Grinding method for workpieces

Abstract

To recover a condition of a grinding wheel while sucking and holding a workpiece with a chuck table.SOLUTION: A method of grinding a workpiece includes: a holding step of holding one surface side of the workpiece with a chuck table capable of rotating around a predetermined rotation axis; and a grinding step of grinding the other surface side of the workpiece with a grinding wheel of a grinding unit having a spindle and the grinding wheel installed at a tip end portion of the spindle. The grinding step includes a whole surface grinding step of grinding the whole surface on the other surface side while rotating the spindle and the chuck table, and a groove forming step of forming an arc-shaped groove with depth that does not reach finishing thickness on the other surface side while rotating the spindle and not rotating the chuck table. If a grinding load becomes a threshold value or more during the whole surface grinding step, the whole surface grinding step is temporarily stopped, then the groove forming step is carried out, and the whole surface grinding step is carried out again after the groove forming step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for grinding a workpiece, which involves infeed grinding of the workpiece. [Background technology]

[0002] In the manufacturing process of semiconductor device chips, in order to reduce the thickness of the semiconductor device chip, devices such as ICs (Integrated Circuits) are formed on the surface side of a single-crystal substrate made of silicon or the like, and then the back side of the single-crystal substrate is ground down to thin it (see, for example, Patent Document 1).

[0003] As single-crystal substrates, silicon carbide (SiC), sapphire, gallium nitride (GaN), and other single-crystal substrates with higher hardness than silicon (Si) single-crystal substrates are sometimes used. During grinding of such hard substrates, the condition of the grinding wheel is prone to deterioration due to clogging, chipping, and deformation.

[0004] Continuing grinding with a grinding wheel in poor condition can lead to problems such as an increase in the current required to drive the spindle and surface burning on the workpiece. To prevent such problems, it is necessary to restore the condition of the grinding wheel by regularly dressing it.

[0005] However, dressing a grinding wheel requires, for example, a first replacement operation in which a dressing board is held in place of the workpiece by suction on the chuck table, and a second replacement operation in which, after the grinding wheel has been dressed, the workpiece is again held in place of the dressing board by suction on the chuck table.

[0006] Such replacement work is time-consuming because it is performed, for example, by the grinding machine operator. Furthermore, the time spent on replacement results in downtime during which the workpiece cannot be ground, thus reducing the operating rate of the grinding machine. [Prior art documents]

Patent Document

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention has been made in view of such problems, and an object thereof is to restore the condition of a grinding wheel while sucking and holding a workpiece on a chuck table.

Means for Solving the Problems

[0009] According to one aspect of the present invention, there is provided a grinding method for performing infeed grinding on a workpiece, the method including: a holding step of holding one surface side of the workpiece by a chuck table rotatable around a predetermined rotation axis; after the holding step, a grinding step of grinding the other surface side of the workpiece located on the side opposite to the one surface by a grinding wheel of a grinding unit having a spindle and a grinding wheel including a plurality of grinding wheels annularly arranged at a tip of the spindle, the grinding step including: a full-surface grinding step of relatively approaching the grinding wheel and the chuck table along the longitudinal direction of the spindle in a state where the spindle and the chuck table are rotated to grind the entire surface of the other surface side of the workpiece; and a groove forming step of relatively approaching the spindle and the chuck table along the longitudinal direction of the spindle in a state where the spindle is rotated and the chuck table is not rotated to form an arc-shaped groove having a depth that does not reach a finish thickness on the other surface side. Furthermore, starting from the full-surface grinding step, When a grinding load becomes equal to or greater than a threshold value during the full-surface grinding step, a grinding method for a workpiece is provided, in which the full-surface grinding step is once stopped, then the groove forming step is performed, and after the groove forming step, the full-surface grinding step is performed again.

[0010] Preferably, the groove forming step includes a first groove forming step of arranging the grinding wheel and the chuck table so that the locus of the grinding wheel does not pass through the extension line of the center line on the predetermined rotation axis of the chuck table, and forming an arc-shaped first groove on the other surface side.

[0011] Also preferably, the groove forming step further includes a second groove forming step of adjusting the arrangement of the grinding unit and the chuck table by relatively moving the grinding unit and the chuck table in a predetermined direction orthogonal to the longitudinal direction of the spindle, and then forming an arc-shaped second groove on the other surface side so as not to intersect the first groove on the other surface side.

[0012] Also preferably, the groove forming step further includes an additional first groove forming step of adjusting the arrangement of the chuck table and the grinding wheel by rotating the chuck table by a predetermined angle after the first groove forming step, and then forming an additional first groove on the other surface side.

Advantages of the Invention

[0013] The grinding method according to one aspect of the present invention includes a holding step of holding one surface side of a workpiece, and a grinding step of grinding the other surface side of the workpiece. The grinding step includes a full-surface grinding step of grinding the entire surface on the other surface side of the workpiece, and a groove forming step of forming an arc-shaped groove having a depth that does not reach the finish thickness on the other surface side.

[0014] In particular, in the grinding step, when the grinding load in the full-surface grinding step becomes equal to or greater than a threshold value, the full-surface grinding step is temporarily stopped, the groove forming step is performed, and then the full-surface grinding step is performed again after the groove forming step.

[0015] In the full-surface grinding step after the groove forming step, the grinding wheel is highlighted by the angled edge of the arc-shaped groove, so that an effect substantially the same as dressing the grinding wheel can be obtained. Therefore, the condition of the grinding wheel can be restored while the workpiece is sucked and held by the chuck table. [Brief explanation of the drawing]

[0016] [Figure 1] This is a flowchart of the grinding method. [Figure 2] This is a perspective view of a grinding machine. [Figure 3] This is a partial cross-sectional side view of a grinding machine. [Figure 4] Figure 4(A) is a top view showing full-surface grinding, and Figure 4(B) is a top view of the workpiece after full-surface grinding. [Figure 5] Figure 5(A) is a top view showing the groove formation step, and Figure 5(B) is a top view of the workpiece in which the groove has been formed. [Figure 6] This figure shows a workpiece being thinned down to the final thickness. [Figure 7] This is a flowchart of the grinding method according to the second embodiment. [Figure 8] Figure 8(A) is a top view showing the first groove formation step, and Figure 8(B) is a top view showing the second groove formation step. [Figure 9] Figure 9(A) is a top view showing the third groove formation step, and Figure 9(B) is a top view showing the overall grinding step after the third groove formation step. [Figure 10] This is a flowchart of the grinding method according to the third embodiment. [Figure 11] Figure 11(A) is a top view showing the first groove formation step, and Figure 11(B) is a top view of the workpiece after the fifth additional first groove formation step. [Figure 12] This is a top view showing the full-surface grinding step after the fifth additional first groove formation step. [Modes for carrying out the invention]

[0017] An embodiment of one aspect of the present invention will be described with reference to the attached drawings. Figure 1 is a flowchart of a grinding method in which infeed grinding is performed on a workpiece 11 (see Figures 2 and 3) using a grinding apparatus 2 (see Figures 2 and 3) according to the first embodiment.

[0018] The grinding method of the first embodiment comprises a holding step S10 in which the front surface (one side) 11a side of the workpiece 11 is held by suction using the chuck table 16 (see Figures 2 and 3) of the grinding device 2, and a grinding step S20 in which the back surface (other side) 11b side of the workpiece 11 is ground using the grinding unit 50 (see Figures 2 and 3) of the grinding device 2.

[0019] First, let's explain the grinding device 2 with reference to Figures 2 and 3. Figure 2 is a perspective view of the grinding device 2, and Figure 3 is a partial cross-sectional side view of the grinding device 2. The X-axis direction (front-to-back direction), Y-axis direction (left-to-right direction), and Z-axis direction (up-down direction) shown in Figures 2 and 3 are perpendicular to each other.

[0020] In the first embodiment, the grinding device 2 is a manual type in which the loading and unloading of the workpiece 11 is performed by an operator. However, the grinding device 2 may also be a fully automatic type that automatically performs grinding and cleaning in addition to loading and unloading the workpiece 11.

[0021] The grinding device 2 has a base 4 that supports the components of the grinding device 2. A rectangular opening 4a is formed on the upper surface of the base 4, with its long side aligned along the X-axis. A ball screw type X-axis movement mechanism 6 is provided below the opening 4a.

[0022] In Figure 2, the approximate position of the X-axis movement mechanism 6 is indicated by an arrow, and details of the X-axis movement mechanism 6 are shown in Figure 3. The X-axis movement mechanism 6 has a pair of guide rails (not shown) that are fixed to the base 4 and arranged substantially parallel to the X-axis direction.

[0023] A support plate 8 is slidably fixed on a pair of guide rails. A nut portion 10 is provided on the lower surface of the support plate 8. A screw shaft 12, which is positioned approximately parallel to the X-axis direction, is rotatably connected to the nut portion 10 via a plurality of balls (not shown).

[0024] The screw shaft 12 is positioned between a pair of guide rails. A drive source 14, such as a stepping motor, is connected to one end of the screw shaft 12. When the drive source 14 is operated, the support plate 8 moves along the X-axis direction.

[0025] A disc-shaped chuck table 16 is provided on the upper part of the support plate 8. The chuck table 16 has a disc-shaped frame 18 made of non-porous ceramics or the like. A disc-shaped recess is formed on the upper surface of the frame 18.

[0026] A channel is formed at the bottom of the recess of the frame 18 to transmit negative pressure from a suction source (not shown), such as a vacuum pump, to the recess. A disc-shaped porous plate 20 made of porous ceramics is fixed to the recess of the frame 18.

[0027] The porous plate 20 has a substantially flat bottom surface and a conical top surface in which the central part protrudes slightly compared to the outer periphery. However, the amount of protrusion is, for example, about 20 μm. Therefore, for convenience, in Figure 3, the top surface of the porous plate 20 is shown as substantially flat.

[0028] The upper surface of the porous plate 20 and the upper surface of the frame 18 are substantially flush, forming a holding surface 16a that holds the workpiece 11 by suction. When the negative pressure from the suction source is transmitted to the upper surface of the porous plate 20, the workpiece 11 deforms to conform to the shape of the holding surface 16a.

[0029] The chuck table 16 is rotatably supported by a disc-shaped support plate 22 via bearings (not shown). The support plate 22 is supported by a disc-shaped table base 24.

[0030] Three load cells 24a, 24b, and 24c are provided on the outer circumference of the lower side of the support plate 22 at approximately equal intervals along the circumferential direction of the support plate 22 (see Figure 4(A) for load cell 24c). Load cell 24a is located directly above the fixed shaft 26a.

[0031] Load cell 24b is located directly above one movable shaft 26b, and load cell 24c is located directly above the other movable shaft 26b. Load cells 24a, 24b, and 24c are, for example, diaphragm type, but may also be beam type or column type.

[0032] Furthermore, in load cells 24a, 24b, and 24c, a strain gauge type is used as the load detection method, for example, but a spring type, piezoelectric element type, magnetostrictive type, or capacitance type may also be used.

[0033] Load cells 24a, 24b, and 24c convert the Z-axis load applied to the chuck table 16 into an electrical signal. The controller 62, described later, can determine the load applied to the chuck table 16 based on this electrical signal.

[0034] When grinding the workpiece 11, the load applied from the grinding unit 50 to the chuck table 16 is measured using, for example, a load cell 24a located directly above the fixed axis 26a and / or a load cell 24b located directly above the movable axis 26b. When the workpiece 11 is being ground stably, the load applied to the chuck table 16 is usually less than 200N.

[0035] Conversely, if the condition of the grinding wheel 58 deteriorates due to clogging, chipping, or dulling of the teeth, the workpiece 11 will no longer be ground stably. In this case, even though the workpiece 11 is not being ground, the downward movement of the grinding unit 50 (i.e., grinding feed) continues at a predetermined speed, so the load on the chuck table 16 increases.

[0036] In this embodiment, when the load applied to the chuck table 16 exceeds 200N (grinding load threshold), the controller 62 determines that the workpiece 11 is not being ground stably and that the condition of the grinding wheel 58 has deteriorated.

[0037] The table base 24 is supported by a tilt adjustment mechanism 26. As described above, the tilt adjustment mechanism 26 has one fixed shaft 26a and two movable shafts 26b whose length in the Z-axis direction is variable. The one fixed shaft 26a and the two movable shafts 26b are arranged at approximately equal intervals along the circumferential direction of the table base 24.

[0038] The tilt adjustment mechanism 26 adjusts the tilt of the table base 24 so that a portion of the holding surface 16a is approximately parallel to the XY plane. The tilt adjustment mechanism 26 is supported by the support plate 8 described above.

[0039] Through holes (not shown) of the same diameter are concentrically formed in the radial centers of the support plate 22 and the table base 24. A rotating shaft (a predetermined rotating shaft) 28, whose upper end is fixed to the lower surface of the chuck table 16, is fixed to this through hole. A driven pulley is fixed to the lower end of the rotating shaft 28.

[0040] Incidentally, a rotary drive source (not shown), such as a motor, is fixed to the support plate 8. A drive pulley (not shown) is connected to the output shaft of the rotary drive source, and an endless belt (not shown) is stretched over both the driven pulley and the drive pulley.

[0041] The power from the rotation drive source is transmitted to the rotating shaft 28 via an endless belt or the like. Therefore, the chuck table 16 can rotate around the rotating shaft 28 while tilted according to the inclination of the table base 24. The center line 28a of the rotating shaft 28 is shown by a dashed line.

[0042] Furthermore, the chuck table 16 moves between the loading / unloading area A1 located in front of the opening 4a (one side in the X-axis direction) and the grinding area A2 located behind the opening 4a (the other side in the X-axis direction) by the X-axis movement mechanism 6.

[0043] A disc-shaped workpiece 11 is placed on a chuck table 16 located in the loading / unloading area A1. The workpiece 11 has, for example, a silicon single crystal substrate (wafer). A device (not shown), such as an IC (Integrated Circuit), is formed on the surface 11a side of the workpiece 11.

[0044] However, the workpiece 11 is not limited to a silicon single crystal substrate; it may also have a disc-shaped single crystal substrate made of a compound semiconductor such as silicon carbide (SiC) or gallium nitride (GaN), or a disc-shaped substrate made of other materials.

[0045] If the device is formed on the surface 11a side, a resin protective tape 13 is attached to the surface 11a side. When the surface 11a side is held in place by suction at the holding surface 16a via the protective tape 13, the back surface 11b side, which is located on the opposite side from the surface 11a, is exposed upwards.

[0046] As shown in Figure 2, the holding surface 16a of the chuck table 16 is located above the rectangular table cover 30. On both sides of the table cover 30 in the X-axis direction, there are bellows-shaped cover members 30a that have dustproof and waterproof functions and are expandable and contractible in the X-axis direction.

[0047] A rectangular column 32 is provided on the rear side of the opening 4a. A ball screw type grinding feed mechanism 34 is provided on the front side of the column 32. The grinding feed mechanism 34 has a pair of rails 36 fixed to the front surface of the column 32.

[0048] A pair of rails 36 are arranged along the Z-axis. A movable plate 40 is fixed to the pair of rails 36 via a slider 38 (see Figure 3). A nut portion 42 is provided on the back surface of the movable plate 40.

[0049] A screw shaft 44 is rotatably connected to the nut portion 42 via multiple balls (not shown). The screw shaft 44 is positioned along the Z-axis direction, and a drive source 46, such as a stepping motor, is connected to the upper end of the screw shaft 44.

[0050] When the screw shaft 44 is rotated by the drive source 46, the movable plate 40 moves along the rail 36 in the Z-axis direction. A cylindrical holding member 48 is fixed to the front of the movable plate 40. The holding member 48 holds the grinding unit 50.

[0051] The grinding unit 50 has a cylindrical spindle housing 52 whose longitudinal direction is aligned with the Z-axis direction. A portion of a cylindrical spindle 54 (see Figure 3) is rotatably housed within the spindle housing 52.

[0052] The spindle 54 is positioned such that its longitudinal direction is approximately parallel to the Z-axis direction. A rotational drive source 54a, including a motor, is provided near the upper end of the spindle 54. As the motor of the rotational drive source 54a, for example, an AC motor is used, but a DC motor may also be used.

[0053] The current supplied to the rotational drive source 54a to drive the spindle 54 is monitored and controlled by the motor driver 62a of the controller 62. When the workpiece 11 is being ground stably, the current supplied to the rotational drive source 54a is usually less than 15A.

[0054] However, if the condition of the grinding wheel 58 deteriorates, the workpiece 11 will no longer be ground stably. At this time, the rotational speed of the grinding wheel 58 per unit time decreases due to a resistance force that hinders the rotation of the grinding wheel 58.

[0055] In response, the motor driver 62a attempts to maintain the rotational speed of the spindle 54 at a predetermined rotational speed per unit time as a processing condition, resulting in an increase in the current supplied to the rotational drive source 54a.

[0056] In this embodiment, when the current supplied to the rotational drive source 54a exceeds 15A (grinding load threshold), the controller 62 determines that the workpiece 11 is not being ground stably and that the condition of the grinding wheel 58 has deteriorated.

[0057] The lower end (tip) 54b (see Figure 3) of the spindle 54 protrudes below the lower surface of the retaining member 48 through a through hole provided in the lower surface of the retaining member 48. A disc-shaped wheel mount 56 is fixed to the lower end 54b of the spindle 54.

[0058] An annular grinding wheel 58 is attached to the lower side of the wheel mount 56 by fixing members such as screws (not shown). In other words, the grinding wheel 58 is attached to the lower end portion 54b of the spindle 54 via the wheel mount 56.

[0059] The grinding wheel 58 has an annular wheel base 58a made of a metal material such as an aluminum alloy. Multiple grinding wheels 58b are arranged on the lower surface of the wheel base 58a at approximately equal intervals (i.e., in an annular shape) along the circumferential direction of the wheel base 58a.

[0060] The grinding wheel 58b is formed by mixing abrasive grains such as diamond and cBN (cubic boron nitride) with a binder (bonding material) such as metal, ceramics, or resin, and then molding and firing the mixture. In the grinding wheel 58b, the abrasive grains are fixed in place by the bonding material.

[0061] Below the grinding unit 50, a grinding water supply nozzle (not shown) is provided for supplying grinding water such as pure water. The grinding water supply nozzle, also called an internal nozzle, supplies grinding water from the inside of the grinding wheel 58 to the area to be ground 11c (see Figure 4(A)).

[0062] A thickness measuring device 60 is provided near the opening 4a. The thickness measuring device 60 measures the thickness of the workpiece 11, which is held by suction on the holding surface 16a of the chuck table 16 located in the grinding area A2. Note that the thickness measuring device 60 is shown in Figure 2 but omitted in Figure 3.

[0063] The thickness measuring instrument 60 has, for example, a pair of contact gauges. One contact gauge contacts the back surface 11b of the workpiece 11, and the other contact gauge contacts the upper surface (holding surface 16a) of the frame 18. The thickness of the workpiece 11 is measured by the difference in height positions measured by the pair of contact gauges.

[0064] The operation of the components of the grinding apparatus 2 is controlled by a controller (control unit) 62. The controller 62 has a computer that includes, for example, a processor (processing unit) represented by a CPU (Central Processing Unit) and memory (storage device).

[0065] The storage device includes main memory such as DRAM (Dynamic Random Access Memory), SRAM (Static Random Access Memory), and ROM (Read Only Memory), and auxiliary storage such as flash memory, hard disk drives, and solid-state drives.

[0066] The auxiliary storage device stores software, including a predetermined program. The controller 62's functions are realized by operating the processing unit and other components according to this software.

[0067] As described above, the controller 62 includes a motor driver 62a. The motor driver 62a is, for example, a semiconductor package including an integrated circuit. The motor driver 62a may be fixed to the motherboard (not shown) that constitutes the controller 62, or it may be electrically connected to the motherboard at a distance.

[0068] The controller 62 also includes a determination unit 62b. The determination unit 62b is composed of, for example, a program stored in an auxiliary storage device. The determination unit 62b compares a predetermined grinding load threshold with the current grinding load in the grinding device 2.

[0069] In this embodiment, the grinding load refers to either or both of the load applied to the chuck table 16 and the current value supplied to the rotational drive source 54a to drive the spindle 54. Note that if only the current value is used to determine whether the current value (i.e., the grinding load) exceeds a threshold, the load cells 24a, 24b, and 24c for detecting the load can be omitted.

[0070] In contrast, when determining whether the load (i.e., grinding load) exceeds a threshold using only the load, the ammeter (not shown) for detecting the current value supplied to the rotational drive source 54a can be omitted. In this way, when using either the current value or the load, the number of parts in the grinding device 2 is reduced compared to when both are used, thus reducing the manufacturing cost of the grinding device 2.

[0071] Furthermore, when using both the current value and the load (i.e., grinding load) to determine whether they exceed a threshold, the grinding load in the rotational direction (i.e., lateral direction) of the spindle 54 can be measured using the current value, and the grinding load in the longitudinal direction (i.e., vertical direction) of the spindle 54 can be measured using the load. Therefore, the grinding load can be measured more accurately compared to using only one of the current value or the load.

[0072] As mentioned above, when determining the grinding load threshold by load, the threshold is 200N, and when determining the grinding load threshold by current value, the threshold is 15A. However, due to instantaneous spikes in the grinding load, it frequently occurs that the grinding load momentarily exceeds the threshold.

[0073] Therefore, when the controller 62 determines whether the grinding load has exceeded a threshold, it does not use the instantaneous peak value of the grinding load, but rather the criterion of whether the grinding load (the load and / or current value mentioned above) has remained above the threshold for a predetermined time (for example, 2 seconds to 5 seconds).

[0074] Next, the grinding method for the workpiece 11 will be explained according to each step in Figure 1. First, the chuck table 16 is placed in the loading / unloading area A1, and the workpiece 11 is held by the holding surface 16a with suction so that the back surface 11b of the workpiece 11 is exposed upwards (holding step S10).

[0075] After the holding step S10, the chuck table 16 is placed in the grinding area A2. Then, the grinding step S20 is performed to grind the back surface 11b of the workpiece 11. In the grinding step S20, grinding of the entire back surface 11b of the workpiece 11 is started first (start of full-surface grinding S22).

[0076] In full-surface grinding, the grinding wheel 58 and the chuck table 16 are brought relatively closer together along the Z-axis while the chuck table 16 and spindle 54 are rotated at predetermined speeds.

[0077] In this embodiment, with the height position of the chuck table 16 fixed, the grinding unit 50 is moved downward at a predetermined processing feed speed by the grinding feed mechanism 34 (i.e., grinding feed). Furthermore, in addition to grinding feed, grinding water is supplied from the grinding water supply nozzle at a predetermined flow rate.

[0078] In one example, if the diameter of the grinding wheel 58 is 200 mm, the chuck table 16 is set to 300 rpm, the spindle 54 to 4000 rpm, the machining feed rate to 0.4 μm / s, and the grinding water flow rate to 4.0 L / min. However, these values ​​are not limited to this example.

[0079] Figure 4(A) is a top view showing full-surface grinding. The holding surface 16a is positioned such that a portion of it, which is approximately parallel to the XY plane, is at the top due to the tilt adjustment mechanism 26 described above. The portion of the workpiece 11 on the back surface 11b side (i.e., the grinding area 11c) corresponding to this topmost portion is ground by the grinding wheel 58.

[0080] In Figure 4(A), the range of the workpiece grinding area 11c is indicated by a double-headed arrow. The workpiece grinding area 11c is an arc-shaped region extending from the center to the outer circumference of the back surface 11b. However, since the chuck table 16 rotates during full-surface grinding, the entire surface of the workpiece 11 on the back surface 11b is ground.

[0081] The grinding method shown in Figure 4(A) is an external-internal grinding method in which the grinding wheel 58b moves from the outside to the inside of the holding surface 16a, and is an internal cutting grinding method in which the workpiece 11 is ground with the inner circumferences of multiple grinding wheels 58b.

[0082] During full-surface grinding, the determination unit 62b determines whether the workpiece 11 has been thinned to the target finish thickness 11d (see Figure 6) based on the thickness of the workpiece 11 acquired in real time by the thickness measuring instrument 60.

[0083] If the workpiece 11 is thinned to a finished thickness of 11d (YES in S24), grinding is terminated. Conversely, if the workpiece has not been thinned to a finished thickness of 11d (NO in S24), full-surface grinding is continued.

[0084] Furthermore, during full-surface grinding, the controller 62 monitors in real time either or both the load on the chuck table 16 and the current supplied to the rotational drive source 54a to drive the spindle 54.

[0085] In other words, the full-surface grinding step S27 of this embodiment performs full-surface grinding, monitors the thickness of the workpiece 11 (S24), and monitors the grinding load (S26).

[0086] If the grinding load is below the threshold (i.e., load of 200N and / or current of 15A), full-surface grinding continues (NO in S26). Conversely, if the grinding load exceeds the threshold, the controller 62 temporarily stops full-surface grinding (YES in S26).

[0087] If the full-surface grinding step S27 is to be stopped, specifically, the grinding feed is stopped, and the grinding unit 50 is raised so that the grinding wheel 58b is positioned above the back surface 11b. In addition, the rotation of the chuck table 16 is also stopped.

[0088] Figure 4(B) is a top view of the back surface 11b of the workpiece 11 after full surface grinding. Grinding marks (saw marks) resulting from full surface grinding are formed on the back surface 11b. After temporarily stopping the full surface grinding step S27, an arc-shaped groove 11e (see Figure 5(B)) is formed on the back surface 11b of the workpiece 11 (groove forming step S28).

[0089] Figure 5(A) is a top view of the chuck table 16 showing the groove forming step S28. When forming the groove 11e, the chuck table 16 is kept stationary without rotation, and the spindle 54 is rotated at a predetermined speed (for example, the same speed as during full surface grinding), while the grinding wheel 58 and the chuck table 16 are brought relatively close together along the Z-axis direction.

[0090] As a result, as shown in Figure 5(A), the arc-shaped region 11f where the grinding wheel 58 and the workpiece 11 overlap in the Z-axis direction is ground, and a groove 11e is formed connecting two points on the outer circumference of the back surface 11b.

[0091] However, as mentioned above, the rotation axis 28 of the chuck table 16 is slightly tilted. Therefore, the depth of the groove 11e in the lower outer circumference B3 (see Figure 5(B)) is shallower than that in the central part B1 and the upper outer circumference B2 (see Figure 5(B)).

[0092] In groove forming step S28, the groove 11e is formed such that the depth of the relatively deep groove 11e located between the central part B1 and the upper outer peripheral part B2 does not reach the target finished thickness 11d of the workpiece 11. Grinding water is also supplied from the internal nozzle during grinding of the workpiece 11 in which the groove 11e is formed.

[0093] The depth of the groove 11e in the central part B1 and the upper outer peripheral part B2 is, for example, several μm to 20 μm. Figure 5(B) is a top view of the workpiece 11 in which the groove 11e is formed. After the groove forming step S28, the full surface grinding step S27 is performed again.

[0094] In the full-surface grinding step S27 following the groove forming step S28, the angular edges of the arc-shaped grooves 11e formed in the groove forming step S28 sharpen the grinding wheel 58b, thus achieving approximately the same effect as dressing the grinding wheel 58b.

[0095] Therefore, the condition of the grinding wheel 58b of the grinding wheel 58 can be restored while the workpiece 11 is held in place by the chuck table 16 without having to replace the workpiece 11 with a dressing board.

[0096] In this way, the condition of the grinding wheel 58b can be restored while the workpiece 11 is held in place by the chuck table 16, thereby reducing the operator's workload and, furthermore, shortening the downtime of the grinding device 2 by eliminating the need for replacement work.

[0097] Figure 6 shows the workpiece 11 after groove formation step S28, which is thinned down to a finished thickness of 11d by grinding the entire surface again. Note that the protective tape 13 is not shown in Figure 6. Once the workpiece 11 has been thinned down to a finished thickness of 11d, grinding is terminated.

[0098] The groove-forming step S28 is not limited to one time. After the start of full-surface grinding S22, the groove-forming step S28 may be performed each time the grinding load exceeds a threshold. Also, monitoring the thickness of the workpiece 11 (S24) and monitoring the grinding load (S26) do not necessarily have to be in this order; they may be in the reverse order or performed simultaneously.

[0099] (Second Embodiment) Next, a second embodiment will be described with reference to Figures 7 to 9(B). Figure 7 is a flowchart of the grinding method according to the second embodiment. In the second embodiment as well, the holding step S10 and the grinding step S20 are performed sequentially.

[0100] However, if the grinding load exceeds the threshold (YES in S26), in the groove forming step S28, multiple arc-shaped grooves 11e (first groove 11e) are formed. a , second groove 11e b , 3rd groove 11e c (See Figure 9(B)) is formed on the back surface 11b side.

[0101] Figure 8(A) is a top view showing the first groove forming step S28a. In Figure 8(A), the trajectories of the movement of the multiple grinding wheels 58b accompanying the rotation of the spindle 54 are simplified by the ring 58b1, and the center line 28a of the rotation axis 28 of the chuck table 16 is shown as a point on the back surface 11b.

[0102] In the first groove forming step S28a, the relative positional relationship between the grinding wheel 58 and the chuck table 16 in the X-axis direction (a predetermined direction) is adjusted so that the ring 58b1 does not pass along the extension of the center line 28a.

[0103] In the first groove forming step S28a shown in Figure 8(A), the center line 28a is positioned inside the ring 58b1, but the center line 28a may also be positioned outside the ring 58b1. With the grinding wheel 58 and chuck table 16 positioned in this manner, the grinding unit 50 is fed through the grinding process to form an arc-shaped first groove 11e with a depth not reaching the finished thickness 11d. a It forms (see Figure 8(B)).

[0104] Thereafter, the grinding wheel 58 is raised so that the grinding wheel 58b is positioned above the back surface 11b. Subsequently, in the second groove forming step S28b, first, as shown in FIG. 8(B), the chuck table 16 and the grinding unit 50 are relatively moved along the X-axis direction.

[0105] Thereby, the arrangement of the grinding wheel 58 and the chuck table 16 is adjusted so that the annular ring 58b1 passes along the extension line of the center line 28a. In the example shown in FIG. 8(B), the chuck table 16 is moved forward by a predetermined distance C.

[0106] FIG. 8(B) is a top view showing the second groove forming step S28b. After arranging as described above, by feeding the grinding unit 50 for grinding, an arc-shaped second groove 11e having a depth that does not reach the finish thickness 11d and not intersecting with the first groove 11e a is formed. b (see FIG. 9(A)).

[0107] Thereafter, the grinding wheel 58 is raised so that the grinding wheel 58b is positioned above the back surface 11b. Subsequently, in the third groove forming step S28c, in the Y-axis direction, the third groove 11e is formed on the opposite side of the first groove 11e with respect to the second groove 11e b a c .

[0108] FIG. 9(A) is a top view showing the third groove forming step S28c. In the third groove forming step S28c, first, the arrangement of the grinding wheel 58 and the chuck table 16 is adjusted by relatively moving the chuck table 16 and the grinding unit 50 along the X-axis direction so that the center line 28a is disposed outside the annular ring 58b1.

[0109] In the example shown in FIG. 9(A), compared with the example shown in FIG. 8(B), the chuck table 16 is moved forward by a predetermined distance C. Then, the grinding unit 50 is fed for grinding, and an arc-shaped third groove 11e having a depth that does not reach the finish thickness 11d and not intersecting with the second groove 11e b is formed.​​c (See Figure 9(B))

[0110] In this way, the first grooves 11e each have different lengths. a , second groove 11e b and 3 groove 11e c After forming the grooves, the process returns to the full-surface grinding step S27. Figure 9(B) is a top view showing the full-surface grinding step S27 after the third groove forming step S28c.

[0111] In this embodiment, since multiple grooves are formed in the groove forming step S28, a higher dressing effect can be obtained on the grinding wheel 58b in the full-surface grinding step S27 compared to the first embodiment.

[0112] Note that the first groove 11e a , second groove 11e b and 3 groove 11e c The formation sequence is not limited to the example described above. First, the third groove 11e c After forming the second groove 11e b Forms the first groove 11e a It may form.

[0113] (Third Embodiment) Next, a third embodiment will be described with reference to Figures 10 to 12(B). Figure 10 is a flowchart of the grinding method according to the third embodiment. In the third embodiment as well, the holding step S10 and the grinding step S20 are performed sequentially.

[0114] However, if the grinding load exceeds the threshold (YES in S26), in the groove forming step S28, multiple arc-shaped grooves of approximately the same length (first groove 11e a , and additional first groove 11e a1 ,11e a2 ,11e a3 ,11e a4 ,11e a5 (See Figure 11(B)) is formed on the back surface 11b side.

[0115] Figure 11(A) is a top view showing the first groove forming step S28a. In the first groove forming step S28a, the relative positional relationship between the grinding wheel 58 and the chuck table 16 in the X-axis direction is adjusted so that the trajectories of the movement of the multiple grinding wheels 58b do not pass along the extension of the center line 28a.

[0116] In the example shown in Figure 11(A), the grinding wheel 58 and the chuck table 16 are positioned such that the arc defined by the two intersections of the ring 58b1 and the outer circumference of the workpiece 11 divides the outer circumference of the workpiece 11 into six equal parts, by moving the chuck table 16 and the grinding unit 50 relative to each other along the X-axis.

[0117] Then, the grinding unit 50 is fed through the grinding process to create an arc-shaped first groove 11e with a depth not reaching the finished thickness 11d. a This forms (see Figure 11(B)). After the first groove forming step S28a, the grinding wheel 58 is raised so that the grinding wheel 58b is positioned above the back surface 11b.

[0118] Then, the arrangement of the chuck table 16 and the grinding wheel 58 is adjusted by rotating the chuck table 16 by a predetermined angle (60° in this example). After that, the grinding unit 50 is fed through the grinding process to create the additional first groove 11e. a1 This is the first additional groove forming step S28a-1. Then, the grinding wheel 58 is raised again.

[0119] Then, similarly, by rotating the chuck table 16 by a predetermined angle, the arrangement of the chuck table 16 and the grinding wheel 58 is adjusted, and the grinding unit 50 is fed through the grinding process to create the additional first groove 11e. a2 This is formed (second additional first groove forming step S28a-2).

[0120] Subsequently, the third additional first groove formation step S28a-3, the fourth additional first groove formation step S28a-4, and the fifth additional first groove formation step S28a-5 are performed in the same manner, and an additional first groove 11e is formed. a3 ,11ea4 and 11e a5 It forms.

[0121] Figure 11(B) is a top view of the workpiece 11 after the fifth additional first groove forming step S28a-5. As shown in Figure 11(B), the first groove 11e a , and additional first groove 11e a1 ,11e a2 ,11e a3 ,11e a4 and 11e a5 It forms a petal pattern.

[0122] In particular, in this embodiment, since the ring 58b1 does not pass along the extension of the center line 28a during the groove forming step S28, the groove forming step S28 can be performed without retracting the thickness measuring instrument 60.

[0123] Therefore, one contact gauge of the thickness measuring instrument 60 remains in contact with some part of the annular region D located inside the petal pattern shown by the dashed line in Figure 11(B). This is beneficial in terms of shortening the time required to perform the groove forming step S28 and ensuring the operational stability of the thickness measuring instrument 60 during the full-surface grinding step S27 after the groove forming step S28.

[0124] After the fifth additional first groove forming step S28a-5, the process returns to the full surface grinding step S27. Figure 12 is a top view showing the full surface grinding step S27 after the fifth additional first groove forming step S28a-5.

[0125] In this embodiment as well, since multiple grooves are formed in the groove forming step S28, a higher dressing effect can be obtained on the grinding wheel 58b in the full-surface grinding step S27 compared to the first embodiment.

[0126] In the third embodiment, an example was described in which six grooves of approximately the same length are formed along the circumferential direction of the workpiece 11, but the number of grooves can be two or more, and is not limited to six. The grooves may be spaced apart from each other.

[0127] The grinding method for the workpiece 11 according to the above embodiment is particularly effective when grinding hard substrates such as SiC, sapphire, and GaN, or when grinding composite materials to expose metal terminals embedded in a resin substrate. Of course, it may also be applied when grinding other substrates such as Si single crystal substrates.

[0128] Furthermore, the structures, methods, etc., according to the embodiments described above can be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of Symbols]

[0129] 2: Grinding device, 4: Base, 4a: Opening, 6: X-axis movement mechanism 8: Support plate, 10: Nut part, 12: Screw shaft, 14: Drive source 11: Workpiece, 11a: Front side (one side), 11b: Back side (other side) 11c: grinding area, 11d: finish thickness 11e: Groove, 11e a :1st groove, 11e b :2nd groove, 11e c :3rd groove 11e a1 ,11e a2 ,11e a3 ,11e a4 ,11e a5 :Additional 1st groove 11f: Arc-shaped area, 13: Protective tape 16: Chuck table, 16a: Holding surface, 18: Frame, 20: Porous plate 22: Support plate, 24: Table base, 24a, 24b, 24c: Load cells 26: Tilt adjustment mechanism, 26a: Fixed axis, 26b: Movable axis 28: Axis of rotation (predetermined axis of rotation), 28a: Centerline 30: Table cover, 30a: Cover component 32: Column, 34: Grinding feed mechanism, 36: Rail, 38: Slider, 40: Moving plate 42: Nut section, 44: Screw shaft, 46: Drive source, 48: Holding member, 50: Grinding unit 52: Spindle Housing 54: Spindle, 54a: Rotation drive source, 54b: Lower end (tip) 56: Wheel mount, 58: Grinding wheel, 58a: Wheel base 58b: Grinding wheel, 58b1: Ring 60: Thickness measuring instrument, 62: Controller, 62a: Motor driver, 62b: Judgment unit A1: Loading / unloading area, A2: Grinding area B1: Center, B2, B3: Outer periphery, C: Predetermined distance, D: Annular area S10: Holding step, S20: Grinding step S22: Start of full-surface grinding, S27: Full-surface grinding step S28: Groove forming step S28a: First groove forming step S28b: Second groove forming step, S28c: Third groove forming step S28a-1: First additional groove forming step S28a-2: Second additional first groove forming step S28a-3: Third additional first groove forming step S28a-4: Fourth additional first groove forming step S28a-5: Fifth additional first groove forming step

Claims

1. A method for grinding a workpiece, comprising applying infeed grinding to the workpiece, A holding step involves holding one side of the workpiece with a chuck table that is rotatable around a predetermined axis of rotation, The grinding step includes, after the holding step, grinding the other side of the workpiece located opposite to the one side, using the grinding wheel of a grinding unit having a spindle and a grinding wheel including a plurality of grinding wheels mounted on the tip of the spindle and arranged in an annular shape, The grinding step is, A full-surface grinding step in which the spindle and the chuck table are rotated and the grinding wheel and the chuck table are brought relatively close to each other along the longitudinal direction of the spindle to grind the entire surface of the other side of the workpiece, A groove forming step in which, with the spindle rotating and the chuck table not rotating, the spindle and the chuck table are brought relatively close together along the longitudinal direction of the spindle to form an arc-shaped groove on the other side that does not reach the finished thickness, This includes and begins with the full-surface grinding step, A method for grinding a workpiece, characterized in that, if the grinding load exceeds a threshold during the full-surface grinding step, the full-surface grinding step is temporarily stopped, the groove forming step is performed, and the full-surface grinding step is performed again after the groove forming step.

2. The method for grinding a workpiece according to claim 1, characterized in that the groove forming step includes a first groove forming step of arranging the grinding wheel and the chuck table such that the trajectory of the grinding wheel does not pass through the extension of the center line of the chuck table on the predetermined axis of rotation of the chuck table, thereby forming an arc-shaped first groove on the other side.

3. The method for grinding a workpiece according to claim 2, characterized in that the groove forming step further includes a second groove forming step of adjusting the arrangement of the chuck table and the grinding wheel by moving the grinding unit and the chuck table relative to each other in a predetermined direction perpendicular to the longitudinal direction of the spindle, and forming an arc-shaped second groove on the other side such that it does not intersect with the first groove on the other side.

4. The method for grinding a workpiece according to claim 2, characterized in that the groove forming step further includes an additional first groove forming step, in which, after the first groove forming step, the arrangement of the chuck table and the grinding wheel is adjusted by rotating the chuck table by a predetermined angle, and an additional first groove is formed on the other side.

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