Method for grinding a workpiece

Abstract

Provided is a workpiece grinding method capable of suppressing the occurrence of processing defects. The workpiece grinding method has: a groove forming step in which a workpiece is ground while a spindle is rotated without rotating a chuck table that holds the workpiece, thereby forming a circular-arc-shaped groove on the back surface side of the workpiece, the groove having a depth that does not reach a finished thickness; a groove removing step in which the chuck table is started to rotate while the spindle is rotated after the groove forming step, thereby grinding the side wall of the groove and removing the groove from the workpiece; and a surface grinding step in which the entire back surface side of the workpiece is ground until the workpiece becomes the finished thickness while the spindle and the chuck table are rotated after the groove removing step.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for grinding a workpiece held by a chuck table using a grinding wheel. BACKGROUND

[0002] In a manufacturing process of a device chip, a wafer in which devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integrations) are respectively formed in regions divided by a plurality of division-preliminary-line (streets) crossing each other is used. By dividing the wafer along the division-preliminary-line, a plurality of device chips each having a device are manufactured. The device chip is mounted on various electronic equipment such as mobile phones and personal computers.

[0003] In recent years, with the miniaturization of electronic equipment, thinning of device chips is also required. Therefore, a method of thinning a wafer by performing grinding processing on the wafer before division is used. In the grinding of the wafer, a grinding device having a chuck table that attracts and holds the wafer and a grinding unit that grinds the wafer is used. A grinding wheel having a plurality of grinding stones arranged in a ring shape is installed on the grinding unit.

[0004] The grinding stone is formed by fixing abrasive grains made of diamond or the like with a bonding material (joining material). In grinding the wafer, in a state where the wafer is attracted and held by the chuck table, the chuck table and the grinding wheel are rotated while the grinding stone is brought into contact with the wafer (for example, refer to Patent Literature 1).

[0005] The abrasive grains protruding from the bonding material of the grinding stone are brought into contact with the wafer to grind the wafer, and thus it is desirable to maintain a state where the abrasive grains are moderately protruding from the bonding material during grinding. When the bonding material is scraped due to processing chips or the like generated during grinding, the bonding material in the surface of the grinding stone located at an action surface facing the wafer is pried up.

[0006] With the reduction of the bonding material, the abrasive grains fall off from the bonding material, but when grinding is continued after the abrasive grains fall off, new abrasive grains are exposed (spontaneous sharpening) from the bonding material due to the wear of the bonding material. By this spontaneous sharpening, the state where the abrasive grains protrude from the bonding material is maintained, and the decrease in the grinding ability of the grinding stone is prevented.

[0007] Patent Literature 1: Japanese Patent Application Laid-Open No. 2009-90389

[0008] However, depending on the material of the wafer, the material of the ground surface of the wafer, and the like, the timing of the detachment of the abrasive grains is sometimes advanced. For example, when an oxide film that is relatively hard is formed on the ground surface, detachment (leakage) of the abrasive grains is likely to occur. In such a case, the period from the detachment of the abrasive grains to the completion of the self-sharpening becomes longer, that is, the period during which the workpiece is ground in a state in which the grinding ability of the grinding tool is low, and processing failure is likely to occur. SUMMARY

[0009] The present application has been achieved in view of this problem, and has an object to provide a grinding method of a workpiece in which occurrence of processing failure is suppressed.

[0010] According to one embodiment of the present application, a grinding method of a workpiece is provided, in which a workpiece is ground using a grinding device having a chuck table that holds the workpiece and a grinding unit having a spindle to which a grinding wheel having a plurality of grinding tools arranged in a ring shape is attached, the workpiece being ground while the grinding wheel is rotated about the spindle, the grinding method including: a groove forming step of forming a groove having a depth that does not reach a finished thickness on a back surface side of the workpiece by grinding the workpiece while the spindle is rotated and the grinding unit is fed in a grinding manner without rotating the chuck table that holds the workpiece; a groove removing step of removing the groove by grinding a side wall of the groove while the chuck table is rotated after the groove forming step; and a full-face grinding step of grinding the entire back surface side of the workpiece until the workpiece becomes the finished thickness by grinding the workpiece while the spindle and the chuck table are rotated after the groove removing step.

[0011] Preferably, in the groove removing step, the chuck table is rotated while the grinding unit is fed in a grinding manner.

[0012] A grinding method of a workpiece according to one embodiment of the present application includes: a groove forming step of forming a groove on a back surface side of the workpiece by rotating a spindle without rotating a chuck table that holds the workpiece; a groove removing step of removing the groove by grinding a side wall of the groove while the chuck table is rotated after the groove forming step; and a full-face grinding step of grinding the entire back surface side of the workpiece.

[0013] In the groove forming step, grinding is mainly performed using the bottom surface of the grinding tool, but in the groove removing step, grinding can be performed mainly using the side surface of the grinding tool. Therefore, in the groove removing step, deterioration of the condition of the bottom surface of the grinding tool (i.e., reduction of the grinding ability) can be alleviated compared to a case where the entire back surface side is ground mainly using the bottom surface of the grinding tool.

[0014] Also, in the surface grinding step after the groove removing step, the entire back surface side of the workpiece from which the groove has been removed is ground. In this surface grinding step, grinding is mainly performed using the bottom surface of the grinding tool, and in particular, grinding can be performed in a state where deterioration of the condition of the bottom surface of the grinding tool is alleviated. Therefore, even in a case where a relatively hard oxide film is formed on the back surface side, generation of processing defects of the workpiece can be suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a perspective view of a grinding device.

[0016] Figure 2 (A) of FIG. 1 is a side view showing a grinding wheel or the like in the groove forming step, Figure 2 (B) of FIG. 1 is a plan view showing the grinding wheel or the like in the groove forming step.

[0017] Figure 3 is a plan view of the workpiece after the groove forming step.

[0018] Figure 4 (A) of FIG. 2 is a side view showing a grinding wheel or the like in the groove removing step, Figure 4 (B) of FIG. 2 is a plan view showing the grinding wheel or the like in the groove removing step.

[0019] Figure 5 is a side view showing a grinding wheel or the like in the surface grinding step.

[0020] Figure 6 is a flowchart showing a grinding method.

[0021] Figure 7 is a graph showing time variations of a current value of a motor that drives the spindle and a rotational speed of a chuck table.

[0022] REFERENCE NUMERALS

[0023] 2: grinding device; 4: base; 4a: opening; 6: robot; 8a, 8b: cassette arrangement area; 10a, 10b: cassette; 11: workpiece; 11a: front surface; 11b: back surface; 11c: groove; 11d: side wall; 12: alignment mechanism; 14: loading arm; 16: rotary table; 18: chuck table; 18a: holding surface; 20: rotary drive source; 22a, 22b: support structure; 24a, 24b: grinding feed unit; 26: guide rail; 28: moving plate; 30: ball screw; 32: pulse motor; 34a, 34b: grinding unit; 36: housing; 38: spindle; 40: rotary drive source; 41: arrow; 42: mounting seat; 44a, 44b: grinding wheel; 46: annular base; 48: grinding tool; 48a: bottom surface; 48b: inner peripheral side surface; 48c: outer peripheral side surface; 50: thickness gauge; 52a: 1st height gauge; 52b: 2nd height gauge; 54: unloading arm; 56: cleaning unit; 58: control section; A: in-out position; B: rough grinding position; C: fine grinding position; D1, D2, E1, E2: graph. DETAILED DESCRIPTION

[0024] Hereinafter, an embodiment relating to one mode of the present application will be described with reference to the drawings. First, a configuration example of a grinding device 2 capable of performing a grinding method of a workpiece 11 of the present embodiment will be described. Figure 1 is a perspective view showing the grinding device 2.

[0025] In the following description, an X-axis direction (left-right direction), a Y-axis direction (front-rear direction), and a Z-axis direction (grinding feed direction, up-down direction, height direction) are perpendicular to each other. In addition, in the drawings, a functional block is sometimes used to represent a part of the constituent elements of the grinding device 2.

[0026] The grinding device 2 has a base 4 that supports or houses each constituent element. A rectangular opening 4a is provided on the upper surface side of the front end portion of the base 4. A horizontal multi-joint type robot (1st conveyance unit) 6 that conveys the workpiece 11 is provided in the opening 4a.

[0027] Cassette arrangement areas 8a, 8b are provided on both sides of the robot 6 in the X-axis direction. A cassette 10a that houses the workpieces 11 before grinding and a cassette 10b that houses the workpieces 11 after grinding are respectively arranged on the cassette arrangement areas 8a, 8b.

[0028] A plurality of workpieces 11 before grinding are housed in the cassette 10a. In contrast, a plurality of workpieces 11 after grinding are housed in the cassette 10b. The workpieces 11 are disc-shaped silicon wafers having a prescribed diameter (for example, about 200 mm in diameter).

[0029] The workpiece 11 has a front surface 11a and a back surface lib. The thickness of the workpiece 11 (length from the front surface 11a to the back surface lib) is a predetermined value of 200 μm or more and 800 μm or less (for example, 725 μm), and a heat-oxidized film having a thickness of 200 nm or more and 800 nm or less is formed on the back surface lib side a heat-oxidized film having a thickness of 200 nm or more and 800 nm or less.

[0030] A plurality of division predetermined lines (partition lines) are provided in a lattice shape on the front surface 11a. A device (not shown) such as an IC (Integrated Circuit) or LSI (Large Scale Integration) is provided on each of the front surface 11a side in a rectangular region divided by the plurality of division predetermined lines.

[0031] In addition, the kind, material, size, shape, configuration, and the like of the workpiece 11 are not limited. The workpiece 11 can also be a wafer or substrate formed of a compound semiconductor other than silicon (GaN, SiC, or the like), glass, ceramic, resin, metal, or the like. In addition, the kind, number, shape, configuration, size, arrangement, and the like of the device formed on the workpiece 11 are not limited. The device can also not be formed on the workpiece 11.

[0032] A positioning mechanism 12 is provided on the rear side of one side in the X-axis direction of the opening 4a. The workpiece 11 housed in the cassette 10a is carried to the positioning mechanism 12 by the robot arm 6, and is positioned at a prescribed position by the positioning mechanism 12.

[0033] On the other side in the X-axis direction, a load arm (second carrying unit) 14 that carries the workpiece 11 is provided at a position adjacent to the positioning mechanism 12. The load arm 14 has a suction pad that suctions and holds the back surface lib side of the workpiece 11 at the tip end portion.

[0034] After the load arm 14 holds the workpiece 11 positioned by the positioning mechanism 12 with the suction pad, the suction pad is rotated about the rotation axis located at the base end portion, and the workpiece 11 is carried toward the carry-in and carry-out position A.

[0035] A disc-shaped rotary table 16 is provided on the rear side of the load arm 14. A rotary drive source (not shown) such as a motor is connected to the lower portion of the rotary table 16. The rotary table 16 is rotated about a rotation axis that is substantially parallel to the Z-axis direction by the rotary drive source.

[0036] On the rotary table 16, three chuck tables 18 that hold the workpiece 11 are arranged at substantially equal intervals along the circumferential direction of the rotary table 16. Each of the chuck tables 18 is positioned at the carry-in and carry-out position A, the rough grinding position B, and the fine grinding position C by the rotation of the rotary table 16.

[0037] For example, the one chuck table 18 positioned at the carry-in / out position A is positioned at the rough grinding position B by rotating the rotary table 16 approximately 120 degrees clockwise in plan view.

[0038] Subsequently, the chuck table 18 is positioned at the finish grinding position C by further rotating the rotary table 16 approximately 120 degrees clockwise in plan view. Then, the chuck table 18 is positioned from the finish grinding position C to the carry-in / out position A by further rotating the rotary table 16 approximately 240 degrees counterclockwise in plan view.

[0039] A rotary drive source 20 (refer to (A) and the like of FIG. 1) whose output shaft is linked to the lower portion of each chuck table 18 is provided. Figure 2 The rotary drive source 20 rotates the chuck table 18 about a rotation axis that is substantially parallel to the Z-axis direction.

[0040] A columnar support structure 22a is provided behind the rough grinding position B, and a columnar support structure 22b is provided behind the finish grinding position C. A grinding feed unit 24a is provided on the front surface side of the support structure 22a, and a grinding feed unit 24b is provided on the front surface side of the support structure 22b.

[0041] The grinding feed units 24a, 24b each have a pair of rails 26 that are provided substantially parallel to the Z-axis direction. A moving plate 28 is provided on the pair of rails 26 in a state capable of sliding along the rails 26.

[0042] A nut portion (not shown) is provided on the rear surface side of the moving plate 28, and a ball screw 30 that is provided substantially parallel to the rails 26 is linked to the nut portion in a rotatable manner.

[0043] A pulse motor 32 is linked to the upper end portion of the ball screw 30. When the ball screw 30 is rotated by the pulse motor 32, the moving plate 28 moves in the Z-axis direction. A grinding unit 34a that performs rough grinding of the workpiece 11 is fixed on the front surface side of the moving plate 28 of the grinding feed unit 24a.

[0044] In contrast, a grinding unit 34b that performs finish grinding of the workpiece 11 is fixed on the front surface side of the moving plate 28 of the grinding feed unit 24b. The grinding feed units 24a, 24b raise and lower the grinding units 34a, 34b.

[0045] The grinding units 34a, 34b each have a cylindrical housing 36. A portion of a cylindrical main shaft 38 (refer to (A) of FIG. 1) that is provided along the Z-axis direction is housed inside the housing 36. Figure 2

[0046] ​A rotation driving source 40 such as a motor is provided at the upper end portion of the main shaft 38 to rotate the main shaft 38. In addition, as shown in (A) of FIG. 1, Figure 2 the lower end portion of the main shaft 38 is exposed from the housing 36, and the central portion of the upper surface of a disc-shaped mounting seat 42 is fixed to the lower end portion.

[0047] A grinding wheel 44a for rough grinding is attached to the lower surface side of the mounting seat 42 of the grinding unit 34a. The grinding wheel 44a has a ring-shaped base 46 having substantially the same diameter as the mounting seat 42. A plurality of grinding tools 48 are discretely arranged along the circumferential direction of the ring-shaped base 46 on the lower surface side of the ring-shaped base 46.

[0048] That is, as shown in (B) of FIG. 1, Figure 2 the plurality of grinding tools 48 are arranged in a ring shape on the lower surface side of the ring-shaped base 46. The grinding tool 48 has a substantially rectangular parallelepiped shape, and is formed by fixing abrasive grains formed of diamond, cBN (cubic boron nitride), or the like with a bonding material such as metal, resin, or ceramic.

[0049] The chuck table 18 has a frame formed of ceramic in a disc shape. A recessed portion formed of a disc shape is formed in the upper portion of the frame, and a porous plate formed of porous ceramic is fixed in the recessed portion.

[0050] The porous plate is connected to a suction source (not shown) such as an ejector via a flow path (not shown) formed in the inside of the frame. The upper surface of the porous plate and the upper surface of the frame are in the same plane, and constitute a holding surface 18a that holds the workpiece 11 by suction.

[0051] The holding surface 18a has a conical shape that slightly protrudes from the outer periphery toward the center. However, since the amount of protrusion of the holding surface 18a is extremely small (for example, 30 μm), in (A) of FIG. 1, Figure 2 the holding surface 18a is depicted as a flat surface that is substantially parallel to the X-axis direction and the Y-axis direction for convenience (as in (A) of FIG. 2 and Figure 4 (B) of FIG. 2 to be described later). Figure 5

[0052] When the suction source is activated to apply negative pressure to the upper surface of the porous plate, the workpiece 11 or the like arranged on the holding surface 18a is held by suction by the holding surface 18a in a manner that imitates the shape of the holding surface 18a.

[0053] In addition, the rotation axis of the chuck table 18 is slightly inclined with respect to the Z-axis direction in a manner that the grinding surface defined by the lower surfaces of the plurality of grinding tools 48 is substantially parallel to a portion of the holding surface 18a. However, since the inclination angle of the rotation axis of the chuck table 18 is extremely small, in Figure 2 ​In (A) of FIG. 1, for convenience, the inclination of the rotation axis is depicted as being substantially parallel to the Z-axis direction (in the later-described Figure 4 (A) and Figure 5 (B) of FIG. 1).

[0054] The grinding wheel 44a is disposed above the chuck table 18, and a portion of the grinding wheel 44a partially covers the upper surface of the chuck table 18 in such a manner as to pass through the center of rotation of the chuck table 18 (refer to (B) of FIG. 1). Figure 2

[0055] Figure 1 The grinding unit 34b is configured in the same manner as the grinding unit 34a. A grinding wheel 44b for finish grinding is attached to the lower surface side of the mounting base 42 of the grinding unit 34b.

[0056] The grinding wheel 44b has the same structure as the grinding wheel 44a, but the average particle diameter of the abrasive grains included in the grinding tool 48 of the grinding wheel 44b is smaller than the average particle diameter of the abrasive grains included in the grinding tool 48 of the grinding wheel 44a.

[0057] Inside or outside the grinding units 34a, 34b, a grinding water supply unit (not shown) for supplying a liquid such as pure water (grinding fluid) to the machining point is provided. A thickness gauge 50 is provided in the vicinity of each of the rough grinding position B and the finish grinding position C.

[0058] The thickness gauge 50 has a first height gauge 52a that measures the height of the upper surface of the workpiece 11 held by the chuck table 18, and a second height gauge 52b that measures the height of the holding surface 18a.

[0059] The thickness of the workpiece 11 is calculated from the difference between the heights measured by the first height gauge 52a and the second height gauge 52b. An unloading arm (third conveyance unit) 54 is provided on the other side in the X-axis direction of the loading arm 14.

[0060] The unloading arm 54 has a suction pad that holds the back surface 11b side of the workpiece 11. After the workpiece 11 located in the load / unload position A is held by the suction pad, the unloading arm 54 rotates the suction pad about the rotation axis located at the base end portion, and conveys the workpiece 11 to a cleaning unit 56.

[0061] The workpiece 11 cleaned by the cleaning unit 56 is housed in the cassette 10b by the mechanical arm 6. The grinding device 2 has a control unit 58 that controls the operation of each of the constituent elements.

[0062] ​The control section 58 controls the operation of the robot arm 6, the alignment mechanism 12, the loading arm 14, the rotary table 16, the chuck table 18, the rotary drive source 20, the grinding feed units 24a, 24b, the grinding units 34a, 34b, the thickness gauge 50, the unloading arm 54, the cleaning unit 56, and the like.

[0063] The control section 58 is constituted by a computer, which includes, for example, a processor (processing device) typified by a CPU (Central Processing Unit), a main storage device such as a DRAM (Dynamic Random Access Memory), a SRAM (Static Random Access Memory), a ROM (ReadOnly Memory), and the like, and an auxiliary storage device such as a flash memory, a hard disk drive, a solid state drive, and the like.

[0064] A software including a prescribed program is stored in the auxiliary storage device. The processing device and the like are caused to operate in accordance with the software, thereby realizing the function of the control section 58. Next, a grinding method of the workpiece 11 using the grinding device 2 will be described.

[0065] First, the cassette 10a in which the workpiece 11 is accommodated is arranged on the cassette arrangement region 8a, and one workpiece 11 is carried from the cassette 10a to the alignment mechanism 12 by the robot arm 6.

[0066] After the alignment of the workpiece 11 by the alignment mechanism 12, the workpiece 11 is carried from the alignment mechanism 12 to the chuck table 18 arranged at the in-out position A by the loading arm 14.

[0067] At this time, the workpiece 11 is arranged on the chuck table 18 with the back surface 11b side exposed upward, and the front surface 11a side is suction-held by the holding surface 18a (see Figure 2 (A)).

[0068] Further, when a device is formed on the front surface 11a side, a protective tape for protecting the device can be attached to the front surface 11a side. In this case, the front surface 11a side is suction-held by the holding surface 18a with the protective tape interposed therebetween.

[0069] Next, the rotary table 16 is rotated clockwise by substantially 120 degrees in plan view, and the chuck table 18 holding the workpiece 11 is arranged at the rough grinding position B. Then, the workpiece 11 is rough-ground by the grinding unit 34a.

[0070] In the present embodiment, the workpiece 11 is ground by the grinding unit 34a in a state where the chuck table 18 is not rotated, thereby forming a circular-arc-shaped groove 11c on the back surface 11b side (groove forming step S10).

[0071] Figure 2 (A) of FIG. 10 is a side view of the grinding wheel 44a and the like that illustrates the groove forming step S10. If the rotation drive source 40 is activated, the grinding wheel 44a rotates around the spindle 38.

[0072] In the groove forming step S10, the spindle 38 is set to a predetermined rotational speed (for example, 3500 rpm), and the grinding unit 34a is fed at a predetermined grinding feed rate (for example, 0.5 μm / sec).

[0073] When the spindle 38 is rotated and the grinding unit 34a is fed while the grinding tool 48 is brought into contact with the back surface 11b side, the back surface 11b side is mainly ground by the bottom surface 48a of the grinding tool 48. Figure 2 (B) of FIG. 10 is a plan view of the grinding wheel 44a and the like that illustrates the groove forming step S10.

[0074] In the groove forming step S10, the chuck table 18 is not rotated, and thus the back surface 11b side is ground along the trace of the rotating grinding tool 48, thereby forming a circular-arc-shaped groove 11c on the back surface 11b side along the trace of the grinding tool 48.

[0075] The groove 11c has a depth that is deeper than the depth of the oxide film formed on the back surface 11b side and does not reach the finished thickness of the workpiece 11. For example, in a case where the thickness of the workpiece 11 before grinding is 725 μm and the finished thickness is 50 μm, the grinding feed amount is set to 20 μm from the height position at which the grinding surface of the grinding unit 34a is brought into contact with the back surface 11b to the lower side.

[0076] Figure 3 (B) of FIG. 10 is a plan view of the grinding wheel 44a and the like that illustrates the groove forming step S10.

[0077] In the groove forming step S10, the bottom surface 48a of the grinding tool 48 is mainly used to form one groove 11c, and thus, as compared with a case where the entire back surface 11b side is ground mainly using the bottom surface 48a of the grinding tool 48, the deterioration of the condition of the bottom surface 48a of the grinding tool 48 (i.e., the reduction of the grinding ability) can be alleviated.

[0078] After the grinding unit 34a is ground in by the prescribed grinding in-feed amount, the chuck table 18 is started to rotate while the spindle 38 is kept rotating at the prescribed rotational speed. Thereby, the side wall lid of the groove 11c is ground mainly by the inner peripheral side surface 48b and the outer peripheral side surface 48c of the grinding stone 48, and the groove 11c is removed from the back surface lib side (groove removal step S20).

[0079] Figure 4 (A) is a side view showing the grinding stone 44a and the like in the groove removal step S20, Figure 4 (B) is a plan view showing the grinding stone 44a and the like in the groove removal step S20. As shown in Figure 4 (B), in the groove removal step S20, the back surface lib side is ground mainly by the inner peripheral side surface 48b and the outer peripheral side surface 48c of the grinding stone 48, as indicated by the arrow 41.

[0080] Thus, the groove removal step S20 is performed immediately after the groove formation step S10. In the groove removal step S20, the grinding unit 34a is ground in at a prescribed grinding in-feed speed (for example, 0.5 μm / sec) while the chuck table 18 is rotated at a prescribed rotational speed (for example, 100 rpm).

[0081] In the groove removal step S20, instead of the bottom surface 48a of the grinding stone 48 mainly used in the groove formation step S10, the back surface lib side is ground and the oxide film is removed by the inner peripheral side surface 48b and the outer peripheral side surface 48c of the grinding stone 48 which are in a comparatively good condition.

[0082] In the groove removal step S20, compared with the case where the entire back surface lib side is continuously ground by the bottom surface 48a of the grinding stone 48 mainly used in the groove formation step S10, the deterioration of the condition of the bottom surface 48a of the grinding stone 48 can be alleviated.

[0083] After the groove removal step S20, the grinding unit 34a is ground in while the spindle 38 and the chuck table 18 are rotated, and the entire back surface lib side of the workpiece 11 is ground until the thickness of the workpiece 11 becomes the finished thickness (entire surface grinding step S30).

[0084] Figure 5 is a side view showing the grinding stone and the like in the entire surface grinding step S30. The rotational speeds of the spindle 38 and the chuck table 18 and the grinding in-feed speed are the same as those in the groove removal step S20.

[0085] In the surface grinding step S30, the back surface 11b side is ground (1st surface grinding) using the grinding unit 34a mainly using the bottom surface 48a of the grinding tool 48 while the thickness of the workpiece 11 is measured using the thickness gauge 50 until the workpiece 11 becomes a prescribed thickness thicker than the finished thickness.

[0086] In the groove removal step S20, the workpiece 11 is ground mainly using the inner peripheral side surface 48b and the outer peripheral side surface 48c of the grinding tool 48, and therefore, in the surface grinding step S30, the deterioration of the state of the bottom surface 48a of the grinding tool 48 is mitigated (i.e., the state is relatively good). Therefore, even in the case where the relatively hard oxide film is formed on the back surface 11b side, the occurrence of processing defects can be suppressed.

[0087] After the workpiece 11 is thinned to the prescribed thickness using the grinding unit 34a, the rotary table 16 is rotated, and the workpiece 11 is positioned at the finish grinding position C. Then, the workpiece 11 is ground (2nd surface grinding) using the grinding unit 34b while the thickness of the workpiece 11 is measured using the thickness gauge 50.

[0088] In the 2nd surface grinding, after the workpiece 11 is thinned until the workpiece 11 becomes the finished thickness, the surface grinding step S30 is ended, the rotary table 16 is rotated, and the workpiece 11 is positioned at the carry-in / carry-out position A.

[0089] The workpiece 11 is carried to the cleaning unit 56 by the unloading arm 54, and the workpiece 11 cleaned using the cleaning unit 56 is carried into the cassette 10b by the robot arm 6. In addition, Figure 6 is a flowchart showing the grinding method of the present embodiment.

[0090] As described above, the grinding method of the workpiece 11 of the present embodiment has: a groove forming step S10 of forming a circular-arc-shaped groove 11c; a groove removal step S20 of rotating the chuck table 18 while keeping the state of rotating the spindle 38 unchanged, thereby grinding the side wall 11d of the groove 11c and removing the groove 11c; and a surface grinding step S30.

[0091] In the groove forming step S10, the grinding is mainly performed using the bottom surface 48a of the grinding tool 48, but in the groove removal step S20, the grinding can be mainly performed using the inner peripheral side surface 48b and the outer peripheral side surface 48c of the grinding tool 48.

[0092] Therefore, compared to a case where the entire back surface 1 lb side is ground mainly using the bottom surface 48a of the grinding tool 48, it is possible to alleviate the deterioration of the condition of the bottom surface 48a of the grinding tool 48. Therefore, in the entire surface grinding step S30 where grinding is performed mainly using the bottom surface 48a of the grinding tool 48, it is possible to suppress the occurrence of processing defects of the workpiece 11.

[0093] Next, the use of Figure 7 An experiment comparing the grinding method of the present embodiment with a conventional grinding method will be described. In the experiment, a silicon wafer (about 200 mm in diameter and about 725 μm in thickness) having a thermal oxidation film of about 1 μm in thickness formed on the back surface 1 lb side was used as the workpiece 11.

[0094] In addition, as the grinding unit, a grinding unit 34b was used, which was provided with a grinding wheel 44b having a grinding tool 48 in which diamond abrasive grains of a particle size #3000 were fixed with a ceramic adhesive.

[0095] Figure 7 is a graph Dl (solid line) and D2 (dotted line) showing the time change of the current value of the motor that drives the spindle 38, and a graph El (dotted line) and E2 (single dotted line) showing the time change of the rotational speed of the chuck table 18.

[0096] The conventional grinding method is a method in which the back surface 1 lb side is ground mainly using the bottom surface 48a of the grinding tool 48 all the time without forming the groove 11c. In the conventional grinding method, as shown in the graph E2, the rotational speed of the chuck table 18 was constant at 100 rpm from time 0 to time t4.

[0097] On the other hand, in the grinding method of the present embodiment, as shown in the graph El, the chuck table 18 was not rotated and was stationary from time 0 to time t2 (groove forming step S10), and the chuck table 18 was started to rotate at time t2 (groove removing step S20). Then, the rotational speed was maintained at 100 rpm until time exceeded 150 seconds (entire surface grinding step S30).

[0098] In both the grinding method of the present embodiment and the conventional method, the grinding feed speed of the grinding unit 34b disposed above the chuck table 18 was set to 0.5 μm / sec. In addition, in both the grinding method of the conventional method and the present embodiment, the bottom surface 48a of the grinding tool 48 was brought into contact with the back surface 1 lb at time tl, and the grinding was started.

[0099] ​In the conventional grinding method, the current value gradually increases (refer to graph D2). The grinding feed is stopped at time t4, and the grinding is ended. From the rising of the current value from time 120 seconds to time t4, it is known that in the conventional grinding method, the processing load of the grinding tool 48 becomes relatively high.

[0100] On the other hand, in the grinding method of the present embodiment, during the period from time t1 to time t2, the groove formation step S10 is performed, and the groove 11c is formed (groove formation step S10). Next, the state of rotating the spindle 38 is maintained, and the chuck table 18 is started to rotate at time t2 (groove removal step S20).

[0101] As shown in graph D1, at time t2, the current value rises in a sharp peak, but the current value does not reach the allowable upper limit value and immediately starts to decrease. From this time t2 to time t3, it corresponds to the groove removal step S20.

[0102] From time t2 to time t3, it is about 1 second, which is the time during which the chuck table 18 can rotate approximately one and a half turns. That is, the groove 11c is removed during the period during which the chuck table 18 rotates approximately one and a half turns.

[0103] From time t3 to time t4, it corresponds to the whole surface grinding step S30. In the whole surface grinding step S30, the condition of the bottom surface 48a of the grinding tool 48 is relatively good compared to the conventional grinding method, and thus the grinding load (i.e., the current value) becomes relatively low. In addition, in the whole surface grinding step S30, it is considered that the self-sharpening of the grinding tool 48 is also effectively generated.

[0104] In this way, in the experiment, the effectiveness of the grinding method of the present embodiment is confirmed. In addition, at time t4, the grinding feed is stopped, and the grinding is ended. From time t4 to time t5, it is in a state in which the grinding tool 48 is not in contact with the back surface 11b and is idling.

[0105] Furthermore, the configuration, method, and the like of the above-described embodiment can be appropriately changed and implemented as long as it does not deviate from the scope of the object of the present application. For example, in the above-described embodiment, in the groove removal step S20, the grinding unit 34a is subjected to the grinding feed, but as long as the groove 11c can be removed, it can also be possible not to perform the grinding feed.

Claims

1. A grinding method of a workpiece, which grinds a workpiece using a grinding device having: a chuck table which holds the workpiece; and a grinding unit which has a spindle on which a grinding wheel having a plurality of grinding stones arranged in a ring shape is mounted, and grinds the workpiece held by the chuck table in a state in which the grinding wheel is rotated about the spindle, characterized by comprising: a groove forming step of grinding the workpiece while feeding the grinding unit in a state in which the chuck table holding the workpiece is not rotated, thereby forming a circular-arc-shaped groove having a depth which does not reach a finished thickness on a back surface side of the workpiece; a groove removing step of removing the groove from the workpiece by grinding a side wall of the groove while starting rotation of the chuck table in a state in which the rotation of the spindle is maintained after the groove forming step; and a full-face grinding step of grinding the entire back surface side of the workpiece until the workpiece becomes the finished thickness while feeding the grinding unit in a state in which the chuck table and the spindle are rotated after the groove removing step. a chuck table that holds the workpiece; 2. The grinding method of a workpiece according to claim 1, characterized in that, in the groove removing step, the chuck table is rotated while the grinding unit is fed. ​ ​ ​ ​ ​ ​ ​ ​

Images