Grinding method for workpieces

Abstract

To provide a grinding method for a workpiece, the grinding method enabling reduction of consumption amount of a grinding stone.SOLUTION: A grinding method for a workpiece is provided, for grinding a workpiece by using a grinding device. The grinding device comprises: a chuck table which holds the workpiece at a holding surface; a grinding unit which has a spindle in which a grinding wheel having a grinding stone is mounted to the distal end thereof; and a grinding surface adjustment unit which adjusts the state of the grinding surface side contacting the workpiece of the grinding stone. The grinding method includes: a holding step of holding the workpiece; and a grinding step of grinding the workpiece. In the grinding step, the grinding device grinds the workpiece while adjusting the state of the grinding stone by the grinding surface adjustment unit when a value corresponding to a grinding load is equal to or greater than a prescribed reference value, and grinds the workpiece without adjusting the state of the grinding stone by the grinding surface adjustment unit when the value corresponding to the grinding load is less than the prescribed reference value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for grinding a workpiece using a grinding apparatus.

Background Art

[0002] Device chips including devices are manufactured by dividing a wafer on which a plurality of devices are formed into individual pieces. Further, a package substrate is formed by mounting a plurality of device chips on a predetermined substrate and coating and sealing the device chips with a resin layer (mold resin). By dividing this package substrate into individual pieces, a package device including a plurality of packaged device chips is manufactured. The device chips and package devices are incorporated into various electronic devices such as mobile phones and personal computers.

[0003] In recent years, with the miniaturization of electronic devices, there has been a demand for thinning of device chips and package devices. Therefore, a process of grinding and thinning a wafer or a package substrate before division using a grinding apparatus may be performed. The grinding apparatus includes a chuck table for holding a workpiece and a grinding unit for performing grinding on the workpiece. A spindle is built into the grinding unit, and an annular grinding wheel including a plurality of grinding grains is mounted on the tip of the spindle. By holding the workpiece on the chuck table and bringing the grinding into contact with the workpiece while rotating the chuck table and the grinding wheel, the workpiece is ground and thinned (see Patent Document 1).

[0004] The grinding grains of the grinding wheel are formed by fixing abrasive grains with a bonding material (bonding material). The workpiece is ground when the abrasive grains exposed from the bonding material collide with the workpiece. When the grinding of the workpiece by the grinding wheel is continued, the bonding material is consumed (worn), the exposed abrasive grains fall off, and the abrasive grains embedded inside the bonding material are newly exposed. This phenomenon is called self-generated cutting edge, and the grinding ability of the grinding wheel is maintained by the self-generated cutting edge.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2014-124690 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] When grinding a workpiece with a grinding machine, the grinding wheel's abrasive disc comes into contact with the workpiece, and a force (grinding load) acts on the disc. The grinding load varies depending on the material of the workpiece being ground, and the grinding load tends to be higher when grinding workpieces made of materials that are difficult to grind (hard-to-machine materials). If grinding continues under a high grinding load, processing defects such as chipping are likely to occur in the workpiece.

[0007] Therefore, when grinding workpieces made of difficult-to-machine materials, grinding wheels that wear down easily upon contact with the workpiece are used. This promotes the self-sharpening of the grinding wheel during grinding, allowing the workpiece to be ground while maintaining a high grinding capacity of the grinding wheel. As a result, the grinding load acting on the grinding wheel is reduced, and the occurrence of processing defects is suppressed.

[0008] However, grinding equipment is used to grind various types of workpieces. Therefore, when a grinding wheel containing easily worn grinding wheels is mounted on a grinding unit, these easily worn grinding wheels are used not only for grinding difficult-to-machine materials (such as SiC wafers and sapphire wafers) but also for grinding easily grindable materials (such as silicon wafers). In this case, when grinding easily grindable workpieces, the grinding wheels are worn out more than necessary, even though frequent self-sharpening is not required. As a result, the grinding time required to thin the workpiece to the desired thickness increases, reducing processing efficiency. In addition, the rapid wear of grinding wheels increases the frequency of grinding wheel replacement, leading to increased costs.

[0009] Furthermore, even when grinding the same type of workpiece with a grinding machine, the grinding load may fluctuate during the grinding process. For example, the condition of the grinding wheel may change over time during grinding, and the grinding load may gradually increase as the grinding process progresses. Also, when grinding a silicon wafer with an oxide film (SiO2 film) formed on the back side, the oxide film, which is difficult to grind, and the single-crystal silicon, which is easy to grind, are continuously ground, causing the grinding load to fluctuate during the grinding process. In such cases, if a grinding wheel that wears out easily is used to prioritize keeping the grinding load low, the grinding wheel will be unnecessarily worn even while the workpiece is being ground at a low grinding load, leading to decreased processing efficiency and increased costs.

[0010] This invention has been made in view of the above problems, and aims to provide a method for grinding a workpiece that can reduce the amount of wear on the grinding wheel. [Means for solving the problem]

[0011] According to one aspect of the present invention, a method for grinding a workpiece using a grinding device, the grinding device comprising: a chuck table that holds the workpiece on a holding surface; a grinding unit having a spindle with a grinding wheel having a grinding wheel mounted at its tip; and a grinding surface adjustment unit that wears the grinding surface side of the grinding wheel that contacts the workpiece, the method comprising: a holding step of holding the workpiece with the chuck table; and rotating the grinding wheel while the grinding wheel is held by the chuck table The process includes a grinding step of grinding a workpiece by bringing it into contact with an object, wherein in the grinding step, if the value corresponding to the grinding load is equal to or greater than a predetermined reference value, the grinding surface adjustment unit grinds the workpiece while wearing down the grinding surface side of the grinding wheel, and if the value corresponding to the grinding load is less than a predetermined reference value, the grinding surface adjustment unit grinds the workpiece without wearing down the grinding surface side of the grinding wheel, and the reference value is the value corresponding to the grinding load when grinding a first workpiece that is equal to or greater than the reference value. The material is different from the first workpiece.A method for grinding a workpiece is provided, wherein the value corresponding to the grinding load is set to be less than a reference value when grinding a second workpiece. Furthermore, according to another aspect of the present invention, a method for grinding a workpiece using a grinding device is provided, the grinding device comprising: a chuck table that holds the workpiece on a holding surface; a grinding unit having a grinding wheel with a grinding wheel attached to its tip; and a grinding surface adjustment unit that wears the grinding surface side of the grinding wheel that contacts the workpiece, the method comprising: a holding step of holding the workpiece with the chuck table; and a grinding step of grinding the workpiece by rotating the grinding wheel and bringing the grinding wheel into contact with the workpiece held by the chuck table. The grinding step provides a method for grinding a workpiece in which, if the value corresponding to the grinding load is greater than or equal to a predetermined reference value, the workpiece is ground while the grinding surface adjustment unit wears down the grinding surface side of the grinding wheel, and if the value corresponding to the grinding load is less than a predetermined reference value, the workpiece is ground without wearing down the grinding surface side of the grinding wheel, and the reference value is set such that when grinding the first layer contained in the workpiece, the value corresponding to the grinding load is greater than or equal to the reference value, and when grinding the second layer contained in the workpiece, the value corresponding to the grinding load is less than the reference value.

[0012] The grinding surface adjustment unit may spray fluid onto the grinding surface side of the grinding wheel, or irradiate the grinding surface side of the grinding wheel with a laser beam or ultrasonic waves. The grinding surface adjustment unit may also be equipped with a dressing board or brush that contacts the grinding surface side of the grinding wheel.

[0013] The value corresponding to the grinding load may be the current value of the motor that rotates the spindle. Alternatively, the value corresponding to the grinding load may be the load value applied to the chuck table or the spindle. [Effects of the Invention]

[0014] In a workpiece grinding method according to one aspect of the present invention, when the grinding load is high, the condition of the grinding wheel is adjusted to maintain a high grinding capacity while grinding the workpiece. On the other hand, when the grinding load is low, the workpiece is ground while suppressing wear of the grinding wheel without adjusting its condition. This makes it possible to reduce the amount of wear on the grinding wheel while preventing the occurrence of processing defects due to increased grinding load. [Brief explanation of the drawing]

[0015] [Figure 1] This is a perspective view showing a grinding machine. [Figure 2] This is a perspective view showing the chuck table and grinding unit. [Figure 3] This is a cross-sectional view showing a chuck table. [Figure 4] This flowchart shows the grinding method for a workpiece. [Figure 5] This is a perspective view showing a grinding machine that holds a workpiece in a chuck table. [Figure 6] Figure 6(A) is a perspective view showing a grinding apparatus that grinds a workpiece while adjusting the condition of the grinding wheel, and Figure 6(B) is a perspective view showing a grinding apparatus that grinds a workpiece without adjusting the condition of the grinding wheel. [Figure 7] This is a plan view showing the chuck table and grinding wheel. [Figure 8] Figure 8(A) is a perspective view showing grinding surface adjustment using a laser beam on a grinding wheel, and Figure 8(B) is a perspective view showing a grinding surface adjustment unit that uses ultrasonic waves on a grinding wheel. [Figure 9] Figure 9(A) is a perspective view showing a grinding surface adjustment unit equipped with a dressing board that contacts the grinding wheel, and Figure 9(B) is a perspective view showing a grinding surface adjustment unit equipped with a brush that contacts the grinding wheel. [Modes for carrying out the invention]

[0016] Hereinafter, an embodiment according to an aspect of the present invention will be described with reference to the accompanying drawings. First, a configuration example of a grinding apparatus that can be used for implementing a method of grinding a workpiece according to the present embodiment will be described. FIG. 1 is a perspective view showing a grinding apparatus 2 for grinding a workpiece 11. In FIG. 1, the X-axis direction (processing feed direction, first horizontal direction, front-rear direction), the Y-axis direction (second horizontal direction, left-right direction), and the Z-axis direction (vertical direction, up-down direction, height direction) are perpendicular to each other.

[0017] For example, the workpiece 11 is a disk-shaped wafer made of a semiconductor material such as single crystal silicon, and includes surfaces (first surface) 11a and back surfaces (second surface) 11b that are generally parallel to each other. The workpiece 11 is partitioned into a plurality of rectangular regions by a plurality of streets (division planned lines) arranged in a grid pattern so as to intersect each other. Further, on the surface 11a side of the plurality of regions partitioned by the streets, devices (not shown) such as IC (Integrated Circuit), LSI (Large Scale Integration), LED (Light Emitting Diode), and MEMS (Micro Electro Mechanical Systems) devices are formed.

[0018] By dividing the workpiece 11 along the street, a plurality of device chips each including a device are manufactured. For dividing the workpiece 11, various processing apparatuses such as a cutting apparatus that cuts the workpiece 11 with an annular cutting blade and a laser processing that processes the workpiece 11 by irradiating a laser beam can be used. Further, before dividing the workpiece 11, if the back surface 11b side of the workpiece 11 is ground by the grinding apparatus 2 to thin the workpiece 11, a thinned device chip can be obtained.

[0019] However, there are no restrictions on the type, material, size, shape, structure, etc., of the workpiece 11. For example, the workpiece 11 may be a disc-shaped wafer (substrate) made of semiconductors other than silicon (GaAs, InP, GaN, SiC, etc.), sapphire, glass, ceramics, resin, metal, etc. Furthermore, there are no restrictions on the type, quantity, shape, structure, size, arrangement, etc., of the devices, and the workpiece 11 does not even need to have devices formed on it.

[0020] The grinding device 2 includes a base 4 that supports or accommodates each component that makes up the grinding device 2. A rectangular opening 4a is provided on the upper surface of the base 4, with its longitudinal direction aligned with the X-axis. In addition, a rectangular parallelepiped support structure 6 is provided on the upper surface of the rear end of the base 4, aligned with the Z-axis.

[0021] Inside the opening 4a, a chuck table (holding table) 8 is provided for holding the workpiece 11. The upper surface of the chuck table 8 is a flat surface that is generally parallel to the horizontal plane (XY plane) and constitutes a holding surface 8a for holding the workpiece 11. An X-axis movement unit 10 is connected to the chuck table 8 to move the chuck table 8 along the X-axis direction.

[0022] The X-axis movement unit 10 is, for example, a ball screw type movement mechanism and is installed inside the opening 4a. Specifically, the X-axis movement unit 10 comprises an X-axis ball screw (not shown) arranged along the X-axis direction and an X-axis pulse motor (not shown) that rotates the X-axis ball screw. The X-axis movement unit 10 also includes a flat table cover 12 that surrounds the chuck table 8. The front and rear of the table cover 12 are provided with bellows-shaped dustproof and waterproof covers 14 that can be extended and retracted along the X-axis direction. The table cover 12 and the dustproof and waterproof covers 14 are installed so as to cover the components of the X-axis movement unit 10 (X-axis ball screw, X-axis pulse motor, etc.) that are housed inside the opening 4a.

[0023] When the X-axis movement unit 10 is activated, the chuck table 8 moves along the X-axis direction and is positioned at the front end (conveying position) or rear end (grinding position) of the opening 4a. The chuck table 8 is also connected to a rotational drive source (not shown), such as a motor, which rotates the chuck table 8 around a rotation axis that is approximately parallel to the Z-axis direction.

[0024] A Z-axis movement unit 16 is provided on the front side of the support structure 6. The Z-axis movement unit 16 includes a pair of Z-axis guide rails 18 arranged along the Z-axis direction. A flat Z-axis movement plate 20 is also mounted on the pair of Z-axis guide rails 18 so as to be slidable along the Z-axis guide rails 18.

[0025] A nut portion (not shown) is provided on the back (rear) side of the Z-axis moving plate 20. A Z-axis ball screw 22, which is positioned along the Z-axis direction between a pair of Z-axis guide rails 18, is screwed into this nut portion. A Z-axis pulse motor 24, which rotates the Z-axis ball screw 22, is connected to the end of the Z-axis ball screw 22. When the Z-axis pulse motor 24 rotates the Z-axis ball screw 22, the Z-axis moving plate 20 moves (up and down) along the Z-axis guide rails 18 in the Z-axis direction.

[0026] A support member 26 is fixed to the front surface of the Z-axis moving plate 20. The support member 26 supports a grinding unit 28 that performs grinding on the workpiece 11. The grinding unit 28 includes a cylindrical housing 30 supported by the support member 26. The housing 30 also houses a cylindrical spindle 32 arranged along the Z-axis direction. The tip (lower end) of the spindle 32 protrudes downward from the lower surface of the housing 30.

[0027] A disc-shaped mount 34 made of metal or the like is fixed to the tip of the spindle 32. An annular grinding wheel 36 for grinding the workpiece 11 is detachably mounted on the underside of the mount 34. For example, the grinding wheel 36 is fixed to the mount 34 by fasteners (not shown), such as fastening bolts. In this way, the grinding wheel 36 is attached to the tip of the spindle 32 via the mount 34.

[0028] The grinding wheel 36 comprises an annular wheel base 38 and a plurality of grinding wheels 40 fixed to the wheel base 38. The wheel base 38 is made of a metal such as an aluminum alloy and is formed to be approximately the same diameter as the mount 34. On the lower surface of the wheel base 38, the plurality of grinding wheels 40 are arranged in an annular shape at approximately equal intervals along the outer edge of the wheel base 38. The lower surface of each grinding wheel 40 constitutes a grinding surface 40a (see Figure 2) that contacts the workpiece 11 and grinds the workpiece 11.

[0029] The grinding wheel 40 is formed, for example, in a rectangular parallelepiped shape and includes abrasive grains made of diamond, cBN (cubic boron nitride), etc., and a binder (bonding material) that fixes the abrasive grains. As the binder, metal bonds, resin bonds, vitrified bonds, etc., can be used. However, there are no restrictions on the number, shape, material, size, etc. of the grinding wheel 40.

[0030] A grinding fluid supply passage (not shown) for supplying a liquid (grinding fluid) such as pure water is provided inside or near the grinding unit 28. During grinding of the workpiece 11, grinding fluid is supplied from the grinding fluid supply passage to the workpiece 11 and the grinding wheel 40. This cools the workpiece 11 and the grinding wheel 40, and washes away the debris (grinding debris) generated by grinding the workpiece 11.

[0031] Below the grinding unit 28, a grinding surface adjustment unit 42 is provided to adjust the condition of the grinding surface 40a (see Figure 2) of the grinding wheel 40. The grinding surface adjustment unit 42 wears down the grinding surface 40a of the grinding wheel 40 to promote the self-sharpening of the grinding wheel 40, and also adjusts the condition of the grinding wheel 40 by removing foreign matter such as grinding debris adhering to the grinding surface 40a of the grinding wheel 40. Details of the configuration and function of the grinding surface adjustment unit 42 will be described later.

[0032] Furthermore, the grinding device 2 includes a control unit (control unit, control device) 44 that controls the grinding device 2. The control unit 44 is connected to each component of the grinding device 2 (chuck table 8, X-axis movement unit 10, Z-axis movement unit 16, grinding unit 28, grinding surface adjustment unit 42, etc.). The control unit 44 controls the operation of the grinding device 2 by outputting control signals to each component of the grinding device 2.

[0033] For example, the control unit 44 is composed of a computer and includes a calculation unit that performs calculations for operating the grinding machine 2, and a storage unit that stores various information (data, programs, etc.) used for operating the grinding machine 2. The calculation unit includes a processor such as a CPU (Central Processing Unit). The storage unit includes memory such as ROM (Read Only Memory) and RAM (Random Access Memory).

[0034] Figure 2 is a perspective view showing the chuck table 8 and the grinding unit 28. The chuck table 8 comprises a cylindrical frame (main body) 50 made of metal such as SUS (stainless steel), glass, ceramics, resin, etc. A cylindrical recess 50b is provided in the center of the upper surface 50a of the frame 50. A disc-shaped holding member 52 made of a porous material such as porous ceramics is fitted into the recess 50b. The holding member 52 includes a flow path formed by a plurality of voids that communicate from the upper surface to the lower surface of the holding member 52. The upper surface of the holding member 52 constitutes a circular suction surface 52a that attracts the workpiece 11 when the chuck table 8 holds the workpiece 11.

[0035] The depth of the recess 50b and the thickness of the retaining member 52 are approximately the same, and the upper surface 50a of the frame 50 and the suction surface 52a of the retaining member 52 constitute the retaining surface 8a of the chuck table 8. The retaining surface 8a (suction surface 52a) is connected to a suction source (not shown), such as an ejector, via a void in the retaining member 52, a flow path 50c (see Figure 3) formed inside the frame 50, a valve (not shown), etc.

[0036] Figure 3 is a cross-sectional view showing the chuck table 8. The holding surface 8a of the chuck table 8 is formed in a conical shape with the center of the holding surface 8a as its apex, and is slightly inclined with respect to the radial direction of the holding surface 8a. The chuck table 8 is positioned at a slight inclination so that the holding area 8b, which corresponds to a part of the holding surface 8a and extends from the center of the holding surface 8a to its outer edge, is parallel to the horizontal plane. The axis of rotation of the chuck table 8 is set along a direction perpendicular to the radial direction of the holding surface 8a, and is slightly inclined with respect to the vertical direction.

[0037] Note that in Figure 3, the inclination of the holding surface 8a is exaggerated for illustrative purposes, but the actual inclination of the holding surface 8a is small. For example, when the diameter of the holding surface 8a is approximately 290 mm to 310 mm, the difference in height between the center and the outer edge of the holding surface 8a (corresponding to the height of the cone) is set to approximately 20 μm to 40 μm.

[0038] As shown in Figure 2, a load measuring unit 54 is connected to the chuck table 8 to measure the load applied to the chuck table 8. For example, the load measuring unit 54 is a load cell connected to the chuck table 8, which converts the load applied to the chuck table 8 into an electrical signal and outputs it. The signal corresponding to the load value applied to the chuck table 8 is then input from the load measuring unit 54 to the control unit 44.

[0039] A grinding unit 28 is provided above the chuck table 8. A motor 56 is connected to the grinding unit 28 to rotate the spindle 32 at a predetermined rotational speed. When a control signal is output from the control unit 44 to the motor 56 to drive the motor 56, the spindle 32, mount 34, and grinding wheel 36 rotate around a rotation axis that is approximately parallel to the Z-axis direction. In addition, while the motor 56 is being driven, the current value of the motor 56 is input from the motor 56 to the control unit 44. The current value of the motor 56 corresponds to the torque of the motor 56 required to maintain the rotational speed of the spindle 32, mount 34, and grinding wheel 36 at a predetermined value.

[0040] Furthermore, the grinding unit 28 is connected to a load measuring unit 58 that measures the load applied to the spindle 32, mount 34, and grinding wheel 36. For example, the load measuring unit 58 is a load cell connected to the spindle 32, which converts the load applied to the spindle 32 into an electrical signal and outputs it. The signal corresponding to the load value applied to the spindle 32 is then input from the load measuring unit 58 to the control unit 44.

[0041] When the motor 56 is driven, the grinding wheel 36 rotates due to the power transmitted from the motor 56 via the spindle 32 and mount 34. As a result, each of the multiple grinding wheels 40 moves along an annular movement path (rotational trajectory) that is roughly parallel to the horizontal plane (XY plane). The workpiece 11 is held in the chuck table 8, and the workpiece 11 is ground by bringing the grinding wheels 40 into contact with the workpiece 11 while rotating the chuck table 8 and the grinding wheel 36.

[0042] Furthermore, if grinding of the workpiece 11 with the grinding wheel 40 is continued, a phenomenon called "cloggedness" may occur, in which the abrasive grains exposed from the binder of the grinding wheel 40 become smoothed due to wear, reducing the grinding capacity of the grinding wheel 40. Alternatively, a phenomenon called "clogging" may occur, in which foreign matter such as grinding debris adheres to the grinding surface 40a of the grinding wheel 40, embedding some or all of the abrasive grains. When cloggedness or clogging occurs, the grinding capacity of the grinding wheel 40 decreases, and the force acting on the grinding wheel 40 (grinding load) increases. If grinding of the workpiece 11 is continued under a high grinding load, processing defects such as chipping are more likely to occur in the workpiece 11.

[0043] Therefore, the grinding device 2 is equipped with a grinding surface adjustment unit 42 that adjusts the condition of the grinding surface 40a side of the grinding wheel 40. The grinding surface adjustment unit 42 promotes the self-sharpening of the grinding wheel 40 by wearing down the grinding surface 40a side of the grinding wheel 40. In addition, the grinding surface adjustment unit 42 removes foreign matter such as grinding debris adhering to the grinding wheel 40 by cleaning the grinding surface 40a side of the grinding wheel 40. This adjusts the condition of the grinding wheel 40.

[0044] The grinding surface adjustment unit 42 is equipped with a nozzle 60 that sprays fluid 62 onto the grinding surface 40a side of the grinding wheel 40. For example, the nozzle 60 is positioned to the side of the chuck table 8 so as to overlap with the grinding wheel 40.

[0045] As the fluid 62, a liquid such as pure water pressurized by a pump (high-pressure water) can be used. For example, the nozzle 60 sprays the fluid 62 onto the grinding surface 40a of the grinding wheel 40 at a pressure of 0.1 MPa or more (preferably 2 MPa or more and 13 MPa or less). However, there are no restrictions on the type of fluid 62. For example, the fluid 62 may be a liquid such as pure water containing abrasive particles (high-pressure water containing abrasive particles). Alternatively, the fluid 62 may be a mixed fluid containing a mixture of liquids (such as pure water) and gases (such as air).

[0046] When the fluid 62 sprayed from the nozzle 60 collides with the grinding surface 40a of the grinding wheel 40, the binder of the grinding wheel 40 is partially destroyed and worn away, causing exposed abrasive grains to fall off and new abrasive grains embedded inside the binder to become exposed. This restores the grinding capacity of the grinding wheel 40. In addition, foreign matter such as grinding debris adhering to the grinding surface 40a of the grinding wheel 40 is washed away and removed by the fluid 62. As a result, the abrasive grains are properly exposed on the grinding surface 40a of the grinding wheel 40, and clogging is resolved. In this way, the condition of the grinding wheel 40 is adjusted by the load measuring unit 54.

[0047] Furthermore, the grinding device 2 selects whether or not to adjust the state of the grinding wheel 40 using the grinding surface adjustment unit 42, depending on the force (grinding load) applied to the grinding wheel 40 when grinding the workpiece 11. Specifically, the control unit 44 includes a determination unit 44a that determines whether or not to adjust the grinding wheel 40, and a storage unit 44b that stores information used for the determination by the determination unit 44a.

[0048] During grinding of the workpiece 11, values ​​corresponding to the grinding load are sequentially input to the determination unit 44a. In addition, a reference value (threshold) for the grinding load is pre-stored in the storage unit 44b. The determination unit 44a then compares the value corresponding to the grinding load with the reference value to determine whether or not to adjust the condition of the grinding wheel 40.

[0049] Specifically, the load on the chuck table 8 is measured by the load measuring unit 54, and a signal corresponding to the load value on the chuck table 8 is input to the determination unit 44a. In addition, a signal corresponding to the current value of the motor 56 that rotates the spindle 32 at a predetermined rotational speed is input to the determination unit 44a. Furthermore, the load on the spindle 32 is measured by the load measuring unit 58, and a signal corresponding to the load value on the spindle 32 is input to the determination unit 44a.

[0050] The load value of the chuck table 8, the current value of the motor 56, and the load value of the spindle 32 each correspond to the force (grinding load) acting on the grinding wheel 40 in contact with the workpiece 11. In other words, as the grinding load increases, the load value of the chuck table 8, the current value of the motor 56, and the load value of the spindle 32 also increase. Therefore, the grinding load can be monitored by measuring the load value of the chuck table 8, the current value of the motor 56, and the load value of the spindle 32 while grinding the workpiece 11.

[0051] Furthermore, it is sufficient to acquire at least one value corresponding to the grinding load. That is, one or two values ​​selected from the load value of the chuck table 8, the current value of the motor 56, and the load value of the spindle 32 may be input to the determination unit 44a.

[0052] If the value corresponding to the grinding load is above a predetermined standard value, the determination unit 44a determines that the state of the grinding wheel 40 needs to be adjusted. The control unit 44 then activates the grinding surface adjustment unit 42 and ejects fluid 62 from the nozzle 60. As a result, the grinding device 2 grinds the workpiece 11 while adjusting the state of the grinding wheel 40. Consequently, the workpiece 11 is ground by the grinding wheel 40, which is free from blockage and clogging and maintained in a state of high grinding capacity, thereby suppressing the occurrence of processing defects.

[0053] On the other hand, if the value corresponding to the grinding load is less than a predetermined standard value, the determination unit 44a determines that adjustment of the grinding wheel 40 is unnecessary. The control unit 44 then does not activate the grinding surface adjustment unit 42 and does not eject the fluid 62 from the nozzle 60. As a result, the grinding device 2 grinds the workpiece 11 without adjusting the grinding wheel 40. Consequently, the workpiece 11 is ground while the wear of the grinding wheel 40 is suppressed.

[0054] Next, a specific example of a method for grinding a workpiece 11 using the grinding device 2 will be explained. As an example, the case where the back surface 11b of the workpiece 11 is ground using the grinding device 2 will be described. Figure 4 is a flowchart showing the grinding method for the workpiece.

[0055] When grinding the workpiece 11 with the grinding device 2, the first step is to hold the workpiece 11 with the chuck table 8 (holding step). Figure 5 is a perspective view showing the grinding device 2 holding the workpiece 11 with the chuck table 8.

[0056] The workpiece 11 is placed on the chuck table 8 such that its front surface 11a faces the holding surface 8a and its back surface 11b is exposed upwards. At this time, the workpiece 11 is positioned so that the center of the workpiece 11 and the center of the holding surface 8a coincide, and the entire suction surface 52a (see Figure 2) is covered by the workpiece 11. In this state, when the suction force (negative pressure) of the suction source is applied to the holding surface 8a, the workpiece 11 is held by the chuck table 8 through suction (step S1).

[0057] More precisely, as mentioned above, the holding surface 8a of the chuck table 8 is formed in a conical shape (see Figure 3). Therefore, when the workpiece 11 is held by the chuck table 8, the workpiece 11 is held in a slightly deformed state along the holding surface 8a. The portion of the workpiece 11 supported by the holding area 8b is positioned approximately horizontally.

[0058] A protective sheet may be fixed to the surface 11a side of the workpiece 11 to protect the workpiece 11. This covers and protects the surface 11a side (device, etc.) of the workpiece 11 with the protective sheet. The workpiece 11 is then held by the holding surface 8a of the chuck table 8 via the protective sheet.

[0059] For example, a protective sheet may be used that includes a circular film-like substrate and an adhesive layer (glue layer) provided on the substrate. The substrate is made of a resin such as polyolefin, polyvinyl chloride, or polyethylene terephthalate. The adhesive layer is made of an epoxy, acrylic, or rubber-based adhesive. The adhesive layer may also be made of an ultraviolet-curable resin.

[0060] Next, the grinding wheel 36 is rotated while the grinding wheel 40 is brought into contact with the workpiece 11 held by the chuck table 8, thereby grinding the workpiece 11 (grinding step). The grinding apparatus 2 in the grinding step is shown in Figures 6(A) and 6(B). Figure 6(A) is a perspective view showing the grinding apparatus 2 grinding the workpiece 11 while adjusting the state of the grinding wheel 40, and Figure 6(B) is a perspective view showing the grinding apparatus 2 grinding the workpiece 11 without adjusting the state of the grinding wheel 40.

[0061] In the grinding step, the relative positions of the chuck table 8 and the grinding wheel 36 are first adjusted. Specifically, the chuck table 8 is positioned below the grinding unit 28 so that the center of the workpiece 11 coincides with the movement path of the grinding wheel 40. Then, the chuck table 8 and the grinding wheel 36 are rotated in a predetermined direction at a predetermined speed. For example, the rotation speed of the chuck table 8 is set to 60 rpm or more and 300 rpm or less, and the rotation speed of the grinding wheel 36 is set to 3000 rpm or more and 6000 rpm or less.

[0062] Figure 7 is a plan view showing the chuck table 8 and the grinding wheel 36. Note that the wheel base 38 of the grinding wheel 36 is not shown in Figure 7. When the positional relationship between the chuck table 8 and the grinding wheel 36 is adjusted, the movement path of the grinding wheel 40 is positioned to overlap with the nozzle 60 of the grinding surface adjustment unit 42 installed on the side of the chuck table 8 in the Z-axis direction. Note that two or more grinding surface adjustment units 42 may be installed. In this case, the movement path of the grinding wheel 40 will be arranged to overlap with multiple nozzles 60 in the Z-axis direction.

[0063] Next, with the chuck table 8 and grinding wheel 36 rotating, the grinding unit 28 is lowered along the Z-axis to bring the workpiece 11 and the grinding wheel 36 closer together. The downward speed of the grinding wheel 36 at this time, that is, the relative movement speed of the chuck table 8 (workpiece 11) and the grinding wheel 36 in the Z-axis direction, corresponds to the machining feed rate (grinding feed rate). The machining feed rate is set to, for example, 0.1 μm / s or more and 1 μm / s or less. However, the machining feed rate can be appropriately set according to the material of the workpiece 11, the material of the grinding wheel 40, the amount of grinding of the workpiece 11 (difference in thickness of the workpiece 11 before and after grinding), etc.

[0064] As the grinding wheel 36 is lowered, the grinding wheel 40, which rotates along an annular movement path, comes into contact with the back surface 11b of the workpiece 11 held by the chuck table 8. This starts grinding of the workpiece 11, and the back surface 11b of the workpiece 11 is removed (step S2).

[0065] The grinding wheel 40 contacts the portion of the workpiece 11 that is supported by the holding area 8b (see Figure 3) of the chuck table 8 or a nearby area, and grinds the workpiece 11 in an arc shape along the direction from the outer edge of the workpiece 11 toward the center. Then, as the chuck table 8 rotates, the entire back surface 11b of the workpiece 11 is ground by the grinding wheel 40, and the workpiece 11 is thinned.

[0066] During grinding of the workpiece 11, a value corresponding to the force (grinding load) applied to the grinding wheel 40 is measured. For example, as mentioned above, the load applied to the chuck table 8, the current value of the motor 56 (see Figure 2), or the load applied to the spindle 32 is measured as a value corresponding to the grinding load and is sequentially input to the determination unit 44a (see Figure 2) of the control unit 44. The determination unit 44a then compares the value corresponding to the grinding load with a reference value stored in the storage unit 44b (see Figure 2) to determine whether the value corresponding to the grinding load is greater than or less than the reference value.

[0067] If the value corresponding to the grinding load is greater than or equal to the reference value (YES in step S3), the grinding surface adjustment unit 42 is activated as shown in Figure 6(A), and fluid 62 is sprayed from the nozzle 60 onto the grinding surface 40a side of the grinding wheel 40. As a result, the workpiece 11 is ground while the grinding surface adjustment unit 42 adjusts the state of the grinding wheel 40 (step S4). Consequently, the workpiece 11 is ground by the grinding wheel 40, which is free from blockage and clogging and maintained in a state of high grinding capacity, thereby suppressing the occurrence of processing defects.

[0068] On the other hand, if the value corresponding to the grinding load is less than the reference value (NO in step S3), the grinding surface adjustment unit 42 does not operate, as shown in Figure 6(B), and the fluid 62 is not sprayed from the nozzle 60. As a result, the workpiece 11 is ground without the grinding surface adjustment unit 42 adjusting the state of the grinding wheel 40 (step S5). Consequently, wear of the grinding wheel 40 during grinding of the workpiece 11 is suppressed. Furthermore, when the grinding load is low, processing defects are unlikely to occur even if the workpiece 11 is ground without adjusting the state of the grinding wheel 40.

[0069] The grinding of the workpiece 11 described above continues until the thickness of the workpiece 11 reaches the finish thickness (NO in step S6, steps S3 to S5). When the thickness of the workpiece 11 reaches the finish thickness (YES in step S6), the grinding wheel 36 rises and moves away from the workpiece 11, and the grinding of the workpiece 11 stops. This completes the grinding of the workpiece 11.

[0070] As described above, in the workpiece grinding method according to this embodiment, when the grinding load is high, the state of the grinding wheel 40 is adjusted to maintain a high grinding capacity while grinding the workpiece 11. On the other hand, when the grinding load is low, the workpiece 11 is ground while suppressing the wear of the grinding wheel 40 without adjusting the state of the grinding wheel 40. This makes it possible to reduce the amount of wear on the grinding wheel 40 while preventing the occurrence of processing defects due to increased grinding load.

[0071] For example, grinding apparatus 2 may grind both a first workpiece made of a material that is difficult to grind (such as a SiC wafer or sapphire wafer) and a second workpiece made of a material that is easy to grind (such as a silicon wafer). In this case, the grinding load is high when grinding the first workpiece and low when grinding the second workpiece. Therefore, grinding apparatus 2 grinds the first workpiece while adjusting the condition of the grinding wheel 40, and grinds the second workpiece without adjusting the condition of the grinding wheel 40. This suppresses the occurrence of processing defects when grinding the first workpiece. In addition, it suppresses the wear of the grinding wheel 40 when grinding the second workpiece.

[0072] Furthermore, during grinding of the workpiece 11, the condition of the grinding wheel 40 may change over time, and the grinding load may gradually increase as the grinding process progresses. In this case, the grinding device 2 grinds the workpiece 11 without adjusting the condition of the grinding wheel 40 in the early stages of grinding when the grinding load is small, and grinds the workpiece 11 while adjusting the condition of the grinding wheel 40 in the later stages of grinding when the grinding load is large. This reduces the amount of wear on the grinding wheel 40 while suppressing the occurrence of processing defects.

[0073] Furthermore, if the workpiece 11 contains multiple layers of different materials, the grinding load will fluctuate during the grinding of the workpiece 11. For example, if the workpiece 11 is a silicon wafer and an oxide film (SiO2 film) is formed on the back surface 11b of the workpiece 11, the oxide film, which is difficult to grind, and the single-crystal silicon, which is easy to grind, will be continuously ground, causing the grinding load acting on the grinding wheel 40 to fluctuate during the grinding process. In this case, the grinding device 2 grinds the workpiece 11 while adjusting the state of the grinding wheel 40 when grinding the oxide film, and grinds the workpiece 11 without adjusting the state of the grinding wheel 40 when grinding the single-crystal silicon. This reduces the amount of wear on the grinding wheel 40 while suppressing the occurrence of processing defects.

[0074] In the above embodiment, a grinding surface adjustment unit 42 equipped with a nozzle 60 for injecting fluid 62 was described (see Figure 2). However, there are no restrictions on the configuration of the grinding surface adjustment unit as long as it is possible to adjust the condition of the grinding wheel 40. For example, the grinding apparatus 2 may be equipped with a grinding surface adjustment unit that irradiates the grinding surface 40a side of the grinding wheel 40 with a laser beam or ultrasonic waves. Modified examples of the grinding surface adjustment unit are shown in Figures 8(A) and 8(B).

[0075] Figure 8(A) is a perspective view showing a grinding surface adjustment unit 42A that irradiates a grinding wheel 40 with a laser beam 74. The grinding surface adjustment unit 42A adjusts the condition of the grinding wheel 40 by irradiating the grinding surface 40a side of the grinding wheel 40 with a laser beam 74.

[0076] Specifically, the grinding surface adjustment unit 42A includes a laser irradiation unit 64. For example, the laser irradiation unit 64 includes a laser oscillator 66, a mirror 68 that reflects the laser beam 74 emitted from the laser oscillator 66, and a light concentrator 70 that focuses the laser beam 74. The light concentrator 70 is composed of multiple optical elements and includes a lens 72 such as a cylindrical lens that shapes the laser beam 74. For example, the lens 72 shapes the laser beam 74 into a linear shape.

[0077] The laser beam 74 emitted from the laser oscillator 66 is reflected by the mirror 68 and then incident on the light concentrator 70. The laser beam 74, shaped into a linear form by the lens 72, is then focused on the grinding surface 40a of the grinding wheel 40. The irradiation conditions for the laser beam 74 can be set, for example, as follows. Wavelength: 1030nm Repetition frequency: 200kHz Pulse width: 8 ps Average output: 30W

[0078] When preparing the grinding wheel 40, a laser beam 74 is irradiated from the laser irradiation unit 64 onto the grinding surface 40a of the grinding wheel 40. This partially melts and wears down the binder on the grinding surface 40a of the grinding wheel 40, promoting the self-sharpening of the blades. In addition, foreign matter such as grinding debris adhering to the grinding surface 40a of the grinding wheel 40 is melted and removed.

[0079] As described above, the grinding surface adjustment unit 42A adjusts the condition of the grinding wheel 40 by irradiating it with a laser beam 74. Note that two or more grinding surface adjustment units 42A may be installed. In this case, the laser beam 74 will be simultaneously irradiated at two or more locations along the movement path of the grinding wheel 40.

[0080] Figure 8(B) is a perspective view showing a grinding surface adjustment unit 42B that irradiates the grinding wheel 40 with ultrasonic waves 78. The grinding surface adjustment unit 42B adjusts the condition of the grinding wheel 40 by irradiating the grinding surface 40a side of the grinding wheel 40 with ultrasonic waves 78.

[0081] Specifically, the grinding surface adjustment unit 42B is equipped with an ultrasonic transmitter 76 that emits ultrasonic waves 78. When adjusting the condition of the grinding wheel 40, ultrasonic waves 78 are irradiated from the ultrasonic transmitter 76 onto the grinding surface 40a side of the grinding wheel 40. This applies vibrations with frequencies belonging to the ultrasonic band to the wheel base 38 and the grinding wheel 40, making the grinding wheel 40 more susceptible to wear when it comes into contact with the workpiece 11. As a result, dulling and clogging of the grinding wheel 40 are eliminated, and the grinding capacity of the grinding wheel 40 is maintained at a high level.

[0082] As described above, the grinding surface adjustment unit 42B adjusts the condition of the grinding wheel 40 by irradiating it with ultrasonic waves 78. Note that two or more grinding surface adjustment units 42B may be installed. In this case, ultrasonic waves 78 are simultaneously irradiated at two or more locations along the movement path of the grinding wheel 40.

[0083] Furthermore, the grinding device 2 may be equipped with a dressing board or brush that contacts the grinding surface 40a side of the grinding wheel 40. Other modifications of the grinding surface adjustment unit are shown in Figures 9(A) and 9(B).

[0084] Figure 9(A) is a perspective view showing a grinding surface adjustment unit 42C equipped with a dressing board 86 that contacts the grinding wheel 40. The grinding surface adjustment unit 42C adjusts the condition of the grinding wheel 40 by bringing the dressing board 86 into contact with the grinding surface 40a side of the grinding wheel 40.

[0085] The grinding surface adjustment unit 42C is equipped with a lifting mechanism 80. For example, the lifting mechanism 80 is composed of an air cylinder and includes a rod 82 that moves up and down along the Z-axis direction. A disc-shaped support base 84 is fixed to the upper end of the rod 82, and a disc-shaped dressing board 86 is fixed on the support base 84.

[0086] The dressing board 86 is formed by fixing abrasive grains, such as white alundum (WA) and green carborundum (GC), with a binder such as a vitrified bond. The diameter of the dressing board 86 is larger than the length and width of the grinding wheel 40.

[0087] During grinding of the workpiece 11, the dressing board 86 is raised by the lifting mechanism 80, causing the upper surface of the dressing board 86 to be pressed against the grinding surface 40a of the rotating grinding wheel 40. This wears down the grinding surface 40a of the grinding wheel 40, promoting self-sharpening, and also removes foreign matter adhering to the grinding surface 40a of the grinding wheel 40.

[0088] As described above, the grinding surface adjustment unit 42C adjusts the condition of the grinding wheel 40 by bringing the dressing board 86 into contact with the grinding wheel 40. Note that two or more sets of the grinding surface adjustment unit 42C may be installed. In this case, the grinding wheel 40 and the dressing board 86 will come into contact at two or more points along the movement path of the grinding wheel 40.

[0089] Figure 9(B) is a perspective view showing a grinding surface adjustment unit 42D equipped with a brush 92 that contacts the grinding wheel 40. The grinding surface adjustment unit 42D adjusts the condition of the grinding wheel 40 by bringing the brush 92 into contact with the grinding surface 40a side of the grinding wheel 40.

[0090] The grinding surface adjustment unit 42D is equipped with a lifting mechanism 88. For example, the lifting mechanism 88 is composed of an air cylinder and includes a rod 90 that moves up and down along the Z-axis. A brush 92 is fixed to the upper end of the rod 90.

[0091] For example, a cylindrical brush can be used as the brush 92. Specifically, the brush 92 comprises a cylindrical section 94 and a bristle section 96 supported by the cylindrical section 94. The bristle section 96 is constructed by bundling together bristles made of a resin such as polyamide or polyester, with the base ends of each bristle fixed to the cylindrical section 94. However, there are no restrictions on the type or structure of the brush 92.

[0092] During grinding of the workpiece 11, the brush 92 is raised by the lifting mechanism 88, causing the upper end of the bristles 96 of the brush 92 to come into contact with the grinding surface 40a of the rotating grinding wheel 40. This wears down the grinding surface 40a of the grinding wheel 40, promoting self-sharpening, and also removes foreign matter adhering to the grinding surface 40a of the grinding wheel 40.

[0093] As described above, the grinding surface adjustment unit 42D adjusts the condition of the grinding wheel 40 by bringing the brush 92 into contact with the grinding wheel 40. Note that two or more grinding surface adjustment units 42D may be installed. In this case, the grinding wheel 40 and the brush 92 will come into contact at two or more points along the movement path of the grinding wheel 40.

[0094] The grinding device 2 may also be equipped with two or more grinding surface adjustment units from among grinding surface adjustment units 42, 42A, 42B, 42C, and 42D. In this case, the condition of the grinding wheel 40 can be adjusted in two or more ways along the movement path of the grinding wheel 40.

[0095] Furthermore, the structures, methods, etc., according to the above embodiments can be modified as appropriate without departing from the scope of the objectives of the present invention. [Explanation of Symbols]

[0096] 11 Workpiece 11a Surface (first side) 11b Back side (2nd side) 2. Grinding device 4 bases 4a aperture 6 Support structure 8. Chuck table (holding table) 8a Holding surface 8b Holding area 10 X-axis movement unit 12 Table Covers 14 Dustproof and splashproof cover 16 Z-axis movement unit 18 Z-axis guide rail 20 Z-axis moving plate 22 Z-axis ball screw 24 Z-axis pulse motor 26 Support member 28 Grinding Unit 30 Housing 32 spindles 34 Mount 36 Grinding Wheels 38 Wheel base 40 grinding wheels 40a Grinding surface 42, 42A, 42B, 42C, 42D Grinding surface adjustment unit 44 Control Unit (Control Unit, Control Device) 44a Judgment part 44b Storage section 50 frame 50a top 50b recess 50c flow path 52 Retaining member 52a Suction surface 54 Load Measurement Unit 56 Motor 58 Load Measurement Unit 60 nozzles 62 Fluid 64 Laser irradiation units 66 Laser Oscillator 68 Mirror 70. Light concentrator 72 lenses 74 laser beams 76 Ultrasonic transmitters 78 Ultrasound 80 Lifting mechanism 82 rods 84 Support base 86 Dressing board 88 Lifting mechanism 90 rods 92 brushes 94 Cylinder part 96 Hair part

Claims

1. A method for grinding a workpiece using a grinding device, The grinding device is A chuck table that holds the workpiece on its holding surface, A grinding unit comprising a spindle with a grinding wheel having a grinding disc attached to its tip, The system includes a grinding surface adjustment unit that wears down the grinding surface side of the grinding wheel that comes into contact with the workpiece, A holding step of holding the workpiece with the chuck table, The process includes a grinding step of grinding a workpiece by rotating the grinding wheel and bringing the grinding wheel into contact with the workpiece held in the chuck table, In the grinding step, If the value corresponding to the grinding load is greater than or equal to a predetermined standard value, the grinding surface adjustment unit grinds the workpiece while wearing down the grinding surface side of the grinding wheel. If the value corresponding to the grinding load is less than a predetermined standard value, the grinding surface adjustment unit grinds the workpiece without wearing down the grinding surface side of the grinding wheel. A method for grinding a workpiece, characterized in that the reference value is set such that when grinding a first workpiece, the value corresponding to the grinding load is equal to or greater than the reference value, and when grinding a second workpiece made of a different material than the first workpiece, the value corresponding to the grinding load is less than the reference value.

2. A method for grinding a workpiece using a grinding device, The grinding device is A chuck table that holds the workpiece on its holding surface, A grinding unit comprising a spindle with a grinding wheel having a grinding disc attached to its tip, The system includes a grinding surface adjustment unit that wears down the grinding surface side of the grinding wheel that comes into contact with the workpiece, A holding step of holding the workpiece with the chuck table, The process includes a grinding step of grinding a workpiece by rotating the grinding wheel and bringing the grinding wheel into contact with the workpiece held in the chuck table, In the grinding step, If the value corresponding to the grinding load is greater than or equal to a predetermined standard value, the grinding surface adjustment unit grinds the workpiece while wearing down the grinding surface side of the grinding wheel. If the value corresponding to the grinding load is less than a predetermined standard value, the grinding surface adjustment unit grinds the workpiece without wearing down the grinding surface side of the grinding wheel. A method for grinding a workpiece, characterized in that the reference value is set such that when grinding the first layer contained in the workpiece, the value corresponding to the grinding load is equal to or greater than the reference value, and when grinding the second layer contained in the workpiece, the value corresponding to the grinding load is less than the reference value.

3. The grinding surface adjustment unit is characterized by spraying fluid onto the grinding surface side of the grinding wheel, or irradiating the grinding surface side of the grinding wheel with a laser beam or ultrasonic waves, as described in claim 1 or 2.

4. The method for grinding a workpiece according to claim 1 or 2, characterized in that the grinding surface adjustment unit comprises a dressing board or brush that contacts the grinding surface side of the grinding wheel.

5. The method for grinding a workpiece according to claim 1 or 2, characterized in that the value corresponding to the grinding load is the current value of the motor that rotates the spindle.

6. The method for grinding a workpiece according to claim 1 or 2, characterized in that the value corresponding to the grinding load is the load value applied to the chuck table or the spindle.

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