Method for grinding a workpiece

Abstract

The present invention provides a workpiece grinding method that, when grinding a plate-shaped workpiece provided with a device on the front surface side from the back surface side, can suppress the probability of device breakage to be low without greatly extending the time required for completion of grinding. The workpiece grinding method includes the following steps: a first grinding step of grinding the workpiece from the back surface side to form a first thin plate portion in the shape of a circular plate and a first thick plate portion in the shape of a ring surrounding the first thin plate portion on the workpiece; a second grinding step of grinding the first thin plate portion from the back surface side after the first grinding step to form a second thin plate portion in the shape of a circular plate that is thinner and has a smaller diameter than the first thin plate portion and a second thick plate portion in the shape of a ring surrounding the second thin plate portion on the first thin plate portion; and a third grinding step of grinding the second thick plate portion and the second thin plate portion from the back surface side using a second grinding tool including abrasive grains that are smaller than the abrasive grains of the first grinding tool to form a third thin plate portion in the shape of a circular plate that is thinner and has a larger diameter than the second thin plate portion.

Description

Technical Field

[0001] The present invention relates to a grinding method for workpieces used in grinding plate-shaped workpieces such as wafers. Background Technology

[0002] In order to achieve small and lightweight device chips, there are increasing opportunities to thin wafers with integrated circuits and other devices on the front side. For example, by using a chuck stage to hold the front side of the wafer, a grinding wheel with an abrasive grain (grinding wheel) fixed on it and the chuck stage rotate relative to each other, while a liquid such as pure water is supplied and the grinding wheel is pressed against the back side of the wafer, thereby thinning the wafer by grinding.

[0003] However, when the wafer is thinned as described above, its rigidity is significantly reduced, making it difficult to manipulate the wafer in subsequent processes. Therefore, a technique has been proposed that grinds the central (inner) region of the wafer on which the devices are located, while leaving the outer (outer) region un-grinded, thereby maintaining the rigidity of the ground wafer at a sufficient level (see, for example, Patent Document 1).

[0004] In this technology, a grinding wheel is first used, which has an abrasive grain containing a certain size fixed on it. This wheel coarsely grinds the central region of the wafer, forming a thin, circular plate-shaped portion and a thick, annular portion around the thin plate on the wafer. Thus, by using a grinding wheel with an abrasive grain containing large abrasive grains, the grinding time required for the wafer can be shortened compared to using a grinding wheel with an abrasive grain containing relatively small abrasive grains.

[0005] On the other hand, when a wafer is ground using a grinding wheel with a grinding wheel containing large abrasive grains, a damage layer containing the damage and strain caused by the grinding is generated on the ground surface, and the mechanical strength (bending strength) of the thin plate portion is easily insufficient. Therefore, after rough grinding the wafer, the thin plate portion is further ground using a grinding wheel with a grinding wheel containing relatively small abrasive grains to remove the damage layer.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2009-176896

[0007] However, when removing the damaged layer by grinding the thin plate portion, the thick plate portion may sometimes be damaged when the grinding wheel comes into contact with the side surface of the thick plate portion. Therefore, when removing the damaged layer, only the central area of ​​the thin plate portion is ground in a manner that prevents the grinding wheel from contacting the thick plate portion. However, in this method, the damaged layer remains in the area on the outer edge of the thin plate portion (the area near the boundary with the thick plate portion). As a result, during subsequent handling, cracks can extend from the remaining damaged layer to the front side of the wafer, making the device prone to breakage.

[0008] By thickening the thin plate portion to sufficiently increase the distance from the device on the front side to the damage layer, device breakage due to cracks extending from the damage layer can be prevented. However, in this case, to achieve the final thickness of the thin plate portion, a large portion of the wafer must be removed using a grinding wheel with a relatively small abrasive grain that can remove a small amount per unit time. That is, the time required until grinding is complete is significantly extended. Summary of the Invention

[0009] Therefore, the object of the present invention is to provide a grinding method for a workpiece that, when grinding a plate-shaped workpiece on which a device is provided on the front side from the back side, minimizes the probability of device breakage without significantly extending the time until grinding is completed.

[0010] According to one aspect of the present invention, a grinding method for a workpiece is provided, wherein a plate-shaped workpiece having multiple devices disposed on its front side is ground from a back side opposite to the front side using a grinding wheel mounted on a rotating spindle, wherein the grinding method for the workpiece includes the following steps: an adhesive step, wherein a protective member is adhesively attached to the front side of the workpiece; a first grinding step, wherein, with the workpiece held on a first holding surface of a first chuck table with the protective member in between, a first grinding wheel having a first grinding tool containing abrasive grains and the first chuck table are moved relative to each other in a direction intersecting the first holding surface to grind the workpiece from the back side, thereby forming a circular plate-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion on the workpiece; and a second grinding step, wherein, after the first grinding step... The first grinding wheel and the first chuck table move relative to each other in a direction intersecting the first holding surface to grind the first thin plate portion from the back side, forming a second thin plate portion with a smaller diameter and thinner than the first thin plate portion and an annular second thick plate portion surrounding the second thin plate portion on the first thin plate portion; and a third grinding step, after the second grinding step, with the workpiece held on the second holding surface of the second chuck table through the protective member, the second grinding wheel with a second grinding tool containing abrasive grains smaller than those of the first grinding tool and the second chuck table move relative to each other in a direction intersecting the second holding surface to grind the second thick plate portion and the second thin plate portion from the back side, forming a third thin plate portion with a larger diameter and thinner than the second thin plate portion.

[0011] Preferably, the first chuck table is used as the second chuck table. Furthermore, in the third grinding step, it is preferable to increase the relative movement speed of the second grinding wheel and the second chuck table when grinding only the second thick plate portion, compared to the relative movement speed of the second grinding wheel and the second chuck table when grinding the region containing the second thin plate portion.

[0012] In addition, preferably in the first grinding step, the first thin plate portion is formed to ensure that cracks extending from the first damage layer containing damage or strain generated in the workpiece through the first grinding step do not reach the thickness of the device, and in the second grinding step, the second thin plate portion is formed to ensure that the second damage layer containing damage or strain generated in the workpiece through the second grinding step does not reach the thickness of the region that becomes the third thin plate portion.

[0013] In one aspect of the present invention, a grinding method for a workpiece is performed, after a first grinding step (grinding the workpiece using a first grinding wheel having a first grinding tool containing relatively large abrasive grains, forming a first thin plate portion in the shape of a circular plate and a first thick plate portion surrounding the first thin plate portion) and a second grinding step (grinding the first thin plate portion using the same first grinding wheel, forming a second thin plate portion in the shape of a circular plate with a smaller diameter and thinner than the first thin plate portion and an annular second thick plate portion surrounding the second thin plate portion), a third grinding step is performed (grinding the second thick plate portion and the second thin plate portion using a second grinding wheel having a second grinding tool containing relatively small abrasive grains, forming a third thin plate portion in the shape of a circular plate with a larger diameter and thinner than the second thin plate portion).

[0014] Therefore, compared to the case where the third grinding step is performed without a second grinding step after the first grinding step, the amount (volume) removed by the third grinding step is reduced according to the amount removed by the second grinding step. In other words, by adding a second grinding step that is completed in a short time using a first grinding wheel that removes a larger amount per unit time, the time required for the third grinding step can be shortened. Therefore, compared to the case where the third grinding step is performed without a second grinding step after the first grinding step, the time required until grinding is complete can be shortened.

[0015] Therefore, even if the first thin plate portion is thickened to sufficiently increase the distance from the device to the damage layer in order to prevent device breakage due to cracks extending from the damage layer containing damage or strain generated by the first grinding step, the time until grinding is completed will not be significantly extended. Thus, the grinding method for the workpiece according to one aspect of the present invention can suppress the probability of device breakage to a low level without significantly extending the time until grinding is completed. Attached Figure Description

[0016] Figure 1 It is a perspective view schematically showing the situation of attaching protective parts to a plate-shaped workpiece.

[0017] Figure 2 It is a schematic cross-sectional view showing the workpiece being held on the chuck table through a protective component.

[0018] Figure 3 It is a schematic cross-sectional view showing the grinding of the workpiece by the first grinding wheel.

[0019] Figure 4 It is a schematic cross-sectional view showing a portion of the workpiece after it has been ground by the first grinding wheel.

[0020] Figure 5 It is a schematic cross-sectional view showing the relative movement of the chuck table and the first grinding wheel in a direction along the upper surface of the chuck table.

[0021] Figure 6 It is a schematic cross-sectional view showing the grinding of the first thin plate portion of the workpiece by the first grinding wheel.

[0022] Figure 7 It is a schematic cross-sectional view showing a portion of the workpiece after the first sheet portion has been ground by the first grinding wheel.

[0023] Figure 8 This is a schematic cross-sectional view showing the grinding of the second thick plate portion and the second thin plate portion of the workpiece by the second grinding wheel.

[0024] Figure 9 It is a schematic cross-sectional view of a portion of the workpiece after the second thick plate portion and the second thin plate portion have been ground by the second grinding wheel.

[0025] Label Explanation

[0026] 11: Workpiece; 11a: Front side; 11b: Back side; 11c: First thin plate section; 11d: First thick plate section; 11e: Damaged layer (first damaged layer); 11f: Second thin plate section; 11g: Second thick plate section; 11h: Damaged layer (second damaged layer); 11i: Third thin plate section; 13: Pre-defined dividing line (spacer); 15: Device; 21: Protective component; 21a: Front side; 21b: Back side; 2: Grinding device; 4: Chuck table (first chuck table, second chuck table); 6: Frame; 6a: Recess; 6b: Flow path; 8: Holding plate; 8a: Upper surface (first holding surface, second holding surface); 8b: Vertex; 10: First grinding unit (rough grinding unit); 12: Spindle; 14: Mounting base; 16: Bolt; 18: First grinding wheel (rough grinding wheel); 20: Grinding wheel base; 22: First grinding tool (rough grinding tool); 24: Second grinding unit (fine grinding unit); 26: Spindle; 28: Mounting base; 30: Bolt; 32: Second grinding wheel (fine grinding wheel); 34: Grinding wheel base; 36: Second grinding tool (fine grinding tool). Detailed Implementation

[0027] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the grinding method of the workpiece in this embodiment, a protective member is first attached to the plate-shaped workpiece that is to be ground (attachment step). Figure 1 This is a perspective view schematically showing the case where the protective component 21 is attached to the plate-shaped workpiece 11.

[0028] The workpiece 11 is typically a wafer in the shape of a disc formed from semiconductors such as silicon (Si). The front side 11a of the workpiece 11 is divided into multiple small regions by intersecting predetermined dividing lines (spacers) 13, and devices such as ICs (integrated circuits) 15 are formed in each small region. In this embodiment, a portion of the workpiece 11 corresponding to the region where the devices 15 are formed (the device region) is ground from the back side 11b, opposite to the front side 11a, thereby thinning a portion of the workpiece 11.

[0029] Furthermore, in this embodiment, a wafer in the shape of a disc formed of a semiconductor such as silicon is used as the workpiece 11, but there are no restrictions on the material, shape, structure, size, etc. of the workpiece 11. For example, a substrate formed of other semiconductors, ceramics, resins, metals, etc., can also be used as the workpiece 11. Similarly, there are no restrictions on the type, number, shape, structure, size, arrangement, etc. of the devices 15.

[0030] The protective component 21, which is attached to the workpiece 11, is typically a circular strip (film) with a diameter approximately the same as that of the workpiece 11, a resin substrate, or a wafer of the same or different type as the workpiece 11. An adhesive layer that exhibits adhesion to the workpiece 11 is provided on the front side 21a of the protective component 21.

[0031] Therefore, by making the front side 21a of the protective member 21 fit tightly against the workpiece 11, the protective member 21 can be adhered to the workpiece 11. In this embodiment, as... Figure 1 As shown, the protective member 21 is attached to the front side 21a of the workpiece 11 by pressing the protective member 21 against the front side 11a of the workpiece 11. As a result, when grinding the workpiece 11 from the back side 11b, the impact applied to the front side 11a can be mitigated, and the device 15 and the like can be protected.

[0032] After the protective component 21 is attached to the front side 11a of the workpiece 11, the workpiece 11 is held in place by the holding surface of the chuck table through the protective component 21 (holding step). That is, the back side 21b of the protective component 21 attached to the workpiece 11 is held in place by the chuck table. Figure 2 This is a schematic cross-sectional view showing the workpiece 11 being held on the chuck table 4 via the protective member 21. Furthermore, in the following processes, the following steps utilize... Figure 2 Grinding device 2 as shown.

[0033] The grinding apparatus 2 has chuck tables (first chuck table and second chuck table) 4 configured to hold the workpiece 11. The chuck table 4 includes, for example, a circular plate-shaped frame 6 made of a metal such as stainless steel. A recess 6a with a circular opening at the upper end is formed on the upper surface of the frame 6. A circular plate-shaped retaining plate 8 made of a porous material such as ceramic is fixed in the recess 6a.

[0034] The upper surface 8a of the retaining plate 8 is configured, for example, in a shape equivalent to the lateral side of a cone, and functions as a retaining surface for holding the protective member 21. In this embodiment, the back surface 21b of the protective member 21 is in contact with the upper surface (first retaining surface, second retaining surface) 8a. The lower surface of the retaining plate 8 is connected to an suction source (not shown) such as an injector via a flow path 6b and a valve (not shown) provided inside the frame 6.

[0035] Therefore, by bringing the back surface 21b of the protective component 21 into contact with the upper surface 8a of the retaining plate 8, the valve is opened, and a negative pressure from the suction source is applied, thereby attracting the back surface 21b of the protective component 21 through the chuck table 4. That is, the workpiece 11 is held by the chuck table 4 through the protective component 21 that is attached to it.

[0036] And, as Figure 2 As shown, the back surface 11b of the workpiece 11 is exposed laterally upwards. Additionally, in Figure 2 In the above, the shape of the upper surface 8a of the retaining plate 8 is exaggerated. In reality, the height difference between the vertex 8b of the upper surface 8a (equivalent to the vertex of the cone) and the outer periphery of the upper surface 8a is about 10μm to 30μm.

[0037] A rotary drive source, such as an electric motor (not shown), is connected to the lower part of the frame 6. The chuck table 4 rotates about an axis along the vertical direction or an axis slightly inclined relative to the vertical direction with the vertex 8b as the center of rotation, by the force generated by this rotary drive source. In addition, the frame 6 is supported by a chuck table moving mechanism (not shown), and the chuck table 4 moves horizontally by the force generated by this chuck table moving mechanism.

[0038] After the workpiece 11 is held in place by the chuck table 4 with the protective member 21 in between, for example, rough grinding is performed on the area of ​​the workpiece 11 corresponding to the area where the device 15 is formed (device area) from the back side 11b (first grinding step). Figure 3 This is a cross-sectional view showing the rough grinding of the workpiece 11. Additionally, in Figure 3 In the image, for ease of explanation, a portion of the elements are shown from the side.

[0039] like Figure 3 As shown, a first grinding unit (rough grinding unit) 10 is arranged above the chuck table 4 of the grinding apparatus 2. The first grinding unit 10 includes, for example, a cylindrical spindle housing (not shown). A cylindrical spindle 12 is housed in the space inside the spindle housing.

[0040] At the lower end of the spindle 12, for example, a circular plate-shaped mounting base 14 with a diameter smaller than that of the workpiece 11 and the protective component 21 is provided. Multiple holes (not shown) extending through the mounting base 14 in the thickness direction are formed on the outer periphery of the mounting base 14, and bolts 16 or the like are inserted into each hole. A first grinding wheel (rough grinding wheel) 18, with a diameter approximately equal to that of the mounting base 14, is fixed to the lower surface of the mounting base 14 by bolts 16 or the like.

[0041] The first grinding wheel 18 includes a circular grinding wheel base 20 made of a metal such as stainless steel or aluminum. A plurality of first grinding tools (rough grinding tools) 22 are fixed to the lower surface of the grinding wheel base 20 along its circumference. The first grinding tools 22, for example, have a structure in which larger abrasive grains formed of diamond or the like are dispersed in a binder formed of resin or the like.

[0042] When the first grinding wheel 18, which includes the first grinding tool 22, is used, the amount of workpiece 11 that can be removed per unit time increases. On the other hand, a damage layer containing damage or strain is easily formed on the ground surface side of the workpiece 11. A rotary drive source (not shown), such as an electric motor, is connected to the upper end of the spindle 12. The first grinding wheel 18 rotates about an axis that is vertical or slightly inclined relative to the vertical direction by the force generated by the rotary drive source.

[0043] Next to or inside the first grinding wheel 18, a nozzle (not shown) is provided in a manner that allows the supply of grinding fluid (typically water) to the first grinding tool 22, etc. The spindle housing is supported, for example, by a first grinding unit moving mechanism (not shown), and the first grinding unit 10 moves in the vertical direction by the force generated by the first grinding unit moving mechanism.

[0044] When grinding the workpiece 11 using the first grinding unit 10 (first grinding wheel 18), the chuck table 4 is first moved to a position directly below the first grinding unit 10. Specifically, the chuck table 4 is moved horizontally using the chuck table moving mechanism, with the first grinding wheel 18 (all the first grinding tools 22) positioned directly above the area where the device 15 is formed.

[0045] Then, as Figure 3 As shown, the chuck table 4 and the first grinding wheel 18 are rotated respectively, and the first grinding unit 10 (first grinding wheel 18) is lowered while liquid is supplied from the nozzle. That is, the first grinding wheel 18 and the chuck table 4 move relative to each other in a direction intersecting the upper surface 8a, and the workpiece 11 is ground by the first grinding wheel 18. The descent speed of the first grinding unit 10 (grinding feed rate) is adjusted within the range where the first grinding tool 22 presses against the workpiece 11 with appropriate pressure.

[0046] Figure 4 This is a schematic cross-sectional view showing a portion of the workpiece 11 after grinding by the first grinding wheel 18. As described above, the area of ​​the workpiece 11 corresponding to the area where the device 15 is formed is ground from the back side 11b, thereby... Figure 4 As shown, a first thin plate portion 11c in the shape of a circular plate corresponding to the area where the device 15 is formed and a first thick plate portion 11d in the shape of an annulus surrounding the first thin plate portion 11c can be formed on the workpiece 11.

[0047] Furthermore, a damage layer (first damage layer) 11e containing damage or strain is formed on the back side 11b side (the ground surface) of the first thin plate portion 11c. Therefore, it is desirable that the first thin plate portion 11c is formed to a thickness such that even if a crack extends from the damage layer 11e during subsequent handling, the crack will not reach the device 15 on the front side 11a side.

[0048] There are no major restrictions on specific grinding conditions. To achieve efficient grinding of the workpiece 11, the rotational speed of the chuck table 4 is set to 100 rpm to 600 rpm, typically 300 rpm, and the rotational speed of the first grinding wheel 18 is set to 1000 rpm to 7000 rpm, typically 4500 rpm. Furthermore, the descent speed of the first grinding unit 10 is set to 0.8 μm / s to 10 μm / s, typically 6.0 μm / s.

[0049] After the workpiece 11 is ground from the back side 11b to form a circular first thin plate portion 11c and an annular first thick plate portion 11d surrounding the first thin plate portion 11c, the first thin plate portion 11c is rough ground from the back side 11b using the same first grinding wheel 18 (second grinding step). In this embodiment, the chuck table 4 and the first grinding wheel 18 are first moved relative to each other so that the first grinding wheel 18 moves away from the inner side of the first thick plate portion 11d.

[0050] More specifically, the chuck table 4 and the first grinding wheel 18 are moved relative to each other in a direction along the upper surface 8a of the chuck table 4, forming a gap between the first grinding wheel 18 and the first thick plate portion 11d. Figure 5 It is a schematic cross-sectional view showing the relative movement of the chuck table 4 and the first grinding wheel 18 along the direction of the upper surface 8a.

[0051] Among them, Figure 5 In the image, for ease of explanation, a portion of the elements are shown from the side. Additionally, in... Figure 5 In this process, while maintaining the rotation of the chuck table 4 and the first grinding wheel 18, the chuck table 4 and the first grinding wheel 18 are moved relative to each other in the direction along the upper surface 8a. However, the chuck table 4 and the first grinding wheel 18 can also be moved relative to each other in the direction along the upper surface 8a after their rotation has stopped. There are no major restrictions on the speed or distance of movement; here, the speed of movement is set to 1.0 mm / s to 2.0 mm / s, and the distance of movement is set to 3.0 mm to 6.0 mm.

[0052] After the chuck table 4 and the first grinding wheel 18 are moved relative to each other to form a gap between the first grinding wheel 18 and the first thick plate portion 11d, the first grinding unit 10 (the first grinding wheel 18) is lowered while liquid is supplied from the nozzle. That is, the first grinding wheel 18 and the chuck table 4 are moved relative to each other in a direction intersecting the upper surface 8a, and the first thin plate portion 11c is ground by the first grinding wheel 18.

[0053] Figure 6 This is a schematic cross-sectional view showing the grinding of the first thin plate portion 11c of the workpiece 11 by the first grinding wheel 18. Additionally, in Figure 6 For ease of explanation, a portion of the elements are shown in a side view. The descent speed (grinding feed speed) of the first grinding unit 10 is adjusted within the range where the first grinding wheel 22 is pressed against the first thin plate portion 11c with appropriate pressure.

[0054] Figure 7 This is a schematic cross-sectional view showing a portion of the workpiece 11 after the first thin plate portion 11c has been ground by the first grinding wheel 18. As described above, the first thin plate portion 11c is ground from the back side 11b, thereby... Figure 7 As shown, a circular second thin plate portion 11f and an annular second thick plate portion 11g surrounding the second thin plate portion 11f can be formed on the first thin plate portion 11c of the workpiece 11. After the second thin plate portion 11f and the second thick plate portion 11g are formed, the first grinding unit 10 is raised, and the grinding of the first grinding wheel 18 ends.

[0055] Furthermore, a damage layer (second damage layer) 11h containing damage or strain is formed on the back side 11b side (the side to be ground) of the second thin plate portion 11f. Therefore, it is desirable that the second thin plate portion 11f be formed to a thickness such that the damage layer 11h can be sufficiently removed by grinding the second thin plate portion 11f to the desired thickness.

[0056] There are no major restrictions on specific grinding conditions. In order to achieve efficient grinding of the workpiece 11, the rotational speed of the chuck table 4 is set to 100 rpm to 600 rpm, typically 300 rpm, and the rotational speed of the first grinding wheel 18 is set to 1000 rpm to 7000 rpm, typically 4500 rpm.

[0057] Furthermore, the descent speed of the first grinding unit 10 can be set to 0.8 μm / s to 10 μm / s. Alternatively, the descent speed of the first grinding unit 10 can be changed according to the grinding progress. Typically, the speeds of 6.0 μm / s, 3.0 μm / s, and 1.0 μm / s are set sequentially according to the grinding progress.

[0058] After grinding by the first grinding wheel 18, the second thick plate portion 11g and the second thin plate portion 11f are ground with higher precision from the back side 11b (third grinding step). Figure 8 This is a cross-sectional view showing the case where the workpiece 11 is ground with high precision. Additionally, in Figure 8 In the image, for ease of explanation, a portion of the elements are shown from the side.

[0059] like Figure 8 As shown, a second grinding unit (fine grinding unit) 24, different from the first grinding unit 10, is arranged above the chuck table 4 of the grinding apparatus 2. The second grinding unit 24 includes, for example, a cylindrical spindle housing (not shown). A cylindrical spindle 26 is housed in the space inside the spindle housing.

[0060] At the lower end of the spindle 26, for example, a circular plate-shaped mounting base 28 with a diameter smaller than that of the workpiece 11 and the protective component 21 is provided. Multiple holes (not shown) extending through the mounting base 28 in the thickness direction are formed on its outer periphery, and bolts 30 or the like are inserted into each hole. A second grinding wheel (fine grinding wheel) 32, with a diameter approximately equal to that of the mounting base 28, is fixed to the lower surface of the mounting base 28 by bolts 30 or the like.

[0061] The second grinding wheel 32 includes a circular grinding wheel base 34 made of a metal such as stainless steel or aluminum. A plurality of second grinding tools (fine grinding tools) 36 are fixed circumferentially on the lower surface of the grinding wheel base 34. The second grinding tools 36 have, for example, a structure in which smaller abrasive grains formed of diamond or the like are dispersed in a binder formed of resin or the like. Specifically, the size (typically the average grain size) of the abrasive grains included in the second grinding tool 36 is smaller than the size of the abrasive grains included in the first grinding tool 22.

[0062] When using the second grinding wheel 32, which includes the second grinding tool 36, the amount of workpiece 11 that can be removed per unit time decreases. On the other hand, it is less likely to form a damage layer containing damage or strain on the ground surface side of the workpiece 11. A rotary drive source (not shown), such as an electric motor, is connected to the upper end of the spindle 26. The second grinding wheel 32 rotates about an axis that is vertical or slightly inclined relative to the vertical direction by the force generated by the rotary drive source.

[0063] Next to or inside the second grinding wheel 32, a nozzle (not shown) is provided in a manner that allows for the supply of grinding fluid (typically water) to the second grinding tool 36, etc. The spindle housing is supported, for example, by a second grinding unit moving mechanism (not shown), and the second grinding unit 24 moves in the vertical direction by the force generated by this second grinding unit moving mechanism.

[0064] When grinding the second thick plate portion 11g and the second thin plate portion 11f using the second grinding unit 24 (second grinding wheel 32), the chuck table 4 is first moved to a position directly below the second grinding unit 24. Specifically, the second grinding wheel 32 (all the second grinding tools 36) is positioned directly above the second thick plate portion 11g and the second thin plate portion 11f, and the chuck table moving mechanism moves the chuck table 4 horizontally.

[0065] Then, as Figure 8 As shown, the chuck table 4 and the second grinding wheel 32 are rotated respectively, and the second grinding unit 24 (second grinding wheel 32) is lowered while liquid is supplied from the nozzle. This causes the second grinding wheel 32 and the chuck table 4 to move relative to each other in a direction intersecting the upper surface 8a. The descent speed of the second grinding unit 24 (grinding feed rate) is adjusted within the range where the second grinding wheel 36 presses against the workpiece 11 with appropriate pressure.

[0066] Figure 9 This is a schematic cross-sectional view of a portion of the workpiece 11 after the second thick plate portion 11g and the second thin plate portion 11f have been ground by the second grinding wheel 32. As described above, by grinding the second thick plate portion 11g and the second thin plate portion 11f from the back side 11b, it is possible to achieve the following: Figure 9 As shown, a third thin plate portion 11i, which is larger in diameter and thinner than the second thin plate portion 11f, is formed on the workpiece 11. In addition, the damaged layer 11h of the second thin plate portion 11f is removed by grinding using the second grinding wheel 32.

[0067] There are no major restrictions on specific grinding conditions. In order to achieve efficient and high-precision grinding of the workpiece 11, the rotation speed of the chuck table 4 is set to 100 rpm to 600 rpm, typically 300 rpm, and the rotation speed of the second grinding wheel 32 is set to 1000 rpm to 7000 rpm, typically 4000 rpm.

[0068] Furthermore, during grinding with the second grinding wheel 32, after grinding only the second thick plate portion 11g, the region including the second thin plate portion 11f (and the second thick plate portion 11g) is ground. Here, the area of ​​the ground surface is small when only the second thick plate portion 11g is ground, so the descent speed of the second grinding unit 24 can be increased in the stage of grinding only the second thick plate portion 11g compared to the stage of grinding the region including the second thin plate portion 11f.

[0069] Therefore, in this embodiment, the descent speed of the second grinding unit 24 in the stage of grinding only the second thick plate portion 11g is set to 0.8 μm / s to 5.0 μm / s, and the descent speed of the second grinding unit 24 in the stage of grinding the region including the second thin plate portion 11f is set to 0.1 μm / s to 0.8 μm / s.

[0070] That is, compared to the speed at which the second grinding wheel 32 and the chuck table 4 move relative to each other when grinding only the second thick plate portion 11g, the speed at which the second grinding wheel 32 and the chuck table 4 move relative to each other is increased when grinding only the second thick plate portion 11g. Typically, in grinding only the second thick plate portion 11g, a speed of 1.6 μm / s is set, and in grinding the region containing the second thin plate portion 11f, speeds of 0.6 μm / s and 0.3 μm / s are sequentially set according to the progress of grinding.

[0071] Therefore, the grinding time required can be shortened to improve efficiency, and the amount of damage or strain formed in the third thin plate portion 11i can be significantly reduced. That is, the damage layer 11h, which is close to the device 15 on the front side 11a and is prone to cracking into the device 15 during subsequent handling, can be removed without significantly extending the time required until grinding is completed. In particular, when the second thin plate portion 11f has a thickness that does not reach the area of ​​the third thin plate portion 11i, the damage layer 11h is sufficiently removed along with the formation of the third thin plate portion 11i.

[0072] Furthermore, a damaged layer 11e remains on the outer periphery of the second thick plate portion 11g (the portion in contact with the first thick plate portion 11d) that was not ground by the second grinding wheel 32. However, the distance from this damaged layer 11e to the device 15 on the front side 11a is greater than the distance from the damaged layer 11h to the device 15. Therefore, the probability of a crack extending from the remaining damaged layer 11e to the device 15 on the front side 11a is low, and it will not be a major problem. In particular, since the first thin plate portion is formed to ensure that cracks extending from the damaged layer 11e do not reach the thickness of the device 15, the problem caused by this crack is more appropriately eliminated.

[0073] Next, examples and comparative examples will be described to confirm the effectiveness of the grinding method for the workpiece according to this embodiment. In the examples and comparative examples, the time required to grind a first thin plate portion 11c with a thickness of 200 μm to form a third thin plate portion 11i with a thickness of 100 μm was confirmed. In the examples, the first thin plate portion 11c was first ground using the first grinding wheel 18 to form a second thin plate portion 11f with a thickness of 130 μm and a second thick plate portion 11g with a thickness of 200 μm.

[0074] The speed at which the first grinding wheel 18 descends during grinding of the first thin plate portion 11c (grinding feed rate) is set to 6.0 μm / s, 3.0 μm / s, and 1.0 μm / s. The distance the first grinding wheel 18 descends at each speed (i.e., the thickness removed by grinding) is 10 μm at 6.0 μm / s, 30 μm at 3.0 μm / s, and 30 μm at 1.0 μm / s.

[0075] Then, the second thick plate portion 11g and the second thin plate portion 11f are ground using the second grinding wheel 32 to form a third thin plate portion 11i with a thickness of 100 μm. Specifically, after grinding only the second thick plate portion 11g, the area including the second thin plate portion 11f (and the second thick plate portion 11g) is ground. The speed at which the second grinding wheel 32 descends (grinding feed rate) when grinding only the second thick plate portion 11g is set to 1.6 μm / s. The distance by which the second grinding wheel 32 descends is 70 μm.

[0076] On the other hand, the speed at which the second grinding wheel 32 descends during grinding of the region including the second thin plate portion 11f is set to 0.6 μm / s and 0.3 μm / s. The distance the second grinding wheel 32 descends at each speed is 20 μm at 0.6 μm / s and 10 μm at 0.3 μm / s. That is, in this embodiment, approximately 152 seconds are required until the grinding process is complete.

[0077] In the comparative example, the first thin plate portion 11c with a thickness of 200 μm was ground using the second grinding wheel 32, thinning the first thin plate portion 11c to a thickness of 100 μm (the thickness corresponding to the third thin plate portion 11i). The speed at which the second grinding wheel 32 descends during grinding the first thin plate portion 11c was set to 0.6 μm / s and 0.3 μm / s. The distance the second grinding wheel 32 descends at each speed is 90 μm at 0.6 μm / s and 10 μm at 0.3 μm / s. That is, in the comparative example, approximately 183 s is required until the grinding is completed.

[0078] Thus, in this embodiment, the time until the grinding is completed is about 31 seconds shorter than in the comparative example. In the grinding method of the workpiece in this embodiment, before grinding the first thin plate portion 11c, there is an additional time (1.5s to 6.0s) for the chuck table 4 and the first grinding wheel 18 to move relative to each other in the direction along the upper surface 8a. However, even taking this time into account, the grinding method of the workpiece in this embodiment can be said to be sufficiently effective.

[0079] As described above, in the grinding method of the workpiece in this embodiment, the workpiece 11 is ground using a first grinding wheel 18 having a first grinding tool 22 containing relatively large abrasive grains, thereby forming a first thin plate portion 11c in the shape of a circular plate and a first thick plate portion 11d surrounding the first thin plate portion 11c (first grinding step) on the workpiece 11. The first thin plate portion 11c is ground using the same first grinding wheel 18, thereby forming a thick plate portion 11d surrounding the first thin plate portion 11c. The first thin plate portion 11c is thinner and smaller in diameter than the second thin plate portion 11f, which is a circular plate shape, and the second thick plate portion 11g is annular around the second thin plate portion 11f (second grinding step). Then, the second thick plate portion 11g and the second thin plate portion 11f are ground using a second grinding wheel 32 with a second grinding tool 36 containing relatively small abrasive grains, thereby forming a third thin plate portion 11i, which is thinner and larger in diameter than the second thin plate portion 11f (third grinding step).

[0080] Therefore, compared with conventional grinding methods for workpieces without the second thin plate portion 11f and the second thick plate portion 11g, the amount (volume) removed using the second grinding wheel 32 is reduced compared to the amount removed using the first grinding wheel 18 when forming the second thin plate portion 11f and the second thick plate portion 11g. In other words, while the grinding time using the first grinding wheel 18, which removes a larger amount per unit time, is slightly increased, the grinding time using the second grinding wheel 32 can be significantly shortened. Therefore, overall, the time required until grinding is complete can be reduced.

[0081] Therefore, even if the first thin plate portion 11c is thickened to sufficiently increase the distance from the device 15 to the damage layer 11e, in order to prevent breakage of the device 15 due to cracks extending from the damage layer (first damage layer) 11e formed in the first thin plate portion 11c, the time until grinding is completed will not be significantly extended. Thus, the grinding method for the workpiece according to this embodiment can suppress the probability of breakage of the device 15 to a low level without significantly extending the time until grinding is completed.

[0082] Furthermore, the present invention is not limited to the embodiments described above, and various modifications and implementations are possible. For example, in the above embodiments, after grinding the workpiece 11 held by the chuck table 4 using the first grinding wheel 18, the workpiece 11 held by the chuck table 4 is ground using the second grinding wheel 32. That is, the first chuck table used when grinding the workpiece 11 using the first grinding wheel 18 is directly used as the second chuck table used when grinding the workpiece 11 using the second grinding wheel 32.

[0083] Conversely, after grinding the workpiece 11 held by the chuck table 4 using the first grinding wheel 18, the workpiece 11 held by a different chuck table than the chuck table 4 can be ground using the second grinding wheel 32. That is, the first chuck table when grinding the workpiece 11 using the first grinding wheel 18 and the second chuck table when grinding the workpiece 11 using the second grinding wheel 32 can be different chuck tables. Similarly, the workpiece grinding method of the present invention can be performed using multiple grinding devices.

[0084] Furthermore, in the above embodiment, the first thin plate portion 11c is ground after the chuck table 4 and the first grinding wheel 18 are moved relative to each other in the direction along the upper surface 8a of the chuck table 4. However, the first thin plate portion 11c can also be ground using other methods. For example, the first thin plate portion 11c can be ground while the chuck table 4 and the first grinding wheel 18 are moved relative to each other in the direction along the upper surface 8a of the chuck table 4. In addition, in this case, the inner side surface of the second thick plate portion 11g is inclined relative to the front surface 11a, etc.

[0085] Furthermore, in the above embodiment, after the chuck table 4 and the first grinding wheel 18 are moved relative to each other in the direction along the upper surface 8a of the chuck table 4, the first thin plate portion 11c is ground. Therefore, sometimes the central area of ​​the first thin plate portion 11c is not ground and remains. In such cases, for example, when the second thick plate portion 11g is ground using the second grinding wheel 32, the remaining portion of the first thin plate portion 11c can be removed along with it.

[0086] In addition, the above-described embodiments and variations can be appropriately modified and implemented as long as they do not depart from the scope of the present invention.

Claims

1. A method for grinding a workpiece, comprising grinding a plate-shaped workpiece having multiple components disposed on its front side from a back side opposite to the front side using a grinding wheel mounted on a rotating spindle, wherein, The grinding method for the workpiece includes the following steps: The pasting step involves pasting the protective component onto the front side of the workpiece. In the first grinding step, with the workpiece held on the first holding surface of the first chuck table through the protective member, the first grinding wheel having a first grinding tool containing abrasive grains and the first chuck table are moved relative to each other in a direction intersecting the first holding surface to grind the workpiece from the back side, forming a circular plate-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion on the workpiece; In the second grinding step, after the first grinding step, the first grinding wheel and the first chuck table are moved relative to each other in a direction intersecting the first holding surface to grind the first thin plate portion from the back side, forming a second thin plate portion in the shape of a circular plate with a smaller diameter and thinner than the first thin plate portion, and a second thick plate portion in the shape of an annular shape surrounding the second thin plate portion. as well as In the third grinding step, after the second grinding step, with the workpiece held on the second holding surface of the second chuck table via the protective member, a second grinding wheel having a second grinding tool containing abrasive grains smaller than those of the first grinding tool and the second chuck table are moved relative to each other in a direction intersecting the second holding surface. This grinds the inner peripheral portion of the second thick plate portion and the entirety of the second thin plate portion from the back side, forming a circular plate-shaped third thin plate portion that is thinner and has a larger diameter than the second thin plate portion and a smaller diameter than the first thin plate portion. This removes all the damage layer formed on the second thin plate portion, leaving only a residual damage layer on the outer peripheral portion of the second thick plate portion that was not ground by the second grinding wheel. In the first grinding step, the first thin plate portion is formed to ensure that cracks extending from the damaged layer containing damage or strain generated in the workpiece during the subsequent transport will not reach the thickness of the device.

2. The grinding method for a workpiece according to claim 1, wherein, The first chuck worktable is used as the second chuck worktable.

3. The grinding method for a workpiece according to claim 1 or 2, wherein, In the third grinding step, compared with the speed at which the second grinding wheel and the second chuck table move relative to each other when grinding only the second thick plate portion, the speed at which the second grinding wheel and the second chuck table move relative to each other when grinding only the second thick plate portion is increased.

4. The grinding method for a workpiece according to claim 1 or 2, wherein, In the second grinding step, the second thin plate portion is formed to ensure that the second damage layer containing damage or strain generated in the workpiece through the second grinding step does not reach the thickness of the area that becomes the third thin plate portion.

5. The grinding method for a workpiece according to claim 3, wherein, In the second grinding step, the second thin plate portion is formed to ensure that the second damage layer containing damage or strain generated in the workpiece through the second grinding step does not reach the thickness of the area that becomes the third thin plate portion.

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