly thicker peripheral portion Wb other than the central portion Wa of the wafer W is ground. Therefore, by grinding in the second grinding step, the thickness of the wafer W can be uniformly finished to the thickness t1 of the depression W1 formed in the central portion Wa of the wafer W in the first grinding step. Therefore, it is not necessary to remove the top of the holding surface 11a of the chuck table 10 so as not to generate the depression W1 in the central portion Wa of the wafer W, and it does not take a long time to form the holding surface 11a. Therefore, the wafer W can be efficiently ground to a uniform thickness t1 in a short time.

Here, FIG6 (a) shows the radial thickness distribution of the wafer ground by the method of the present invention, and FIG6 (b) shows the radial thickness distribution of the wafer ground by the conventional grinding method. However, in the wafer ground by the conventional grinding method, as shown in FIG6 (b), a depression is generated in the central portion, whereas in the wafer ground by the method of the present invention, as shown in FIG6 (a), no depression is generated in the central portion, and the radial thickness shows an almost uniform distribution. In addition, in FIG6, the horizontal axis is the radial distance from the center of the wafer (the center is taken as 0), and the vertical axis is the thickness of the wafer.

In addition, in the above embodiment, in the first grinding step and the second grinding step, the axis CL1 of the chuck table 10 is tilted by the first angle α and the second angle respectively with respect to the axis CL2 of the spindle 24 . In the state β, the wafer W is ground by the annular grindstone 26 b. However, the wafer W can also be ground by inclining the axis CL2 of the spindle 24 with respect to the axis CL1 of the chuck table 10 by the first angle α and the second angle respectively. In the state of angle β, the wafer W is ground by the annular grindstone 26b.

In addition, the present invention is not limited to the embodiments described above, and it is natural that various modifications can be made within the scope of the invention claims and the technical ideas described in the specification and drawings.

1: Grinding device 10: Chuck table 10A: Frame 10a: Concave portion of frame 11: Porous member 11a: Holding surface 12: Rotating shaft 13: Flange 20: Cutting unit 21: Holding seat 22: Spindle housing 23: Spindle motor 24: Spindle 25: Mounting part 26: Grinding wheel 26a: Base 26b: Ring grindstone 30: Thickness gauge 31: First contactor 32: Second contactor 40: Grinding feed means 41: Column 42: Lifting plate 43: Guide rail 44: Ball screw 45: Electric motor 46: Bracket 50: Nozzle 70: Tilt adjustment mechanism 71: Actuator 72: Pivot 80: Horizontal movement mechanism 81: Internal base 82: Slide 83: Guide rail 84: Ball screw 85: Electric motor 86: Bearing 100: Base 100a: Opening of base 101: Cover 102,103: Telescopic cover CL1: Axis of chuck table CL2: Axis of spindle R: Grinding area T: Protective film t1: Thickness of the center of the wafer t2: Maximum thickness of the outer peripheral part of the wafer W: Wafer W1: Concave of the wafer Wa: Center of the wafer Wb: The outer periphery of the wafer

FIG. 1 is a perspective view showing a portion of a wafer grinding device for implementing the method of the present invention. FIG. 2 is a top view showing the positional relationship between the wafer and the annular grindstone. FIG. 3 is a partial cross-sectional view showing the first grinding step in the method of the present invention in the direction of arrow A of FIG. 2. FIG. 4 is a partial cross-sectional view showing the second grinding step in the method of the present invention in the direction of arrow A of FIG. 2. FIG. 5 (a) is a longitudinal cross-sectional view of a wafer ground in the first grinding step of the method of the present invention, and FIG. 5 (b) is a longitudinal cross-sectional view of a wafer ground in the second grinding step of the method of the present invention. FIG6 (a) is a diagram showing the radial thickness distribution of a wafer ground by the method of the present invention, and FIG6 (b) is a diagram showing the radial thickness distribution of a wafer ground by a conventional grinding method.

10:Chuck table

10A: Frame

11: Porous components

11a: Keep the face

12: Rotation axis

24: Main axis

25:Installation parts

26:Grinding wheel

26a:Abutment

26b: Ring-shaped grinding stone

40: Grinding feeding means

CL1: Chuck table axis

CL2: Spindle axis

W: Wafer

β: Second angle

Claims (2)

A wafer grinding method, which grinds the wafer by contacting a rotating annular grindstone with a conical holding surface held on a chuck table and grinding the radial portion of the rotating wafer, and includes: a holding step, which Hold the wafer on the holding surface; In the first grinding step, the lower surface of the annular grindstone is brought into contact with the radial portion of the wafer held on the holding surface, and a minute depression is formed in the central portion of the wafer while grinding the wafer. The outer peripheral part is ground slightly thicker; and The second grinding step, after the first grinding step, relatively changes the inclination of the chuck table and the annular grinding stone in such a way that the lower surface of the annular grinding stone does not contact the center of the wafer, and grinds outside the central part of the wafer. The wafer grinding method of claim 1, wherein the first grinding step is performed by moving the grinding stone in a direction close to the holding surface until the thickness of the wafer reaches a predetermined thickness, and the second grinding step is performed by stopping the movement of the annular grinding stone in a direction close to the holding surface and grinding the portion other than the central portion of the wafer with the rotating annular grinding stone.