Wafer grinding method

Abstract

To grind a wafer to a uniform thickness while enhancing productivity.SOLUTION: A wafer grinding method includes: a first thickness measurement step of measuring a thickness of a wafer ground to a first thickness; a first thickness tendency calculation step of calculating, as a first thickness difference, a difference between a thickness at one measurement point as a reference and a thickness at another measurement point, among the thicknesses measured in the first thickness measurement step; second thickness measurement step of measuring a thickness of the wafer ground to a second thickness; a second thickness tendency calculation step of calculating, as a second thickness difference, a difference between a thickness at one measurement point as a reference and a thickness measured at another measurement point, among the thicknesses measured in the second thickness measurement step; a thickness difference calculation step of calculating a difference between the first thickness difference and the second thickness difference; a first grinding step; a first grinding thickness measurement step; a first grinding thickness tendency calculation step; an inclination changing step of changing an inclination of a chuck table; and a second grinding step of grinding the wafer ground in the first grinding step.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for grinding a wafer to a desired thickness by a first grinding mechanism including a first grinding stone and a second grinding mechanism including a second grinding stone.

Background Art

[0002] A grinding apparatus for grinding a wafer rotates a chuck table holding the wafer on a holding surface together with the wafer, and brings a rotating annular grinding wheel into contact with the wafer to grind the wafer. The holding surface of the chuck table is formed in a conical shape having a center as a vertex. For this reason, the wafer is ground while adjusting the parallelism between the holding surface of the chuck table and the lower surface of the grinding wheel so that the in-plane thickness of the wafer becomes uniform (see, for example, Patent Document 1). And in Patent Document 1, grinding is temporarily stopped before the wafer reaches the finish thickness, the thickness of the wafer is measured by a thickness measuring device, the inclination of the chuck table is adjusted based on the measured thickness, and then the wafer is ground again until it reaches the desired finish thickness. A method has been proposed.

[0003] Further, in Patent Document 2, a chuck table holding a wafer is moved to a first grinding position and a second grinding position, the shape of the wafer ground at the first grinding position is measured by a first sensor, and the shape of the wafer ground at the second grinding position is measured by a second sensor. Based on the shape of the wafer measured by the first sensor, the inclination of the chuck table at the first grinding position is adjusted, and based on the shape of the wafer measured by the second sensor, a correction is added to the adjustment of the inclination of the chuck table at the first grinding position. Thus, a method for grinding a wafer so as to grind the wafer to a uniform thickness has been proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, as proposed in Patent Document 1, before the wafer reaches the finished thickness, grinding is temporarily stopped, the thickness of the wafer is measured by a thickness measuring device, and after adjusting the inclination of the chuck table based on the measured thickness, when the wafer is ground again until it reaches the desired finished thickness, there is a problem that the grinding time becomes long and productivity decreases.

[0006] Further, according to the method proposed in Patent Document 2, since it is necessary to repeat the correction of the inclination of the chuck table at the first grinding position until the shape of the wafer measured by the second sensor becomes the desired shape, there is a problem that the total grinding time becomes long and productivity decreases.

[0007] The present invention has been made in view of the above problems, and an object thereof is to provide a wafer grinding method capable of grinding a wafer to a uniform thickness while increasing productivity.

Means for Solving the Problems

[0008] The present invention for solving the above problems includes a chuck table that holds a wafer by a conical holding surface, a table rotation mechanism that rotates the chuck table about the center of the holding surface, a first grinding mechanism that grinds the wafer with a first grinding wheel mounted on a first spindle, a second grinding mechanism that grinds the wafer with a second grinding wheel mounted on a second spindle, an alignment mechanism that positions the chuck table at a grinding position of the first grinding wheel and a grinding position of the second grinding wheel, a thickness measuring device that measures the thickness of the wafer at three measurement points including the center portion, the outer peripheral portion, and the radial intermediate portion of the wafer, and an inclination changing mechanism that changes the inclination of the chuck table. The wafer grinding method is carried out using these components. The method includes a first thickness measurement step of grinding the wafer to a first thickness with the first grinding wheel and measuring the thickness of the wafer at the three measurement points; a first thickness trend calculation step of calculating, as a first thickness difference, the difference between the thickness at one of the three measurement points and the thicknesses at the other two measurement points, with the thickness at one of the three measurement points measured in the first thickness measurement step as a reference; a second thickness measurement step of grinding the wafer to a second thickness smaller than the first thickness with the second grinding wheel and measuring the thickness of the wafer at the three measurement points; a second thickness trend calculation step of calculating, as a second thickness difference, the difference between the thickness at one of the three measurement points and the thicknesses at the other two measurement points, with the thickness at one of the three measurement points measured in the second thickness measurement step as a reference; a thickness difference calculation step of calculating the difference between the first thickness difference calculated in the first thickness trend calculation step and the second thickness difference calculated in the second thickness trend calculation step; a first grinding step of grinding the wafer held on the holding surface of the chuck table to the first thickness with the first grinding wheel; a first grinding thickness measurement step of measuring the thickness of the wafer at the three measurement points ground in the first grinding step; a first grinding thickness trend calculation step of calculating the difference between the thickness at one of the three measurement points and the thicknesses at the other two measurement points, with the thickness at one of the three measurement points measured in the first grinding thickness measurement step as a reference; an inclination changing step of changing the inclination of the chuck table based on the three calculated values calculated in the first grinding thickness trend calculation step and the three calculated values calculated in the thickness difference calculation step; after the inclination change,A second grinding step of grinding the wafer ground in the first grinding step to the second thickness with the second grindstone, characterized by comprising:

Advantages of the Invention

[0009] According to the present invention, in the second grinding step, in the inclination change step which is the previous step, a thickness difference that cancels out the thickness differences at the three measurement points calculated in the thickness difference calculation step is calculated, and the inclination of the chuck table is changed so that the calculated thickness difference occurs at the three measurement points. Therefore, the thickness of the wafer to be finish-ground in the second grinding step becomes uniform, and the wafer is finish-ground to a uniform thickness.

[0010] And in the wafer grinding method according to the present invention, before performing the second grinding step which is the finish grinding step, the inclination of the chuck table is changed so that the thickness differences at the three measurement points calculated in the thickness difference calculation step can be canceled out. Therefore, there is no need to change the inclination of the chuck table in the second grinding step, and as a result, the total grinding time is shortened and the productivity is improved.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for carrying out the invention

[0012] Hereinafter, embodiments of the present invention will be described based on the accompanying drawings.

[0013] First, the configuration of the grinding apparatus for implementing the wafer grinding method according to the present invention will be described based on FIGS. 1 to 3. In the following description, the directions of the arrows shown in FIG. 1 are taken as the X-axis direction, the Y-axis direction, and the Z-axis direction (vertical direction), respectively.

[0014] [Configuration of grinding apparatus] The grinding apparatus 1 shown in FIG. 1 is an apparatus for grinding a disk-shaped wafer W, and includes a rotatable disk-shaped turntable 2 constituting a positioning mechanism, three chuck tables 10 disposed on the turntable 2, a table rotation mechanism 40 (see FIG. 2) for rotating (self-rotating) each chuck table 10 around the central axis, an inclination changing mechanism 80 for changing the inclination of the chuck table 10, a rough grinding mechanism (first grinding mechanism) 20 for roughly grinding the wafer W held on the chuck table 10 and a finish grinding mechanism (second grinding mechanism) 30 for finish grinding, contact type thickness measuring instruments 50 and 51 for measuring the thickness of the wafer W, a non-contact type thickness measuring instrument 90, a cleaning unit 60 for cleaning the upper surface (ground surface) of the wafer W after finish grinding, and a transfer unit 70 for transferring the wafer W as main components. Here, in the present embodiment, the wafer W as an object to be ground is a thin disk-shaped member made of single crystal silicon or the like.

[0015] Next, the configurations of the turntable 2, the chuck table 10, the table rotation mechanism 40, the inclination changing mechanism 80, the rough grinding mechanism 20 and the finish grinding mechanism 30, the contact type thickness measuring instruments 50 and 51 and the non-contact type thickness measuring instrument 90, the cleaning unit 60 and the transfer unit 70, which are the main components of the grinding apparatus 1, will be described respectively.

[0016] (Turntable) The turntable 2 is a member that intermittently rotates horizontally around a central axis perpendicular to the Z-axis direction. In the fan-shaped regions partitioned by partition walls 2a extending radially from the center, chuck tables 10 are respectively arranged rotatably around the central axis. This turntable 2 constitutes a positioning mechanism that positions the wafer W held on the holding surface of the chuck table 10 in the wafer loading / unloading region R1, the rough grinding region R2, and the finish grinding region R3 in sequence by rotating by 120° each time by a rotation mechanism (not shown).

[0017] (Chuck Table) The three chuck tables 10 rotatably arranged on the turntable 2 are disk-shaped members and are arranged on the turntable 2 that intermittently rotates around a central axis perpendicular to the Z-axis direction at an equal angular pitch (120° pitch) in the circumferential direction. And these chuck tables 10 revolve by 120 degrees each time around the axis center perpendicular to the Z-axis direction of the turntable 2 by the intermittent rotation of the turntable 2 and sequentially move between the wafer loading / unloading region R1, the rough grinding region R2, and the finish grinding region R3, and rotate at a predetermined speed around the axis center CL1 by the table rotation mechanism 40 shown in FIG. 2.

[0018] Also, in each chuck table 10, as shown in FIG. 2, disk-shaped porous members 10A made of porous ceramics or the like are respectively incorporated in the upper central part of the disk-shaped frame 11. The upper surface of each porous member 10A constitutes a conical holding surface 10a with the center as the apex. Here, the porous member 10A is selectively connected to a suction source (not shown), and the wafer W is suction-held on the holding surface 10a. In FIG. 2, the conical shape of the holding surface 10a of the porous member 10A is exaggeratedly shown, but actually, the inclination of the cone of the holding surface 10a is so minute that it cannot be confirmed with the naked eye.

[0019] (Table Rotation Mechanism) The table rotation mechanism 40 shown in FIG. 2 is a mechanism for rotating each chuck table 10 around the axis center CL1, and includes a drive motor 41 as a rotation drive source, a small-diameter drive pulley 42 attached to an output shaft (motor shaft) 41a extending vertically upward from the drive motor 41, a large-diameter driven pulley 43 attached to the lower end of a rotation shaft 12 extending vertically downward from the center of the chuck table 10, and an endless timing belt 44 wound around the drive pulley 42 and the driven pulley 43. The drive motor 41 is electrically connected to the control unit 110, and its drive is controlled by the control unit 110.

[0020] Therefore, when the drive motor 41 is activated and the output shaft 41a rotates at a predetermined speed, the rotation is decelerated through the drive pulley 42, the timing belt 44, and the driven pulley 43 and transmitted to the rotation shaft 12, and the rotation shaft 12 and the chuck table 10 rotate at a predetermined speed around the axis center CL1 of the rotation shaft 12.

[0021] (Tilt change mechanism) The tilt change mechanism 80 shown in FIG. 2 is a mechanism for changing the tilt of the chuck table 10. The rotation shaft 12 of the chuck table 10 is rotatably supported by a flange 81 via a bearing 13. A part of the flange 81 is tiltably supported by a horizontal frame 83 by a pivot 82. A motor 84 is attached to the lower surface of the frame 83 by a bracket 85, and an output shaft (motor shaft) 84A extends upward through the frame 83 from the motor 84. Here, a male screw 84a formed at the upper end of the output shaft 84A of the motor 84 is screwed into a female screw 81a formed in a part of the flange 81. The motor 84 is electrically connected to the control unit 110, and its operation is controlled by the control unit 110. The motor 84 uses a servo motor or a stepping motor.

[0022] Therefore, when the motor 84 is started to rotate the output shaft 84A forward and backward, the flange 81 formed with the female screw 81a that engages with the male screw 84a formed on the output shaft 84A tilts about the pivot 82 with respect to the horizontal frame 83. As a result, the inclination of the rotary shaft 12 supported by the flange 81 and the chuck table 10 is changed. Specifically, the axial center CL1 of the rotary shaft 12 is tilted by the illustrated angle α with respect to the vertical line, and the chuck table 10 is tilted by the same angle α with respect to the horizontal plane.

[0023] (Rough grinding mechanism and finish grinding mechanism) As shown in FIG. 1, the rough grinding mechanism 20, which is the first grinding mechanism, and the finish grinding mechanism 30, which is the second grinding mechanism, are vertically arranged along the X-axis direction at the +Y-axis end of a rectangular box-shaped base 100 that is long in the Y-axis direction. Here, the rough grinding mechanism 20 is a mechanism for rough grinding the upper surface of the wafer W held on the holding surface 10a of the chuck table 10 located in the rough grinding region R2, and the finish grinding mechanism 30 is a mechanism for finish grinding the upper surface of the wafer W held on the holding surface 10a of the chuck table 10 located in the finish grinding region R3. The basic configurations of both are the same.

[0024] That is, the rough grinding mechanism 20 includes a spindle motor 22 fixed to a holder 21, a vertical spindle 23 rotationally driven by the spindle motor 22, a disk-shaped mount 24 attached to the lower end of the spindle 23, and a grinding wheel 25 detachably mounted on the lower surface of the mount 24. Here, the grinding wheel 25 is composed of a disk-shaped base 25a and a plurality of annular rough grinding abrasive wheels 25b, which are cutting tools annularly attached to the lower surface of the base 25a, and is rotationally driven around the axial center CL2 of the spindle 23, which is the grinding wheel rotation axis (see FIG. 2).

[0025] Also, similar to the rough grinding mechanism 20, the finish grinding mechanism 30 includes a spindle motor 32 fixed to a holder 31, a vertical spindle 33 rotationally driven by the spindle motor 32, a disk-shaped mount 34 attached to the lower end of the spindle 33, and a grinding wheel 35 detachably attached to the lower surface of the mount 34. Here, the grinding wheel 35 is composed of a disk-shaped base 35a and a plurality of finish grinding wheels 35b which are cutting tools annularly attached to the lower surface of the base 35a. The finish grinding wheels 35b are composed of finer abrasive grains than the rough grinding wheels 25b of the rough grinding mechanism 20.

[0026] Incidentally, the rough grinding mechanism 20 and the finish grinding mechanism 30 are respectively supported by lifting mechanisms 3 provided on the -Y-axis direction end faces of a pair of block-shaped columns 101 vertically erected along the X-axis direction at the +Y-axis direction end of the base 100 so as to be liftable. Here, since the configurations of both lifting mechanisms 3 are the same, hereinafter, corresponding components will be described with the same reference numerals.

[0027] Each lifting mechanism 3 is for moving the rough grinding mechanism 20 and the finish grinding mechanism 30 up and down along the Z-axis direction, and includes a lifting plate 4 in the shape of a rectangular plate and a pair of left and right guide rails 5 for guiding the lifting movement of the lifting plate 4. Here, the rough grinding mechanism 20 and the finish grinding mechanism 30 are respectively attached to each lifting plate 4. Also, the pair of front and rear guide rails 5 are arranged vertically and parallel to each other on the front surface of the column 101.

[0028] And between the pair of left and right guide rails 5, a rotatable ball screw 6 is vertically erected along the Z-axis direction. The upper end of the ball screw 6 is connected to a servo motor 7 which can rotate forward and backward and is a drive source. Also, the lower end of the ball screw 6 is rotatably supported by the column 101 by a bearing (not shown). A nut member (not shown) horizontally protruding rearward (+Y-axis direction) from the back surface of the lifting plate 4 is screwed onto the ball screw 6.

[0029] Therefore, when the servo motors 7 of each lifting mechanism 3 configured as described above are respectively activated to rotate the ball screws 6 forward and backward, the lifting plates 4, to which nut members (not shown) screwed onto the ball screws 6 are protruding, move up and down along the pair of left and right guide rails 5. As a result, the rough grinding mechanism 20 and the finish grinding mechanism 30 attached to the lifting plate 4 also move up and down independently of each other along the Z-axis direction. As shown in FIG. 2, each lifting mechanism 3 is electrically connected to the control unit 110, and its operation is controlled by the control unit 110.

[0030] (Contact type thickness measuring instrument) The contact type thickness measuring instrument 50 is a height gauge that measures the thickness of the wafer W during rough grinding. It includes a first probe 50a that contacts the upper surface of the wafer W during rough grinding and a second probe 50b that contacts the upper surface of the frame body 11 (see FIG. 2) of the chuck table 10. By subtracting the upper surface height of the frame body 11 measured by the second probe 50b from the upper surface height of the wafer W measured by the first probe 50a, the thickness of the wafer W during rough grinding is measured. Also, the contact type thickness measuring instrument 51 is a height gauge that measures the thickness of the wafer W during finish grinding. It includes a first probe 51a that contacts the upper surface of the wafer W during finish grinding and a second probe 51b that contacts the upper surface of the frame body 11 (see FIG. 2) of the chuck table 10. By subtracting the upper surface height of the frame body 11 measured by the second probe 51b from the upper surface height of the wafer W measured by the first probe 51a, the thickness of the wafer W during finish grinding is measured. These contact type thickness measuring instruments 50 and 51 are electrically connected to the control unit 110 shown in FIG. 2. The control unit 110 calculates the thickness of the wafer W during rough grinding and the thickness of the wafer W during finish grinding by receiving the detection signals from the respective contact type thickness measuring instruments 50 and 51.

[0031] (Non-contact type thickness measuring instrument) The non-contact thickness measuring device 90 optically and non-contact measures the thicknesses at three locations in the radial direction (points a, b, and c shown in Fig. 3) of the wafer W that has been roughly ground and the wafer W that has been finish ground. It is arranged above the holding surface 10a of the chuck table 10 and includes a light projecting unit (not shown) that projects measurement light toward the upper surface of the wafer W held by the chuck table 10, and a light receiving unit (not shown) that receives the reflected light reflected by the lower surface of the wafer W.

[0032] As shown in Fig. 3, the non-contact thickness measuring device 90 is attached to the tip of an arm 92 that extends horizontally from the upper end of the output shaft of a motor 91, which is a rotational drive source. By the arm 92 pivoting in the horizontal plane with the motor 91 as the starting point, the non-contact thickness measuring device 90 optically and non-contact measures the thicknesses of the wafer W at three locations shown in Fig. 3, specifically, the measurement point a at the center of the wafer W, the measurement point b at the outer peripheral part, and the measurement point c at the middle between the measurement point a and the measurement point b in the radial direction of the wafer W.

[0033] Note that the non-contact thickness measuring device 90 may measure the thickness of the wafer W during the grinding process. That is, as shown in Fig. 1, it may measure the thickness of the wafer W being finish ground by the finish grinding mechanism 30. Also, the non-contact thickness measuring device 90 may be arranged near the contact thickness measuring device 50 so that it can measure the thickness of the wafer W being roughly ground by the rough grinding mechanism 20. Further, the non-contact thickness measuring device 90 may utilize ultrasonic vibration.

[0034] (Cleaning Unit) The cleaning unit 60 cleans the wafer W that has been finish ground by the finish grinding mechanism 30 and removes grinding chips and the like adhering to the ground surface (upper surface). It includes a spinner table 61 that holds and rotates the wafer W after finish grinding, and a cleaning water nozzle 62 that sprays cleaning water (pure water) toward the ground surface of the wafer W.

[0035] (Conveying Unit) In the grinding apparatus 1 according to the present embodiment, as shown in FIG. 1, at the -Y-axis direction end of the base 100, a cassette 201 for storing a plurality of wafers W before grinding and a cassette 202 for storing the wafers W after grinding are arranged. Here, the transfer unit 70 includes a loading / unloading robot 71 that takes in and out the wafer W with respect to the cassette 201 and transfers the wafer W taken out from the cassette 201 to the alignment table 102, a first transfer means 72 that transfers the wafer W aligned on the alignment table 102 to the chuck table 10 located in the wafer loading / unloading region R1, and a second transfer means 73 that takes out the wafer W finish-ground by the finish grinding mechanism 30 from the chuck table 10 located in the finish grinding region R3 and transfers it to the cleaning unit 60.

[0036] [Wafer Grinding Method] Next, a method for grinding the wafer W according to the present invention, which is implemented using the grinding apparatus 1 configured as described above, will be described.

[0037] The method for grinding the wafer W according to the present invention is, as shown in FIG. 4, 1) First Thickness Measurement Step: 2) First Thickness Trend Calculation Step: 3) Second Thickness Measurement Step: 4) Second Thickness Trend Calculation Step: 5) Thickness Difference Calculation Step: 6) First Grinding Step: 7) First Ground Thickness Measurement Step: 8) First Ground Thickness Trend Calculation Step: 9) Inclination Change Step: 10) Second Grinding Step: is a method of grinding the wafer W to a predetermined thickness through these steps in sequence. Hereinafter, each step will be described respectively.

[0038] 1) First Thickness Measurement Step: In the first thickness measurement step, the wafer W held on the chuck table 10 positioned in the rough grinding region R2 shown in FIG. 1 is roughly ground to the first thickness by the rough grinding mechanism 20, and the thicknesses at three locations in the radial direction of the roughly ground wafer W, that is, the three measurement points a, b, and c shown in FIG. 3, are measured. Specifically, the wafer W accommodated in the cassette 201 shown in FIG. 1 is taken out by the transfer-in / out robot 71 and conveyed to the alignment table 102, and the alignment (centering) of the wafer W is performed on this alignment table 102.

[0039] The wafer W aligned on the alignment table 102 is held by the first transfer means 72 and delivered to the chuck table 10 positioned in the wafer transfer-in / out region R1, and is sucked and held on the holding surface 10a of the chuck table 10. That is, when the porous member 10A of the chuck table 10 is connected to a suction source (not shown), a negative pressure is generated in the porous member 10A, and the wafer W is sucked and held on the conical holding surface 10a of the chuck table 10 as shown in FIG. 2 by this negative pressure. Then, the turntable 2 is rotated by 120° in the direction of the arrow in FIG. 1 around the central axis by a rotation mechanism (not shown), and the chuck table 10 holding the wafer W moves from the wafer transfer-in / out region R1 to the rough grinding region R2.

[0040] As described above, when the chuck table 10 holding the wafer W moves to the rough grinding region R2, the wafer W held on this chuck table 10 is roughly ground to the first thickness by the rough grinding wheel 25b of the rough grinding mechanism 20. That is, as shown in FIG. 2, the chuck table 10 is rotationally driven at a predetermined speed in the arrow direction by the table rotation mechanism 40 in a state where its axis center CL1 is inclined by the illustrated angle α with respect to the vertical line.

[0041] Also, the grinding wheel 25 of the rough grinding mechanism 20 is rotationally driven at a predetermined speed in the direction of the arrow by the spindle motor 22 shown in FIG. 1 above the chuck table 10. From this state, the grinding wheel 25 descends in the -Z axis direction by the elevating mechanism 3, and the rough grinding wheel 25b contacts the upper surface of the wafer W, whereby the wafer W is roughly ground to the first thickness. During this rough grinding, grinding water (pure water) is supplied to the contact portion (processing portion) between the radius region of the wafer W and the rough grinding wheel 25b to cool the contact portion, and the grinding chips generated by rough grinding are washed away by the grinding water. Further, the thickness of the wafer W in rough grinding is measured by the contact type thickness measuring device 50, and the measurement signal is transmitted to the control unit 110, whereby the wafer W is roughly ground to the first thickness. Note that the thickness of the wafer W may be measured using the non-contact type thickness measuring device 90, and the measurement signal may be transmitted to the control unit 110 to perform rough grinding to the first thickness.

[0042] Then, when the wafer W is roughly ground to the first thickness by the rough grinding wheel 25b, the grinding wheel 25 is moved above the wafer W by the elevating mechanism 3, and the thicknesses at three measurement points a, b, c (see FIG. 3) in the radial direction of the roughly ground wafer W are measured by the non-contact type thickness measuring device 90. Here, examples of the radial distribution of the thickness of the wafer W in each process are shown in FIGS. 5 to 7 as the first example to the third example, respectively.

[0043] In any of the first example shown in FIG. 5, the second example shown in FIG. 6, and the third example shown in FIG. 7, the thickness of the wafer W at the measurement points a, b, c measured in the first thickness measurement step is the thickness t at the measurement point a in the central portion 1a which is the smallest, and the thickness gradually increases toward the outer peripheral portion, and the thickness t at the measurement point b 1b is the largest. Therefore, among the thicknesses t of the wafer W at the measurement points a, b, c 1a , t 1b , t 1c , the magnitude relationship of t 1a < t 1c < t 1b is established.

[0044] 2) First Thickness Trend Calculation Step: In the first thickness trend calculation step, among the thicknesses at three measurement points a, b, and c of the wafer W after rough grinding measured in the first thickness measurement step, the difference between the thickness at one measurement point and the thicknesses at the other two measurement points is calculated as the first thickness difference with the thickness at one measurement point as a reference. Specifically, in the first example shown in FIG. 5, the second example shown in FIG. 6, and the third example shown in FIG. 7, the thickness t 1a at the measurement point a in the central portion of the wafer W is used as a reference, and the difference between this thickness t 1a and the thicknesses t 1b , t 1c at the other two measurement points b and c, i.e., the difference Δt 1b (= t 1b - t 1a ), Δt 1c (= t 1c - t 1a ) are respectively calculated as the first thickness differences.

[0045] 3) Second Thickness Measurement Step: In the second thickness measurement step, the roughly ground wafer W is finish-ground by the finish grinding mechanism 30 to a second thickness smaller than the first thickness, and the thicknesses of the wafer W at three positions in the radial direction, i.e., the three measurement points a, b, and c shown in FIG. 3, are measured. Specifically, when the turntable 2 rotates by 120° in the direction of the arrow in FIG. 1 by a rotation mechanism (not shown) and the roughly ground wafer W and the chuck table 10 holding it move to the finish grinding area R3, the finish grinding of the wafer W is performed by the finish grinding mechanism 30 in the same manner as the rough grinding. Note that the measurement of the thickness of the wafer W in this finish grinding is performed by the contact type thickness measuring instrument 51 shown in FIG. 1. Also, the thickness of the wafer W may be measured using the non-contact type thickness measuring instrument 90, and the measurement result may be transmitted to the control unit 110 to perform finish grinding until the second thickness.

[0046] And in this second thickness measurement step, when the wafer W is finish-ground to the second thickness by the finish grinding wheel 35b, the grinding wheel 35 is moved upward above the wafer W by the elevating mechanism 3, and the thicknesses at the measurement points a, b, and c (see FIG. 3) of the finish-ground wafer W are measured by the non-contact thickness measuring instrument 90. Here, in the first example shown in FIG. 5, the wafer W is uniformly ground over the entire surface, and the thicknesses of the wafer W measured at the measurement points a, b, and c show the same value (t 2a =t 2b =t 2c ).

[0047] Also, in the second example shown in FIG. 6, the thicknesses at the measurement points a, b, and c (see FIG. 3) of the wafer W measured by the non-contact thickness measuring instrument 90 are such that the thickness t 2a at the measurement point in the central part is the largest, and the upper surface of the wafer W is ground in a conical shape with the center as the apex. Therefore, among the thicknesses t 2a , t 2b , t 2c at the measurement points a, b, and c of the wafer W, the relationship t 2a >t 2c >t 2b holds. Further, in the third example shown in FIG. 7, the thicknesses at the measurement points a, b, and c (see FIG. 3) of the wafer W measured by the non-contact thickness measuring instrument 90 are such that the thickness t 2a at the measurement point a in the central part is the smallest, and the thickness t 2b at the measurement point b in the outer peripheral part is the largest, and the upper surface of the wafer W is ground in an inverted conical shape with the center as the apex. Therefore, among the thicknesses t 2a , t 2b , t 2c at the measurement points a, b, and c of the wafer W, the relationship t 2b >t 2c >t 2a holds.

[0048] 4) Second Thickness Trend Calculation Step: The second thickness tendency calculation step is a step of calculating, as a second thickness difference, the difference between the thickness at one measurement point and the thicknesses at the other two measurement points among the thicknesses at three measurement points a, b, and c of the wafer W after finish grinding measured in the second thickness measurement step, with the thickness at one measurement point as a reference.

[0049] Specifically, in the first example shown in FIG. 5, the thicknesses t 2a , t 2b , t 2c of the wafer W at the three measurement points a, b, and c measured in the second thickness measurement step are the same (t 2a = t 2b = t 2c ), so the second thickness difference is 0. Also, in the second example shown in FIG. 6, with the thickness t 2b at the measurement point b on the outer peripheral portion of the wafer W as a reference, the differences Δt 2b between this thickness t 2a , t 2c and the thicknesses t 2a (= t 2a - t 2b ), Δt 2c (= t 2c - t 2b ) at the other two measurement points a and c are calculated as the second thickness difference. Further, in the third example shown in FIG. 7, with the thickness t 2a at the measurement point a in the central portion of the wafer W as a reference, the differences Δt 2a between this thickness t 2b , t 2c and the thicknesses t 2b (= t 2b - t 2a ), Δt 2c (= t 2c - t 2a ) at the other two measurement points b and c are calculated as the second thickness difference.

[0050] 5) Thickness difference calculation step: The thickness difference calculation step is a step of calculating the difference between the first thickness difference calculated in the first thickness tendency calculation step and the second thickness difference calculated in the second thickness tendency calculation step.

[0051] Specifically, in the first example shown in FIG. 5, since the second thickness difference calculated in the second thickness trend calculation step is 0, the difference between the first thickness difference and the second thickness difference is equal to the first thickness difference, and the thickness difference at measurement point a = 0, the thickness difference at measurement point b = Δt 1b , the thickness difference at measurement point c = Δt 1c . Also, in the second example shown in FIG. 6, the thickness difference at measurement point a = Δt 2a , the thickness difference at measurement point b = Δt 1b , the thickness difference at measurement point c = Δt 1c - Δt 2c . Furthermore, in the third example shown in FIG. 7, the thickness difference at measurement point a = 0, the thickness difference at measurement point b = Δt 1b - Δt 2b , the thickness difference at measurement point c = Δt 1c - Δt 2c .

[0052] 6) First grinding step: In the first grinding step, in the rough grinding region R2 shown in FIG. 1, the wafer W held on the holding surface 10a of the chuck table 10 is rough ground to the first thickness by the rough grinding wheel 25b of the rough grinding mechanism 20 in the same manner as described above. In this first grinding step, in the first example shown in FIG. 5, the second example shown in FIG. 6, and the third example shown in FIG. 7, it is assumed that the wafer W is rough ground to a uniform first thickness t 1 . Thus, due to the processing heat of the grinding process, the heat generation of the motor of the drive unit, etc., the thickness trend of the wafer W at the time of the first thickness measurement step may be different from the thickness trend of the wafer W in the first grinding step.

[0053] 7) First grinding thickness measurement step: The first grinding thickness measurement step is a step of measuring the thickness of the wafer W rough ground in the first grinding step at three measurement points a, b, c shown in FIG. 3 by a non-contact thickness measuring instrument 90. In the first example shown in FIG. 5, the second example shown in FIG. 6, and the third example shown in FIG. 7, the thicknesses of the wafer W at the three measurement points a, b, c measured by the non-contact thickness measuring instrument 90 show a uniform value t 1 .

[0054] 8) First grinding thickness trend calculation step: The first grinding thickness trend calculation step is a step of calculating the difference between the thickness at one measurement point and the thicknesses at the other two measurement points, with the thickness at one of the three measurement points a, b, and c measured in the first grinding thickness measurement step as a reference. However, in the present embodiment, as described above, in the first example shown in FIG. 5, the second example shown in FIG. 6, and the third example shown in FIG. 7, the thicknesses of the wafer W at the three measurement points a, b, and c measured by the non-contact thickness measuring instrument 90 are uniform values t 1 Therefore, the thickness difference calculated in this first grinding thickness trend calculation step becomes 0.

[0055] 9) Tilt change step: The tilt change step calculates a thickness difference that cancels out the difference between the three calculated values calculated in the first grinding thickness trend calculation step (in this embodiment, the thickness difference = 0) and the three calculated values calculated in the thickness difference calculation step, and changes the tilt α (see FIG. 2) of the chuck table 10 so that the calculated thickness difference occurs at the three measurement points a, b, and c.

[0056] Here, in the first example shown in FIG. 5, the broken line indicating the thickness difference calculated in the second grinding thickness trend calculation step is represented by the hypotenuse of a triangle obtained by inverting the shape hatched in the diagram of the thickness difference calculation step upside down. That is, the thickness difference calculated in the second grinding thickness trend calculation step is a thickness difference = Δt at the measurement point a 1b , a thickness difference = 0 at the measurement point b, and a thickness difference = Δt at the measurement point c 1b -Δt 1c and becomes.

[0057] Also, in the second example shown in FIG. 6, the broken line indicating the thickness difference calculated in the second grinding thickness trend calculation step is represented by the hypotenuse of a triangle obtained by inverting the shape hatched in the diagram of the thickness difference calculation step upside down. That is, the thickness difference calculated in the second grinding thickness trend calculation step is a thickness difference = Δt at the measurement point a 1b +Δt 2aAt measurement point b, the thickness difference = 0, and at measurement point c, the thickness difference = Δt 1b -(Δt 1c -Δt 2c ) is obtained.

[0058] Furthermore, in the third example shown in FIG. 7, the broken line indicating the thickness difference calculated in the second grinding thickness tendency calculation step is represented by the hypotenuse of a triangle obtained by inverting the shape with hatching in the diagram of the thickness difference calculation step upside down. That is, the thickness difference calculated in the second grinding thickness tendency calculation step is such that the thickness difference = Δt at the measurement point 1b -Δt 2b , the thickness difference = 0 at measurement point b, and the thickness difference = Δt at measurement point c 1b -Δt 2b -(Δt 1c -Δt 2c ) is obtained.

[0059] 10) Second grinding process: The second grinding process is a process of finish-grinding the wafer W rough-ground in the first grinding process with the finish grinding wheel 35b of the finish grinding mechanism 30 to a second thickness smaller than the first thickness after the inclination of the chuck table 10 is changed by the inclination changing process, and this finish grinding is also performed in the same manner as described above.

[0060] Thus, in this second grinding process, in the inclination changing process which is the previous process, the thickness difference that cancels out the thickness differences at the three measurement points a, b, c calculated in the thickness difference calculation step is calculated in the second grinding thickness tendency calculation step, and since the inclination of the chuck table 10 is changed so that the calculated thickness difference occurs at the three measurement points a, b, c, the thickness t of the wafer W finish-ground in the second grinding process 2 becomes uniform in any of the first example shown in FIG. 5, the second example shown in FIG. 6, and the third example shown in FIG. 7, and the wafer W is finish-ground to a uniform thickness t 2 .

[0061] And in the grinding method according to the present invention, before performing the second grinding process which is the finish grinding process, the inclination of the chuck table 10 is changed so as to cancel out the thickness differences at the three measurement points a, b, and c calculated in the thickness difference calculation process. As a result, there is no need to change the inclination of the chuck table 10 in the second grinding process, and thus the total grinding time is shortened and the productivity is increased.

[0062] Then, in the finish grinding region R3 shown in FIG. 1, when the wafer W is finish ground (second grinding) to a uniform thickness by the finish grinding mechanism 30, the finish grinding mechanism 30 is lifted in the +Z axis direction by the lifting mechanism 3 and the finish grinding grindstone 35b is separated from the upper surface of the wafer W. Then, the turntable 2 shown in FIG. 1 rotates by 120° around its vertical axis center, and the finish ground wafer W and the chuck table 10 holding the same move to the wafer loading / unloading region R1. In this wafer loading / unloading region R1, the wafer W is removed from the chuck table 10 by the second transfer means 73 and transferred to the cleaning unit 60.

[0063] In the cleaning unit 60, the wafer W is sucked and held by the spinner table 61, and the spinner table 61 and the wafer W sucked and held thereon are rotationally driven at a predetermined speed around the vertical axis center by a rotation mechanism (not shown). Then, when cleaning water is sprayed from the cleaning water nozzle 62 toward the rotating wafer W, the grinding debris adhering to the surface of the wafer W is washed away and removed.

[0064] Thereafter, the wafer W is removed from the spinner table 61 by the loading / unloading robot 71 and transferred to the cassette 202, stored in the cassette 202, and a series of grinding processes for the wafer W are completed.

[0065] In the above embodiments, the non-contact thickness measuring instrument 90 is rotated horizontally to measure the thicknesses at three measurement points a, b, and c in the radial direction of the wafer W. However, a configuration may be adopted in which three non-contact thickness measuring instruments are arranged with respect to the measurement points a, b, and c.

[0066] Also, in the above embodiments, in the first thickness measurement step and the second thickness measurement step, the thickness of the wafer W held by the chuck table 10 is measured. However, a configuration may be adopted in which the thickness of the wafer W removed from the chuck table 10 is measured. For example, a non-contact thickness measuring instrument 90 may be arranged in the cleaning unit 60 to measure the thickness of the wafer W in the cleaning unit 60.

[0067] Furthermore, the first thickness measurement step and the second thickness measurement step may be performed by measuring the thickness of the wafer by using a device that can be taken out of the grinding device and measure the thickness of a wafer different from the grinding device.

[0068] Also, the first thickness measurement step, the second thickness measurement step, the first grinding thickness measurement step, and the second grinding thickness measurement step may be performed by using the contact thickness measuring instrument 50 and the contact thickness measuring instrument 51. That is, the first probes 50a and 50b that contact the upper surface of the wafer W and measure the upper surface height may be configured to include a moving mechanism that moves in the radial direction of the wafer W or may be arranged in three for three measurement points.

[0069] In the second thickness measurement step, the wafer on which the first thickness measurement step has been performed may be ground to the second thickness and the thickness of the wafer may be measured, or the wafer on which the first thickness measurement step has not been performed may be ground to the second thickness and the thickness of the wafer may be measured.

[0070] In addition, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications are possible within the scope of the technical idea described in the claims, the specification, and the drawings.

Explanation of Reference Numerals

[0071] 1: Grinding device, 2: Turntable (positioning mechanism), 2a: Partition wall, 3: Lifting mechanism, 4: Lifting plate, 5: Guide rail, 6: Ball screw, 7: Servo motor, 10: Chuck table, 10A: Porous member, 10a: Holding surface, 11: Frame body, 12: Rotation axis, 13: Bearing, 20: Rough grinding mechanism (first grinding mechanism), 21: Holder, 22: Spindle motor, 23: Spindle, 24: Mount, 25: Grinding wheel, 25a: Base, 25b: Rough grinding abrasive (first abrasive), 30: Finish grinding mechanism (second grinding mechanism), 31: Holder, 32: Spindle motor, 33: Spindle, 34: Mount, 35: Grinding wheel, 35a: Base, 35b: Finish grinding abrasive (second abrasive), 40: Table rotation mechanism, 41: Drive motor, 41a: Output shaft (motor shaft), 42: Drive pulley, 43: Driven pulley, 44: Timing belt, 50, 51: Contact type thickness measuring instrument, 50a, 51a: First probe, 50b, 51b: Second probe, 60: Cleaning unit, 61: Spin table, 62: Cleaning water nozzle, 70: Conveying unit, 71: Loading / unloading robot, 72: First conveying means, 73: Second conveying means, 80: Tilt change mechanism, 81: Flange, 81a: Female screw, 82: Pivot, 83: Frame, 84: Motor, 84A: Output shaft (motor shaft) 84a: Male screw, 90: Contact type thickness measuring instrument, 91: Motor, 92: Arm, 100: Base, 101: Column, 102: Alignment table, 110: Control unit, 201, 202: Cassette, CL1: Axis center of chuck table, CL2: Axis center of spindle, R1: Wafer loading / unloading area, R2: Rough grinding area, R3: Finish grinding area, W: Wafer, α: Tilt angle of first chuck table

Claims

【Claim 1】 A wafer grinding method implemented using a chuck table that holds a wafer by a conical holding surface, a table rotation mechanism that rotates the chuck table about the center of the holding surface, a first grinding mechanism that grinds the wafer with a first grinding wheel mounted on a first spindle, a second grinding mechanism that grinds the wafer with a second grinding wheel mounted on a second spindle, an alignment mechanism that positions the chuck table at a grinding position of the first grinding wheel and a grinding position of the second grinding wheel, a thickness measuring device that measures the thickness of the wafer at three measurement points including a center portion, an outer peripheral portion, and a radially intermediate portion of the wafer, and an inclination changing mechanism that changes the inclination of the chuck table, comprising: a first thickness measurement step of grinding the wafer to a first thickness with the first grinding wheel and measuring the thickness of the wafer at the three measurement points; a first thickness trend calculation step of calculating, as a first thickness difference, a difference between the thickness at one of the three measurement points and the thicknesses at the other two measurement points, with the thickness at one of the three measurement points measured in the first thickness measurement step as a reference; a second thickness measurement step of grinding the wafer to a second thickness smaller than the first thickness with the second grinding wheel and measuring the thickness of the wafer at the three measurement points; a second thickness trend calculation step of calculating, as a second thickness difference, a difference between the thickness at one of the three measurement points and the thicknesses at the other two measurement points, with the thickness at one of the three measurement points measured in the second thickness measurement step as a reference; a thickness difference calculation step of calculating a difference between the first thickness difference calculated in the first thickness trend calculation step and the second thickness difference calculated in the second thickness trend calculation step; a first grinding step of grinding the wafer held on the holding surface of the chuck table to the first thickness with the first grinding wheel; a first ground thickness measurement step of measuring the thickness of the wafer at the three measurement points ground in the first grinding step; a first ground thickness trend calculation step of calculating a difference between the thickness at one of the three measurement points and the thicknesses at the other two measurement points, with the thickness at one of the three measurement points measured in the first ground thickness measurement step as a reference; an inclination changing step of changing the inclination of the chuck table based on the three calculated values calculated in the first ground thickness trend calculation step and the three calculated values calculated in the thickness difference calculation step; After the slope change step, a second grinding step of grinding the wafer ground in the first grinding step with the second grindstone to the second thickness; A wafer grinding method, characterized by comprising:

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