Surface grinding method and surface grinding apparatus

Abstract

The method employs a technique where one side of the workpiece is held in place by suction while the opposite side is ground, ensuring that any waviness in the workpiece is reliably removed. [Solution] When grinding both sides of a plate-shaped workpiece W with a grinding wheel (grinding wheel) 6 while the workpiece W is held in place by a chuck table (workpiece holding means) 3, a first grinding step is performed in which the second surface Wb of the workpiece W is ground while the first surface Wa of the workpiece W is held in place by the chuck table 3 near its center (first region). After the first grinding step, a second grinding step is performed in which the first surface Wa of the workpiece W is ground while the second surface Wb of the workpiece W is held in place by the chuck table 3 over substantially the entire surface (second region).

Description

Technical Field

[0001] The present invention relates to a surface grinding method and a surface grinding apparatus for grinding a plate-shaped workpiece.

Background Art

[0002] As a surface grinding apparatus for grinding both surfaces of a thin plate-shaped workpiece such as a semiconductor wafer, there is known one configured to grind the opposite surface while holding the entire surface of one side of the workpiece by vacuum adsorption or the like. When the workpiece is ground one side at a time by this type of surface grinding apparatus (hereinafter referred to as the first grinding method), as a problem, when there is a waviness such as a saw mark in the workpiece before grinding, it is difficult to completely remove the waviness by grinding.

[0003] That is, in the case of the first grinding method, the workpiece is first ground on one side while being adsorbed and held on its entire surface by a vacuum adsorption chuck or the like. At this time, since the wavy workpiece is elastically deformed by being vacuum adsorbed on the chuck surface and the one side is ground and flattened in this state, when the vacuum adsorption is released after grinding, the elastically deformed workpiece returns to its original state, and as a result, there is a problem that the waviness remains.

[0004] On the other hand, for example, in Patent Document 1, a method of grinding a plate-shaped workpiece without adsorbing and fixing it (hereinafter referred to as the second grinding method) has been proposed, and it is said that the distortion originally possessed by the workpiece can be surely removed by this second grinding method.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the second grinding method described above has a problem in that the central part of the workpiece lifts up during grinding, and as the central part is mainly ground down, the central part of the workpiece becomes thinner than the surrounding part.

[0007] In view of the above-mentioned problems of the conventional methods, the present invention aims to provide a surface grinding method and a surface grinding apparatus that can reliably remove waviness from a workpiece while employing a method similar to the first grinding method described above, in which one side of the workpiece is held by suction and the opposite side is ground. [Means for solving the problem]

[0008] The surface grinding method according to the present invention is a surface grinding method in which a plate-shaped workpiece is held by a workpiece holding means by suction, and both sides of the workpiece are ground with a grinding wheel while the workpiece holding means is rotated, comprising: a first grinding step in which the second surface of the workpiece is ground while the first surface of the workpiece is held by the workpiece holding means by suction in a first region near its center; and a second grinding step in which, after the first grinding step, the first surface of the workpiece is ground while the second surface of the workpiece is held by the workpiece holding means by suction in a second region.

[0009] In this case, the second region may correspond to substantially the entire surface of the workpiece. Alternatively, the first grinding step may be performed with the outer circumference of the workpiece guided non-rotatably relative to the workpiece holding means by a guide means provided on the workpiece holding means.

[0010] Furthermore, the first grinding step and the second grinding step may be configured to be performed by switching the suction area of ​​one of the workpiece holding means, or the first grinding step and the second grinding step may be configured to be performed using separate workpiece holding means with different suction areas.

[0011] The first surface grinding apparatus according to the present invention comprises a workpiece holding means capable of adsorbing and holding a plate-shaped workpiece, and a grinding wheel for grinding the workpiece held by the workpiece holding means, wherein the surface grinding apparatus is equipped with an adsorption area switching means capable of switching the adsorption area of ​​the workpiece by the workpiece holding means between a first area near the center and a second area different from the first area, and the adsorption area switching means is made possible when adsorbing and holding the first surface side of the workpiece and grinding the second surface side, and then adsorbing and holding the second surface side of the workpiece and grinding the first surface side.

[0012] Furthermore, the second surface grinding apparatus according to the present invention comprises a workpiece holding means capable of adsorbing and holding a plate-shaped workpiece on a workpiece holding section, and a grinding wheel for grinding the workpiece held by the workpiece holding means, wherein the workpiece holding means comprises a first workpiece holding means that has a first region near the center as an adsorption region, and a second workpiece holding means that has a second region different from the first region as an adsorption region, and the workpiece holding means used can be changed depending on whether the first surface of the workpiece is adsorbed and held to grind the second surface, or whether the second surface of the workpiece is then adsorbed and held to grind the first surface.

[0013] In this case, the workpiece holding portion of the first workpiece holding means may be formed from a non-porous material, and the workpiece holding portion of the second workpiece holding means may be formed from a porous material. [Effects of the Invention]

[0014] According to the surface grinding method of the present invention, it is possible to reliably remove waviness from a workpiece while grinding the opposite side while holding one side of the workpiece by suction.

[0015] Furthermore, the surface grinding apparatus according to the present invention makes it possible to easily perform the above surface grinding method and reliably remove waviness from the workpiece. [Brief explanation of the drawing]

[0016] [Figure 1] It is a perspective view of a vertical surface grinding machine showing the first embodiment of the present invention. [Figure 2] It is a side sectional view of the main part of the surface grinding machine. [Figure 3] It is a plan view of the chuck table. [Figure 4] It is an exploded perspective view of the chuck table. [Figure 5] It is a perspective view showing a guide ring and a block corresponding to a work having a notch. [Figure 6] It is a plan view of the base plate constituting the chuck table. [Figure 7] It is an explanatory view showing the steps of a surface grinding method showing the first embodiment of the present invention. [Figure 8] It is a side sectional view of the chuck table showing the second embodiment of the present invention. [Figure 9] It is an explanatory view showing the steps of a surface grinding method showing the second embodiment of the present invention. [Figure 10] It is an explanatory view showing a modification example of the first vacuum circuit operating in the first grinding step. [Figure 11] It is an explanatory view of a method for adjusting the adsorption range and adsorption force for a work. [Figure 12] It is an explanatory view of a method for adjusting the adsorption range and adsorption force for a work.

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] Hereinafter, the first embodiment of the present invention will be described in detail based on the drawings. FIGS. 1 to 7 illustrate the first embodiment of the present invention. The vertical surface grinding machine (surface grinding device) according to this embodiment, as shown in FIG. 1, includes a bed 1, an index table 2 rotatably arranged on the bed 1, two sets of chuck tables 3 arranged at equal positions on the index table 2, a column 4 erected on the rear side of the bed 1, a spindle 5 arranged vertically movably on the front side of the column 4, and a grinding wheel 6 detachably attached to the lower end side of the spindle 5.

[0018] The two sets of chuck tables 3 arranged on the index table 2 are for adsorbing and holding a thin plate-like workpiece W such as a semiconductor wafer. When the index table 2 rotates around the vertical axis 2a by the drive of a drive motor or the like (not shown), it is selectively positioned at the grinding position A corresponding to the lower side of the grinding wheel 6 and the loading / unloading position B. The spindle 5 is supported by the column 4 so as to be movable up and down above the grinding position A, and is rotationally driven around the vertical axis by a drive source such as a built-in motor (not shown).

[0019] The grinding wheel (grinding stone) 6 is detachably mounted below the flange 7 provided on the lower end side of the spindle 5 and is configured to rotate around the vertical axis as the spindle 5 rotates. As shown in FIG. 2 and the like, it includes an annular grindstone base material 8 disposed substantially horizontally, and a grindstone 9 fixed to the lower surface side of the grindstone base material 8. As shown in FIGS. 2 and 3, the grindstone 9 is formed in an annular shape with an outer diameter larger than the radius of the workpiece W, and the grinding wheel 6 is disposed eccentrically with respect to the chuck table 3 at the grinding position A such that the blade width of the grindstone 9 passes through the center of the workpiece W.

[0020] The chuck table (work holding means) 3 includes a base plate 11 disposed substantially horizontally, a substantially disc-shaped porous plate 12 disposed at the center of the upper surface side of the base plate 11, and a guide ring (guide means) 13 disposed on the outer peripheral side of the porous plate 12, and is rotatable around the vertical axis by the drive of a drive source such as a drive motor (not shown) at the grinding position A.

[0021] The base plate 11 is formed in a substantially disc shape from a material such as stainless steel or ceramics, and on the upper surface side thereof, a porous plate mounting portion 14 is formed at the center, and a guide ring mounting portion 15 is further formed on the outer peripheral side of the porous plate mounting portion 14. The porous plate mounting portion 14 is a substantially circular recess corresponding to the porous plate 12, and the recess depth is formed to be the same as the plate thickness of the porous plate 12, and the porous plate 12 is fitted from above.

[0022] The porous plate 12 is made of porous ceramics, for example, and is formed in a substantially circular shape that is the same shape as the workpiece W but has an outer diameter slightly smaller than the outer diameter of the workpiece W. The workpiece W is held in place by adsorption on its upper surface and is fixed to the base plate 11 by adhesive or the like when fitted into the porous plate mounting section 14 from above. In this embodiment, the workpiece W is a semiconductor wafer with an orientation flat 16a formed on its outer circumference as an example of a non-circular portion, and correspondingly the porous plate 12 also has a flat portion 12a formed on its outer circumference.

[0023] The guide ring mounting section 15 is a roughly annular groove corresponding to the guide ring 13, and is provided on the outer circumference side of the porous plate mounting section 14, separated by a thin partition wall 14a. The groove depth is formed to be shallower than the thickness of the guide ring 13. The guide ring 13 is for holding the workpiece W placed on the porous plate 12 on its outer circumference. It is fitted onto the guide ring mounting section 15 from above and fixed to the base plate 11 by bolts. As shown in Figure 2, the guide ring 13 mounted and fixed to the guide ring mounting section 15 protrudes above the groove that constitutes the guide ring mounting section 15. However, its upper surface is higher than the upper surface of the porous plate 12 and lower than the upper surface of the workpiece W after grinding, so the grinding wheel 9 does not come into contact with the guide ring 13 during grinding.

[0024] Furthermore, a block 17 is detachably attached to the guide ring 13 at a predetermined location on its circumference. The block 17 is intended to prevent the workpiece W from rotating freely by engaging with the non-circular portion of the workpiece W, and has a flat portion 17a that corresponds to the orientation flat of the workpiece W. Figure 5 shows an example of a workpiece W with a notch 16b formed as a non-circular portion, and a block 17 with a projection 17b that engages with the notch 16b. Of course, the block 17 may also be formed integrally with the guide ring 13.

[0025] Furthermore, as shown in Figure 2, the base plate 11 has suction passages 23 and 24 formed therein, which constitute two vacuum circuits 21 and 22, respectively. The first suction passage 23 constitutes a part of the terminal side of the first vacuum circuit 21 and is made up of a through hole with a predetermined cross-sectional shape (here, a circular cross-section) that penetrates the base plate 11 vertically, corresponding to the center of the porous plate mounting section 14 (i.e., the center of the workpiece W). The upper end of this first suction passage 23 is in close contact with the lower surface of the porous plate 12, and the lower end is connected to the vacuum suction source 20 (first vacuum circuit 21).

[0026] The second suction passage 24 constitutes a part of the terminal end of the second vacuum circuit 22 and consists of a suction groove 25 formed on the bottom surface of the porous plate mounting section 14 and one or more (two in this case) through holes 26 that penetrate the base plate 11 vertically, corresponding to predetermined locations in the suction groove 25. The suction groove 25 is spread almost evenly across the entire bottom surface of the porous plate mounting section 14, and its upper side is tightly closed by the porous plate 12. In this embodiment, it consists of a plurality of (four in this case) concentrically arranged ring grooves 25a and a plurality of (four in this case) radial grooves 25b that connect these ring grooves 25a in the radial direction.

[0027] Note that the arrangement of the suction grooves 25 is not limited to this; the number of ring grooves 25a and radial grooves 25b may be changed, or any arrangement such as multiple radial grooves or multiple fan-shaped grooves may be adopted. However, since the first vacuum circuit 21 and the second vacuum circuit 22 are separate systems, the suction grooves 25 must be arranged so as not to communicate with the first suction passage 23 on the first vacuum circuit 21 side. The through hole 26 has its upper end communicating with the suction groove 25 from below, and its lower end is connected to the vacuum suction source 20 (second vacuum circuit 22).

[0028] As shown in Figure 2, the first vacuum circuit 21 and the second vacuum circuit 22 are individually connected to the vacuum suction source 20, and their connection to the vacuum suction source 20 can be individually switched by a switching means (suction area switching means) 27 such as a solenoid valve. In the following description, the state in which the first vacuum circuit 21 and the second vacuum circuit 22 are connected to the vacuum suction source 20 and performing vacuum suction will be referred to as "operation" of the first vacuum circuit 21 and the second vacuum circuit 22, respectively.

[0029] When only the first vacuum circuit 21 is operating, a negative pressure is generated near the center of the porous plate 12 via the first suction passage 23, thereby holding the workpiece W in the vicinity of its center (first region). When only the second vacuum circuit 22 is operating, a negative pressure is generated in the peripheral region of the porous plate 12 excluding the center via the second suction passage 24, i.e., the through hole 26 and suction groove 25, thereby holding the workpiece W in the peripheral region outside of the vicinity of the center (first region). When the first and second vacuum circuits 21 and 22 are operating simultaneously, the workpiece W is held by adsorption over almost the entire area (second region), including the vicinity of the center and its surrounding region.

[0030] Next, the planar grinding method using the vertical planar grinding machine (planar grinding device) described above will be explained with reference to Figure 7, etc. In the planar grinding method of this embodiment, the first grinding step is performed first, followed by the second grinding step.

[0031] In the first grinding step (Figure 7(a)), only the first vacuum circuit 21 of the first and second vacuum circuits 21 and 22 is activated, and the second vacuum circuit 22 is not activated. In other words, one side of the workpiece W (the first surface Wa side) is held by suction near its center (the first region) (Figure 7(a1)), and grinding is performed on the opposite side (the second surface Wb side). In this state, with only the first vacuum circuit 21 activated, the workpiece W is held by suction only near its center (the first region). Therefore, if there are undulations such as saw marks on the workpiece W, these undulations are not corrected by elastic deformation, and the second surface Wb side is ground while maintaining its natural shape (Figure 7(a2)). As a result, the peaks of the undulations on the second surface Wb of the workpiece W are ground, and the entire surface is flattened. This flattened second surface Wb becomes the reference surface for grinding in the next second grinding step.

[0032] In the first grinding step, since only the vicinity of the center of the workpiece W is held by suction, the holding force of the workpiece W is weaker compared to the case of normal full-surface suction. However, in the surface grinding machine of the present invention, the workpiece W is ground while its outer circumference is guided by the guide ring 13 and block 17 so that it cannot rotate relative to the chuck table (workpiece holding means) 3. Therefore, displacement or ejection of the workpiece W due to grinding resistance can be effectively prevented.

[0033] Once the first grinding process is complete, the second grinding process is performed. In this second grinding process (Figure 7(b)), the first surface Wa is ground with the workpiece turned over so that the second surface Wb, which was ground in the first grinding process, faces downwards (Figure 7(b1)). Unlike the first grinding process, this second grinding process is performed with both the first and second vacuum circuits 21 and 22 activated, that is, with the workpiece W held by suction over almost its entire surface (second region). In this second grinding process, only the second surface Wb, which was flattened to its natural shape in the first grinding process, is held by suction over almost the entire surface of the workpiece W. Therefore, even if almost the entire surface of the workpiece W is held by suction, no elastic deformation that would correct the waviness occurs. Through this second grinding process, the peaks of the waviness on the first surface Wa of the workpiece W are ground down, and the entire surface becomes flat (Figure 7(b2)).

[0034] As described above, the surface grinding method of this embodiment grinds both sides of a plate-shaped workpiece W with a grinding wheel (grinding wheel) 6 while the workpiece W is held in place by a chuck table (workpiece holding means) 3. The first grinding step involves holding the first surface Wa side of the workpiece W in place by the chuck table 3 near its center (first region) while grinding the second surface Wb side of the workpiece W. After the first grinding step, the chuck table 3 grinds the second surface Wb side of the workpiece W over substantially the entire surface (second region). The system includes a second grinding step in which the first surface Wa side of the workpiece W is ground while the workpiece W is held in place by suction. Therefore, in the first grinding step, the second surface Wb side can be flattened while the workpiece W maintains its natural shape without elastic deformation, and in the subsequent second grinding step, the first surface Wa side can be flattened while the flattened second surface Wb side is held in place by suction. This method of grinding the opposite side while holding one side of the workpiece W in place by suction makes it possible to reliably remove the waviness of the workpiece W.

[0035] Furthermore, since the first grinding process is performed with the outer circumference of the workpiece W guided non-rotatably relative to the chuck table (workpiece holding means) 3 by the guide ring 13 and block 17 (guide means) provided on the chuck table 3, even though only the area near the center of the workpiece W (first region) is held by suction, displacement or ejection of the workpiece W due to grinding resistance can be effectively prevented.

[0036] Furthermore, the vertical surface grinding machine (surface grinding device) of this embodiment includes a chuck table (workpiece holding means) 3 capable of adsorbing and holding a plate-shaped workpiece W, a grinding wheel (grinding wheel) 6 for grinding the workpiece W held by the chuck table 3, and an adsorption area switching means 27 that can switch the adsorption area of ​​the workpiece W by the chuck table 3 between a first area near the center and a second area corresponding to substantially the entire surface. The adsorption area switching means 27 can be switched depending on whether the first surface Wa side of the workpiece W is adsorbed and held to grind the second surface Wb side, or whether the second surface Wb side of the workpiece W is then adsorbed and held to grind the first surface Wa side. As a result, the surface grinding method described above can be easily executed, and the waviness of the workpiece W can be reliably removed.

[0037] Figures 8 and 9 illustrate a second embodiment of the present invention, showing an example in which the first embodiment is partially modified to use dedicated chuck tables for the first grinding process and the second grinding process, respectively. In the first embodiment, a common chuck table 3 using a porous plate 12 is used in both the first and second grinding processes, and grinding is performed by switching the adsorption area. Therefore, even in the first grinding process, where the area near the center (first region) should be adsorbed and held, the suction by the first suction passage 23 (Figure 2) in the center affects the entire workpiece surface via the porous plate 12, resulting in overall adsorption or a situation close to it, which may prevent obtaining the desired grinding result. This embodiment was made to resolve such concerns in the first embodiment.

[0038] In this embodiment, the first grinding step is performed using a chuck table 3a specialized for suction and holding of the area near the center (first region), and the second grinding step is performed using a chuck table 3b specialized for suction and holding of almost the entire area (second region). These two chuck tables 3a and 3b are arranged, for example, at equally spaced positions on the index table 2. The main difference between this embodiment and the first embodiment is the configuration of the chuck tables in the vertical surface grinding machine; the configuration of parts not specifically mentioned in the following description is the same as in the first embodiment.

[0039] As shown in Figure 8(a), the chuck table (first workpiece holding means) 3a comprises a base plate 11a positioned substantially horizontally and a guide ring (guide means) 13 positioned on the upper surface of the base plate 11a, and is rotatable around a vertical axis at grinding position A (Figure 1) by the drive of a drive source such as a drive motor (not shown).

[0040] The base plate 11a is formed in a substantially disc shape from a material such as stainless steel, and a workpiece holding portion 31 for adsorbing and holding the workpiece W is formed in the center of its upper surface. The workpiece holding portion 31 is substantially circular in shape corresponding to the workpiece W, and its upper surface is a flat workpiece holding surface 31a. The shape of the workpiece W is the same as in the first embodiment (Figures 3 to 5, etc.). In this chuck table 3a, a porous plate like the chuck table 3 of the first embodiment is not attached, and the workpiece holding portion 31 is made of the same stainless steel as the base plate 11a and is formed integrally with the base plate 11a. Note that stainless steel is merely one example of a non-porous material, and the workpiece holding portion 31 may be formed from a non-porous material other than stainless steel (such as ceramic).

[0041] Furthermore, a guide ring mounting portion 15 is formed on the outer circumference of the workpiece holding portion 31 on the base plate 11a. The guide ring mounting portion 15 is a substantially annular groove corresponding to the guide ring 13, and its groove depth is formed to be shallower than the plate thickness of the guide ring 13. The guide ring 13 is for holding the workpiece W placed on the workpiece holding portion 31 on its outer circumference, and is fitted onto the guide ring mounting portion 15 from above and fixed to the base plate 11a by bolts. This guide ring 13, including the block 17, is the same as the chuck table 3 of the first embodiment (Figures 3 to 5, etc.).

[0042] Furthermore, a suction passage 23a, which constitutes the vacuum circuit 21a, is formed in the base plate 11a. The suction passage 23a forms a part of the end of the vacuum circuit 21a and is composed of a through hole with a predetermined cross-sectional shape (in this case, a circular cross-section) that penetrates the base plate 11a vertically, corresponding to the center of the workpiece holding portion 31 (i.e., the center of the workpiece W). The upper end of this suction passage 23a opens on the workpiece holding surface 31a and the lower end is connected to the vacuum suction source 20 (vacuum circuit 21a).

[0043] As shown in Figure 8(b), the chuck table (second workpiece holding means) 3b comprises a base plate 11b positioned substantially horizontally and a substantially circular porous plate 12 positioned in the center of the upper surface of the base plate 11b, and is rotatable around a vertical axis by a drive source such as a drive motor (not shown) at the grinding position A (Figure 1). The base plate 11b is formed in a substantially circular shape from a material such as stainless steel or ceramics, and a porous plate mounting portion 14 is formed in the center of its upper surface.

[0044] The porous plate mounting section 14 is a roughly circular recess corresponding to the porous plate 12, and its recess depth is formed to be the same as the thickness of the porous plate 12, into which the porous plate 12 is fitted from above. The porous plate 12, as in the first embodiment, is made of, for example, porous ceramics, and is formed in a roughly circular shape that is the same shape as the workpiece W and has an outer diameter slightly smaller than the outer diameter of the workpiece W, and is designed to hold the workpiece W by adsorption on its upper surface, and is fixed to the base plate 11b by adhesive or the like while fitted into the porous plate mounting section 14 from above. In this embodiment, the chuck table 3b can firmly hold the workpiece W by full-surface adsorption, so a guide ring 13 is not placed on the base plate 11b, but a guide ring 13 may be placed on the base plate 11b as in the chuck table 3 of the first embodiment.

[0045] Furthermore, the base plate 11b has suction passages 23b and 24b formed therein, which constitute two vacuum circuits 21b and 22b, respectively. The first suction passage 23b constitutes a part of the terminal side of the first vacuum circuit 21b and is composed of a through-hole with a predetermined cross-sectional shape (in this case, a circular cross-section) that penetrates the base plate 11b vertically, corresponding to the center of the porous plate mounting section 14 (i.e., the center of the workpiece W). The upper end of this first suction passage 23b is in close contact with the lower surface of the porous plate 12, and the lower end is connected to the vacuum suction source 20 (first vacuum circuit 21b).

[0046] The second suction passage 24b constitutes a portion of the terminal side of the second vacuum circuit 22b and consists of a suction groove 25 formed on the bottom surface of the porous plate mounting portion 14 and one or more (two in this case) through holes 26 that penetrate the base plate 11 vertically, corresponding to predetermined locations in the suction groove 25. The configuration of the suction groove 25, through holes 26, etc. is the same as that of the chuck table 3 in the first embodiment (Figures 4, 6, etc.). The upper end of the through hole 26 communicates with the suction groove 25 from below, and the lower end is connected to the vacuum suction source 20 (second vacuum circuit 22b).

[0047] The first vacuum circuit 21b and the second vacuum circuit 22b are individually connected to the vacuum suction source 20, and their connection to the vacuum suction source 20 can be individually switched by a switching means (suction area switching means) 27 such as a solenoid valve. In the second grinding step of this embodiment, the first and second vacuum circuits 21b and 22b are operated simultaneously, and the workpiece W is held by suction over substantially its entire surface (second region), including the area near the center and its surrounding region.

[0048] Next, the surface grinding method of this embodiment will be described with reference to Figure 9 and other figures. In the surface grinding method of this embodiment, the first grinding step is performed first, followed by the second grinding step.

[0049] In the first grinding step (Figure 9(a)), the chuck table 3a (Figure 8(a)) is used, and with the vacuum circuit 21a activated, that is, with one side of the workpiece W (first surface Wa side) held by suction near its center (first region) (Figure 9(a1)), grinding is performed on the opposite side (second surface Wb side). In this way, with the vacuum circuit 21a activated on the chuck table 3a, the workpiece W is held by suction only near its center (first region). Therefore, if there are undulations such as saw marks on the workpiece W, these undulations are not corrected by elastic deformation, and the second surface Wb side is ground while maintaining its natural shape (Figure 9(a2)). As a result, the peaks of the undulations on the second surface Wb of the workpiece W are ground, and the entire surface is flattened. This flattened second surface Wb becomes the reference surface for grinding in the next second grinding step.

[0050] Furthermore, in the chuck table 3a of this embodiment, the workpiece holding portion 31 is not made of a porous material, but is made of stainless steel (a non-porous material) integrated with the base plate 11a. Therefore, the suction from the central suction passage 23a (Figure 9(a)) does not affect the entire workpiece surface through the porous plate, and the workpiece W can be reliably held only in the vicinity of its center (first region). In this way, the first grinding process is performed with the workpiece W held by suction only in the vicinity of its center, so the holding force of the workpiece W is weaker compared to the case of normal full surface suction. However, in the chuck table 3a of this embodiment, the outer circumference of the workpiece W is guided so that it cannot rotate by the guide ring 13 and block 17, so displacement or ejection of the workpiece W due to grinding resistance can be effectively prevented.

[0051] Once the first grinding process is complete, the second grinding process is performed. In this second grinding process (Figure 9(b)), the chuck table 3b (Figure 8(b)) is used, and the first surface Wa side is ground with the workpiece turned over so that the second surface Wb, which was ground in the first grinding process, faces downwards (Figure 9(b1)). This second grinding process is performed with both the first and second vacuum circuits 21b and 22b activated, that is, with the workpiece W held by suction over almost its entire surface (second region). In this second grinding process, only the second surface Wb side, which was flattened to its natural shape in the first grinding process, is held by suction, so even if almost the entire surface of the workpiece W is held by suction, no elastic deformation that would correct the waviness occurs. Through this second grinding process, the peaks of the waviness on the first surface Wa of the workpiece W are ground down, and the entire surface becomes flat (Figure 9(b2)).

[0052] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these embodiments, and various modifications are possible. For example, although the embodiments illustrate a surface grinding method using a vertical surface grinding machine, any grinding device that holds one side of a workpiece by suction and grinds the opposite side can be used in this surface grinding method, regardless of whether it is vertical or horizontal. In addition, the spindle may be set to two axes to provide two grinding positions, and the chuck table may be one or three or more.

[0053] Regarding the first vacuum circuit 21 operated in the first grinding process, in the first embodiment, as shown in Figure 2, the upper end of the first suction passage 23 is located below the porous plate 12, and a configuration is adopted in which the vicinity of the center of the workpiece W is vacuum-suctioned through the porous plate 12. However, the invention is not limited to this configuration, and for example, as shown in Figure 10, a configuration may be adopted in which the upper end of the first suction passage 23 penetrates the central part of the porous plate 12 and directly vacuums the vicinity of the center of the workpiece W.

[0054] In the first embodiment, the suction range and suction force on the workpiece W by the chuck table 3 can be adjusted by adjusting the negative pressure of the vacuum suction source, changing the thickness of the porous plate 12, changing the protrusion and diameter size of the suction passage formed in the base plate 11, etc. By adjusting the negative pressure of the vacuum suction source, the suction force near the center of the workpiece in the first grinding process can be easily changed, for example. Figure 11(a) shows an example in which the thickness of the porous plate 12 is smaller than in the first embodiment, and Figure 11(b) shows an example in which the diameter size of the tip side (workpiece W side) of the first suction passage 23 is smaller than in the first embodiment, and the thickness of the porous plate 12 is also reduced in correspondence with the first suction passage 23. Figure 12 also shows an example in which the diameter size and number of the first suction passages 23 are changed in the example of Figure 10, that is, in a configuration in which the upper end of the first suction passage 23 penetrates the central part of the porous plate 12 and directly vacuums the area near the center of the workpiece W. Furthermore, the modified suction passage 23 shown in Figure 12 can also be applied as a modified suction passage 23a of the chuck table 3a in the second embodiment.

[0055] In the first embodiment, an example was shown in which only the vicinity of the center of the workpiece W is held by suction by activating the first vacuum circuit 21 in the first grinding step. However, it is also possible to configure the system to partially hold multiple locations in addition to the vicinity of the center. The same applies to the first grinding step in the second embodiment. In this case, it is essential to adjust the suction range and suction force on the workpiece W so as not to distort the natural shape of the workpiece W, but it is also possible to improve the overall shape accuracy (SORI / WARP) of the workpiece. Here, "SORI" and "WARP" are parameters that represent the shape when the wafer (workpiece) is held without vacuum suction. "SORI" represents the sum of the heights of the highest and lowest points on the wafer surface relative to the least-squares plane of the wafer, and "WARP" represents the sum of the heights of the highest and lowest points on the wafer surface as a deviation from the three reference points of the wafer.

[0056] In the second grinding step, it is most desirable to operate both the first and second vacuum circuits 21 (or 21b) and 22 (or 22b) together to hold the workpiece W in suction over substantially its entire surface (second region) while grinding, as in the first and second embodiments, but it is not limited to this. That is, the second region of the workpiece W held in suction in the second grinding step may be a narrower region than the entire surface of the workpiece W. For example, only the first vacuum circuit 21 (or 21b) of the first and second vacuum circuits 21 (or 21b) and 22 (or 22b) may be operated to hold only the vicinity of the center of the workpiece W in suction while grinding is performed. [Explanation of Symbols]

[0057] 3. Chuck table (workpiece holding means) 3a Chuck table (first workpiece holding means) 3b Chuck table (second workpiece holding means) 6. Grinding Wheel (Grinding Wheel) 12 Porous plate 13 Guide ring (guide means) 17 Blocks (Guidance means) 27 Adsorption area switching means 31 Workpiece holding section Double job wa Page 1 Wb 2nd page

Claims

1. A surface grinding method comprising grinding both sides of a plate-shaped workpiece with a grinding wheel while the workpiece holding means is held in place by suction, the workpiece holding means is rotated, A first grinding step in which the second surface of the workpiece is ground while the first surface of the workpiece is held by the workpiece holding means in a first region near its center, The apparatus further comprises a second grinding step, in which, after the first grinding step, the first surface of the workpiece is ground while the second surface of the workpiece is held in a second region by the workpiece holding means. A surface grinding method characterized by the following features.

2. The second region corresponds to substantially the entire surface of the workpiece. The surface grinding method according to feature 1.

3. The first grinding step is performed with the outer circumference of the workpiece guided non-rotatably relative to the workpiece holding means by the guide means provided on the workpiece holding means. The surface grinding method according to claim 1 or 2.

4. The first grinding step and the second grinding step are performed by switching the suction area of ​​one of the workpiece holding means. The surface grinding method according to feature 1.

5. The first grinding step and the second grinding step are performed using separate workpiece holding means with different suction areas. The surface grinding method according to feature 1.

6. A workpiece holding means capable of holding a plate-shaped workpiece by suction, A grinding wheel for grinding the workpiece held by the workpiece holding means, In a surface grinding apparatus equipped with, The workpiece holding means is equipped with a suction region switching means that can switch the suction region of the workpiece between a first region near the center and a second region different from the first region. The suction area switching means allows switching of the suction area depending on whether the first surface of the workpiece is held by suction and the second surface is ground, or whether the second surface of the workpiece is held by suction and the first surface is ground afterward. A surface grinding apparatus characterized by the following features.

7. A workpiece holding means capable of holding a plate-shaped workpiece by suction on a workpiece holding section, A grinding wheel for grinding the workpiece held by the workpiece holding means, In a surface grinding apparatus equipped with, The workpiece holding means comprises a first workpiece holding means that has a first region near the center as an adsorption region, and a second workpiece holding means that has a second region different from the first region as an adsorption region. The workpiece holding means used can be changed depending on whether the first surface of the workpiece is held by suction and the second surface is ground, or whether the second surface of the workpiece is held by suction and the first surface is ground afterward. A surface grinding apparatus characterized by the following features.

8. The workpiece holding portion in the first workpiece holding means is formed from a non-porous material. The workpiece holding portion in the second workpiece holding means is formed from a porous material. The surface grinding apparatus according to feature 7.

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