Wafer grinding method and grinding apparatus

Abstract

To efficiently grind even a wafer of hard material in relatively short time while preventing wear of a grinding wheel.SOLUTION: A wafer grinding method is characterized in that a wafer W is ground to predetermined thickness through: a lowering speed setting step of setting a plurality of lowering speeds of a grind wheel 25b; a total ground amount setting step of setting a total ground amount of the wafer W; a ratio setting step of setting ratio of a ground amount at each lowering speed of the grind wheel 25b to the total ground amount; a calculation step of calculating the ground amount at each lowering speed of the grind wheel 25b from the ratio set in the ratio setting step and the total ground amount set in the total ground amount setting step; and a grinding step of grinding the wafer W by the ground amount calculated in the calculation step while lowering the grind wheel 25b at each lowering speed set in the lowering speed setting step.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a wafer grinding method and grinding apparatus that are particularly suitable for grinding wafers made of hard materials. [Background technology]

[0002] A grinding device for grinding wafers is a device that grinds the wafer by bringing a rotating annular grinding wheel into contact with the wafer while rotating a chuck table that holds the wafer on its holding surface together with the wafer. For example, Patent Documents 1 and 2 propose a grinding method in which the speed at which the grinding wheel is lowered is changed over time.

[0003] However, when grinding wafers made of a hard material such as silicon carbide (SiC), the abrasive grains of the grinding wheel wear out, causing an increase in the load current of the motor that rotates the spindle to which the grinding wheel is attached.

[0004] Therefore, Patent Document 3 proposes a method for solving the above problem, in which a wafer made of a hard material is ground while a grinding wheel is raised and lowered. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-148389 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-178139 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-226625 Summary of the Invention [Problem to be solved by the invention]

[0006] However, as proposed in Patent Document 3, when grinding a wafer made of a hard material while raising and lowering the grinding wheel, a problem occurs in that the grinding time becomes long.

[0007] The present invention has been made in consideration of the above problems, and its object is to provide a wafer grinding method and grinding device that can grind wafers efficiently in a relatively short time while preventing wear of the grinding wheel, even when the wafer is made of a hard material. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a wafer grinding method for grinding the top surface of a wafer held on a chuck table with a grinding wheel that descends from above the wafer, the method comprising the steps of: a descending speed setting step for setting the descending speed of the grinding wheel to a plurality of values ​​that sequentially slow over time; a total grinding amount setting step for setting a total grinding amount of the wafer; a ratio setting step for setting a ratio of the grinding amount at each descending speed of the grinding wheel to the total grinding amount; a calculating step for calculating the grinding amount at each descending speed of the grinding wheel from the ratio set in the ratio setting step and the total grinding amount set in the total grinding amount setting step; and a grinding step for grinding the wafer by the grinding amount calculated in the calculating step while descending the grinding wheel at each descending speed set in the descending speed setting step.

[0009] The present invention also provides a wafer grinding device comprising a chuck table for holding a wafer, a grinding unit for grinding the wafer held on the chuck table with a grinding wheel, an elevation mechanism for raising and lowering the grinding unit, a grinding amount measuring unit for measuring the grinding amount of the wafer held on the chuck table, and a control unit for controlling the lowering speed of the grinding wheel, wherein the control unit includes a lowering speed setting unit for setting the lowering speed of the grinding wheel to a plurality of values ​​that become gradually slower over time, a total grinding amount setting unit for setting the total grinding amount of the wafer, and a control unit for controlling the lowering speed of the grinding wheel. The grinding apparatus is characterized in that it comprises a ratio setting unit that sets the ratio of the grinding amount at each lowering speed of the grinding wheel to the total grinding amount, and a calculation unit that calculates the grinding amount at each lowering speed of the grinding wheel from the ratio set in the ratio setting unit and the total grinding amount set in the total grinding amount setting unit, and when the grinding amount of the wafer measured by the grinding amount measuring unit reaches the grinding amount at each lowering speed calculated by the calculation unit, the grinding wheel is lowered at the plurality of lowering speeds set by the lowering speed setting unit in order to grind the wafer. [Effects of the Invention]

[0010] According to the present invention, the lowering speed of the grinding wheel is set to a plurality of values ​​that become gradually slower over time in the lowering speed setting step, and the amount of wafer ground at each lowering speed is divided into a plurality of parts according to the proportion to the total amount of wafer ground set in the proportion setting step, so that even when grinding wafers made of hard materials, the grinding load on the grinding wheel is gradually reduced as grinding progresses. Therefore, even without separating the grinding wheel from the wafer during grinding, it is possible to prevent the abrasive grains from wearing out or falling off the grinding wheel, and even wafers made of hard materials can be ground efficiently in a relatively short time. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a perspective view of a wafer grinding device according to the present invention; [Figure 2] 2 is a cutaway side view of the main part (chuck table and grinding wheel part) of the grinding device shown in FIG. [Figure 3]FIG. 2 is a block diagram showing the configuration of a control unit. [Figure 4] 3 is a flowchart showing steps of a wafer grinding method according to the present invention. [Figure 5] 3 is a flowchart showing the procedure of a grinding step in the wafer grinding method according to the present invention. [Figure 6] FIG. 10 is a diagram showing the change over time in the height of the grinding surface of the grinding wheel. [Figure 7] 10 is a time chart showing the change over time in the descending speed of the grinding wheel. [Figure 8] 1 is a diagram showing, in table form, a first example of the grinding wheel lowering speed, the ratio of each grinding amount to the total grinding amount, and the grinding amount in the wafer grinding method according to the present invention. FIG. [Figure 9] FIG. 10 is a diagram showing, in table form, a second example of the grinding wheel lowering speed, the ratio of each grinding amount to the total grinding amount, and the grinding amount in the wafer grinding method according to the present invention. [Figure 10] FIG. 10 is a table showing a third example of the grinding wheel lowering speed, the ratio of each grinding amount to the total grinding amount, and the grinding amount in the wafer grinding method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0013] [Grinding equipment configuration] First, the configuration of the grinding device according to the present invention will be described with reference to Figures 1 and 2. In the following description, the directions of the arrows shown in Figure 1 are the X-axis (left-right direction), the Y-axis (front-rear direction), and the Z-axis (up-down direction), respectively.

[0014] The grinding apparatus 1 shown in Fig. 1 is an apparatus for grinding a disk-shaped wafer W (see Fig. 2), and includes as its main components a rotatable disk-shaped turntable 2, three chuck tables 10 arranged on the turntable 2, a table rotation mechanism 40 (see Fig. 2) for rotating each chuck table 10 about its axis (spinning), a rough grinding mechanism 20 for rough grinding the wafer W held on the chuck table 10, and a finish grinding mechanism 30 for finish grinding the wafer W, contact-type thickness gauges 50 and 51 constituting a thickness measurement unit for measuring the thickness of the wafer W, a cleaning unit 60 for cleaning the top surface (surface to be ground) of the wafer W after finish grinding, a transport unit 70 for transporting the wafer W, and a control unit 80. Here, in this embodiment, the wafer W, which is the workpiece to be ground, is a thin disk-shaped member made of a hard material such as silicon carbide (SiC), sapphire, or diamond.

[0015] Next, we will explain the configuration of the main components of the grinding device 1, namely, the turntable 2, chuck table 10, table rotation mechanism 40, rough grinding mechanism 20 and finish grinding mechanism 30 that make up the grinding unit, contact-type thickness measuring devices 50, 51, cleaning unit 60, transport unit 70, and control unit 80.

[0016] (Turntable) The turntable 2 is a disk-shaped member that intermittently rotates horizontally around a central axis perpendicular to the Z-axis direction, and on its upper surface, three chuck tables 10 that can rotate (spin) around their axes are arranged at equal angular pitches (120° pitches) in the circumferential direction. The turntable 2 is intermittently rotated at 120° intervals by a rotation mechanism (not shown), thereby constituting a positioning mechanism that sequentially 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.

[0017] (Chuck table) The three chuck tables 10, which are rotatably arranged on the turntable 2, are disk-shaped members and are arranged at equal angular pitches (120° pitches) in the circumferential direction on the turntable 2, which rotates intermittently around a central axis perpendicular to the Z-axis direction. These chuck tables 10 revolve at 120° intervals around the axis of the turntable 2 perpendicular to the Z-axis direction as the turntable 2 intermittently rotates, and move sequentially between the wafer loading / unloading region R1, the rough grinding region R2, and the finish grinding region R3, and are also rotated at a predetermined speed around the axis center CL1 by a table rotation mechanism 40 shown in FIG.

[0018] As shown in FIG. 2, each chuck table 10 includes a disk-shaped porous member 10A made of porous ceramic or the like mounted in the upper center of a disk-shaped frame 11. The upper surface of each porous member 10A forms a conical holding surface with its apex at the center. The porous member 10A is selectively connected to a suction source 15, such as a vacuum pump, via a suction path 10a formed at the axial center of the chuck table 10, suction paths 12a and 13a formed at the axial centers of a rotary shaft 12 and a rotary joint 13 (described below), and piping 14, so that a wafer W is suction-held on the holding surface. The axial center CL1 of the chuck table 10 is tilted by an angle α (shown in the figure) with respect to a perpendicular line N by a tilt adjustment mechanism (not shown). Although the conical shape of the holding surface of the porous member 10A is exaggerated in FIG. 2, the tilt of the cone of the holding surface is actually so slight that it is not visible to the naked eye.

[0019] As shown in FIG. 2, a protective tape T is attached to the surface of the wafer W (the lower surface in FIG. 2), and the wafer W is suction-held on the holding surface of the chuck table 10 with the protective tape T facing downward.

[0020] (table rotation mechanism) The table rotation mechanism 40 shown in Figure 2 is a mechanism that rotates each chuck table 10 around the axis center CL1 at a predetermined speed in the direction of the arrow in the figure, and is composed of a drive motor 41 which is a rotational 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 the 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.

[0021] Therefore, when the drive motor 41 is started and the output shaft 41a rotates at a predetermined speed, the rotation is decelerated and transmitted to the rotating shaft 12 via the drive pulley 42, timing belt 44, and driven pulley 43, and the rotating shaft 12 and the chuck table 10 rotate at a predetermined speed in the direction of the arrow shown in the figure around the axial center CL1 of the rotating shaft 12.

[0022] (Rough grinding mechanism and finish grinding mechanism) 1, the rough grinding mechanism 20 and the finish grinding mechanism 30 that constitute the grinding unit are installed side by side vertically along the X-axis direction at the +Y-axis direction 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 that roughly grinds the top surface of the wafer W held on the holding surface of the chuck table 10 located in the rough grinding region R2, and the finish grinding mechanism 30 is a mechanism that finish grinds the top surface of the wafer W held on the holding surface of the chuck table 10 located in the finish grinding region R3, and both have the same basic configuration.

[0023] That is, the rough grinding mechanism 20 includes a spindle motor 22 fixed to a holder 21, a vertical spindle 23 that is 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 that is detachably attached to the underside of the mount 24. Here, as shown in Fig. 2, the grinding wheel 25 is composed of a disk-shaped base 25a and a plurality of annular grinding stones 25b that are processing tools that are attached in an annular shape to the underside of the base 25a, and is rotationally driven around a vertical axis center CL2 of the spindle 23 that is the grinding stone rotation axis.

[0024] Similarly to the rough grinding mechanism 20, the finish grinding mechanism 30 also includes a spindle motor 32 fixed to a holder 31, a vertical spindle 33 that is rotated by the spindle motor 32, a disk-shaped mount 34 attached to the lower end of the spindle 33, and a grinding wheel 35 that is detachably attached to the underside of the mount 34. As shown in Fig. 2, the grinding wheel 35 is composed of a disk-shaped base 35a and a plurality of finish grinding stones 35b that are processing tools attached in an annular shape to the underside of the base 35a, and the finish grinding stones 35b are composed of finer abrasive grains than the grinding stones 25b of the rough grinding mechanism 20.

[0025] The rough grinding mechanism 20 and the finish grinding mechanism 30 are supported so as to be able to rise and fall by lifting mechanisms 3 provided on the respective end faces of the -Y axis direction of a pair of block-shaped columns 101 which are erected vertically along the X axis direction at the +Y axis direction end of the base 100. Here, since both lifting mechanisms 3 have the same configuration, corresponding components will be denoted by the same reference numerals in the following description.

[0026] Each lifting mechanism 3 raises and lowers the rough grinding mechanism 20 and the finish grinding mechanism 30 along the Z-axis direction, and includes a rectangular plate-shaped lifting plate 4 and a pair of left and right guide rails 5 for guiding the lifting and lowering 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. The pair of front and rear guide rails 5 are disposed perpendicular to the front surface of the column 101 and parallel to each other.

[0027] A rotatable ball screw 6 is installed vertically along the Z-axis direction between the pair of left and right guide rails 5, and the upper end of the ball screw 6 is connected to a servo motor 7, which serves as a drive source and can rotate forward and backward. The lower end of the ball screw 6 is rotatably supported on a column 101 by a bearing (not shown), and a nut member (not shown) that protrudes horizontally backward (in the +Y-axis direction) from the back surface of the lifting plate 4 is screwed onto the ball screw 6. Each servo motor 7 is provided with an encoder 8 for detecting the rotation speed and rotation direction of the servo motor 7.

[0028] Therefore, when the servo motors 7 of the lifting mechanisms 3 configured as described above are started to rotate the ball screws 6 forward and backward, the lifting plates 4, from which protruding nut members (not shown) that thread onto the ball screws 6, respectively rise and fall along the pair of left and right guide rails 5, and the rough grinding mechanisms 20 and finish grinding mechanisms 30 attached to the lifting plates 4 also rise and fall independently of each other along the Z-axis direction. Here, as shown in FIG. 1 , the servo motors 7 and the encoders 8 are electrically connected to a control unit 80, and when the rotation direction and rotation speed of each servo motor 7 detected by each encoder 8 are transmitted to the control unit 80, the control unit 80 calculates the vertical movement amount (grinding allowance) and descent speed of the grinding wheel 25b of the rough grinding mechanism 20 and the grinding wheel 35b of the finish grinding mechanism 30.

[0029] (Thickness measuring instrument) The thickness measuring device (contact type thickness measuring device) 50 is a contact type height gauge and is equipped with a first probe 50a that contacts the top surface of the wafer W during rough grinding and a second probe 50b that contacts the top surface of the frame body 11 (see Figure 2) of the chuck table 10, and measures the thickness of the wafer W during rough grinding by subtracting the top surface height of the frame body 11 measured by the second probe 50b from the top surface height of the wafer W measured by the first probe 50a.

[0030] In addition, the thickness measuring device (contact type thickness measuring device) 51 is a contact type height gauge and is equipped with a first probe 51a that contacts the top surface of the wafer W during finish grinding and a second probe 51b that contacts the top surface of the frame body 11 (see Figure 2) of the chuck table 10, and measures the thickness of the wafer W during finish grinding by subtracting the top surface height of the frame body 11 measured by the second probe 51b from the top surface height of the wafer W measured by the first probe 51a.

[0031] The thickness gauges 50 and 51 may be non-contact height gauges. The thickness gauges 50 and 51 may also be non-contact thickness gauges. The non-contact thickness gauges use light and spectral interference to measure the distance between the top and bottom surfaces of the wafer W. The non-contact thickness gauges use ultrasonic vibrations to measure the distance between the top and bottom surfaces of the wafer W.

[0032] Here, the thickness gauges 50, 51 are electrically connected to the control unit 80, and the control unit 80 receives detection signals from the thickness gauges 50, 51 to calculate the thickness of the wafer W during rough grinding and the thickness of the wafer W during finish grinding, respectively. The thickness gauges 50, 51 are used as grinding amount measuring units that measure the grinding amount of the wafer W, which will be described later. Furthermore, the encoder 8 provided in the lifting mechanism 3 may also be used as the grinding amount measuring unit that measures the grinding amount of the wafer W, which will be described later.

[0033] (Cleaning unit) The cleaning unit 60 cleans the wafer W that has been finish-ground by the finish grinding mechanism 30 to remove grinding debris and the like adhering to the ground surface (upper surface), and is configured to include a spinner table 61 that holds and rotates the wafer W after finish grinding, and a cleaning water nozzle 62 that sprays cleaning water toward the ground surface of the wafer W. Note that pure water is preferably used as the cleaning water.

[0034] (Transport unit) 1, in the grinding apparatus 1 according to this embodiment, a cassette 201 for storing a plurality of wafers W before grinding and a cassette 202 for storing wafers W after grinding are disposed at the end of the base 100 in the -Y axis direction. The transport unit 70 includes a transfer robot 71 for loading and unloading wafers W into and from the cassette 201 and transporting the wafers W removed from the cassette 201 to the alignment table 102, a first transport means 72 for transporting the wafers W aligned on the alignment table 102 to the chuck table 10 located in the wafer transfer area R1, and a second transport means 73 for receiving the wafers W finish-ground by the finish grinding mechanism 30 from the chuck table 10 located in the finish grinding area R3 and transporting them to the cleaning unit 60.

[0035] (Control unit) The control unit 80 includes a CPU (Central Processing Unit) that performs arithmetic processing according to a control program, and storage units such as a ROM (Read Only Memory) and a RAM (Random Access Memory). In particular, in this embodiment, the control unit 80 includes, as shown in Fig. 3, a lowering speed setting unit 81 that sets the lowering speed of the grinding wheel 25b of the rough grinding mechanism 20 to a plurality of values ​​that sequentially slow over time, a total grinding amount setting unit 82 that sets the total grinding amount of the wafer W, a ratio setting unit 83 that sets the ratio of the grinding amount at each lowering speed of the grinding wheel 25b to the total grinding amount, and a calculation unit 84 that calculates the grinding amount at each lowering speed of the grinding wheel 25b from the ratio set in the ratio setting unit 83 and the total grinding amount set in the total grinding amount setting unit 82.

[0036] Here, the total grinding amount setting unit 82 includes a finishing thickness setting unit 821 that sets the finishing thickness of the wafer W after rough grinding, and a total grinding amount calculation unit 822 that calculates the total grinding amount by subtracting the finishing thickness set in the finishing thickness setting unit 821 from the thickness of the wafer W before rough grinding measured by the contact thickness measuring device 50.

[0037] The calculation unit 84 also includes a limit value setting unit 841 that sets limit values ​​for the amount of grinding of the wafer W at each lowering speed of the grinding wheel 25b of the rough grinding mechanism 20, and a lowering speed calculation unit 842 that, when the amount of grinding at each lowering speed reaches the limit value, calculates the remaining amount of grinding at each lowering speed of the grinding wheel 25b, subtracting the limit value from the total amount of grinding, based on the remaining proportion of the remaining lowering speed, in order from the fastest of the lowering speeds of the grinding wheel 25b.

[0038] [Wafer grinding method] Next, a method for grinding a wafer W according to the present invention, which is carried out by the grinding apparatus 1 according to the present invention configured as above, will be described.

[0039] The method for grinding a wafer W according to the present invention is a method employed when roughly grinding a wafer W by a rough grinding mechanism 20, and as shown in FIG. 1) Descending speed setting process 2) Total grinding amount setting process 3) Ratio setting process 4) Grinding amount calculation process 5) Grinding process This is a method for roughly grinding the wafer W to a predetermined thickness by sequentially going through the steps. Each step will be explained below.

[0040] 1) Descending speed setting process: The descent speed setting process is a process of setting the descent speed of the grinding stone 25b (see Figure 2) of the grinding wheel 25 to multiple values ​​that gradually slow down over time when the wafer W is ground by the rough grinding mechanism 20.In this embodiment, the descent speed is set to five values, namely, a first descent speed V3 to a fifth descent speed V7, by the descent speed setting unit 81 (see Figure 3) of the control unit 80, as shown in Figures 8 to 10.

[0041] For example, in the first example shown in Figure 8, the second example shown in Figure 9, and the third example shown in Figure 10, the first descent speed V3 is set to 5 μm / sec, the second descent speed V4 is set to 3 μm / sec, the third descent speed V5 is set to 1 μm / sec, the fourth descent speed V6 is set to 0.8 μm / sec, and the fifth descent speed V7 is set to 0.5 μm / sec, and the descent speed of the grinding wheel 25b is set to gradually slow down over time.

[0042] 2) Total grinding amount setting process: As shown in FIG. 4, the total grinding amount setting process includes a finishing thickness setting process S211 and a thickness measurement process S212, and is a process in which a total grinding amount setting unit 82 (see FIG. 3) of the control unit 80 sets a total grinding amount Δ from the input thickness t of the wafer W before grinding, which is input by the operator at the time of initial setting, and the finishing thickness t0 set in a finishing thickness setting unit 821 (see FIG. 3) of the control unit 80, and the total grinding amount Δ is calculated by the following equation. Δ=t-t0…(1)

[0043] For example, the total grinding amount Δ is set to Δ=100 μm in the first example shown in Fig. 8, Δ=120 μm in the second example shown in Fig. 8, and Δ=180 μm in the third example shown in Fig. 8. In the third example shown in Fig. 9, the input thickness t of the wafer W is 950 μm, and the finishing thickness t0 is 770 μm.

[0044] 3) Ratio setting process: The rate setting step is performed by the rate setting unit 83 (see FIG. 3) of the control unit 80, which sets the grinding amount δ in rough grinding at each of the lowering speeds V3 to V7. i The ratio r of the total grinding amount Δ iIn the first example shown in FIG. 8, r1 is set to 40%, r2=r3=r4=r5=15%, and in the second example shown in FIG. 9 and the third example shown in FIG. 10, r1 is set to 30%, r2=r3=20%, r4=r5=15%. i is determined in advance through experiments according to the grinding wheel 25b.

[0045] 4) Grinding amount calculation process: The grinding amount calculation process is performed using the ratio r set in the ratio setting process. i Based on the grinding amount δ in rough grinding at each lowering speed V3 to V7 i is calculated by the following formula: δ i =Δ×r i …(2)

[0046] Therefore, the grinding amount δ in rough grinding at each lowering speed V3 to V7 calculated by equation (2) i In the first example shown in Fig. 8, δ1 = 40 µm, δ2 = δ3 = δ4 = δ5 = 15 µm, and in the second example shown in Fig. 9, δ1 = 36 µm, δ2 = δ3 = 24 µm, and δ4 = δ5 = 18 µm. In the third example shown in Fig. 10, δ1 = 54 µm, δ2 = δ3 = 36 µm, and δ4 = δ5 = 27 µm. In the third example shown in Fig. 10, the thicknesses of the wafer W roughly ground by the grinding wheel 25b descending at each of the descending velocities V3 to V7 are 896 µm, 860 µm, 824 µm, 797 µm, and 770 µm (finished thickness), respectively.

[0047] 5) Grinding process: The grinding step is a step of roughly grinding the wafer W by the grinding amounts δ1 to δ5 calculated in the calculation step while lowering the grinding wheel 25b at each of the lowering speeds V3 to V7 set in the lowering speed setting step.

[0048] When rough grinding the wafer W, the wafer W stored in the cassette 201 shown in FIG. 1 is taken out by the transfer robot 71 and transported to the alignment table 102, where the wafer W is aligned (centered).

[0049] The wafer W aligned on the alignment table 102 is held by the first transport means 72 and transferred to the chuck table 10 located in the wafer loading / unloading area R1, where it is suction-held on the holding surface of the chuck table 10 with the protective tape T facing downward. That is, when the porous member 10A of the chuck table 10 is connected to the suction source 15, a negative pressure is generated in the porous member 10A, and the wafer W is attracted by this negative pressure and held by suction on the conical holding surface of the chuck table 10 with the protective tape T facing downward, as shown in Fig. 2. Then, the turntable 2 is rotated by a rotation mechanism (not shown) around its central axis by an angle of 120° in the direction of the arrow in Fig. 1, and the chuck table 10 holding the wafer W moves from the wafer loading / unloading area R1 to the rough grinding area R2.

[0050] As described above, when the chuck table 10 holding the wafer W moves to the rough grinding region R2, the wafer W held on the chuck table 10 is roughly ground in the following procedure by the grinding wheel 25b of the rough grinding mechanism 20. The procedure for rough grinding the wafer W will be described below with reference to FIGS. 5 to 7.

[0051] While the chuck table 10 and the wafer W held thereon are rotated in the direction of the arrow by the table rotation mechanism 40 shown in Fig. 2, and the spindle motor 22 of the rough grinding mechanism 20 shown in Fig. 1 is started to rotate the grinding wheel 25 in the direction of the arrow at a predetermined speed in Fig. 2, the grinding wheel 25 is lowered by the lifting mechanism 3 shown in Fig. 1 from the standby position Z0 shown in Fig. 6 at a high lowering speed V1 (see Figs. 6 and 7) while idling (step S11 in Fig. 5). Then, the height of the grinding surface (lower surface) of the grinding wheel 25b is detected by the encoder 8 shown in Fig. 1 (step S12), and a control unit (not shown) determines whether the height of the grinding surface of the grinding wheel 25b has reached the height position Z1 at which air cutting starts (step S13 in Fig. 5).

[0052] If the result of the above judgment is that the grinding surface of the grinding wheel 25b has not yet reached the height position Z1 where air cutting starts (step S13: No), the processes of steps S11 to S13 are repeated, and if the grinding surface of the grinding wheel 25b has descended by the time interval T1 shown in Figure 6 and reached the height position Z1 (point a in Figure 6) where air cutting starts (step S13: Yes), air cutting is performed while the grinding wheel 25b is descended at a descending speed V2 slower than the descending speed V1, as shown in Figures 6 and 7 (step S14).

[0053] While the air cut is being performed, it is determined whether the grinding surface of the grinding wheel 25b has contacted the upper surface of the wafer W (step S15 in FIG. 5). The grinding wheel 25b descends at a descending speed V2 for a time interval T2 shown in FIGS. 6 and 7. When the grinding surface of the grinding wheel 25b reaches a height position Z2 (point b in FIG. 6), the grinding wheel 25b comes into contact with the upper surface of the wafer W (step S15: Yes). As the grinding wheel 25b descends at a first descending speed V3, rough grinding of the upper surface of the wafer W by the grinding wheel 25b begins (step S16 in FIG. 5). During this rough grinding of the wafer W, the thickness of the wafer W is measured by the contact-type thickness gauge 50 shown in FIG. 1 (step S17). Note that contact of the grinding wheel 25b with the wafer W is detected by a sudden increase in the load current value of the spindle motor 22, and therefore the time interval T2 increases or decreases. Note that contact of the grinding wheel 25b with the wafer W can also be detected by a change in the value of the first probe 50a that contacts the upper surface of the wafer W. Here, if the lowering speed V2 and the lowering speed V3 are the same, the grinding wheel 25b will shift to the lowering speed V3 after the set time interval T2 has elapsed without detecting that it has contacted the wafer W, and will grind the wafer W while measuring its thickness. Note that the lowering speed V2 may be slower than the first lowering speed V3.

[0054] When the upper surface of the wafer W is being roughly ground by the grinding wheel 25b descending at the first descending speed V3 as described above, it is determined whether the thickness of the wafer W measured by the contact-type thickness measuring device 50 is equal to or greater than the finishing thickness (step S18).

[0055] 6 and 7, when the grinding amount of the wafer W reaches δ1 (step S18: Yes), the upper surface of the wafer W is roughly ground by the grinding wheel 25b descending at a second descending speed V4 slower than the first descending speed V3 (step S19 in FIG. 5). Note that when the grinding wheel 25b descends to a height position Z3 (point c in FIG. 6) shown in FIG. 6, the wafer W is ground by a predetermined grinding amount δ1, and this grinding amount δ1 is indicated by (Z2-Z3) in FIG. 6.

[0056] As described above, when the upper surface of the wafer W is being roughly ground by the grinding wheel 25b while descending at the second descending speed V4, it is determined whether the grinding amount has reached the predetermined grinding amount δ2 (step S20).

[0057] 6 and 7 while the grinding wheel 25b descends at the second descending speed V4, if the amount of grinding of the wafer W reaches δ2 (step S20: Yes), the upper surface of the wafer W is roughly ground by the grinding wheel 25b descending at a third descending speed V5 slower than the second descending speed V4 (step S21 in FIG. 5). Note that when the grinding wheel 25b descends to a height position Z4 (point d in FIG. 6) shown in FIG. 6, the wafer W is ground by a predetermined amount of grinding δ2, and this grinding amount δ2 is indicated by (Z4-Z3) in FIG. 6.

[0058] As described above, when the upper surface of the wafer W is being roughly ground by the grinding wheel 25b while being lowered at the third lowering speed V5, it is determined whether the amount of grinding has reached the predetermined amount of grinding δ3 (step S22).

[0059] 6 and 7 while the grinding wheel 25b descends at the third descending speed V5, if the amount of grinding of the wafer W reaches δ3 (step S22: Yes), the upper surface of the wafer W is roughly ground by the grinding wheel 25b while descending at a fourth descending speed V6 slower than the third descending speed V5 (step S23 in FIG. 5). Note that when the grinding wheel 25b descends to the height position Z5 (point e in FIG. 6) shown in FIG. 6, the wafer W is ground by a predetermined amount of grinding δ3, and this amount of grinding δ3 is indicated by (Z4-Z5) in FIG. 6.

[0060] As described above, when the upper surface of the wafer W is roughly ground by the grinding wheel 25b while descending at the fourth descending speed V6, it is determined whether the grinding amount has reached the predetermined grinding amount δ4 (step S24).

[0061] 6 and 7 while the grinding wheel 25b descends at the fourth descending speed V6, if the amount of grinding of the wafer W reaches δ4 (step S24: Yes), the upper surface of the wafer W is roughly ground by the grinding wheel 25b descending at a fifth descending speed V7 that is slower than the fourth descending speed V6 (step S25 in FIG. 5). Note that when the grinding wheel 25b descends to the height position Z6 (point f in FIG. 6) shown in FIG. 6, the wafer W is ground by a predetermined amount of grinding δ4, and this grinding amount δ4 is indicated by (Z5-Z6) in FIG. 6.

[0062] As described above, when the upper surface of the wafer W is being roughly ground by the grinding wheel 25b while descending at the fifth descending speed V7, it is determined whether the grinding amount has reached the predetermined grinding amount δ5 (step S26).

[0063] 6 and 7 while the grinding wheel 25b descends at the fifth descending speed V7, and as a result the grinding amount of the wafer W reaches δ5 (step S26: Yes), the wafer W is ground by the total grinding amount Δ (= δ1 + δ2 + δ3 + δ4 + δ5) set in the total grinding amount setting step (step S2 in FIG. 5) so as to have a predetermined finished thickness. Note that this total grinding amount Δ is indicated by (Z6 - Z7) in FIG. 6.

[0064] In the above description, the lowering speed is sequentially switched after the wafer W has been roughly ground for a predetermined time interval at each lowering speed. Alternatively, the lowering speed may be sequentially switched in response to a change in the value of the contact-type thickness gauge 50. In other words, the grinding surface height, which is the vertical axis of the graph in FIG. 6, can be considered to represent the thickness of the wafer W, and points b to g in FIG. 6 can be considered to represent the thickness of the wafer W. Points b to g in FIG. 6 can also be considered to represent the height of the top surface of the wafer W. In other words, the lowering speed may be switched in response to a change in the height of the top surface of the wafer W by monitoring only the value of the height gauge measuring the height of the top surface of the wafer W with the contact-type thickness gauge 50.

[0065] As described above, when the upper surface of the wafer W has been ground by the grinding wheel 25b by the total grinding amount Δ, a spark-out cut is performed for a time interval T8 shown in Fig. 6 (step S27). This spark-out cut is performed by stopping the descent of the grinding wheel 25b (descent speed V8 shown in Fig. 6 = 0), and rotating the grinding wheel 25b for a set time while holding it at the height position Z7 shown in Fig. 6 (points g and h in Fig. 6).

[0066] Thereafter, an escape cut is performed in which the grinding wheel 25b is rotated while being raised at a constant speed V9 by the lifting mechanism 3 shown in Fig. 1 (step S28). The escape cut is performed to remove contact marks that are generated on the top surface of the wafer W due to contact with the first probe 50a of the contact-type thickness measuring device 50 during grinding of the wafer W by the grinding wheel 25b, and this escape cut flattens the top surface of the wafer W. Note that this escape cut is performed only during a time interval T9 until the grinding wheel 25b is raised to a height position Z8 (point i in Fig. 6) where it is separated from the wafer W.

[0067] 1 moves the grinding wheel 25b up to the standby position Z0 at a relatively high retraction speed V10 during a time interval T10 (step S29), completing a series of rough grinding steps for the wafer W (step S30). During the rough grinding of the wafer W, grinding water (pure water) is supplied from a grinding water supply source (not shown) to the contact portion (grinding portion) between the grinding wheel 25b and the wafer W, and the contact portion (grinding portion) between the grinding wheel 25b and the wafer W is cooled by the grinding water, and grinding chips generated by grinding the wafer W are washed away and removed by the grinding water.

[0068] 1 rotates by an angle of 120° in the direction of the arrow, and the chuck table 10 and the wafer W held thereon move from the rough grinding region R2 to the finish grinding region R3, where the wafer W is finish-ground by the finish grinding mechanism 30. As in the rough grinding, the finish grinding is also performed by switching between multiple lowering speeds. Note that in the rough grinding, the wafer W may be ground to a predetermined thickness at one lowering speed, and then only in the finish grinding, the finish grinding may be performed by switching between multiple lowering speeds.

[0069] 1 rotates by an angle of 120° in the direction of the arrow, and the chuck table 10 and the wafer W held thereon move from the finish grinding area R3 to the wafer transfer area R1. The finish-ground wafer W is then transferred from the chuck table 10 to the cleaning unit 60 by the second transfer means 73. In the cleaning unit 60, the wafer W is held on the upper surface of the spinner table 61 and rotated together with the spinner table 61 at a predetermined speed, and cleaning water is sprayed from the cleaning water nozzles 62 toward the upper surface of the wafer W. As a result, grinding debris adhering to the upper surface of the wafer W is washed away and removed by the cleaning water.

[0070] As described above, the wafer W cleaned in the cleaning unit 60 is transported from the cleaning unit 60 to the cassette 202 by the loading / unloading robot 71, and the series of processing steps for the wafer W in the grinding apparatus 1 is completed when the wafer W is stored in the cassette 202.

[0071] Although not shown in FIGS. 5 and 6, in this embodiment, in the rough grinding process of the wafer W, a limit value of the grinding amount of the wafer W at the lowering speed V3 of the grinding wheel 25b (maximum grinding amount that can be ground) is set, and the grinding amount δ at each lowering speed V3 of the grinding wheel 25b is i exceeds the limit value set by the limit value setting unit 841 (see FIG. 3) of the control unit 80, the remaining grinding amount obtained by subtracting the limit value from the total grinding amount Δ is calculated in the lowering speed calculation unit 842 (see FIG. 3) of the control unit 80, and the grinding amount for the remaining lowering speeds (V4 to V7) is calculated based on the ratio set for each lowering speed (V4 to V7) for the remaining lowering speeds. Note that the limit value for the grinding amount of the wafer W at each lowering speed of the grinding wheel 25b is set in advance by test grinding the wafer W. Also, the limit value for the grinding amount may be set for each lowering speed.

[0072] As described above, in the method for grinding the wafer W according to the present invention, the lowering speed of the grinding wheel 25b is set to five values ​​V3 to V7 that become gradually slower over time in the lowering speed setting step, and the amount of grinding of the wafer W at each of the lowering speeds V3 to V7 is set as a ratio r to the total amount of grinding Δ set in the ratio setting step. i Since the load is divided into five values ​​δ1 to δ5 by (i=1 to 5), the grinding load on the grinding wheel 25b is gradually reduced as the grinding progresses, even when grinding a hard wafer W. This prevents the abrasive grains of the grinding wheel 25b from being worn out or falling off without the need to separate the grinding wheel 25b from the wafer W during grinding, and provides the effect of enabling the wafer W to be continuously and efficiently ground in a relatively short time, even if the wafer W is made of a hard material.

[0073] In the above embodiment, the lowering speed of the grinding wheel 25b is set to five values ​​V3 to V7, and the ratio r of the grinding amounts δ1 to δ5 to the total grinding amount Δ is set to each of the lowering speeds V3 to V7. i (i=1 to 5) are set, respectively, but the number of settings for the lowering speed of the grinding wheel 25b is not limited to five and can be any number as long as it is plural, and should be set to an appropriate number depending on the hardness of the wafer W or the material and configuration of the grinding wheel 25b.

[0074] Furthermore, the present invention is not limited to the application of the above-described embodiments, and it goes without saying that various modifications are possible within the scope of the claims and the technical ideas described in the specification and drawings. [Explanation of symbols]

[0075] 1: Grinding device, 2: Turntable, 3: Lifting mechanism, 4: Lifting plate, 5: Guide rail, 6: Ball screw, 7: Servo motor (drive source), 8: Encoder (grinding amount measurement part), 10: chuck table, 10A: porous member, 10a: suction path, 11: frame body, 12: Rotating shaft, 12a: Suction passage, 13: Rotary joint, 13a: Suction passage, 14: Piping, 15: Suction source, 20: Rough grinding mechanism (grinding unit), 21: Holder, 22: spindle motor, 23: spindle, 24: mount, 25: grinding wheel, 25a: base, 25b: grinding wheel, 30: finish grinding mechanism (grinding unit), 31: holder, 32: spindle motor, 33: spindle, 34: mount, 35: grinding wheel, 35a: base, 35b: grinding stone, 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 (grinding amount measuring part), 50a, 51a: first probe, 50b, 51b: second probe, 60: cleaning unit, 61: spinner table, 62: cleaning water nozzle, 70: transport unit, 71: Carry-in / out robot, 72: First conveying means, 73: Second conveying means, 80: Control unit, 81: Lowering speed setting unit, 82: Total grinding amount setting unit, 821: Finishing thickness setting unit, 822: total grinding amount calculation unit, 83: ratio setting unit, 84: calculation unit, 841: limit setting unit, 842: descent speed calculation unit, 100: base, 101: column, 102: alignment table, 201, 202: cassette, CL1: axial center of chuck table, CL2: axial center of spindle, N: perpendicular line, R1: Wafer loading / unloading area, R2: Rough grinding area, R3: Finish grinding area, W: Wafer, α: Tilt angle of the chuck table

Claims

1. A wafer grinding method for grinding an upper surface of a wafer by a grinding wheel that descends from above the wafer held on a chuck table, comprising: a lowering speed setting step of setting the lowering speed of the grinding wheel to a plurality of values ​​that become gradually slower over time; a total grinding amount setting step of setting a total grinding amount of the wafer; a ratio setting step of setting a ratio of the grinding amount at each lowering speed of the grinding wheel to the total grinding amount; a calculation step of calculating a grinding amount at each lowering speed of the grinding wheel from the ratio set in the ratio setting step and the total grinding amount set in the total grinding amount setting step; a grinding step of grinding the wafer by the grinding amount calculated in the calculation step while lowering the grinding wheel at each of the lowering speeds set in the lowering speed setting step; A wafer grinding method characterized by grinding the wafer by a total grinding amount through the steps of:

2. In the calculation step, 2. A wafer grinding method according to claim 1, characterized in that a limit value for the amount of wafer grinding at each lowering speed of the grinding wheel is set, and when the amount of grinding at each lowering speed of the grinding wheel reaches the limit value, the remaining amount of grinding is calculated by subtracting the limit value from the total amount of grinding, based on the remaining ratio for the remaining lowering speeds.

3. In the total grinding amount setting step, a finishing thickness setting step of setting a finishing thickness when the wafer is ground by the grinding wheel; a thickness measuring step of measuring the thickness of the wafer held on the chuck table, 2. The wafer grinding method according to claim 1, wherein the total grinding amount is determined by subtracting the finished thickness from the thickness of the wafer before grinding measured in the thickness measuring step.

4. A wafer grinding device comprising: a chuck table for holding a wafer; a grinding unit for grinding the wafer held on the chuck table with a grinding wheel; a lifting mechanism for raising and lowering the grinding unit; a grinding amount measuring unit for measuring the amount of grinding of the wafer held on the chuck table; and a control unit for controlling the descending speed of the grinding wheel, The control unit a lowering speed setting unit that sets the lowering speed of the grinding wheel to a plurality of values ​​that become gradually slower over time; a total grinding amount setting unit that sets a total grinding amount of the wafer; a ratio setting unit that sets a ratio of the grinding amount at each lowering speed of the grinding wheel to the total grinding amount; a calculation unit that calculates the grinding amount at each lowering speed of the grinding wheel from the ratio set in the ratio setting unit and the total grinding amount set in the total grinding amount setting unit; and when the grinding amount of the wafer measured by the grinding amount measuring unit reaches the grinding amount at each lowering speed calculated by the calculation unit, the grinding wheel is lowered at a plurality of lowering speeds set by the lowering speed setting unit in order to grind the wafer.

5. a thickness measuring device for measuring the thickness of the wafer; 5. The wafer grinding apparatus according to claim 4, wherein said grinding amount measuring unit measures a change in the value of said thickness measuring device.

6. the lifting mechanism includes an encoder for detecting the lifting position of the grinding unit; 5. The wafer grinding device according to claim 4, wherein said grinding amount measuring unit measures a change in the value of said encoder.

7. The total grinding amount setting unit a finishing thickness setting unit that sets a finishing thickness of the wafer; a total grinding amount calculation unit that calculates the total grinding amount by subtracting the finishing thickness set in the finishing thickness setting unit from the thickness of the wafer before grinding measured by the thickness measuring device; 6. The wafer grinding apparatus according to claim 5, further comprising:

8. The calculation unit a limit value setting unit that sets a limit value for the amount of wafer grinding at each lowering speed of the grinding wheel; a lowering speed calculation unit that calculates the amount of grinding at each lowering speed of the grinding wheel in order from the fastest one, and when the amount of grinding at each lowering speed reaches the limit value, calculates the remaining amount of grinding obtained by subtracting the limit value from the total amount of grinding based on the remaining ratio for the remaining lowering speeds; 5. The wafer grinding apparatus according to claim 4, further comprising:

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