Workpiece processing method

Abstract

To reduce partial peeling of a coating layer when edge trimming is performed.SOLUTION: A processing method for a workpiece having a substrate with a chamfered portion on its outer periphery and a coating layer provided on one surface of the substrate including the outer periphery includes a first cutting step of cutting the lower end of the cutting edge of a first cutting blade into the outer periphery of the workpiece at a depth corresponding to or deeper than the thickness of the coating layer, thereby forming a first annular step portion on the outer periphery of the workpiece, and a second cutting step of positioning one surface of the cutting edge of a second cutting blade that is closer to the rotation axis of the holding surface in a planar view of the holding surface on the inner periphery of the first step portion or positioned further outward than the inner periphery, thereby forming a second annular step portion on the outer periphery of the workpiece, in the second cutting step, the second depth from the bottom surface of the first step portion to the lower end of the cutting edge of the second cutting blade is made greater than the first depth from the surface of the workpiece to the bottom surface of the first step portion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for processing a workpiece having a substrate with a chamfered portion on its outer periphery and a coating layer provided on one surface of the substrate including the outer periphery of the substrate, with the coating layer exposed on the surface, and particularly to edge trimming for removing the chamfered portion on the surface of the workpiece. [Background technology]

[0002] A semiconductor wafer (i.e., workpiece) having a disk-shaped silicon single crystal substrate usually has chamfered portions (also called bevel portions) formed on the outer periphery of each of its front and back surfaces. Therefore, when the back surface of the workpiece is ground to thin the workpiece to, for example, half or less of its original thickness, a so-called knife edge (also called sharp edge) is formed on the outer periphery of the workpiece.

[0003] In order to prevent the formation of a knife edge in the workpiece after thinning, a method has been proposed in which the chamfered portion on the outer periphery of the front surface is removed by cutting it with an annular cutting blade prior to grinding the back surface, a method known as edge trimming (see, for example, Patent Document 1).

[0004] Incidentally, devices such as ICs (Integrated Circuits) and LEDs (Light Emitting Diodes) may be provided on the surface of the workpiece. In such cases, a coating layer such as an oxide film is provided on the entire surface, including the chamfered portion, to protect or electrically insulate the devices.

[0005] When edge trimming is performed on a workpiece having a coating layer on its surface, there is a problem that the outer periphery of the coating layer is partially peeled off during the edge trimming. In particular, the coating layer comes into contact with a substantially flat surface of the cutting blade, rather than the outer peripheral side surface of the cutting blade that mainly contributes to cutting, resulting in partial peeling (i.e., chipping) on ​​the outer periphery of the coating layer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-173961 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above problems, and aims to reduce partial peeling of a coating layer when edge trimming is performed on the surface of a workpiece in which the coating layer is exposed on the surface. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided a method for processing a workpiece having a substrate with a chamfered portion on its outer periphery and a coating layer provided on one surface of the substrate including the outer periphery, with the coating layer exposed on the surface, the method comprising the steps of: holding a back surface of the workpiece, the back surface being located opposite the front surface in the thickness direction of the workpiece, on a holding surface of a chuck table that is rotatable around a predetermined rotation axis; and, after the holding step, cutting a bottom end of a cutting edge of a first cutting blade attached to a tip of a first spindle that is disposed longitudinally along the holding surface into the outer periphery of the workpiece at a depth position corresponding to the thickness of the coating layer or at a depth deeper than the depth position corresponding to the thickness of the coating layer, by rotating the chuck table around the predetermined rotation axis. The present invention provides a method for processing a workpiece, comprising: a first cutting step for forming a ring-shaped first step portion on the outer periphery; and a second cutting step for, after the first cutting step, positioning one surface of a cutting edge of a second cutting blade attached to the tip of a second spindle whose longitudinal direction is arranged along the holding surface, which surface is closer to the predetermined rotation axis in a planar view of the holding surface, at the inner periphery of the first step portion or outward from the inner periphery edge in the radial direction of the workpiece, and rotating the chuck table around the predetermined rotation axis, thereby forming a ring-shaped second step portion on the outer periphery of the workpiece, wherein in the second cutting step, a second depth from the bottom surface of the first step portion to the lower end of the cutting edge of the second cutting blade is made larger than a first depth from the surface of the workpiece to the bottom surface of the first step portion.

[0009] Preferably, a first cutting volume removed by the first cutting blade cutting the workpiece in the first cutting step is smaller than a second cutting volume removed by the second cutting blade cutting the workpiece in the second cutting step.

[0010] Preferably, in the second cutting step, an inner annular region of the bottom surface of the first step portion that is located radially inward is left uncut, and an outer annular region of the bottom surface of the first step portion that is located radially outward of the inner annular region is cut.

[0011] Also preferably, the first cutting blade and the second cutting blade are identical, and the first spindle and the second spindle are identical.

[0012] Preferably, the method for cutting a workpiece further includes, after the second cutting step, a grinding step of thinning the workpiece by removing the back surface of the workpiece by grinding until the thickness of the workpiece becomes equal to or less than the thickness from the front surface to the bottom surface of the second step portion. [Effects of the Invention]

[0013] In a method for processing a workpiece according to one aspect of the present invention, edge trimming is performed in two stages: a first cutting step and a second cutting step. In the first cutting step, a first annular step having a first depth is formed on the outer periphery of the workpiece, and a coating layer is removed at this first step.

[0014] In the subsequent second cutting process, one face of the cutting blade located closer to the rotation axis of the chuck table is positioned on the inner periphery of the first step portion or outside the inner periphery in the radial direction of the workpiece, and a second annular step portion is formed.

[0015] In particular, in the second cutting step, the second depth from the bottom surface of the first step portion to the lower end of the cutting edge of the second cutting blade is set to be greater than the first depth from the surface of the workpiece to the bottom surface of the first step portion in the first cutting step. In other words, the cutting depth of the cutting blade in the first cutting step is relatively shallow.

[0016] Unlike the outer peripheral side surface of the cutting blade, which mainly contributes to cutting, the abrasive grains do not usually protrude properly from the one surface of the cutting blade, so cutting the coating layer with the one surface of the cutting blade can lead to peeling of the coating layer.

[0017] In contrast, in a method for processing a workpiece according to one aspect of the present invention, a relatively shallow first step portion is formed in the first cutting step, thereby reducing the contact length between one surface of the cutting blade and the coating layer. This reduces the area of ​​the coating layer cut by one surface of the cutting blade, thereby reducing partial peeling of the coating layer.

[0018] Furthermore, in the second cutting step, one surface of the cutting blade is positioned on the inner periphery of the first step portion or on the outer side of the inner periphery, so the coating layer is not substantially cut by the one surface of the cutting blade. Therefore, peeling of the coating layer in the second cutting step can be substantially eliminated. In this way, partial peeling of the coating layer can be reduced. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a flow diagram of a method for processing a workpiece. [Figure 2] FIG. 2(A) is a top view of the workpiece, and FIG. 2(B) is a cross-sectional view taken along line A-A of FIG. 2(A). [Figure 3] FIG. 3(A) is a top view of the holding step, and FIG. 3(B) is a partial cross-sectional side view of the holding step. [Figure 4] FIG. 4(A) is a top view of the first cutting step, and FIG. 4(B) is a partially cross-sectional side view of the first cutting step. [Figure 5] FIG. 5(A) is a cross-sectional view showing the outer periphery of the workpiece after the first cutting step, and FIG. 5(B) is a cross-sectional view showing a modified example of the outer periphery of the workpiece after the first cutting step according to a modified example. [Figure 6] Figure 6(A) is a side view of the workpiece when edge trimming is performed with a relatively deep cutting depth, Figure 6(B) is a top view of the workpiece showing the contact length between one surface of the cutting blade and the coating layer in Figure 6(A), Figure 6(C) is a side view of the workpiece when edge trimming is performed with a relatively shallow cutting depth, and Figure 6(D) is a top view of the workpiece showing the contact length between one surface of the cutting blade and the coating layer in Figure 6(C). [Figure 7]Figure 7(A) is a top view of the workpiece showing how the coating layer is cut with one side of the cutting blade, and Figure 7(B) is a partially enlarged view of the outer periphery of the workpiece showing partial peeling of the coating layer. [Figure 8] FIG. 8(A) is a top view of the second cutting step, and FIG. 8(B) is a partially cross-sectional side view of the second cutting step. [Figure 9] FIG. 10 is a cross-sectional view of the outer periphery of the workpiece after the second cutting step. [Figure 10] FIG. 10(A) is a diagram showing the grinding step, and FIG. 10(B) is a cross-sectional view of the workpiece after the grinding step. [Figure 11] FIG. 11(A) is a cross-sectional view showing a first modified example of the second cutting step, and FIG. 11(B) is a cross-sectional view showing a second modified example of the second cutting step. [Figure 12] FIG. 12(A) is a top view of the first cutting step in the second embodiment, and FIG. 12(B) is a partially sectional side view of the first cutting step in the second embodiment. [Figure 13] Figure 13(A) is a cross-sectional view showing a first example of the outer periphery of the workpiece after the first cutting process, and Figure 13(B) is a cross-sectional view showing a second example of the outer periphery of the workpiece after the first cutting process. [Figure 14] Figure 14(A) is a cross-sectional view showing a first example of the outer periphery of the workpiece after the second cutting process, Figure 14(B) is a cross-sectional view showing a second example of the outer periphery of the workpiece after the second cutting process, and Figure 14(C) is a cross-sectional view showing a third example of the outer periphery of the workpiece after the second cutting process. DETAILED DESCRIPTION OF THE INVENTION

[0020] (First embodiment) An embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a flow diagram of a method for processing a workpiece 11 (see Figs. 2(A) and 2(B)). As shown in Fig. 1, in this embodiment, the steps of a holding step S10, a first cutting step S20, a second cutting step S30, and a grinding step S40 are performed in this order.

[0021] Fig. 2(A) is a top view of workpiece 11, and Fig. 2(B) is a cross-sectional view taken along line A-A of Fig. 2(A). Workpiece 11 includes a silicon single crystal substrate (substrate) 13 having a predetermined diameter. Silicon single crystal substrate 13 has circular one surface 13a and another surface 13b located on opposite sides in the thickness direction.

[0022] A plurality of devices (not shown) such as ICs are formed in circular regions including the central portion of one surface 13a of silicon single crystal substrate 13. A chamfered portion 13c1 is formed in the outer peripheral portion of one surface 13a located outside the circular region including the central portion.

[0023] The chamfered portion 13c1 is formed over the entire circumferential direction of the one surface 13a. When the one surface 13a is viewed from above, the chamfered portion 13c1 is formed in an annular region of 1,000 μm or less from the outermost periphery of the one surface 13a toward the center of the one surface 13a (in one example, a range of about 500 μm from the outermost periphery of the one surface 13a).

[0024] No device is formed on the other surface 13b of the silicon single crystal substrate 13. A chamfered portion 13c2 is formed on the outer periphery of the other surface 13b, which is located outside a circular region including the center. For ease of explanation, the chamfered portions 13c1 and 13c2 are exaggerated in Figure 2(B) and the following figures.

[0025] The chamfered portion 13c2 is also formed over the entire circumferential direction of the other surface 13b. When the other surface 13b is viewed from above, the chamfered portion 13c2 is also formed in an annular region of 1,000 μm or less from the outermost periphery of the other surface 13b toward the center of the other surface 13b (in one example, a range of approximately 500 μm from the outermost periphery of the one surface 13a). Note that, by subjecting the other surface 13b to grinding in the grinding step S40, the workpiece 11 is thinned.

[0026] A coating layer 15 such as an oxide film, nitride film, or metal film is provided on the entire surface 13a of the silicon single crystal substrate 13, including the chamfered portion 13c1. The oxide film, nitride film, metal film, or the like has a thickness of, for example, 1.0 μm or more and 3.0 μm or less.

[0027] In this embodiment in which a silicon single crystal substrate 13 is used, the oxide film is a silicon oxide (e.g., SiO2) film, and the nitride film is a silicon nitride (e.g., Si3N4) film. However, when a single crystal substrate made of a semiconductor material other than silicon is used instead of the silicon single crystal substrate 13, the materials of the oxide film and the nitride film are changed appropriately.

[0028] Oxide films, nitride films, etc. function as so-called passivation films, and have the function of reducing external damage to the device, damage to the device, and intrusion of impurities into the device (i.e., protecting the device), as well as the function of electrically insulating the device from the outside.

[0029] The covering layer 15 may have a single crystal layer including a device and thinned to about 10 μm instead of an oxide film, a nitride film, a metal film, etc. In this case, the workpiece 11 having the silicon single crystal substrate 13 and the covering layer 15 becomes a laminated wafer (i.e., WoW: Wafer on Wafer) in which device chips are stacked in the thickness direction 11c.

[0030] The coating layer 15 is exposed on the front surface 11a of the workpiece 11. The coating layer 15 is not provided on the other surface 13b of the silicon single crystal substrate 13. The other surface 13b of the silicon single crystal substrate 13 is exposed and corresponds to the back surface 11b of the workpiece 11. The back surface 11b is located on the opposite side to the front surface 11a in the thickness direction 11c of the workpiece 11.

[0031] Next, with reference to Figures 4(A) and 4(B), a description will be given of the cutting device 2 used in edge trimming of the workpiece 11. The X-axis, Y-axis, and Z-axis shown in Figures 4(A) and 4(B) are perpendicular to one another. The Z-axis is, for example, approximately parallel to the vertical direction.

[0032] The cutting device 2 has a disk-shaped chuck table 4. The chuck table 4 includes a cylindrical frame body 4a with a bottom. A disk-shaped recessed portion 4b is formed in the radial center of the frame body 4a. An annular suction groove 4c is provided on the upper surface of an annular protrusion of the frame body 4a located outside the recessed portion 4b.

[0033] A negative pressure is transmitted to the suction groove 4c from a vacuum device (not shown) such as a vacuum pump. The upper surface of the annular convex portion of the frame body 4a functions as a holding surface 4d that suction-holds the workpiece 11. The annular holding surface 4d is disposed approximately parallel to the XY plane formed by the X-axis and Y-axis of the cutting device 2.

[0034] In addition, instead of the chuck table 4 having an annular holding surface 4d, a chuck table (not shown) having a frame body with a disk-shaped recess and a porous substrate fixed to the recess of this frame body may be used.

[0035] In the chuck table having the porous substrate, the upper surface of the porous substrate and the upper surface of the frame are substantially flush with each other and form a holding surface that is substantially parallel to the XY plane. This holding surface holds substantially the entire back surface 11b of the workpiece 11 by suction.

[0036] As shown in Fig. 4(B), the upper end of a rotation shaft (predetermined rotation shaft) 4e is connected to the bottom of the chuck table 4. Rotational power is transmitted to the rotation shaft 4e from a motor (not shown). When the power is transmitted, the chuck table 4 rotates around the rotation shaft 4e (i.e., the rotation center 4e1).

[0037] Cutting units (first cutting unit, second cutting unit) 6 are arranged above the chuck table 4. The cutting units 6 have a spindle housing 8 whose longitudinal portion is arranged along the Y axis.

[0038] A portion of a cylindrical spindle (first spindle, second spindle) 10 is rotatably accommodated in the spindle housing 8 by an air bearing (i.e., a hydrostatic air bearing). The longitudinal direction of the spindle 10 is also aligned with the Y axis. In other words, the spindle 10 is aligned with the XY plane and the holding surface 4d.

[0039] A motor (not shown) is provided inside the spindle housing 8, and the spindle 10 can be rotated at high speed by the motor. The tip of the spindle 10 protrudes outside the spindle housing 8.

[0040] A disk-shaped receiving flange 12a is fixed to the tip of the spindle 10 by bolts (not shown) or the like. The receiving flange 12a has a cylindrical boss (not shown) at its radial center. The boss protrudes further than the tip of the spindle 10.

[0041] The boss portion of the receiving flange portion 12a has a circular opening into which the cutting blades (first cutting blade, second cutting blade) 14 are inserted. The cutting blades 14 of this embodiment are so-called hubless type (i.e., washer type) cutting blades, and are composed only of cutting edges containing abrasive grains, bonding material, etc.

[0042] The thickness of the cutting blade is larger than the thickness of cutting blades used in normal dicing (for example, less than 1 mm), and is, for example, a predetermined value of 1 mm or more and 3 mm or less. Note that the cutting blade is not limited to the hubless type, and a so-called hub-type cutting blade in which the cutting blade is fixed to one surface of a disk-shaped base made of metal may also be used.

[0043] The circular opening of the cutting blade 14 and the circular opening of the annular pressing flange 12b are inserted into the boss of the receiving flange 12a, successively. As a result, the receiving flange 12a and the annular pressing flange 12b sandwich the cutting blade 14. A male thread is formed at the tip of the boss.

[0044] The male thread of the boss portion is fastened to the female thread of the annular press nut 12c, which has a female thread formed on its annular inner surface. In this way, the cutting blade 14 is attached to the tip of the spindle 10 while being sandwiched between the receiving flange portion 12a and the press flange portion 12b.

[0045] Next, a method for processing the workpiece 11 will be described with reference to Fig. 3(A) to Fig. 10(B). Fig. 3(A) is a top view of the holding step S10, and Fig. 3(B) is a partially cross-sectional side view of the holding step S10.

[0046] In the holding step S10, the outer periphery of the back surface 11b of the workpiece 11 is suction-held by the holding surface 4d of the chuck table 4 so that the front surface 11a of the workpiece 11 is exposed upward. Note that the chuck table 4 may be the above-mentioned chuck table having a porous substrate.

[0047] After the holding step S10, the process proceeds to the first cutting step S20. Fig. 4(A) is a top view of the first cutting step S20, and Fig. 4(B) is a partially cross-sectional side view of the first cutting step S20. Fig. 5(A) is a cross-sectional view showing the outer periphery of the workpiece 11 after the first cutting step S20 and before the second cutting step S30.

[0048] In the first cutting step S20, the cutting blade 14 is rotated around the spindle 10 at high speed (e.g., 30,000 rpm), and the height position of the lower end of the rotating cutting blade 14 is positioned at a depth position Z1 (see FIG. 4(B)) corresponding to the thickness of the coating layer 15. The depth position Z1 is, for example, 1.0 μm or more and 3.0 μm or less from the surface 11a.

[0049] In addition, the position of one surface 14a of the cutting blade 14 in the Y-axis direction is adjusted to a predetermined position of 1 mm to 3 mm from the outer peripheral edge of the workpiece 11. The position of one surface 14a in the Y-axis direction corresponds to the inner peripheral edge 21 described later.

[0050] After alignment in the Z-axis and Y-axis directions, the chuck table 4 is translated in the X-axis direction, causing the cutting blade 14 to cut into the outer periphery of the workpiece 11 (i.e., performing a slide-in cut) until the extension line of the rotation center 10a of the spindle 10 intersects with the rotation center 4e1 of the chuck table 4 (see Figure 4(A)).

[0051] As a result, the lower end of the cutting blade 14 cuts into the outer periphery of the surface 11a of the workpiece 11 to a depth position Z1. In the Z-axis direction, the depth position Z1 with respect to the surface 11a corresponds to a first depth 19 (see FIG. 5(A)).

[0052] Next, rotation of the chuck table 4 is started. For example, the rotation angle per unit time of the rotation axis 4e is set to a predetermined value of 3° / s or more and 5° / s or less, and the cutting mode is down cutting. During cutting, cutting water such as pure water is supplied to the cutting point at a predetermined flow rate.

[0053] When the cutting blade 14 has a relatively large cutting edge thickness (i.e., the length in the Y-axis direction), a ring-shaped first step portion 17 (see FIG. 5(A)) can be formed on the outer periphery of the surface 11a of the workpiece 11 by rotating the chuck table 4 once around the rotation axis 4e. The bottom surface 23 of the first step portion 17 becomes one surface 13a of the silicon single crystal substrate 13.

[0054] In addition, if the cutting blade 14 has a relatively small cutting thickness, the first step portion 17 may be formed by rotating the chuck table 4 once, stopping the rotation of the chuck table 4, and then repeating slide-out, index feed, and slide-in cut in sequence.

[0055] Specifically, first, the chuck table 4 is moved along the X-axis direction to position the cutting blade 14 outside the holding surface 4d (i.e., slide out). Next, the cutting unit 6 is indexed and fed along the Y-axis direction away from the rotation center 4e1 by a length equivalent to the cutting thickness of the cutting blade 14. After that, the cutting blade 14 performs a slide-in cut again.

[0056] In addition, the cutting depth position of the cutting blade 14 is not limited to the above-mentioned embodiment. In the first cutting step S20, the lower end of the cutting blade 14 is positioned at a depth position Z deeper than the depth position corresponding to the thickness of the coating layer 15 and less than 100 μm from the surface 11 a. A It is also possible to cut into the hole (see FIG. 5(B)).

[0057] FIG. 5(B) is a cross-sectional view showing a modified example of the outer periphery of the workpiece 11 after the first cutting step S20 according to the modified example, in which the lower end of the cutting blade 14 is at a depth position Z A 17 shows a first step portion 17a formed by disposing the first step portion 17a in the

[0058] The bottom surface 23a of the first step portion 17a is located closer to the other surface 13b of the silicon single crystal substrate 13 than to the one surface 13a. A is, for example, 8.0 μm from the surface 11a, but at a depth position Z A may be set to N times the thickness of the coating layer 15 (N is a natural number of 2 or more).

[0059] In edge trimming, due to the nature of machining, the cutting depth may fluctuate in the circumferential direction of the workpiece 11. However, by making the lower end of the cutting blade 14 sufficiently deeper than the depth position corresponding to the thickness of the coating layer 15, it is possible to completely remove the coating layer 15 at the first step portion 17a even if fluctuations in the cutting depth occur.

[0060] Here, referring to Figures 6(A) to 6(D) and Figures 7(A) and 7(B), we will explain the partial peeling of the coating layer 15 that occurs when cutting the coating layer 15 with one surface 14a of the cutting blade 14.

[0061] Figure 6(A) is a side view of the workpiece 11 when edge trimming is performed with a relatively deep cutting depth, and corresponds to the case where the lower end of the cutting blade 14 in the first cutting step S20 is set to depth position Z2 in the second cutting step S30 described below.

[0062] FIG. 6(B) shows the contact length L between the surface 14a of the cutting blade 14 and the coating layer 15 in FIG. 6(A). A 6A and 6B are top views of the workpiece 11 showing the contact length L A It is drawn thickly to emphasize the line.

[0063] The annular region S in Figure 6(B) A is the contact length L in the XY plane when the chuck table 4 is rotated with the cutting blade 14 fixed in position. A This indicates the area through which the line segment indicated by is passed.

[0064] 6(B), if the cutting blade 14 is cut relatively deeply in the first cutting step S20, the area of ​​the coating layer 15 cut by the one surface 14a of the cutting blade 14 becomes relatively large, which makes it easier for partial peeling of the coating layer 15 to occur.

[0065] FIG. 6(C) is a side view of the workpiece 11 when edge trimming is performed with a relatively shallow cutting depth, and corresponds to the case where the lower end of the cutting blade 14 is at depth position Z1 in the first cutting step S20.

[0066] FIG. 6(D) shows the contact length L between the surface 14a of the cutting blade 14 and the coating layer 15 in FIG. 6(C). B 6(C) and 6(D) are top views of the workpiece 11. B It emphasizes:

[0067] The annular region S in Figure 6(D) B is the contact length L in the XY plane when the chuck table 4 is rotated with the cutting blade 14 fixed in position. B This indicates the area through which the line segment indicated by is passed.

[0068] As shown in Fig. 6(D), when the cutting blade 14 is cut relatively shallowly in the first cutting step S20, the area of ​​the coating layer 15 cut by the one surface 14a of the cutting blade 14 is relatively small. Therefore, compared to the case shown in Fig. 6(B), partial peeling of the coating layer 15 is less likely to occur.

[0069] Fig. 7(A) is a top view of the workpiece 11 showing how the coating layer 15 is cut with one surface 14a of the cutting blade 14. Fig. 7(B) is a partially enlarged view of the outer periphery of the workpiece 11 showing partial peeling of the coating layer 15 caused by the cutting shown in Fig. 7(A).

[0070] 7(A), during cutting, as the chuck table 4 rotates, the coating layer 15 moves toward one surface 14a of the cutting blade 14 that has cut into the workpiece 11. As described above, unlike the outer peripheral side surface of the cutting blade 14, abrasive grains do not normally protrude appropriately from one surface 14a of the cutting blade 14.

[0071] When the coating layer 15 is cut on the surface 14a where the abrasive grains do not protrude properly (region R in FIG. 7(A)), A 7B), which leads to partial peeling of the coating layer 15 (the chipped region R B reference).

[0072] In this embodiment, by forming a relatively shallow first step portion 17 in the first cutting process S20 (see Figures 6(C) and 6(D)), the contact length between one surface 14a of the cutting blade 14 and the coating layer 15 can be reduced compared to when the first step portion 17 is made deeper (see Figures 6(A) and 6(B)).

[0073] In this way, by making the first step portion 17 formed in the first cutting step S20 shallower, the area of ​​the coating layer 15 cut by one surface 14a of the cutting blade 14 can be reduced, thereby reducing partial peeling of the coating layer 15.

[0074] After the first cutting step S20, a second cutting step S30 is performed (see FIGS. 8A and 8B). In the second cutting step S30 of this embodiment, the above-described cutting unit 6 is used to form an annular second step portion 27 that is deeper than the first step portion 17 on the outer periphery of the workpiece 11 (see FIG. 9).

[0075] In the second cutting step S30 of this embodiment, the same cutting unit 6 as in the first cutting step S20 is used. That is, in this embodiment, the first cutting blade used in the first cutting step S20 and the second cutting blade used in the second cutting step S30 are the same, and the first spindle used in the first cutting step S20 and the second spindle used in the second cutting step S30 are the same.

[0076] Fig. 8(A) is a top view of the second cutting step S30, and Fig. 8(B) is a partially cross-sectional side view of the second cutting step S30. Fig. 9 is a cross-sectional view of the outer periphery of the workpiece 11 after the second cutting step S30.

[0077] In the second cutting step S30, the cutting blade 14 is rotated around the spindle 10 at high speed (e.g., 30,000 rpm), and the height position of the lower end of the rotating cutting blade 14 is positioned at a depth position Z2. The depth position Z2 is, for example, 100 μm or more and 150 μm or less from the surface 11 a.

[0078] Then, by adjusting the position of the cutting unit 6 in the Y-axis direction, one surface 14a of the cutting edge of the cutting blade 14 that is closer to the rotation axis 4e in a planar view of the holding surface 4d is positioned on the inner peripheral edge 21 of the first step portion 17 (see Figure 9).

[0079] Next, the chuck table 4 is translated in the X-axis direction to cause the cutting blade 14 to cut into the outer periphery of the workpiece 11 until the extension line of the rotation center 10a of the spindle 10 intersects with the rotation center 4e1 of the chuck table 4 (i.e., a slide-in cut is performed).

[0080] Thereafter, the rotation of the chuck table 4 is started. For example, the rotation angle per unit time of the rotation axis 4e is set to a predetermined value of 3° / s or more and 5° / s or less, and the cutting mode is down cutting.

[0081] During cutting, cutting water such as pure water is supplied to the cutting point at a predetermined flow rate. If the cutting blade 14 has a relatively large cutting thickness (i.e., the length in the Y-axis direction), the second step portion 27 can be formed by rotating the chuck table 4 once around the rotation axis 4e.

[0082] In addition, if the cutting blade 14 has a relatively small cutting thickness, the chuck table 4 may be rotated once, and then the rotation of the chuck table 4 may be stopped, followed by sequentially repeating the following: slide-out, indexing feed in a direction away from the rotation center 4e1, and slide-in cutting.

[0083] In particular, in the second cutting process S30, the second depth 29 from the bottom surface 23 of the first step portion 17 to the lower end of the cutting edge of the cutting blade 14 is made larger than the first depth 19 from the surface 11a of the workpiece 11 to the bottom surface 23 of the first step portion 17 (see Figure 9).

[0084] In one example, the first depth 19 is 3.0 μm and the second depth 29 is 97 μm (= 100 μm - 3.0 μm), and in another example, the first depth 19 is 1.0 μm and the second depth 29 is 149 μm (= 150 μm - 1.0 μm). In other words, the second depth 29 is several tens of times larger than the first depth 19.

[0085] Therefore, the second cutting volume V2 removed by the cutting blade 14 cutting the workpiece 11 in the second cutting step S30 can be made larger than the first cutting volume V1 removed by the cutting blade 14 cutting the workpiece 11 in the first cutting step S20 (see FIG. 9). In other words, the first cutting volume V1 is smaller than the second cutting volume V2.

[0086] In this embodiment, forming a relatively shallow first step portion 17 in the first cutting step S20 reduces the contact length between the one surface 14a of the cutting blade 14 and the coating layer 15. Therefore, the area of ​​the coating layer 15 cut by the one surface 14a of the cutting blade 14 can be reduced, thereby reducing partial peeling of the coating layer 15.

[0087] Furthermore, in the second cutting step S30, one surface 14a of the cutting blade 14 is positioned on the inner peripheral edge 21 of the first step portion 17, so that the coating layer 15 is not substantially cut by the one surface 14a of the cutting blade 14. Therefore, peeling of the coating layer 15 in the second cutting step S30 can be substantially eliminated. In this way, partial peeling of the coating layer 15 can be reduced.

[0088] After the second cutting step S30, the workpiece 11 is thinned by performing a grinding step S40. Fig. 10(A) is a diagram showing the grinding step S40. In the grinding step S40, a grinding device 22 is used. The grinding device 22 has a disk-shaped chuck table 24 that holds the workpiece 11 by suction.

[0089] The chuck table 24 has a disk-shaped frame. A disk-shaped recess is formed in the radial center of the frame, and a disk-shaped porous substrate is fixed in this recess. The upper surface of the frame and the upper surface of the porous substrate are substantially flush with each other and form the holding surface of the chuck table 24.

[0090] A negative pressure is transmitted from a vacuum device (not shown) to the holding surface of the chuck table 24, and the workpiece 11 is sucked and held by the holding surface due to this negative pressure. The holding surface has a conical shape with the center protruding slightly (for example, by about 20 μm) compared to the outer periphery.

[0091] The chuck table 24 is rotatably supported around a rotation shaft 24a. The chuck table 24 is rotated around the rotation shaft 24a by a motor (not shown). The chuck table 24 is rotatably supported by a table base.

[0092] The tilt of the table base is adjusted to adjust the tilt of the chuck table 24 and the rotation axis 24a. The rotation axis 24a is tilted at a small angle with respect to the Z-axis direction so that part of the holding surface is approximately parallel to the XY plane.

[0093] A grinding unit 26 is provided above the chuck table 24. The grinding unit 26 has a spindle housing (not shown) whose longitudinal direction is arranged along the Z-axis. A portion of a spindle 28 whose longitudinal direction is arranged along the Z-axis is rotatably housed in the spindle housing.

[0094] The lower end of the spindle 28 protrudes downward beyond the lower end of the spindle housing. A disk-shaped mount 30 is fixed to the lower end of the spindle 28. An annular grinding wheel 32 is attached to the underside of the mount 30 by bolts or the like (not shown).

[0095] The grinding wheel 32 has a metal, annular base 32a. On one surface of the base 32a, a plurality of grinding stones 32b are arranged at approximately equal intervals along the circumferential direction of the base 32a. When the grinding wheel 32 is rotated around the spindle 28, the movement locus of the lower surfaces of the plurality of grinding stones 32b forms an annular grinding surface that is approximately parallel to the XY plane.

[0096] When grinding the back surface 11b of the workpiece 11, the chuck table 24 is rotated at a predetermined rotational speed (e.g., 300 rpm), and the grinding wheel 32 is rotated at a predetermined rotational speed (e.g., 3,000 rpm). In this state, the grinding unit 26 is fed downward for grinding at a predetermined speed (e.g., 3.0 μm / s).

[0097] 10(B) is a cross-sectional view of the workpiece 11 after the grinding step S40. In the grinding step S40, the back surface 11b of the workpiece 11 is removed by grinding until the thickness of the workpiece 11 is equal to or less than the thickness from the front surface 11a to the bottom surface 33 of the second step portion 27, thereby thinning the workpiece 11.

[0098] As described above, abrasive grains do not normally protrude appropriately from the surface 14a of the cutting blade 14, unlike the outer peripheral side surface of the cutting blade 14, which mainly contributes to cutting. Therefore, cutting the coating layer 15 with the surface 14a of the cutting blade 14 can lead to peeling of the coating layer 15.

[0099] In contrast to this, in the first cutting step S20 of this embodiment, by forming a relatively shallow first step portion 17, it is possible to reduce the contact length between one surface 14a of the cutting blade 14 and the coating layer 15. Therefore, it is possible to reduce the range in which the one surface 14a of the cutting blade 14 cuts the coating layer 15, thereby reducing partial peeling of the coating layer 15.

[0100] Furthermore, in the second cutting step S30, one surface 14a of the cutting blade 14 is positioned on the inner peripheral edge 21 of the first step portion 17, so that the coating layer 15 is not substantially cut by the one surface 14a of the cutting blade 14. Therefore, peeling of the coating layer 15 in the second cutting step S30 can be substantially eliminated. In this way, partial peeling of the coating layer 15 can be reduced.

[0101] 11A is a cross-sectional view showing a first modified example of the second cutting step S30. In the first modified example of the second cutting step S30, one surface 14a of the cutting edge of the cutting blade 14 is positioned radially outward of the inner peripheral edge 21 of the workpiece 11, and the chuck table 4 is rotated around the rotation axis 4e to form the second step portion 27.

[0102] As a result, in the second cutting process S30, the inner annular region 31a of the bottom surface 23 of the first step portion 17, which is located radially inside the workpiece 11, is left uncut, and the outer annular region 31b of the bottom surface 23 of the first step portion 17, which is located radially outside the inner annular region 31a, is cut and removed.

[0103] In the first modified example, one surface 14a of cutting blade 14 is spaced apart from inner peripheral edge 21 of first step portion 17, so that partial peeling of coating layer 15 that may occur in the second cutting step S30 described above can be completely prevented.

[0104] (Second Modification of Second Cutting Step S30) Figure 11(B) is a cross-sectional view showing a second modification of the second cutting step S30. Figure 11(B) shows a case where the first modification of the second cutting step S30 (see Figure 11(A)) is applied to the workpiece 11 that has undergone the first cutting step S20 (see Figure 5(B)) according to the modification.

[0105] Second Embodiment Next, a second embodiment will be described with reference to Figures 12(A) to 14(C). In the second embodiment, a cutting device 34 is used, which is a dicing saw with a parallel dual structure in which two spindles are arranged in parallel.

[0106] As shown in Figure 12(A), the cutting device 34 includes a cutting unit 36 ​​as a first cutting unit used in the first cutting process S20, and a cutting unit 6 (see Figure 4(A), not shown in Figure 12(A)) as a second cutting unit used in the second cutting process S30.

[0107] The cutting unit 36 ​​is also disposed above the chuck table 4. The cutting unit 36 ​​has a spindle housing 38 whose longitudinal portion is disposed along the Y axis. A portion of a cylindrical spindle (first spindle) 40 is housed in the spindle housing 38 so that the spindle can rotate via an air bearing (i.e., a hydrostatic air bearing).

[0108] The longitudinal direction of the spindle 40 is also aligned along the Y-axis. In other words, the spindle 40 is aligned along the XY plane and the holding surface 4d. A motor (not shown) is provided inside the spindle housing 38, and the spindle 40 can be rotated at high speed by the motor. The tip of the spindle 40 protrudes outside the spindle housing 8.

[0109] A disk-shaped receiving flange 42a is fixed to the tip of the spindle 40 by bolts (not shown) or the like. The receiving flange 42a has a cylindrical boss (not shown) at its radial center. The boss protrudes further than the tip of the spindle 40.

[0110] A circular opening of the cutting blade (first cutting blade) 44 is inserted into this boss portion. The cutting blade 44 of this embodiment is a so-called hubless type (i.e., washer type) cutting blade, and is composed only of a cutting edge containing abrasive grains, a bond material, etc.

[0111] The thickness of the cutting edge of the cutting blade 44 is thinner than the thickness of the cutting edge of the cutting blade 14, for example, 0.1 mm. Note that the cutting blade is not limited to the hubless type, and a so-called hub-type cutting blade in which the cutting edge is fixed to one surface of a disk-shaped base made of metal may also be used.

[0112] The circular opening of the pressing flange portion 42b is inserted into the boss portion of the receiving flange portion 42a so that the receiving flange portion 42a and the annular pressing flange portion 42b sandwich the cutting blade 44. A male thread is formed at the tip of the boss portion.

[0113] The male thread of the boss portion has a female thread formed on its annular inner surface, and the female thread of the annular presser nut 42c is fastened to the male thread. In this way, the cutting blade 44 is attached to the tip of the spindle 40 while being sandwiched between the receiving flange portion 42a and the presser flange portion 42b.

[0114] As described above, the cutting unit 6 as the second cutting unit has the spindle 10 as the second spindle, and the cutting blade 44 as the second cutting blade is attached to the tip of the spindle 10.

[0115] In the second embodiment, the holding step S10, the first cutting step S20, the second cutting step S30, and the grinding step S40 are also performed in this order. The holding step S10 is performed using the cutting unit .

[0116] FIG. 12(A) is a top view of the first cutting step S20 in the second embodiment, and FIG. 12(B) is a partial cross-sectional side view of the first cutting step S20 in the second embodiment.

[0117] In the first cutting process S20, the cutting blade 44 is rotated around the spindle 40 at high speed (e.g., 30,000 rpm), and the height position of the lower end of the rotating cutting blade 44 is positioned at a depth position Z1 (see Figure 13(B)) corresponding to the thickness of the coating layer 15.

[0118] Then, by moving the chuck table 4 parallel to the X-axis direction, the cutting blade 44 is caused to cut into the outer periphery of the workpiece 11 (i.e., a slide-in cut is performed) until the extension line of the rotation center 40a of the spindle 40 intersects with the rotation center 4e1 of the chuck table 4 (see Figure 12(A)).

[0119] As a result, the lower end of the cutting blade 44 cuts into the outer periphery of the surface 11a of the workpiece 11 to a depth position Z1 that corresponds to the thickness of the coating layer 15. In the Z-axis direction, the depth position Z1 with the surface 11a as the reference corresponds to the first depth 19. Next, rotation of the chuck table 4 begins.

[0120] For example, the rotation angle of the rotary shaft 4e per unit time is set to a predetermined value of 3° / s or more and 5° / s or less, and the cutting mode is down-cut. During cutting, cutting water such as pure water is supplied to the cutting point at a predetermined flow rate. The first step portion 17 is formed by rotating the chuck table 4 around the rotary shaft 4e at least once.

[0121] In the second embodiment, too, by forming a relatively shallow first step portion 17 in the first cutting step S20, it is possible to reduce the contact length between one surface 44a of the cutting blade 44 and the coating layer 15. Therefore, it is possible to reduce the range of cutting of the coating layer 15 by one surface 44a of the cutting blade 44, and thus it is possible to reduce partial peeling of the coating layer 15.

[0122] 13(A) is a cross-sectional view showing a first example of the outer periphery of the workpiece 11 after the first cutting step S20 in the second embodiment. Note that the cutting depth position of the cutting blade 44 is not limited to the aspect shown in FIG. 13(A).

[0123] 13B is a cross-sectional view showing a second example of the outer periphery of the workpiece 11 after the first cutting step S20 in the second embodiment. In the example shown in FIG. 13B, in the first cutting step S20, the lower end of the cutting blade 44 is positioned at a depth Z deeper than the depth corresponding to the thickness of the coating layer 15 and less than 100 μm from the surface 11 a. A Cut to.

[0124] After the first cutting step S20, a second cutting step S30 is performed. In the second cutting step S30 of this embodiment, a cutting unit 6 having a spindle 10 and a cutting blade 14 forms an annular second step portion 27 that is deeper than the first step portion 17 on the outer periphery of the workpiece 11 (see FIG. 14(A)).

[0125] In the second cutting step S30, the cutting blade 14 is rotated around the spindle 10 at high speed (for example, 30,000 rpm), and the height position of the lower end of the rotating cutting blade 14 is positioned at depth position Z2 (see FIG. 14(A)).

[0126] Then, by adjusting the position of the cutting unit 6 in the Y-axis direction, one surface 14a of the cutting edge of the cutting blade 14 that is closer to the rotation axis 4e in a planar view of the holding surface 4d is positioned on the inner peripheral edge 21 of the first step portion 17.

[0127] Next, the chuck table 4 is translated in the X-axis direction to cause the cutting blade 14 to cut into the outer periphery of the workpiece 11 until the extension line of the rotation center 10a of the spindle 10 intersects with the rotation center 4e1 of the chuck table 4 (i.e., a slide-in cut is performed).

[0128] Thereafter, rotation of the chuck table 4 is started. For example, the rotation angle per unit time of the rotation axis 4e is set to a predetermined value of 3° / s or more and 5° / s or less, and the cutting mode is down-cut. During cutting, cutting water such as pure water is supplied to the cutting point at a predetermined flow rate.

[0129] When the cutting blade 14 has a relatively large cutting thickness (that is, the length in the Y-axis direction), the second step portion 27 can be formed by rotating the chuck table 4 once around the rotation axis 4e.

[0130] If the cutting blade 14 has a relatively small cutting thickness, the chuck table 4 may be rotated once, and then the rotation of the chuck table 4 may be stopped, followed by sequentially repeating the following: slide-out, indexing feed away from the rotation center 4e1, and slide-in cutting.

[0131] 14(A) is a cross-sectional view showing a first example of the outer periphery of the workpiece 11 after the second cutting step S30. In the second cutting step S30, the second depth 29 from the bottom surface 23 of the first step portion 17 to the lower end of the cutting edge of the cutting blade 14 is made larger than the first depth 19 from the surface 11a of the workpiece 11 to the bottom surface 23 of the first step portion 17.

[0132] Therefore, the second cutting volume V2 removed by the cutting blade 14 cutting the workpiece 11 in the second cutting step S30 can be made larger than the first cutting volume V1 removed by the cutting blade 14 cutting the workpiece 11 in the first cutting step S20. In other words, the first cutting volume V1 is smaller than the second cutting volume V2.

[0133] In the second cutting step S30, one surface 14a of the cutting blade 14 is positioned on the inner peripheral edge 21 of the first step portion 17, so that the coating layer 15 is not substantially cut by the one surface 14a of the cutting blade 14. Therefore, peeling of the coating layer 15 in the second cutting step S30 can be substantially eliminated. In this way, partial peeling of the coating layer 15 can be reduced.

[0134] After the second cutting step S30, a grinding step S40 is performed using a grinding device 22 shown in Fig. 10, thereby thinning the workpiece 11. Next, with reference to Figs. 14(B) and 14(C), another example of the second cutting step S30 of the second embodiment will be described.

[0135] 14(B) is a cross-sectional view showing a second example of the outer periphery of the workpiece 11 after the second cutting step S30 of the second embodiment. In this second example, one surface 14a of the cutting edge of the cutting blade 14 is positioned outside the inner periphery 21 in the radial direction of the workpiece 11, and the chuck table 4 is rotated around the rotation axis 4e to form the second step portion 27.

[0136] As a result, in the second cutting process S30, the inner annular region 31a of the bottom surface 23 of the first step portion 17, which is located radially inside the workpiece 11, is left uncut, and the outer annular region 31b of the bottom surface 23 of the first step portion 17, which is located radially outside the inner annular region 31a, is cut.

[0137] In the second example, one surface 14a of the cutting blade 14 is spaced apart from the inner peripheral edge 21 of the first step portion 17, so that partial peeling of the coating layer 15 that may occur in the second cutting step S30 of the first example can be completely prevented.

[0138] 14(C) is a cross-sectional view showing a third example of the outer periphery of the workpiece 11 after the second cutting step S30. In the third example, the inner annular region 31a is left uncut, and the outer annular region 31b located radially outward from the inner annular region 31a is cut, but the entire region outside the inner annular region 31a and from the surface 11a to the depth position Z2 is not removed.

[0139] As shown in Figure 14(C), even if an annular convex portion is left on the outer periphery of the surface 11a of the workpiece 11, if the back surface 11b is ground in the grinding step S40 to thin the workpiece 11 until it reaches the depth position Z2, the annular convex portion left in the second cutting step S30 will be removed from the workpiece 11.

[0140] 14(C), by reducing the cutting volume in the second cutting step S30, it is possible to reduce wear on the cutting blade 14. The reduced wear can extend the life of the cutting blade 14.

[0141] Incidentally, the cutting blade 44 of the cutting unit 36 ​​may have a cutting edge for rough cutting with a relatively large average grain size of abrasive grains, and the cutting blade 14 of the cutting unit 6 as the second cutting unit may have a cutting edge for finish cutting with a relatively small average grain size of abrasive grains.

[0142] Since the cutting blade for rough cutting has a higher cutting power than the cutting blade for finish cutting, by using the cutting blade 44 used in the first cutting step S20 for rough cutting, partial peeling of the coating layer 15 that occurs in the first cutting step S20 can be further reduced.

[0143] The abrasive grains used in the cutting blade for rough cutting have a predetermined grain size (e.g., #400) of #240 or more but less than #1500, and the abrasive grains used in the cutting blade for finish cutting have a predetermined grain size (e.g., #1500) of #1500 or more but less than #3000. Generally, the larger the number following the # in the grain size, the smaller the average grain size of the abrasive grain.

[0144] The particle size is specified in accordance with or conforms to JIS R 6001-2:2017 (Particle size of abrasives for grinding wheels - Part 2: Fine powder) as set forth in the JIS (Japanese Industrial Standards). The particle size is determined, for example, using a sedimentation tube test method, an electrical resistance test method, or the like.

[0145] The above describes several embodiments and modified aspects of each embodiment, but the structures, methods, etc. according to the above-described embodiments can be modified as appropriate without departing from the scope of the purpose of the present invention.

[0146] In the first embodiment, a first cutting step S20 may be performed using a first cutting device having a spindle 10 and a cutting blade 14, and then a second cutting step S30 may be performed using a second cutting device having a spindle corresponding to the spindle 10 and a cutting blade corresponding to the cutting blade 14 but different from the first cutting device.

[0147] In addition, in the second embodiment, instead of the cutting device 34, which is a dicing saw with a parallel dual structure, a first cutting device having a cutting unit 36 ​​as a first cutting unit and a chuck table 4 may be used in the first cutting process S20, and a second cutting device having a cutting unit 6 as a second cutting unit and a chuck table 4 may be used in the second cutting process S30.

[0148] Of course, in the second embodiment, the first cutting step S20 shown in Figure 13(B) may be combined with either the second cutting step S30 shown in Figure 14(B) or the second cutting step S30 shown in Figure 14(C). [Explanation of symbols]

[0149] 2:Cutting device 4: Chuck table 4a: Frame, 4b: Recess, 4c: Suction groove, 4d: Holding surface 4e: rotation axis (predetermined rotation axis), 4e1: rotation center 6: Cutting unit (1st cutting unit, 2nd cutting unit) 8: Spindle housing 10: Spindle (first spindle, second spindle), 10a: Rotation center 11: Workpiece, 11a: Front surface, 11b: Back surface, 11c: Thickness direction 12a: Receiving flange part 12b: Presser flange 12c: Presser nut 13: silicon single crystal substrate (substrate), 13a: one surface, 13b: other surface 13c1, 13c2: Chamfered part 14: cutting blade (first cutting blade, second cutting blade), 14a: one side 15: Covering layer 17, 17a: first step portion, 19: first depth 21: Inner edge 23,23a: Bottom 22: Grinding equipment 24: chuck table, 24a: rotation axis 26: Grinding unit, 28: Spindle, 30: Mount 27: second step portion, 29: second depth 31a: Inner annular region, 31b: Outer annular region 32: grinding wheel, 32a: base, 32b: grinding stone 33: Bottom 34: Cutting device, 36: Cutting unit 38: spindle housing, 40: spindle, 40a: rotation center 42a: Receiving flange part 42b: Presser flange 42c: Presser nut 44: cutting blade (first cutting blade), 44a: one side L A ,L B :Contact length R A ,R B :region S10: Holding process S20: 1st cutting process S30: 2nd cutting process S40: Grinding process S A ,S B : Annular region V1: First cutting volume, V2: Second cutting volume Z1, Z2, Z A : Depth position

Claims

1. A method for processing a workpiece having a substrate with a chamfered portion on an outer periphery and a coating layer provided on one surface of the substrate including the outer periphery, the coating layer being exposed on a surface thereof, comprising: a holding step of holding a back surface of the workpiece, which is located on the opposite side to the front surface in the thickness direction of the workpiece, with a holding surface of a chuck table that is rotatable around a predetermined rotation axis; a first cutting step in which, after the holding step, a lower end of a cutting edge of a first cutting blade attached to a tip of a first spindle whose longitudinal direction is arranged along the holding surface is cut into the outer periphery of the workpiece at a depth position corresponding to the thickness of the coating layer or a position deeper than the depth position corresponding to the thickness of the coating layer, and the chuck table is rotated around the predetermined rotation axis, thereby forming an annular first step portion on the outer periphery of the workpiece; a second cutting step in which, after the first cutting step, one surface of a cutting edge of a second cutting blade attached to the tip of a second spindle whose longitudinal direction is arranged along the holding surface, which surface is closer to the predetermined rotation axis in a plan view of the holding surface, is positioned on the inner peripheral edge of the first step portion or positioned outside the inner peripheral edge in the radial direction of the workpiece, and the chuck table is rotated around the predetermined rotation axis to form an annular second step portion on the outer periphery of the workpiece; Equipped with A method for processing a workpiece, characterized in that in the second cutting process, a second depth from the bottom surface of the first step portion to the lower end of the cutting edge of the second cutting blade is made larger than a first depth from the surface of the workpiece to the bottom surface of the first step portion.

2. 2. The method for processing a workpiece according to claim 1, wherein a first cutting volume removed by cutting the workpiece with the first cutting blade in the first cutting step is smaller than a second cutting volume removed by cutting the workpiece with the second cutting blade in the second cutting step.

3. The method for processing a workpiece according to claim 1 or 2, characterized in that in the second cutting step, an inner annular region of the bottom surface of the first step portion located radially inward is left uncut, and an outer annular region of the bottom surface of the first step portion located radially outward of the inner annular region is cut.

4. 2. The method for machining a workpiece according to claim 1, wherein the first cutting blade and the second cutting blade are identical, and the first spindle and the second spindle are identical.

5. 2. The method for processing a workpiece according to claim 1, further comprising, after the second cutting step, a grinding step of thinning the workpiece by removing the back surface of the workpiece by grinding until the thickness of the workpiece becomes equal to or less than the thickness from the front surface to the bottom surface of the second step portion.

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