Wafer grinding method

Abstract

To provide a grinding method of a wafer, which can form a recessed portion having a predetermined depth and having an obtuse angle between its bottom surface and side surface, in a back surface of the wafer even if multiple grinding stones wear in association with grinding of the wafer on a back surface side.SOLUTION: A second relative speed of a grinding wheel and a wafer along a second direction in a grinding step is set such that a relative movement of the grinding wheel and the wafer along a first direction and a relative movement of the grinding wheel and the wafer along the second direction are concurrently initiated and are concurrently finished. Specifically, the second relative speed is set taking into consideration parameters which are arbitrarily set, and a wear amount of multiple grinding stones as known before or in course of the grinding step (the absolute value of an amount of change in thickness of the grinding stones through the grinding step).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a wafer grinding method for forming recesses having a predetermined depth by grinding the back surface side of a wafer having a plurality of devices formed on the front surface side. [Background technology]

[0002] Chips for devices such as integrated circuits (ICs) are essential components in various electronic devices such as mobile phones and personal computers. These chips are manufactured, for example, by dividing a wafer on which multiple devices are formed on its surface into regions containing individual devices.

[0003] The wafer may be thinned before being divided in order to produce smaller chips. For example, a method for thinning the wafer is grinding using a grinding wheel having a plurality of grinding wheels and a wheel base having a mounting surface on which the plurality of grinding wheels are fixed in a circular, discrete manner. This grinding is generally performed in the following order:

[0004] First, the wafer is held with its back surface exposed. Next, while both the wafer and a grinding wheel having an outer diameter longer than the radius of the wafer are rotated, one of multiple grinding stones is brought into contact with the center of the back surface of the wafer. Next, while both the grinding wheel and the wafer are still rotating, the installation surface of the wheel base and the front surface of the wafer are brought closer together in the direction in which the rotation axis of the grinding wheel extends (hereinafter also referred to as the "first direction").

[0005] This grinds the back side of the wafer, thinning the wafer. However, thinning the wafer reduces its rigidity, which can make it difficult to handle in subsequent processes. Therefore, a method has been proposed for grinding the wafer so as to thin only the portions of the wafer that overlap with multiple devices (see, for example, Patent Document 1).

[0006] In this method, the backside of the wafer is ground using a grinding wheel having an outer diameter smaller than the radius of the wafer, leaving the outer periphery of the wafer and forming a disk-shaped recess on the backside of the wafer, which prevents a decrease in the rigidity of the wafer and makes it easier to handle the wafer in subsequent processes.

[0007] Furthermore, rewiring that connects to the devices formed on the front side may be formed on the back side of the wafer by photolithography. When the recesses are formed on the back side of the wafer, the angle between the bottom and side surfaces of the recesses is a right angle.

[0008] In this case, when the chemical solution used in photolithography to dissolve the resist is discharged from the recess, a portion of the chemical solution may remain near the outer periphery of the bottom surface of the recess. In light of this, a method has been proposed for grinding a wafer so as to form a recess in the shape of an inverted truncated cone on the back surface of the wafer (see, for example, Patent Document 2).

[0009] In this method, while both the grinding wheel and the wafer are rotating, the mounting surface of the wheel base and the surface of the wafer are brought closer together in a first direction, and the rotation axis of the grinding wheel and the center of the wafer are brought closer together in a direction perpendicular to the first direction (hereinafter also referred to as the "second direction"), thereby grinding the back side of the wafer.

[0010] In this case, the angle between the bottom and side of the recess formed on the back surface of the wafer is an obtuse angle, which prevents part of the chemical solution from remaining near the periphery of the bottom of the recess when the chemical solution is discharged from the recess, even when rewiring is formed on the back surface of the wafer by photolithography. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-19461 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-54808 Summary of the Invention [Problem to be solved by the invention]

[0012] When a wafer is ground using a grinding wheel, the grinding stones are worn down and the thickness of the grinding stones is reduced. Therefore, if the back surface of the wafer is ground to form an inverted truncated cone-shaped recess on the back surface of the wafer without considering the wear of the grinding stones, the depth of the recess will be shallower than the predetermined depth.

[0013] In such cases, after forming an inverted truncated cone-shaped recess on the back surface of the wafer, the back surface of the wafer may be ground by rotating both the grinding wheel and the wafer and moving the grinding wheel and the wafer relative to each other in a first direction until the depth of the recess reaches a predetermined depth.

[0014] However, when a recess having a predetermined depth is formed on the backside of the wafer using this procedure, the angle between the bottom surface of the recess and the lower end of the side surface becomes a right angle, and in this case, when the chemical solution or the like is discharged from the recess, some of the chemical solution may remain near the outer periphery of the bottom surface of the recess.

[0015] In view of this, an object of the present invention is to provide a wafer grinding method that can form a recess on the back surface of a wafer that has a predetermined depth and has an obtuse angle between the bottom surface and the side surface, even if multiple grinding wheels are worn down during grinding of the back surface of the wafer. [Means for solving the problem]

[0016] According to the present invention, there is provided a method for grinding a wafer, which forms recesses having a predetermined depth by grinding the back surface of a wafer having a plurality of devices formed on its front surface, the method comprising: a holding step of holding the wafer with the back surface exposed; a contact step of bringing one of the plurality of grinding wheels into contact with the center of the back surface of the wafer while rotating both the wafer and a grinding wheel having a wheel base with a mounting surface to which the plurality of grinding wheels are fixed in a circularly spaced relationship; and a grinding step of, after the contact step, bringing the mounting surface of the wheel base and the front surface of the wafer closer together by a first movement amount along a first direction while keeping both the grinding wheel and the wafer rotating, thereby grinding the back surface of the wafer. a grinding step, wherein the first movement amount is a distance obtained by adding the predetermined depth and the wear amounts of the plurality of grinding wheels when the wafer is ground to the predetermined depth, and the second movement amount is an arbitrarily set distance less than the width of each of the plurality of grinding wheels along the second direction, a first relative velocity between the grinding wheel and the wafer along the first direction in the grinding step is a constant velocity that is arbitrarily set, and a second relative velocity between the grinding wheel and the wafer along the second direction in the grinding step is a constant or variable velocity that is set in consideration of the predetermined depth, the wear amounts, the second movement amount, and the first relative velocity so that the relative movement between the grinding wheel and the wafer along the first direction and the relative movement between the grinding wheel and the wafer along the second direction start and end simultaneously.

[0017] Preferably, the wear amount is known prior to the grinding step, and the second relative velocity is a velocity obtained by dividing the second movement amount by the time obtained by dividing the first movement amount by the first relative velocity.

[0018] Alternatively, the recessed portion may include a first portion having an inverted truncated cone shape and a second portion having a side surface that is steeper inclined than the side surface of the first portion, and the grinding step may include moving the installation surface of the wheel base and the front surface of the wafer closer together by a third movement amount along the first direction while both the grinding wheel and the wafer are rotating, and moving the rotation axis of the grinding wheel and the center of the wafer closer together by a fourth movement amount along the second direction, thereby grinding the first portion onto the back surface of the wafer. a preliminary grinding step of forming a second portion on the back surface of the wafer, a measuring step of measuring a depth of the first portion after the preliminary grinding step, and a main grinding step of forming the second portion on the back surface of the wafer by bringing the installation surface of the wheel base and the front surface of the wafer closer together by a fifth movement amount along the first direction and bringing the rotation axis of the grinding wheel and the center of the wafer closer together by a sixth movement amount along the second direction while both the grinding wheel and the wafer are rotating, The second relative velocity in the preliminary grinding step is a velocity obtained by dividing the second movement amount by a time obtained by dividing the predetermined depth by the first relative velocity, the third movement amount is an arbitrarily set distance less than the predetermined depth, the fourth movement amount is a distance obtained by multiplying the second relative velocity in the preliminary grinding step by the time obtained by dividing the third movement amount by the first relative velocity, and the wear amount is the predetermined depth and the third movement amount minus the depth of the first portion. the fifth movement amount is a distance obtained by multiplying the wear amount by a value obtained by dividing the distance obtained by subtracting the third movement amount from the predetermined depth by the depth of the first portion; the sixth movement amount is a distance obtained by subtracting the fourth movement amount from the second movement amount; and the second relative velocity in the main grinding step is a velocity obtained by dividing the sixth movement amount by a time obtained by dividing the fifth movement amount by the first relative velocity. [Effects of the Invention]

[0019] In the present invention, the second relative velocity of the grinding wheel and the wafer along the second direction in the grinding step is set so that the relative movement of the grinding wheel and the wafer along the first direction and the relative movement of the grinding wheel and the wafer along the second direction start and end simultaneously.

[0020] Specifically, this second relative velocity is set in consideration of an arbitrarily set parameter and the amount of wear of the grinding wheels (the absolute value of the amount of change in thickness of the grinding wheels before and after the grinding step) grasped prior to or during the grinding step. As a result, in the present invention, it is possible to form a recess on the back surface of the wafer that has a predetermined depth and has an obtuse angle between the bottom surface and the side surface. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a perspective view schematically showing an example of a grinding device. [Figure 2] FIG. 2 is a cross-sectional view schematically showing an example of a grinding device. [Figure 3] FIG. 3 is a flow chart that schematically illustrates an example of a wafer grinding method. [Figure 4] 4(A) and 4(B) are each a partial cross-sectional side view that schematically shows the state of the contact step. [Figure 5] FIG. 5(A) is a partially cross-sectional side view showing an example of a grinding step, and FIG. 5(B) is a cross-sectional view showing a wafer after the grinding step shown in FIG. 5(A). [Figure 6] FIG. 6 is a flow chart that schematically illustrates steps included in another example of the grinding step. [Figure 7] FIG. 7(A) is a partially sectional side view showing a schematic view of the pre-grinding step, and FIG. 7(B) is a sectional view showing a schematic view of the wafer after the pre-grinding step. [Figure 8]FIG. 8(A) is a partially sectional side view showing a typical state of the main grinding step, and FIG. 8(B) is a typical cross-sectional view showing the wafer after the preliminary grinding step. DETAILED DESCRIPTION OF THE INVENTION

[0022] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a perspective view schematically showing an example of a grinding apparatus, and Fig. 2 is a cross-sectional view schematically showing the example of the grinding apparatus shown in Fig. 1. Note that the X-axis direction (front-back direction) and the Y-axis direction (left-right direction) shown in Fig. 1 and Fig. 2 are directions perpendicular to each other on a horizontal plane, and the Z-axis direction (up-down direction) is a direction (vertical direction) perpendicular to the X-axis direction and the Y-axis direction.

[0023] 1 and 2 has a base 4 that supports each of the components. A rectangular parallelepiped groove 4a extending along the X-axis direction is formed on the top surface of this base 4. A pair of guide rails 6, each extending along the X-axis direction, is provided on the bottom surface of the groove 4a (see FIG. 2). A rectangular parallelepiped X-axis moving plate 8 is attached to the top of the pair of guide rails 6 in a manner that allows it to slide along the X-axis direction.

[0024] A screw shaft 10 extending along the X-axis direction is disposed between the pair of guide rails 6. A pulse motor 12 for rotating the screw shaft 10 is connected to the rear end of the screw shaft 10. A nut portion 14 for accommodating balls that circulate in response to the rotation of the screw shaft 10 is provided on the outer circumferential surface of the screw shaft 10 on which the threads are formed, thereby forming a ball screw.

[0025] The nut portion 14 is fixed to the underside of the X-axis moving plate 8. Therefore, when the screw shaft 10 is rotated by the pulse motor 12, the X-axis moving plate 8 moves along the X-axis direction together with the nut portion 14. Also, provided above the X-axis moving plate 8 are a rotating body having a driven pulley 16 connected to its lower end, and a rotational drive source (not shown) such as a motor connected to a drive pulley (not shown).

[0026] An endless belt (not shown) is stretched between the driven pulley 16 and the drive pulley. Furthermore, an inclination adjustment mechanism having one fixed shaft (not shown) and two movable shafts 18, each of which has a variable length along the Z-axis direction, is provided on the X-axis moving plate 8. The fixed shaft and the two movable shafts 18 are connected to the underside of a table base 20, and support the table base 20.

[0027] A through hole (not shown) is formed in the center of the table base 20, and a rotating body, the lower end of which is connected to the driven pulley 16, passes through this through hole. The upper end of this rotating body is connected to the underside of the disk-shaped chuck table 22. Therefore, when the rotation drive source connected to the drive pulley is operated so as to rotate the endless belt wound around the driven pulley 16, the chuck table 22 rotates in the circumferential direction of the chuck table 22.

[0028] Furthermore, the chuck table 22 is supported by the table base 20 via bearings (not shown). Therefore, even if the chuck table 22 is rotated as described above, the table base 20 does not rotate. On the other hand, when the lengths of the two movable shafts 18 along the Z-axis direction are adjusted in the tilt adjustment mechanism, the tilt of not only the table base 20 but also the chuck table 22 is adjusted.

[0029] The chuck table 22 has a disk-shaped frame 24 made of ceramics or the like. The frame 24 has a disk-shaped bottom wall and cylindrical side walls extending upright from the bottom wall. That is, a disk-shaped recess defined by the bottom wall and the side walls is formed on the upper surface of the frame 24.

[0030] The inner diameter of the side wall of the frame 24 is slightly shorter than the diameter of the wafer 11, which will be described later, and the outer diameter thereof is slightly longer than the diameter of the wafer 11. A flow path (not shown) that opens at the bottom surface of the recess is formed in the bottom wall of the frame 24, and this flow path communicates with a suction source (not shown) such as an ejector.

[0031] Furthermore, a circular porous plate 26 having a diameter roughly equal to that of a recess formed on the upper surface of the frame 24 is fixed to the recess. The porous plate 26 is made of, for example, porous ceramics. The upper surface of the porous plate 26 and the upper surface of the side wall of the frame 24 have a shape corresponding to the side of a cone (a shape in which the center protrudes beyond the outer periphery).

[0032] When a suction source communicating with a flow path formed inside the frame 24 is operated, a suction force acts on the space near the upper surface of the porous plate 26. Therefore, the upper surface of the porous plate 26 and the upper surfaces of the side walls of the frame 24 function as the holding surface 22a of the chuck table 22 (see FIG. 1).

[0033] For example, the wafer 11, which has a protective tape 13 attached to its front surface 11a, is placed on the holding surface 22a of the chuck table 22 so that the back surface 11b of the wafer 11 faces upward, and the suction source is operated to hold the wafer 11 on the chuck table 22.

[0034] The wafer 11 is made of a semiconductor material such as silicon, and has a plurality of devices formed on its front surface 11a. The protective tape 13 is made of a resin, for example, and prevents damage to the devices when the back surface 11b of the wafer 11 is ground.

[0035] Furthermore, a rectangular parallelepiped table cover 28 is provided around the periphery of the chuck table 22 so that the holding surface 22a is exposed. The width (length along the Y-axis direction) of this table cover 28 is approximately equal to the width of the groove 4a formed in the upper surface of the base 4. In addition, dustproof and drip-proof covers 30 that are extendable and contractible along the X-axis direction are provided in front and behind the table cover 28.

[0036] A quadrangular pillar-shaped support structure 32 is provided in an area of ​​the upper surface of the base 4 that is located behind the groove 4a. A pair of guide rails 34, each extending along the Z-axis direction, is provided on the front surface of the support structure 32. A slider 36 is provided on the front side of each of the pair of guide rails 34 in a manner that allows it to slide along the Z-axis direction (see FIG. 2).

[0037] The front end of the slider 36 is fixed to the rear surface side of a rectangular parallelepiped Z-axis moving plate 38. A screw shaft 40 extending along the Z-axis direction is disposed between the pair of guide rails 34. A pulse motor 42 for rotating the screw shaft 40 is connected to the upper end of the screw shaft 40.

[0038] A nut portion 44 that houses balls that circulate in response to the rotation of the screw shaft 40 is provided on the outer circumferential surface of the screw shaft 40, on which the threads are formed, to form a ball screw. The nut portion 44 is fixed to the rear surface side of the Z-axis moving plate 38. Therefore, when the screw shaft 40 is rotated by the pulse motor 42, the Z-axis moving plate 38 moves along the Z-axis direction together with the nut portion 44.

[0039] A grinding unit 46 is provided in front of the Z-axis moving plate 38. This grinding unit 46 has a cylindrical holding member 48 fixed to the front surface of the Z-axis moving plate 38. A cylindrical spindle housing 50 extending along the Z-axis direction is provided inside the holding member 48.

[0040] A cylindrical spindle 52 extending along the Z-axis direction is provided inside the spindle housing 50 (see FIG. 2). The spindle 52 is rotatably supported by the spindle housing 50, and its upper end is connected to a rotational drive source 54 such as a motor.

[0041] The lower end of the spindle 52 is exposed from the spindle housing 50 and is fixed to a disk-shaped wheel mount 56. An annular grinding wheel 58, having an outer diameter roughly equal to the diameter of the wheel mount 56, is attached to the underside of the wheel mount 56 using a fixing member (not shown) such as a bolt.

[0042] The grinding wheel 58 has a plurality of grinding stones 58a and a wheel base 58b having a mounting surface on which the plurality of grinding stones 58a are fixed in a circularly dispersed manner. When the rotary drive source 54 is operated, the wheel mount 56 and grinding wheel 58 rotate together with the spindle 52, with a rotation axis that is a straight line along the Z-axis direction. At this time, the plurality of grinding stones 58a trace a circular locus. The outer diameter of this locus is shorter than the radius of the wafer 11.

[0043] The grinding wheels 58a have abrasive grains such as diamond or cubic boron nitride (cBN) dispersed in a binder such as a vitrified bond or a resin bond. The wheel base 58b is made of a metal material such as stainless steel or aluminum.

[0044] A measuring unit 60 is provided in an area on the upper surface of the base 4, located to the side of the groove 4a and close to the grinding unit 46. This measuring unit 60 has, for example, a pair of height gauges 60a, 60b that measure the height of the positions where the respective measuring probes come into contact.

[0045] The probe of the height gauge 60a can be arranged so as to contact the back surface 11b of the wafer 11 held on the chuck table 22 via the protective tape 13. The probe of the height gauge 60b can be arranged so as to contact the holding surface 22a of the chuck table 22 (specifically, the upper surface of the side wall of the frame 24).

[0046] Therefore, by positioning the measuring probes of each height gauge 60a, 60b in this manner prior to or during grinding of the back surface 11b side of the wafer 11, the sum of the thickness of the wafer 11 and the thickness of the protective tape 13 can be measured in the measuring unit 60.

[0047] Furthermore, by positioning the measuring probes of each height gauge 60a, 60b in this manner before and after grinding the back surface 11b side of the wafer 11, the amount of grinding of the wafer 11 (the amount of change in the thickness of the wafer 11) can be measured in the measuring unit 60.

[0048] FIG. 3 is a flow chart schematically showing an example of a wafer grinding method for forming recesses having a predetermined depth by grinding the back surface 11b side of the wafer 11 in the grinding device 2.

[0049] In this method, first, the wafer 11 is held with the back surface 11b exposed (holding step: S1). In this holding step (S1), first, the chuck table 22 is moved forward. Specifically, the chuck table 22 is moved so as to be separated from the grinding unit 46 and positioned so that the wafer 11 can be loaded onto the holding surface 22a of the chuck table 22.

[0050] Next, the wafer 11 is loaded onto the holding surface 22a of the chuck table 22 via the protective tape 13 so that the center of the wafer 11 and the center of the holding surface 22a of the chuck table 22 are aligned. Next, a suction source communicating with the porous plate 26 via a flow path formed in the frame 24 of the chuck table 22 is operated so that the wafer 11 is held by the chuck table 22. This completes the holding step (S1).

[0051] Next, while both the grinding wheel 58 and the wafer 11 are being rotated, one of the grinding stones 58a is brought into contact with the center of the back surface 11b of the wafer 11 (contact step: S2). Each of Figures 4(A) and 4(B) is a partial cross-sectional side view schematically showing the contact step (S2).

[0052] In this contact step (S2), first, the chuck table 22 is moved backward. Specifically, the chuck table 22 is moved so that, in a plan view, the front end F of the trajectory of the multiple grinding stones 58a when the grinding wheel 58 is rotated overlaps with the center C of the back surface 11b of the wafer 11 in the Z-axis direction (see FIG. 4(A)).

[0053] The inclination of the chuck table 22 may be adjusted as necessary before or after moving the chuck table 22 rearward. Specifically, the inclination of the chuck table 22 may be adjusted so that the generatrix extending rearward from the center of the holding surface 22a of the chuck table 22 becomes parallel to the X-axis direction.

[0054] Next, both the grinding wheel 58 and the chuck table 22 are rotated. Next, while the grinding wheel 58 and the chuck table 22 are still rotating, the grinding unit 46 is lowered until the lower surfaces of the multiple grinding stones 58a come into contact with the back surface 11b of the wafer 11 (see FIG. 4(B)). This completes the contact step (S2).

[0055] Next, while both the grinding wheel 58 and the wafer 11 are rotating, the mounting surface of the wheel base 58b and the front surface 11a of the wafer 11 are moved closer together along the Z-axis direction by a first movement amount, and the rotation axis of the grinding wheel 58 and the center of the wafer 11 are moved closer together along the X-axis direction by a second movement amount, thereby grinding the back surface 11b side of the wafer 11 (grinding step: S3).

[0056] Here, the first movement amount is a distance obtained by adding the depth (predetermined depth) of the recess formed on the back surface 11b of the wafer 11 and the amount of wear of the plurality of grinding wheels 58a when the wafer 11 is ground to the predetermined depth. The second movement amount is a distance that is arbitrarily set to be less than the width of each of the plurality of grinding wheels 58a along the X-axis direction.

[0057] Furthermore, the relative speed between the grinding wheel 58 and the wafer 11 in the Z-axis direction when grinding the wafer 11 (hereinafter also referred to as the "first relative speed") generally has a large effect on the processing quality of the wafer 11. Therefore, in the grinding step (S3), the first relative speed is set to a constant speed suitable for grinding the wafer 11.

[0058] Furthermore, the relative speed between the grinding wheel 58 and the wafer 11 along the X-axis direction in this grinding step (S3) (hereinafter also referred to as the "second relative speed") is set differently depending on whether or not the amount of wear of the multiple grinding stones 58a has been grasped prior to the grinding step (S3).

[0059] The following describes a method for setting the second relative speed when the wear amounts of the grinding wheels 58a are known prior to the execution of the grinding step (S3). Fig. 5(A) is a partially sectional side view that schematically shows the state of the grinding step (S3) in which the second relative speed is set according to this method, and Fig. 5(B) is a sectional view that schematically shows the wafer 11 after the grinding step (S3) shown in Fig. 5(A).

[0060] In this case, the second relative velocity is set to be equal to the velocity obtained by dividing the second movement amount by the time obtained by dividing the first movement amount (the distance obtained by adding the depth of the recess formed on the back surface 11b of the wafer 11 and the wear amount of the multiple grinding wheels 58a) by the first relative velocity.

[0061] That is, if the depth of the recess formed on the back surface 11b of the wafer 11 is D, the amount of wear of the multiple grinding wheels 58a is W, the second movement amount is X0, and the first relative velocity is Zv, the second relative velocity Xv is expressed by the following formula (1) (see Figures 5(A) and 5(B)).

number

[0062] With the second relative velocity set in this manner, when the relative movement between the grinding wheel 58 and the wafer 11 along the Z-axis direction and the relative movement between the grinding wheel 58 and the wafer 11 along the X-axis direction start simultaneously, these movements end simultaneously. As a result, in the above-described method, an inverted truncated cone-shaped recess 15 having a predetermined depth D and in which the angle θ between the bottom surface 15a and the side surface 15b is an obtuse angle is formed on the back surface 11b of the wafer 11.

[0063] The following describes a method for setting the second relative speed when the wear amounts of the grinding wheels 58a are not known prior to the execution of the grinding step (S3). Fig. 6 is a flowchart schematically showing each step included in the grinding step (S3) in which the second relative speed is set according to this method.

[0064] In short, in this grinding step (S3), the back surface 11b of the wafer 11 is slightly ground, and then the wear amounts of the multiple grinding wheels 58a are calculated taking into consideration the depth of recesses formed by this grinding on the back surface 11b of the wafer 11. Then, in this grinding step (S3), the second relative speed is reset taking into consideration the calculated wear amounts, and recesses having a desired depth are formed on the back surface 11b of the wafer 11.

[0065] Specifically, in this grinding step (S3), first, while both the grinding wheel 58 and the wafer 11 are rotating, the installation surface of the wheel base 58b and the front surface 11a of the wafer 11 are moved closer to each other along the Z axis by a third movement amount, and the rotation axis of the grinding wheel 58 and the center of the wafer 11 are moved closer to each other along the X axis by a fourth movement amount, thereby grinding the back surface 11b side of the wafer 11 (pre-grinding step: S31).

[0066] FIG. 7(A) is a partially cross-sectional side view that schematically shows the state of the preliminary grinding step (S31), and FIG. 7(B) is a cross-sectional view that schematically shows the wafer 11 after the preliminary grinding step (S31).

[0067] In this preliminary grinding step (S31), the second relative velocity is set so as to be equal to the velocity obtained by dividing the second movement amount X0 by the time obtained by dividing the predetermined depth D by the first relative velocity Zv. That is, the second relative velocity Xv1 in the preliminary grinding step (S31) is expressed by the following formula (2).

number

[0068] The third movement amount is a distance that is set arbitrarily and is less than the depth (predetermined depth D) of the recess formed on the back surface 11b of the wafer 11. The fourth movement amount is a distance obtained by multiplying the second relative velocity Xv1 in the preliminary grinding step (S31) by the time obtained by dividing the third movement amount by the first relative velocity Zv.

[0069] That is, if the third movement amount is Z1, the fourth movement amount X1 is expressed by the following formula (3).

number

[0070] With the second relative velocity set in this manner, when the relative movement between the grinding wheel 58 and the wafer 11 along the Z-axis direction and the relative movement between the grinding wheel 58 and the wafer 11 along the X-axis direction start simultaneously, these movements end simultaneously. As a result, in the preliminary grinding step (S31), an inverted truncated cone-shaped recess (first portion) 17 is formed on the back surface 11b of the wafer 11, with the angle θ1 between the bottom surface 17a and the side surface 17b being an obtuse angle (see FIGS. 7(A) and 7(B)).

[0071] The preliminary grinding step (S31) is performed in a state where the sum of the thickness of the wafer 11 and the thickness of the protective tape 13 has been measured by the measuring unit 60 (see FIGS. 1 and 2). That is, the preliminary grinding step (S31) is performed in a state where the probe of the height gauge 60a is in contact with the back surface 11b of the wafer 11 and the probe of the height gauge 60a is in contact with the holding surface 22a of the chuck table 22 (specifically, the upper surface of the side wall of the frame 24).

[0072] Next, the depth (depth of the first portion) of the recess 17 formed on the back surface 11b of the wafer 11 is measured (measurement step: S32). Specifically, the depth of the recess 17 is a distance obtained by subtracting the above sum measured by the measurement unit 60 after the preliminary grinding step (S31) from the above sum measured by the measurement unit 60 before the preliminary grinding step (S31).

[0073] Furthermore, if the depth of the recess 17 can be calculated, it is possible to calculate the amount of wear W of the multiple grinding wheels 58a when the wafer 11 is ground to a predetermined depth D. Specifically, the amount of wear W is a distance obtained by multiplying the predetermined depth D by a value obtained by dividing a distance obtained by subtracting the depth of the recess 17 from the third movement amount Z1 by the depth of the recess 17.

[0074] That is, if the depth of the recess 17 is D1, the amount of wear W is expressed by the following formula (4).

number

[0075] The measuring step (S32) is performed, for example, after the grinding unit 46 is raised so that the grinding wheel 58 and the wafer 11 are spaced apart. Alternatively, the measuring step (S32) may be performed immediately after the preliminary grinding step (S31) without raising the grinding unit 46. The measuring step (S32) may be performed while both the grinding wheel 58 and the wafer 11 are rotating, or while the rotation of both is stopped.

[0076] Furthermore, if the grinding wheel 58 and the wafer 11 are separated in the measurement step (S32), prior to the main grinding step (S33) described later, the grinding unit 46 is lowered until the lower surfaces of the multiple grinding stones 58a again contact the back surface 11b of the wafer 11. Similarly, if the rotation of both the grinding wheel 58 and the wafer 11 is stopped in the measurement step (S32), they are both rotated again prior to the main grinding step (S33) described later.

[0077] Next, with both the grinding wheel 58 and the wafer 11 rotating, the mounting surface of the wheel base 58b and the front surface 11a of the wafer 11 are moved closer together along the Z-axis direction by a fifth movement amount, and the rotation axis of the grinding wheel 58 and the center of the wafer 11 are moved closer together along the X-axis direction by a sixth movement amount, thereby grinding the back surface 11b side of the wafer 11 (main grinding step: S33).

[0078] FIG. 8(A) is a partially cross-sectional side view that schematically shows the main grinding step (S33), and FIG. 8(B) is a cross-sectional view that schematically shows the wafer 11 after the main grinding step (S33).

[0079] Here, the fifth movement amount Z2 is a distance obtained by subtracting the third movement amount Z1 from the depth (predetermined depth D) of the recess formed on the back surface 11b of the wafer 11, and adding the distance to the wear amount W of the multiple grinding wheels 58a when the wafer 11 is ground to the predetermined depth D. That is, the fifth movement amount Z2 is expressed by the following formula (5).

number

[0080] The sixth movement amount X2 is a distance obtained by subtracting the fourth movement amount X1 from the second movement amount X0. That is, the sixth movement amount X2 is expressed by the following formula (6).

number

[0081] Furthermore, the second relative velocity in the main grinding step (S33) is a velocity obtained by dividing the sixth movement amount X2 by the time obtained by dividing the fifth movement amount Z2 by the first relative velocity Zv. That is, the second relative velocity Xv2 in the main grinding step (S33) is expressed by the following mathematical formula (7).

number

[0082] With the second relative velocity set in this manner, when the relative movement between the grinding wheel 58 and the wafer 11 along the Z-axis direction and the relative movement between the grinding wheel 58 and the wafer 11 along the X-axis direction start simultaneously, these movements end simultaneously. As a result, in the main grinding step (S33), an inverted truncated cone-shaped recess (second portion) 19 is formed on the back surface 11b of the wafer 11, with the angle θ2 between the bottom surface 19a and the side surface 19b being an obtuse angle (see FIGS. 8(A) and 8(B)).

[0083] As a result of the above, a recess 21 including an inverted truncated cone-shaped recess (first portion) 17 and an inverted truncated cone-shaped recess (second portion) 19 and having a predetermined depth D is formed on the back surface 11b of the wafer 11. In addition, the angle θ2 formed between the bottom surface 19a and the side surface 19b of the second portion 19 is smaller than the angle θ1 formed between the bottom surface 17a and the side surface 17b of the first portion 17. This point will be described in detail below.

[0084] First, since the third movement amount Z1 is longer than the depth D1 of the first portion 17 (Z1 > D1), the distance obtained by subtracting the third movement amount Z1 from the predetermined depth D is shorter than the distance obtained by subtracting the depth D1 of the first portion 17 from the predetermined depth D (D - Z1 < D - D1). In this case, the product of the third movement amount Z1 and the distance obtained by subtracting the depth D1 of the concave portion (first portion) 17 from the predetermined depth D is larger than the product of the depth D1 of the first portion 17 and the distance obtained by subtracting the third movement amount Z1 from the predetermined depth D (Z1×(D - D1) > D1×(D - Z1)).

[0085] Therefore, since the value α included in the above formula (7) is less than 1, the second relative speed Xv2 in this grinding step (S33) is slower than the second relative speed Xv2 in the preliminary grinding step (S31). Also, since the first relative speed Zv is common in the preliminary grinding step (S31) and this grinding step (S33), the side surface 19b of the second portion 19 has a steeper inclination than the side surface 17b of the first portion 17. As a result, the angle θ2 becomes smaller than the angle θ1.

[0086] In the wafer grinding method described above, the second relative speed along the X-axis direction between the grinding wheel 58 and the wafer 11 in the grinding step (S3) is set such that the relative movement between the grinding wheel 58 and the wafer 11 along the Z-axis direction and the relative movement between the grinding wheel 58 and the wafer 11 along the Z-axis direction are started simultaneously and end simultaneously.

[0087] Specifically, this second relative speed is set in consideration of an arbitrarily set parameter and the wear amount W of a plurality of grinding wheels grasped prior to or during the grinding step (S3) (the absolute value of the change amount of the thickness of a plurality of grinding wheels before and after the grinding step). Thereby, in the wafer grinding method described above, it is possible to form the concave portions 15, 19 having a predetermined depth D and having obtuse angles θ, θ2 formed by the bottom surfaces 15a, 19a and the side surfaces 15b, 19b on the back surface 11b of the wafer 11.

[0088] Note that the above is one aspect of the present invention, and the present invention is not limited to the above. For example, the present invention may be implemented using a grinding apparatus provided with a moving mechanism that moves the chuck table 22 along the Z-axis direction and a moving mechanism that moves the grinding unit 46 along the X-axis direction. In other words, in the present invention, it is sufficient that the grinding wheel 58 and the wafer 11 can move relatively along both the X-axis direction and the Z-axis direction, and there is no limitation on the structure for this purpose.

[0089] Furthermore, when the wear amounts of the multiple grinding wheels 58a are known, the present invention may be practiced using a grinding apparatus that does not include a measurement unit 60 having a pair of height gauges 60a, 60b. Furthermore, the present invention may be practiced using a grinding apparatus that includes a non-contact measurement unit instead of the measurement unit 60 having a pair of height gauges 60a, 60b. In other words, in the present invention, it is sufficient to be able to measure the depth of the recesses formed on the back surface 11b of the wafer 11, and there are no limitations on the structure for this purpose.

[0090] In addition, the structures and methods according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0091] 2: Grinding equipment 4: Base (4a: Groove) 6: Guide rail 8: X-axis moving plate 10: Screw shaft 11: Wafer (11a: front surface, 11b: back surface) 12: Pulse motor 13: Protective tape 14: Nut part 15: Recess (15a: bottom surface, 15b: side surface) 16: Driven pulley 17: Recess (first portion) (17a: bottom surface, 17b: side surface) 18: Movable axis 19: Recess (second portion) (19a: bottom surface, 19b: side surface) 20: Table base 21: Recess 22: Chuck table (22a: holding surface) 24:Frame body 26: Porous plate 28: Table cover 30: Dustproof and waterproof cover 32: Support structure 34: Guide rail 36: Slider 38: Z-axis moving plate 40:Screw shaft 42: Pulse motor 44: Nut part 46: Grinding unit 48: Holding member 50: Spindle housing 52: Spindle 54: Rotation drive source 56: Wheel mount 58: Grinding wheel (58a: grinding wheel, 58b: wheel base) 60: Measuring unit (60a, 60b: height gauge)

Claims

1. A wafer grinding method for forming a recess having a predetermined depth by grinding a back surface side of a wafer having a plurality of devices formed on a front surface side, comprising: a holding step of holding the wafer with the backside exposed; a contact step of bringing one of the grinding wheels into contact with the center of the back surface of the wafer while rotating both the wafer and a grinding wheel having a wheel base with a mounting surface on which the grinding wheels are fixed in a circularly spaced relationship; a grinding step of, after the contact step, grinding the back side of the wafer by moving the installation surface of the wheel base and the front side of the wafer closer together by a first movement amount along a first direction while rotating both the grinding wheel and the wafer, and moving the rotation axis of the grinding wheel and the center of the wafer closer together by a second movement amount along a second direction perpendicular to the first direction, the first movement amount is a distance obtained by adding the predetermined depth and the wear amounts of the grinding wheels when the wafer is ground to the predetermined depth, the second movement amount is a distance that is arbitrarily set to be less than the width of each of the plurality of grinding wheels along the second direction, a first relative speed between the grinding wheel and the wafer in the first direction in the grinding step is a constant speed that is arbitrarily set; A method for grinding a wafer, wherein the second relative speed between the grinding wheel and the wafer along the second direction in the grinding step is a constant or variable speed that is set in consideration of the predetermined depth, the amount of wear, the second movement amount, and the first relative speed so that the relative movement between the grinding wheel and the wafer along the first direction and the relative movement between the grinding wheel and the wafer along the second direction start and end simultaneously.

2. The amount of wear is known prior to the grinding step; 2. The wafer grinding method according to claim 1, wherein the second relative velocity is a velocity obtained by dividing the second movement amount by a time obtained by dividing the first movement amount by the first relative velocity.

3. The recess includes a first portion having an inverted truncated cone shape and a second portion having an inverted truncated cone shape with a side surface that is steeper inclined than a side surface of the first portion, The grinding step includes: a preliminary grinding step of forming the first portion on the back surface side of the wafer by moving the installation surface of the wheel base and the front surface of the wafer closer together by a third movement amount along the first direction and moving the rotation axis of the grinding wheel and the center of the wafer closer together by a fourth movement amount along the second direction while both the grinding wheel and the wafer are rotating; a measuring step of measuring a depth of the first portion after the pre-grinding step; a main grinding step of forming the second portion on the back surface side of the wafer by moving the installation surface of the wheel base and the front surface of the wafer closer together by a fifth movement amount along the first direction and moving the rotation axis of the grinding wheel and the center of the wafer closer together by a sixth movement amount along the second direction while both the grinding wheel and the wafer are rotating, the second relative velocity in the preliminary grinding step is a velocity obtained by dividing the second movement amount by a time obtained by dividing the predetermined depth by the first relative velocity; the third movement amount is an arbitrarily set distance less than the predetermined depth, the fourth movement amount is a distance obtained by multiplying the second relative velocity in the preliminary grinding step by a time obtained by dividing the third movement amount by the first relative velocity, the wear amount is a distance obtained by multiplying the predetermined depth by a value obtained by subtracting the depth of the first portion from the third movement amount and dividing the resulting distance by the depth of the first portion; the fifth movement amount is a distance obtained by adding the wear amount to a distance obtained by subtracting the third movement amount from the predetermined depth, the sixth movement amount is a distance obtained by subtracting the fourth movement amount from the second movement amount, 2. The wafer grinding method according to claim 1, wherein the second relative velocity in the main grinding step is a velocity obtained by dividing the sixth movement amount by a time obtained by dividing the fifth movement amount by the first relative velocity.

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