Grinding device and grinding method for workpiece

Abstract

To provide a technique for determining abnormalities in grinding processing, which prevents grinding from stopping due to erroneous determination.SOLUTION: A grinding device includes: a reflected light intensity measurement unit that has a light projecting part that projects measurement light toward a workpiece and a light receiving part that receives reflected light reflected from the workpiece, and measures a light amount of the reflected light; and a control unit that controls each component. The control unit includes: an intensity threshold setting part; a measurement cycle setting part; and a phase difference threshold setting part that sets a phase difference threshold to determine whether or not the phase in which an abnormal value occurs in the current measurement cycle is substantially the same as the phase in which an abnormal value occurs in the previous measurement cycle. The grinding device continues grinding if the phase difference between the phase of the abnormal value in the current measurement cycle and the phase of the abnormal value in the previous measurement cycle is outside the range of the phase difference threshold, and stops grinding if the phase difference falls within the range of the phase difference threshold.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to a grinding device for grinding a workpiece and a grinding method, and more particularly to a technique for performing abnormal determination of grinding.

Background Art

[0002] A semiconductor wafer on which a large number of devices such as IC (integrated circuit) and LSI (Large Scale Integration) are formed on the surface and each device is partitioned by a dicing line (street) is ground on the back surface by a grinding device to be processed to a predetermined thickness, and then the dicing line is cut by a dicing device to be divided into individual devices, and the divided devices are used in electric devices such as mobile phones and personal computers.

[0003] When grinding a wafer, events such as clogging of the grinding wheel, detachment of a mass including abrasive grains constituting the grinding wheel from the grinding wheel, and change in the application state of grinding water occur. When such events occur, an unpredictable load is applied to the wafer, resulting in a processing abnormality in which fine cracks that cannot be confirmed by the naked eye occur inside or outside the wafer.

[0004] Regarding this point, for example, in the grinding device disclosed in Patent Document 1, the power supplied to the motor that drives the spindle on which the grinding wheel is mounted is measured as a load current value to detect processing abnormalities.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the detection of the load current value in the grinding device shown in Patent Document 1, there is a large time lag between the occurrence of a processing abnormality and the appearance of a change in the load current value.In addition, since the load relative to the rotation direction of the spindle is detected, there is a problem in that it is not possible to directly monitor whether the wafer is ground or not.

[0007] Therefore, we investigated a method to judge anomalies by projecting a measurement light directly onto the wafer during grinding and measuring the change in the amount of reflected light. That is, a threshold value for judging anomalies is set in advance, and when the change in the amount of measured reflected light exceeds the threshold value, it is judged that some kind of anomaly has occurred.

[0008] According to this method, when an abnormality is detected, there is little time lag and the equipment can be stopped immediately to stop processing. This prevents the damage to the wafer from expanding due to continued grinding, increases the probability of recovering the workpiece without breaking it, and makes it easier to identify the cause. In addition, since the adverse effects on the equipment, such as the grinding wheel, when an abnormality occurs can be suppressed, the labor required for recovery work such as sharpening the grinding wheel and replacing the grinding wheel can be reduced.

[0009] However, grinding debris and abrasive grains are generated during wafer grinding, and it is known that these can become caught in the grinding wheel and cause scratches on the ground surface of the wafer. If the change in the amount of reflected light from such a scratch is measured, there is a risk that an abnormality will be detected.

[0010] Then, there is a risk of lowering throughput if the local scratch location is immediately judged as abnormal and the equipment is stopped each time. Also, scratches may occur temporarily so that they are removed in the subsequent grinding process, and as a result, grinding may be stopped even though the processing is normal. If a wafer is discarded due to an abnormality judgment based on such a temporarily occurring scratch, there is a risk of lowering product yield.

[0011] Also, if an abnormal determination is made by measuring a location where foreign matter such as grinding chips exists, there is a risk of reducing throughput and yield.

[0012] In view of the above problems, the present invention relates to a technique for making an abnormal determination in grinding, and proposes a novel technique for preventing grinding from being stopped due to an incorrect determination that temporarily occurring scratches or the presence of foreign matter are regarded as abnormal.

Means for Solving the Problem

[0013] The problem to be solved by the present invention is as described above. Next, means for solving this problem will be described.

[0014] According to one aspect of the present invention, there is provided a grinding apparatus for grinding a workpiece, including a chuck table for holding the workpiece, a grinding wheel mounted at the tip of a spindle, a grinding unit that is disposed opposite to the holding surface of the chuck table and grinds the workpiece held by the chuck table, a grinding feed unit that relatively approaches and separates the grinding unit and the chuck table, a light projecting unit that projects measurement light toward the workpiece, a light receiving unit that receives the reflected light reflected by the workpiece, a reflected light intensity measurement unit that measures the light amount of the reflected light, and a control unit that controls each component. The control unit includes an intensity threshold setting unit that sets an intensity threshold for determining whether or not a change amount of the light amount of the reflected light measured by the reflected light intensity measurement unit is an abnormal value, a measurement period setting unit that sets a measurement period for data of the change amount of the light amount of the reflected light measured continuously, and a phase difference threshold setting unit that sets a phase difference threshold for determining whether or not a phase at which an abnormal value appears in the current measurement period and a phase at which an abnormal value appeared in the previous measurement period are substantially the same phase. When the phase difference between the phase of the abnormal value in the current measurement period and the phase of the abnormal value in the previous measurement period is outside the range of the phase difference threshold, grinding is continued, and when it is within the range of the phase difference threshold, grinding is stopped.

[0015] Further, according to one aspect of the present invention, the measurement period is set according to the rotation speed of the chuck table and the number of measurement points of the reflected light intensity measurement unit.

[0016] Further, according to one aspect of the present invention, there is provided a grinding method for grinding a plate-shaped workpiece, comprising: a holding step of holding the workpiece by a chuck table; a grinding unit including a spindle having a grinding wheel attached to its tip, and the chuck table, which are rotated relative to each other while approaching each other, a light projecting unit that projects measurement light toward the workpiece, and a light receiving unit that receives the reflected light reflected by the workpiece, and a grinding step of grinding the workpiece while measuring a change amount of the intensity of the reflected light with a reflected light intensity measurement unit composed of the light projecting unit and the light receiving unit. In the grinding step, a measurement period is set for data of the change amount of the light amount of the continuously measured reflected light, abnormal values of the change amount of the light amount of the reflected light for each measurement period are compared, and grinding is continued when the phase difference between the phase at which the abnormal value of the current measurement period occurs and the phase at which the abnormal value of the previous measurement period occurs is outside the range of the phase difference threshold value, and grinding is stopped when the phase difference is within the range of the phase difference threshold value.

Advantages of the Invention

[0017] The present invention has the following advantages. That is, according to one aspect of the present invention, it is possible to prevent the expansion of damage to the wafer due to continuing grinding after an abnormality occurs, increase the probability of recovering the workpiece without cracking it, and facilitate the identification of the cause. In addition, since the adverse effects on the device side such as the grinding wheel at the time of abnormality occurrence can be suppressed, the man-hours for restoration work such as dressing of the grinding stone and replacement of the grinding wheel can be reduced.

[0018] Further, according to one aspect of the present invention, by ignoring a "temporary value jump" as "noise", it is possible to prevent the grinding from being stopped due to misjudgment. On the other hand, it is possible to surely detect an abnormality that appears periodically. In this way, it is possible to improve throughput and yield.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0020] The embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited by the content described in the following embodiments. Further, the constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Also, various omissions, substitutions, or changes in the configuration can be made without departing from the gist of the present invention.

[0021] An abrasive device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a configuration example of the abrasive device according to Embodiment 1. FIG. 2 is a perspective view schematically showing a rough grinding unit and a finish grinding unit of the abrasive device shown in FIG. 1. FIG. 3 is a side view schematically showing a rough grinding unit and a finish grinding unit of the abrasive device shown in FIG. 1 in a partial cross section. FIG. 4 is a diagram showing the configuration of a reflected light intensity measurement unit of the abrasive device shown in FIG. 1.

[0022] <Workpiece> The abrasive device 1 shown in FIG. 1 is a processing device for grinding a workpiece 200. The workpiece 200 to be processed by the abrasive device 1 shown in FIG. 1 is a wafer such as a disk-shaped semiconductor wafer or an optical device wafer having a substrate such as silicon, sapphire, or gallium. Devices are formed in each region of the workpiece 200 partitioned by division planned lines set in a grid pattern on the surface 201 of the substrate (not shown).

[0023] The devices are, for example, integrated circuits such as IC (Integrated Circuit) or LSI (Large Scale Integration), image sensors such as CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), MEMS (Micro Electro Mechanical Systems), or semiconductor memories (storage devices).

[0024] Also, in the embodiment, the back surface 202 on the back side of the surface 201 of the workpiece 200 is ground by the grinding device 1 and thinned to a predetermined finish thickness. The thinned workpiece 200 is divided into individual devices along the division planned lines by a processing device.

[0025] <Grinding device> The grinding device 1 is a processing device that grinds the back surface 202 of the workpiece 200 to thin the workpiece 200 to a predetermined finish thickness. As shown in FIG. 1, the grinding device 1 includes a device base 2, a turntable 5, a plurality (three in Embodiment 1) of chuck tables 6 installed on the turntable 5, a rough grinding unit 10, a finish grinding unit 20, a grinding feed unit 30, a cassette 7, an alignment unit 40, a loading unit 50, an unloading unit 51, a cleaning unit 60, a loading / unloading unit 52, and a control unit 100.

[0026] The turntable 5 is a disk-shaped table provided on the upper surface of the device base 2, and is rotatably provided around an axis parallel to the Z-axis direction in the horizontal plane, and is rotationally driven at a predetermined timing. The Z-axis direction is a direction parallel to the vertical direction. On this turntable 5, for example, three chuck tables 6 are arranged at equal intervals with a phase angle of, for example, 120 degrees. These three chuck tables 6 have a vacuum chuck table structure provided with a vacuum chuck whose holding surface is connected to a suction source (not shown). The surface 201 side of the workpiece 200 is placed on the holding surface and is sucked by the suction source to suck and hold the workpiece 200 on the holding surface.

[0027] During the grinding process, these chuck tables 6 are rotationally driven around an axis parallel to the Z-axis direction by a rotation drive mechanism. The chuck table 6 is sequentially moved to the loading / unloading area 301, the rough grinding area 302, the finish grinding area 303, and the loading / unloading area 301 by the rotation of the turntable 5.

[0028] The loading / unloading area 301 is an area for loading and unloading the workpiece 200 onto and from the chuck table 6. The rough grinding area 302 is an area for rough grinding the workpiece 200 held on the chuck table 6 by the rough grinding unit 10. The finish grinding area 303 is an area for finish grinding the workpiece 200 held on the chuck table 6 by the finish grinding unit 20.

[0029] The rough grinding unit 10 is a grinding unit equipped with a grinding wheel 11 for rough grinding, in which a grinding stone 12 for rough grinding for rough grinding the back surface 202 exposed above the workpiece 200 held on the chuck table 6 is annularly arranged, and rough grinds the back surface 202 of the workpiece 200 held on the holding surface of the chuck table 6 in the rough grinding area 302. The finish grinding unit 20 is a grinding unit equipped with a grinding wheel 21 for finish grinding, in which a grinding stone 22 for finish grinding for finish grinding the back surface 202 of the workpiece 200 held on the chuck table 6 is annularly arranged, and finish grinds the back surface 202 of the workpiece 200 held on the holding surface of the chuck table 6 in the finish grinding area 303.

[0030] As shown in FIGS. 2 and 3, the grinding units 10 and 20 mount the grinding wheels 11 and 21 at the lower ends (corresponding to the tips) of spindles 14 and 24 (only shown in FIG. 3) rotated by motors 13 and 23 about an axis parallel to the Z-axis direction, and the grinding stones 12 and 22 of the grinding wheels 11 and 21 are arranged to face the holding surface of the chuck table 6. When the spindles 14 and 24 and the grinding wheels 11 and 21 are rotated about the axis by the motors 13 and 23 and grinding water is supplied to the back surface 202 of the workpiece 200 held on the chuck table 6 in the grinding areas 302 and 303, the grinding stones 12 and 22 are brought closer to the chuck table 6 at a predetermined feed rate by the grinding feed unit 30 respectively, thereby rough grinding or finish grinding the back surface 202 of the workpiece 200. Note that when rough grinding or finish grinding the back surface 202 of the workpiece 200, the grinding units 10 and 20 form fine irregularities called Sommer marks 203 (also referred to as machining marks) on the back surface 202 of the workpiece 200 as shown in FIG. 2.

[0031] The two grinding feed units 30 shown in Fig. 2 each move the grinding units 10 and 20 in the Z-axis direction to relatively approach and separate the grinding units 10 and 20 from the chuck table 6. In the embodiment, each grinding feed unit 30 is provided on two standing columns 3 erected from one end in the Y-axis direction parallel to the horizontal direction of the apparatus base 2. The grinding feed unit 30 includes a well-known ball screw rotatably provided around an axis, a well-known motor for rotating the ball screw around the axis, and a well-known guide rail for movably supporting the spindle housings 15 and 25 of the grinding units 10 and 20 in the Z-axis direction.

[0032] In the embodiment, the rough grinding unit 10 and the finish grinding unit 20 are arranged such that the axis that is the rotation center of the grinding wheels 11 and 21 and the axis that is the rotation center of the chuck table 6 are horizontally spaced apart from each other and parallel, and the grinding wheels 12 and 22 pass through the center of the back surface 202 of the workpiece 200 held by the chuck table 6.

[0033] The cassette 7 has a plurality of slots and is a storage container for storing a plurality of workpieces 200. The cassette 7 stores a plurality of workpieces 200 before and after grinding. In the embodiment, a pair of cassettes 7 are provided and are respectively installed on the cassette mounting table 8. The alignment unit 40 is a table for temporarily placing the workpiece 200 taken out from the cassette 7 and performing centering alignment thereon.

[0034] The loading unit 50 has a suction pad for sucking the workpiece 200. The loading unit 50 sucks and holds the workpiece 200 before grinding aligned by the alignment unit 40 and loads it onto the chuck table 6 located in the loading / unloading area 301.

[0035] The unloading unit 51 has a suction pad for sucking the workpiece 200. The unloading unit 51 sucks and holds the workpiece 200 after grinding on the chuck table 6 located in the loading / unloading area 301 and unloads it to the cleaning unit 60.

[0036] The cleaning unit 60 cleans the workpiece 200 after grinding and removes contaminants such as grinding chips adhering to the ground back surface 202.

[0037] The loading / unloading unit 52 takes out the workpiece 200 before grinding from the cassette 7 and conveys it to the alignment unit 40, and takes out the workpiece 200 after grinding from the cleaning unit 60 and conveys it to the cassette 7. The loading / unloading unit 52 is, for example, a robot pick having a U-shaped hand 53, and adsorbs and holds the workpiece 200 by the U-shaped hand 53 and conveys it.

[0038] Further, as shown in FIGS. 1 and 2, the grinding apparatus 1 includes a contact type thickness measurement unit 70 and a reflected light intensity measurement unit 80 in each of the rough grinding region 302 and the finish grinding region 303. Note that FIG. 1 omits the contact type thickness measurement unit 70 in the rough grinding region 302 and omits the reflected light intensity measurement unit 80 in the finish grinding region 303.

[0039] The contact type thickness measurement unit 70 includes a pair of rod-shaped contacts 71, one end of which contacts the holding surface of the chuck table 6 and the other end of which contacts the back surface 202 of the workpiece 200 held by the chuck table 6, and a calculation unit (not shown) that calculates the distance in the Z-axis direction of the tips of the pair of contacts 71. The contact type thickness measurement unit 70 measures the thickness of the workpiece 200 held on the holding surface of the chuck table 6 by the calculation unit calculating the distance in the Z-axis direction of the tips of the pair of contacts 71.

[0040] The contact thickness measurement unit 70 outputs the thickness of the workpiece 200 calculated by the calculation unit to the control unit 100. The function of the calculation unit may be realized by an arithmetic processing device having a microprocessor such as a CPU (Central Processing Unit) performing arithmetic processing according to a computer program stored in a storage device having a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory), or may be realized by a dedicated processing circuit (hardware) such as a single circuit, a composite circuit, a programmed processor, or a parallel-programmed processor.

[0041] The reflected light intensity measurement unit 80 measures the thickness of the workpiece 200 without contacting the back surface 202 of the workpiece 200 sucked and held on the holding surface of the chuck table 6. As shown in FIGS. 1, 2, and 3, the reflected light intensity measurement unit 80 includes an arm 81 whose base end is swingably supported by a motor (not shown) and a measurement head 82 provided at the tip of the arm 81. The reflected light intensity measurement unit 80 has a measurement position shown in FIGS. 2 and 3 where the measurement head 82 provided at the tip of the arm 81 faces the back surface 202 of the workpiece 200 held on the holding surface of the chuck table 6 in the Z-axis direction, and a retracted position where the measurement head 82 retracts from above the back surface 202 of the workpiece 200 held on the holding surface of the chuck table 6, and swings around the base end.

[0042] In addition, as shown in FIG. 4, the reflected light intensity measurement unit 80 includes a light source 83 as a light projecting unit, a light receiving unit 84, and an arithmetic unit 85. The light source 83 projects measurement light 831 toward the back surface 202 of the workpiece 200 held on the holding surface of the chuck table 6. The light source 83 emits light having a broad spectrum in an arbitrary wavelength region of, for example, 0.5 μm to 1500 μm as the measurement light 831. The light source 83 transmits the measurement light 831 to the measurement head 82 through an optical fiber (not shown), and the measurement light 831 passes through the window 821 of the measurement head 82 and is projected onto the back surface 202 of the workpiece 200 held on the holding surface of the chuck table 6. As the light source 83, for example, a super luminescent diode (SLD) is used.

[0043] The measurement light 831 projected through the window 821 of the measurement head 82 is reflected, for example, by the workpiece 200 or the like held on the holding surface of the chuck table 6 disposed below the measurement head 82. The distance between the lower end of the measurement head 82 and the back surface 202 of the workpiece 200 held on the holding surface of the chuck table 6 to be measured is, for example, about 1 mm to 4 mm.

[0044] In the embodiment, a liquid supply port 822 for supplying a liquid such as pure water is provided beside the window 821 of the measurement head 82. When measuring the thickness of the workpiece 200, the lower surface of the window 821 facing the measurement object is covered with the liquid supplied from the liquid supply port 822. Thereby, for example, even when measuring the thickness of the workpiece 200 during grinding, the adhesion of dirt to the lower surface of the window 821 is suppressed. The flow rate of the liquid supplied from the liquid supply port 822 is typically about 0.5 L / min to 1.5 L / min.

[0045] Also, the light reflected from the back surface 202 of the workpiece 200, which is the measurement target of the measurement light 831 projected through the window 821 of the measurement head 82, interferes with the light reflected from the front surface 201 of the workpiece 200, and, for example, reinforces at a wavelength corresponding to the thickness of the workpiece 200. The reflected light 832 that is reflected by and interfered with by the workpiece 200 passes through the window 821 of the measurement head 82.

[0046] The light receiving unit 84 receives the reflected light 832 that is reflected from and interfered with by the back surface 202 of the workpiece 200. The light receiving unit 84 includes a spectroscopic element 841 connected via the window 821 of the measurement head 82 and an optical fiber (not shown) or the like, and a photoelectric conversion element 842. The spectroscopic element 841 transmits the reflected light 832 through an optical fiber and transmits the light 833 of a predetermined wavelength among the reflected light 832 to the photoelectric conversion element 842. For example, a diffraction grating is used as the spectroscopic element 841.

[0047] Note that the amount of light, which is the intensity of the reflected light 832 that is reflected from and interfered with by the back surface 202 of the workpiece 200, decreases as the diffuse reflection of the reflected light 832 increases as the surface roughness of the back surface 202 increases, and increases as the diffuse reflection of the reflected light 832 decreases as the surface roughness of the back surface 202 decreases. For this reason, in a state where the grinding process is performed normally, the surface roughness of the back surface 202 is constant, so the amount of light, which is the intensity of the reflected light 832, is constant. Also, when the surface roughness of the back surface 202 becomes larger than the state where the grinding process is performed normally, the amount of light, which is the intensity of the reflected light 832, decreases compared to the state where the grinding process is performed normally. Further, when the surface roughness of the back surface 202 becomes smaller than the state where the grinding process is performed normally, the amount of light, which is the intensity of the reflected light 832, increases compared to the state where the grinding process is performed normally. Thus, the amount of light of the reflected light 832 that is reflected from and interfered with by the back surface 202 of the workpiece 200 immediately changes depending on the quality of the grinding process and becomes a value that reflects the quality of the grinding process.

[0048] The photoelectric conversion element 842 is irradiated with the light 833 dispersed by the dispersing element 841. As the photoelectric conversion element 842, for example, a line sensor having sensitivity in the wavelength range of 0.5 μm to 1500 μm is used. In that case, the photoelectric conversion element 842 receives the light 833 irradiated at a position corresponding to the wavelength via the dispersing element 841, and outputs an electrical signal corresponding to the intensity of the light 833 of each wavelength to the arithmetic unit 85. That is, the electrical signal output from the photoelectric conversion element 842 includes information corresponding to the relationship between the amount of light (the amount of the reflected light 832 received by the light receiving unit 84) of the reflected light 832 reflected by the measurement target and incident on the window 821 and the wavelength.

[0049] The arithmetic unit 85 receives the electrical signal output from the photoelectric conversion element 842. The arithmetic unit 85 calculates, for example, the thickness of the workpiece 200 by performing fast Fourier transform, filtering process, or the like on the information (information corresponding to the relationship between the amount of light and the wavelength) included in the electrical signal output from the photoelectric conversion element 842.

[0050] Further, the arithmetic unit 85 calculates the amount of the reflected light 832 incident on the window 821 (the amount of the reflected light 832 received by the light receiving unit 84) based on the information included in the electrical signal output from the photoelectric conversion element 842.

[0051] The arithmetic unit 85 outputs the information regarding the calculated thickness of the workpiece 200 to the control unit 100 as thickness information. Further, the arithmetic unit 85 outputs the information regarding the calculated amount of the reflected light 832 to the control unit 100 as light amount information. Note that the function of the arithmetic unit 85 may be realized by an arithmetic processing unit having a microprocessor such as a CPU (Central Processing Unit) performing arithmetic processing according to a computer program stored in a storage device having a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory), or may be realized by a dedicated processing circuit (hardware) such as a single circuit, a composite circuit, a programmed processor, or a parallel programmed processor.

[0052] The reflected light intensity measurement unit 80 with the above-described configuration includes a light source 83, a light receiving unit 84, and an arithmetic unit 85, and calculates the thickness of the workpiece 200 by spectroscopic interference between the light reflected from the surface 201 of the workpiece 200 (corresponding to the reflected light) and the light reflected from the back surface 202 of the workpiece 200 (corresponding to the reflected light) of the measurement light 831 projected through the window 821 of the measurement head 82.

[0053] As shown in FIG. 1, the control unit 100 controls each of the above-described component units constituting the grinding apparatus 1. That is, the control unit 100 causes the grinding apparatus 1 to execute a machining operation on the workpiece 200. The control unit 100 is a computer having an arithmetic processing unit having a microprocessor such as a CPU (Central Processing Unit), a storage device having a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory), and an input / output interface device.

[0054] The arithmetic processing unit of the control unit 100 performs arithmetic processing according to a computer program stored in the storage device, and outputs a control signal for controlling the grinding apparatus 1 to the above-described components of the grinding apparatus 1 via the input / output interface device. Further, the control unit 100 is connected to a display unit 110 constituted by a liquid crystal display device or the like that displays the state and image of the machining operation, an input unit 111 used when an operator registers machining content information and the like, and a notification unit 112 that notifies the operator. The input unit 111 is constituted by at least one of a touch panel provided on the display unit 110 and a keyboard or the like. The notification unit 112 notifies the operator by emitting at least one of sound, light, and a message on the touch panel.

[0055] Further, as shown in FIG. 4, the control unit 100 includes a machining control unit 101, an arithmetic unit 102, a strength threshold setting unit 103, a determination unit 104, a measurement cycle setting unit 105, and a phase difference threshold setting unit 106. Note that FIG. 5 is a diagram showing an example of changes in the amount of change in the amount of reflected light calculated by the arithmetic unit of the control unit of the grinding apparatus shown in FIG. 1. The horizontal axis of FIG. 5 represents time, and the vertical axis of FIG. 5 represents the amount of change in the amount of reflected light. The machining control unit 101 controls each of the above-described constituent units constituting the grinding apparatus 1 to cause the grinding apparatus 1 to perform a machining operation on the workpiece 200.

[0056] As shown in FIG. 4, the arithmetic unit 102 calculates the amount of light from the information on the amount of light of the reflected light 832 input from the arithmetic device 85 of the reflected light intensity measurement unit 80, differentiates the calculated amount of light with respect to time, and calculates the amount of change in the amount of light of the reflected light 832. The amount of change in the amount of light of the reflected light 832 is a value corresponding to the intensity of the reflected light 832 received by the light receiving unit 84. In this way, the arithmetic unit 102 calculates the amount of change in the amount of light of the reflected light 832, which is a value corresponding to the intensity of the reflected light 832 received by the light receiving unit 84.

[0057] As shown in FIG. 4, the strength threshold setting unit 103 sets strength thresholds 401 and 402 (FIG. 5) for the amount of change in the amount of light of the reflected light 832, which is a value corresponding to the intensity of the reflected light 832 received by the light receiving unit 84. The strength threshold setting unit 103 sets the upper limit side strength threshold 401 (FIG. 5) input from the input unit 111 and the lower limit side strength threshold 402 (FIG. 5) smaller than the upper limit side strength threshold 401 as the above-described thresholds.

[0058] Note that, as shown in FIG. 5, the upper limit side strength threshold 401 is a value higher than the amount of change in the amount of light of the reflected light 832 reflected and interfered on the back surface 202 of the workpiece 200 being normally ground. The lower limit side strength threshold 402 is a value lower than the amount of change in the amount of light of the reflected light 832 reflected and interfered on the back surface 202 of the workpiece 200 being normally ground.

[0059] As shown in FIG. 4, the determination unit 104 determines whether the change amount of the light quantity of the reflected light 832 calculated by the calculation unit 102, which is a value corresponding to the intensity of the reflected light 832 received by the light receiving unit 84, is within the range of the two intensity thresholds 401 and 402. When the change amount of the light quantity of the reflected light 832 calculated by the calculation unit 102 is equal to or greater than the lower limit intensity threshold 402 and equal to or less than the upper limit intensity threshold 401 as shown by the solid line L1 in FIG. 5, the determination unit 104 determines that it is within the range of the two intensity thresholds 401 and 402. When the change amount of the light quantity of the reflected light 832 calculated by the calculation unit 102 is less than the lower limit intensity threshold 402 as shown by the alternate long and short dash line L2 in FIG. 5, the determination unit 104 determines that it is outside the range of the two intensity thresholds 401 and 402. When it is less than the lower limit intensity threshold 402, it means that the surface roughness is large. When the change amount of the light quantity of the reflected light 832 calculated by the calculation unit 102 exceeds the upper limit intensity threshold 401 as shown by the broken line L3 in FIG. 5, the determination unit 104 determines that it is outside the range of the two intensity thresholds 401 and 402. When it exceeds the upper limit intensity threshold 401, it means that the surface roughness is small.

[0060] As shown in FIG. 4, when the determination unit 104 determines that the change amount of the light quantity of the reflected light 832 calculated by the calculation unit 102 is within the range of the two intensity thresholds 401 and 402 (FIG. 5), it determines that the grinding process is good. On the other hand, when the determination unit 104 determines that the change amount of the light quantity of the reflected light 832 calculated by the calculation unit 102 is outside the range of the two intensity thresholds 401 and 402, it makes an abnormality determination assuming that the grinding process is defective. In this way, the determination unit 104 makes an abnormality determination of the grinding process based on the change amount of the light quantity of the reflected light 832, which is a value reflecting the quality of the grinding process. In this specification, when the grinding process is "good", it mainly means that the surface roughness is within a predetermined range and uniform grinding has been performed.

[0061] In this way, during the grinding process, the determination unit 104 determines the quality of the grinding process based on the amount of change in the amount of reflected light, which immediately changes depending on the quality of the grinding process and reflects the quality of the grinding process. As a result, it is possible to suppress the time lag from the determination of the quality of the grinding process to the stop of the apparatus, while improving the accuracy of the determination of the quality of the grinding process.

[0062] And, the expansion of the damage to the wafer due to continuing grinding after the occurrence of an abnormality is prevented, the probability of being able to recover the workpiece without breaking it can be increased, and the cause elucidation becomes easier. In addition, since the adverse effects on the apparatus side such as the grinding wheel at the time of the occurrence of an abnormality can be suppressed, the man-hours for recovery work such as dressing of the grinding stone and replacement of the grinding wheel can be reduced.

[0063] Note that the functions of the processing control unit 101, the calculation unit 102, the intensity threshold setting unit 103, and the determination unit 104 shown in FIG. 4 are realized by the arithmetic processing unit performing arithmetic processing according to a computer program stored in the storage device.

[0064] <Grinding method> Next, the grinding method will be described. FIG. 6 is a flowchart showing the flow of the grinding method, and includes a holding step 1001, a grinding step 1002, and an unloading step 1003. This grinding method is also a processing operation of the grinding apparatus 1 that grinds the back surface 202 of the workpiece 200 to thin the workpiece 200 to a predetermined finish thickness. The grinding apparatus 1 has a cassette 7 that houses the workpiece 200 with the back surface 202 facing upward by an operator installed on the cassette mounting table 8 of the apparatus base 2. When the processing conditions are registered in the control unit 100 and the control unit 100 receives an instruction to start the processing operation from the operator, the processing operation is started.

[0065] Note that the processing conditions include the intensity thresholds 401 and 402 described above. For this purpose, when the control unit 100 of the grinding apparatus 1 receives the intensity thresholds 401 and 402, the intensity threshold setting unit 103 sets the received intensity thresholds 401 and 402.

[0066] <Holding Step> Holding step 1001 is a step of holding the workpiece 200 by the chuck table 6. In holding step 1001, the grinding apparatus 1 causes the spindle 14, 24 of each grinding unit 10, 20 to rotate around the axis at the rotational speed determined by the machining conditions by the machining control unit 101 of the control unit 100, and causes the carry-in / carry-out unit 52 to take out one workpiece 200 from one of the cassettes 7 and carry it into the alignment unit 40.

[0067] In holding step 1001, the grinding apparatus 1 causes the machining control unit 101 of the control unit 100 to perform centering of the workpiece 200 in the alignment unit 40, and carries the workpiece 200 aligned in the carry-in unit 50 onto the holding surface of the chuck table 6 located in the carry-in / carry-out area 301. In holding step 1001, the grinding apparatus 1 sucks and holds the workpiece 200 on the chuck table 6 in the carry-in / carry-out area 301, rotates the turntable 5, and moves the chuck table 6 holding the workpiece 200 in the carry-in / carry-out area 301 to the rough grinding area 302.

[0068] <Grinding Step> Grinding step 1002 is a step of relatively approaching the grinding units 10, 20 including the spindles 14, 24 with the grinding wheels 11, 21 mounted at the tips while rotating each around the axis, and grinding the workpiece 200 while measuring the thickness of the workpiece 200 with the reflected light intensity measurement unit 80.

[0069] In grinding step 1002, the grinding apparatus 1 causes the machining control unit 101 of the control unit 100 to rotate the chuck table 6 around the axis, supply grinding water while measuring the thickness of the workpiece 200 with the reflected light intensity measurement unit 80, and rough grind the workpiece 200 with the rough grinding unit 10. In grinding step 1002, after the machining control unit 101 of the control unit 100 rough grinds the workpiece 200, the grinding apparatus 1 rotates the turntable 5 and moves the chuck table 6 holding the workpiece 200 after rough grinding to the finish grinding area 303.

[0070] In grinding step 1002, the grinding apparatus 1 supplies grinding water while the machining control unit 101 of the control unit 100 rotates the chuck table 6 around its axis and the reflection light intensity measurement unit 80 measures the thickness of the workpiece 200, and the finish grinding unit 20 performs finish grinding on the workpiece 200. In grinding step 1002, after the machining control unit 101 of the control unit 100 finishes the finish grinding of the workpiece 200, the turning table 5 is rotated, and the workpiece 200 after the finish grinding is held and moved to the loading / unloading area 301 on the chuck table 6 whose rotation around the axis has stopped.

[0071] Note that in grinding step 1002, the grinding apparatus 1 grinds the workpiece 200, and the arithmetic unit 102 of the control unit 100 calculates the amount of light from the information on the amount of the reflected light 832 input from the arithmetic device 85 of the non-contact thickness measurement unit 80, differentiates the calculated amount of light with respect to time to calculate the change amount of the amount of the reflected light 832, and monitors it. Then, as will be described in detail later, an abnormality determination of the grinding process is performed in grinding step 1002.

[0072] <Unloading step> The unloading step 1003 is a step of unloading the workpiece 200 after the grinding process from the chuck table 6 and loading it into the cassette 7. In the unloading step 1003, the grinding apparatus 1 transports the workpiece 200 after the finish grinding from the chuck table 6 in the loading / unloading area 301 to the cleaning unit 60 by the machining control unit 101 of the control unit 100, cleans it with the cleaning unit 60, and then stores it in the cassette 7. After the unloading step 1003, the grinding apparatus 1 determines whether rough grinding and finish grinding have been performed on all the workpieces 200 in the cassette 7 by the machining control unit 101 of the control unit 100 (step 1004).

[0073] After the unloading step 1003, if the processing control unit 101 of the control unit 100 determines that rough grinding and finish grinding have not been performed on all the workpieces 200 in the cassette 7 (step 1004: No), the grinding apparatus 1 returns to the holding step 1001. In this case, every time the turntable 5 rotates, the grinding apparatus 1 conveys the workpiece 200 after finish grinding from the chuck table 6 in the loading / unloading area 301 that holds the workpiece 200 to the cleaning unit 60, loads the workpiece 200 before grinding onto the chuck table 6 in the loading / unloading area 301 that does not hold the workpiece 200 after finish grinding, rough grinds the workpiece 200 before grinding held by the chuck table 6 in the rough grinding area 302, rough grinds the workpiece 200 after rough grinding held by the chuck table 6 in the finish grinding area 303, positions the chuck table 6 holding the workpiece 200 after rough grinding in the loading / unloading area 301, positions the workpiece 200 held on the holding surface of the chuck table 6 in the rough grinding area 302 and the finish grinding area 303 in sequence, and sequentially performs rough grinding and finish grinding.

[0074] After the unloading step 1003, if the processing control unit 101 of the control unit 100 determines that rough grinding and finish grinding have been performed on all the workpieces 200 in the cassette 7 (step 1004: Yes), the grinding apparatus 1 ends the processing operation.

[0075] Next, the abnormality determination of the grinding process performed during the above-described grinding step 1002 will be described. FIG. 7 is a flowchart showing each step related to the abnormality determination of the grinding process.

[0076] <S1: Strength threshold setting step> In this step S1, an upper limit side strength threshold 401 and a lower limit side strength threshold 402 shown in FIG. 8 are set. This setting is performed by the operator operating the input unit 111 (FIG. 1), and the set numerical values are registered in the strength threshold setting unit 103.

[0077] In FIG. 8, the state where the change amount H of the amount of reflected light exhibits abnormal values H1, H2, and H3 exceeding the upper limit intensity threshold value 401 at the phases T1, T2, and T3 of each measurement cycle is shown. Also, the horizontal axis is the time axis, which can be divided for each measurement cycle, and the first measurement cycle M1 and the second measurement cycle M2 are represented.

[0078] The measurement cycle is a cycle set for the data of the change amount of the amount of reflected light measured continuously. In this embodiment, as shown in FIG. 9, after a certain measurement point W1 of the wafer (workpiece 200) is measured, one rotation of the wafer until it is measured next is defined as one cycle. Therefore, the measurement point W1 is measured once in each measurement cycle, and the change amount of the amount of reflected light for the measurement point W1 appears at the same phase of each measurement cycle.

[0079] For example, when the rotation speed of the chuck table 6 shown in FIG. 9 is 5 (rotations / second) and the number of measurement points of the reflected light intensity measurement unit 80 is 4000 (points / second), 800 points (=4000 / 5) are measured during one rotation of the chuck table 6. In FIG. 8, by allocating these 800 points to the time axis and expressing them, the specific timing of each measurement cycle is defined by the phases from 0 to 799. Such setting of the measurement cycle is performed by the operator operating the input unit 111 (FIG. 1), and the setting is registered in the measurement cycle setting unit 105.

[0080] And the phase T1 in FIG. 8 corresponds to the phase 276 within the first measurement cycle (800 points). In this case, the phase can also be expressed as (276 / 800)*2π.

[0081] <S2: Phase difference threshold setting step> In this step S2, it is a step of setting the phase difference threshold value E shown in FIG. 10. This setting is performed by the operator operating the input unit 111 (FIG. 1), and the setting is registered in the phase threshold setting unit 106.

[0082] The phase difference threshold value E is a threshold value for determining whether the phase T2 at which the abnormal value H2 appears in the measurement period M2 and the phase T1 at which the abnormal value H1 appears in the previous measurement period M1 are substantially the same phase, and is a numerical range with a width.

[0083] For example, as shown in the example of FIG. 10, when one measurement period is 800 points, the phase difference threshold value E is set to 20 points. And in this case, the range of 10 points before and after (266 to 286) with the phase T1 (276) of the first measurement period M1 as the middle is determined as substantially the same phase. Note that "substantially the same phase" is, for example, a range of 2.5% of one measurement period in the case of 20 points out of 800 points, but is not limited to this example, and can be arbitrarily adjusted by the operator setting the numerical value of the phase difference threshold value E.

[0084] Here, in the example of FIG. 10, in the comparison of the abnormal values H1 and H2, the phase difference between the phase T1 and the phase T2 is "2", which is within the range of the phase difference threshold value E "20". Therefore, it is determined that the abnormal value H2 appears at the phase T2 that is substantially the same as the phase T1 at which the abnormal value H1 appears in the first measurement period M1. This means that the abnormality that appeared in the first measurement period M1 remains in the second measurement period M2 without disappearing. Note that "within the range of the phase difference threshold value E" includes the case where it coincides with the upper and lower limits of the numerical range.

[0085] On the other hand, in the comparison of the abnormal values H1 and H3 in FIG. 10, the phase T1 and the phase T3 are outside the range of the phase difference threshold value E. Therefore, it is determined that the abnormal value H3 appears at the phase T3 that is significantly different from the phase T1 at which the abnormal value H1 appears in the first measurement period M1. This means that a new abnormality has occurred in the second measurement period M2 at a position different from the position where the abnormality appeared in the first measurement period M1. Note that "outside the range of the phase difference threshold value E" does not include the case where it coincides with the upper and lower limits of the numerical range.

[0086] <S3: Step for determining the change amount of the light quantity> As shown in FIG. 8, in a step where the determination unit 104 (FIG. 4) determines whether or not the change amount H of the amount of reflected light is within the range of both intensity thresholds 401 and 402.

[0087] When the change amount H is within the range of both intensity thresholds 401 and 402, it is assumed that the processing is good and there is no abnormality, and the grinding is continued. Note that the "within the range of both intensity thresholds 401 and 402" includes the case where it coincides with both intensity thresholds 401 and 402.

[0088] On the other hand, when the change amount H is outside the range of both intensity thresholds 401 and 402, it is assumed that an abnormality may have occurred in the processing, and the following S4: phase difference determination step is performed. Note that the "outside the range of both intensity thresholds 401 and 402" does not include the case where it coincides with both intensity thresholds 401 and 402.

[0089] <S4: Phase difference determination step> As shown in FIG. 10, in a step where the determination unit 104 (FIG. 4) determines whether or not the phases T2 and T3 when the abnormal values H2 and H3 appear in the measurement period M2 are within the range of the phase difference threshold E as compared with the phase T1 when the abnormal value H1 appeared in the measurement period M1 immediately before the measurement period M2.

[0090] In the example of FIG. 10, the phase T2 of the measurement period M2 and the phase T1 of the immediately preceding measurement period M1 are determined to be within the range of the phase difference threshold E. In this case, the abnormality that occurred in the immediately preceding measurement period M1 does not disappear and reappears in the measurement period M2 as well. It is assumed that an abnormality surely occurs at the same location on the wafer, and the grinding is stopped. Also, the notification unit 112 is operated to notify the operator of an error.

[0091] On the other hand, in the example of FIG. 11, the phase T5 of the measurement period M4 is determined to be outside the range of the phase difference threshold E of the phase T4 of the previous measurement period M3. In this case, the abnormality that occurred at the position corresponding to the phase T4 of the previous measurement period M3 disappears, and it is assumed that a new abnormality has occurred at another position of the wafer (the position corresponding to the phase T5) in the measurement period M4, and grinding is continued for the time being.

[0092] In the case of FIG. 11, the abnormality that occurred at T4 of the previous measurement period M3 is a "temporary value jump" and is recognized as "noise", and grinding is continued. The reason for such a "temporary value jump" is that although there were scratches or foreign objects in the previous measurement period M3, they disappeared in the next measurement period M4. In the determination of abnormalities, it is ignored as "noise".

[0093] As described above, as shown in FIGS. 10 and 11, when the phase difference (the absolute value of T1 - T2) between the phase H1 of the abnormal value H2 of the measurement period M2 and the phase T1 of the abnormal value H1 of the previous measurement period M1 is outside the range of the phase difference threshold value E, grinding is continued, and when it is within the range of the phase difference threshold value E, grinding is stopped.

[0094] Thereby, as shown in FIG. 11, "temporary value jumps" can be ignored as "noise", and false judgment-induced grinding stops can be prevented. On the other hand, as shown in FIG. 10, abnormalities that occur periodically can be reliably detected. In this way, throughput and yield can be improved.

Explanation of Reference Numerals

[0095] 1 Grinding apparatus 6 Chuck table 80 Reflective light intensity measurement unit 100 Processing control unit 101 Control unit 103 Intensity threshold setting unit 104 Judgment unit 105 Measurement period setting unit 106 Phase threshold setting unit 200 Workpiece E Phase difference threshold H Change amount of the light quantity of the reflected light H1 Abnormal value H2 Abnormal value H3 Abnormal value M1 First measurement period M2 Second measurement period W1 Measurement point

Claims

1. A grinding apparatus for grinding a workpiece, comprising: a chuck table for holding the workpiece; a grinding unit having a grinding wheel mounted at the tip of a spindle, disposed opposite to the holding surface of the chuck table, and grinding the workpiece held by the chuck table; a grinding feed unit for relatively approaching and separating the grinding unit and the chuck table; a light projecting unit that projects measurement light toward the workpiece, a light receiving unit that receives the reflected light reflected by the workpiece, and a reflected light intensity measurement unit that measures the amount of the reflected light; a control unit for controlling each component; The control unit includes: an intensity threshold setting unit that sets an intensity threshold for determining whether a change amount of the amount of the reflected light measured by the reflected light intensity measurement unit is an abnormal value; a measurement cycle setting unit that sets a measurement cycle for data of the change amount of the amount of the reflected light measured continuously; a phase difference threshold setting unit that sets a phase difference threshold for determining whether a phase at which an abnormal value appears in the current measurement cycle and a phase at which an abnormal value appeared in the previous measurement cycle are substantially the same phase; When the phase difference between the phase of the abnormal value in the current measurement cycle and the phase of the abnormal value in the previous measurement cycle is outside the range of the phase difference threshold, grinding is continued; When it is within the range of the phase difference threshold, the grinding apparatus stops grinding.

2. The measurement cycle is set according to the rotation speed of the chuck table and the number of measurement points of the reflected light intensity measurement unit. The grinding apparatus according to claim 1, characterized in that.

3. A grinding method for grinding a plate-shaped workpiece, comprising: a holding step of holding the workpiece by a chuck table; a grinding step of relatively approaching the grinding unit including a spindle having a grinding wheel mounted at the tip and the chuck table while rotating each of them, and grinding the workpiece while measuring a change amount of the intensity of the reflected light by a reflected light intensity measurement unit including a light projecting unit that projects measurement light toward the workpiece and a light receiving unit that receives the reflected light reflected by the workpiece; and In the grinding step, a measurement cycle is set for data of the change amount of the amount of the reflected light measured continuously, and abnormal values of the change amount of the amount of the reflected light for each measurement cycle are compared; When the phase difference between the phase at which an abnormal value occurs in the current measurement cycle and the phase at which an abnormal value occurred in the previous measurement cycle is When it is outside the range of the phase difference threshold value, grinding is continued, and when it is within the range of the phase difference threshold value, grinding is stopped. A grinding method for grinding a workpiece.

4. The measurement cycle is set according to the rotation speed of the chuck table and the number of measurement points of the reflected light intensity measurement unit, The grinding method according to claim 3, characterized in that.

Images