Method for grinding a workpiece

Abstract

The present application provides a grinding method for a workpiece, which suppresses the occurrence of an adverse condition that is likely to occur in the latter half of grinding when a hard wafer or the like is subjected to multistage grinding in a TAIKO process. The workpiece has a silicon single-crystal substrate, a compound semiconductor single-crystal substrate, a single-crystal sapphire substrate, or a composite oxide single-crystal substrate with a resistivity of 0.1 Ω·cm or less, and the grinding method has: a first grinding step of forming a ring-shaped reinforcing portion, a thin first thin plate portion located radially inside the ring-shaped reinforcing portion, and a second thin plate portion located radially inside the first thin plate portion on the workpiece using a first grinding wheel having a plurality of first grinding tools arranged in a ring shape along the circumference of a first base in a circular ring shape; and a second grinding step of grinding the first thin plate portion and the second thin plate portion using a second grinding wheel having a plurality of second grinding tools each containing abrasive grains having an average particle diameter smaller than the average particle diameter of the abrasive grains of the first grinding tools arranged in a ring shape along the circumference of a second base in a circular ring shape.

Description

Technical Field

[0001] The present invention relates to a grinding method for a workpiece, wherein a single-crystal substrate of the workpiece is ground to form a thin plate portion and an annular reinforcing portion surrounding the outer periphery of the thin plate portion on the workpiece. Background Technology

[0002] With the increasing popularity of System in Package (SiP), which stacks multiple thinned device chips into a single package, there is a growing demand for wafer thinning techniques that offer high yield. One such wafer thinning technique is known as TAIKO (a registered trademark) (hereinafter referred to as the TAIKO process for convenience).

[0003] In the TAIKO process, when grinding the back side of a wafer with a device area on the front side having multiple devices formed thereon, a predetermined area on the back side corresponding to the device area on the front side is ground, thereby leaving the outer peripheral portion of the back side as an annular protrusion (for example, see Patent Document 1).

[0004] Therefore, compared with the case of uniformly thinning the entire back side, the strength of the wafer can be improved, thus having the advantages of suppressing the warping of the thinned wafer and the breakage of the wafer during transport.

[0005] In addition, in the TAIKO process, firstly, after rough grinding of a specified area on the back side using a rough grinding wheel with a rough grinding tool, fine grinding of the specified area after rough grinding is performed using a fine grinding wheel with a fine grinding tool.

[0006] However, in the case of multi-stage grinding (i.e., when coarse grinding and fine grinding are performed in sequence), the condition of the grinding wheel tends to deteriorate in the second half of the grinding process (i.e., fine grinding) when grinding hard wafers such as (1) highly-doped silicon wafers with relatively high impurity concentrations and (2) compound semiconductor wafers (e.g., gallium nitride (GaN) and silicon carbide (SiC)).

[0007] When the condition of the grinding wheel deteriorates, grinding resistance increases, resulting in adverse conditions such as a sharp increase in the current used to drive the spindle.

[0008] Patent Document 1: Japanese Patent Application Publication No. 2007-19461 Summary of the Invention

[0009] The present invention was made in view of this problem, and its purpose is to suppress the defects that are prone to occur in the second half of the grinding process when performing multi-stage grinding on hard wafers and the like in the TAIKO process.

[0010] According to one aspect of the present invention, a grinding method for a workpiece is provided, wherein a thin plate portion and an annular reinforcing portion surrounding the outer periphery of the thin plate portion are formed on the workpiece by grinding the single crystal substrate comprising the workpiece. The single crystal substrate is a silicon single crystal substrate, a compound semiconductor single crystal substrate, a single crystal sapphire substrate, or a composite oxide single crystal substrate with a resistivity of 0.1 Ω·cm or less. The grinding method for the workpiece includes the following steps: a holding step in which the workpiece is held using a chuck stage; and a first grinding step in which a first grinding tool with a plurality of first grinding tools arranged in a ring along the circumference of a first annular base is used. The grinding wheel comprises an annular reinforcing portion formed on the workpiece in the radial direction of the workpiece, a first thin plate portion formed in the radial direction of the annular reinforcing portion and thinner than the annular reinforcing portion, and a second thin plate portion formed in the radial direction of the first thin plate portion and thinner than the first thin plate portion; and a second grinding step, which, after the first grinding step, uses a second grinding wheel with a plurality of second grinding tools arranged in a ring along the circumference of the annular second base to grind the first thin plate portion and the second thin plate portion, wherein the plurality of second grinding tools each contains abrasive grains having an average grain size smaller than the average grain size of the abrasive grains of the first grinding tool.

[0011] Preferably, the first grinding step includes the following steps: an upper processing step to form the annular reinforcing portion and the first thin plate portion; and a lower processing step to form the second thin plate portion after the upper processing step.

[0012] In addition, the first grinding step preferably includes the following steps: an inner processing step to form the second thin plate portion; and an outer processing step to form the first thin plate portion and the annular reinforcing portion after the inner processing step.

[0013] In addition, preferably, in the first grinding step, the single crystal substrate of the workpiece is ground in a state where the rotation trajectory of the plurality of first grinding tools does not pass through the extension line of the rotation axis of the chuck table, thereby forming a cylindrical protrusion located radially inside the second thin plate portion and having the same thickness as the first thin plate portion. In the second grinding step, the first thin plate portion, the second thin plate portion, and the cylindrical protrusion are ground.

[0014] In the second grinding step of the workpiece grinding method according to one aspect of the present invention, firstly, the second grinding wheel is dressed for the first time using the upper surface side of the first thin plate portion. Then, the first thin plate portion can be ground using the second grinding wheel that has undergone the first dressing.

[0015] When further grinding is performed, the second grinding wheel is dressed a second time using the upper surface side of the second thin plate portion. Then, the second thin plate portion can be ground using the second grinding wheel that has undergone the second dressing.

[0016] In other words, in the second grinding step, multiple dressing operations can be performed at intervals through staged grinding. In this way, the condition of the grinding wheel can be restored at different times in the second grinding step, thus suppressing the adverse conditions that are prone to occur in the latter half of the grinding process. Attached Figure Description

[0017] Figure 1 This is a flowchart of the grinding method for the workpiece in the first embodiment.

[0018] Figure 2 It is a three-dimensional view of the workpiece, etc.

[0019] Figure 3 This is a diagram illustrating the holding steps.

[0020] Figure 4 This is a diagram showing the first grinding step.

[0021] Figure 5 It is a cross-sectional view of a portion of the workpiece after the upper processing steps.

[0022] Figure 6 (A) is a partial cross-sectional side view showing the relative movement of the chuck table and the rough grinding unit in the horizontal direction. Figure 6 (B) is a partial sectional side view showing the lower side machining steps.

[0023] Figure 7 It is a cross-sectional view of a portion of the workpiece after the lower processing steps.

[0024] Figure 8 (A) is a partial cross-sectional side view of the workpiece, etc., at the start of the second grinding step. Figure 8 (B) is a partial sectional side view of the workpiece, etc., during the second grinding step.

[0025] Figure 9 This is a cross-sectional view of a portion of the workpiece after the second grinding step.

[0026] Figure 10 This is a flowchart of the grinding method for the workpiece in the second embodiment.

[0027] Figure 11 (A) is a cross-sectional view of a portion of the workpiece after the inner machining steps. Figure 11 (B) is a cross-sectional view of a portion of the workpiece after the outer processing steps.

[0028] Figure 12 It is a cross-sectional view of a portion of the workpiece after the upper processing steps.

[0029] Figure 13 (A) is a top view of the lower processing step in the third embodiment. Figure 13 (B) is a partial cross-sectional side view of the lower side processing step in the third embodiment.

[0030] Figure 14 It is a cross-sectional view of a portion of the workpiece after the lower processing steps.

[0031] Figure 15 (A) is a cross-sectional view of a portion of the workpiece after the cylindrical protrusion has been formed by the inner machining step in the fourth embodiment. Figure 15 (B) is a cross-sectional view of a portion of the workpiece after the outer processing step in the fourth embodiment.

[0032] Label Explanation

[0033] 2: Grinding device; 4: Chuck table; 4a: Holding surface; 4b: Rotation axis; 6: Frame; 8: Porous plate; 10: Rough grinding unit; 12: Spindle; 14: Mounting base; 11: Workpiece; 11a: Radial; 13: Single crystal substrate; 13a: Front side; 13b: Back side; 13c: First thin plate section; 13d: Annular reinforcement section; 13e: Rough surface area; 13f: Second thin plate section; 13g: Third thin plate section; 13h, 13i: Cylindrical protrusions; 15: Pre-dividing line; 17: Device; 19: Protective component; 16: Rough grinding wheel (first grinding wheel); 18a: Grinding wheel base 18b: Rough grinding wheel (first grinding wheel); 20: Fine grinding unit; 22: Spindle; 24: Mounting base; 21a: First annular stepped section; 21b: Second annular stepped section; 21c: Third annular stepped section; 26: Fine grinding wheel (second grinding wheel); 28a: Grinding wheel base (second base); 28b: Fine grinding wheel (second grinding wheel); S10: Holding step; S20: First grinding step; S22: Upper side machining step; S24: Lower side machining step; S26: Inner side machining step; S28: Outer side machining step; S30: Second grinding step. Detailed Implementation

[0034] An embodiment of one aspect of the present invention will be described with reference to the accompanying drawings. Figure 1 It is the workpiece 11 in the first embodiment (see reference). Figure 2 A flowchart of grinding methods (e.g., grinding). Figure 2 As shown, the workpiece 11 includes a disk-shaped single-crystal substrate 13.

[0035] The single-crystal substrate 13 in this embodiment is a silicon single-crystal substrate, a compound semiconductor single-crystal substrate, or a composite oxide single-crystal substrate with a resistivity of 0.1 Ω·cm or less. A silicon single-crystal substrate with a resistivity of 0.001 Ω·cm or more and 0.1 Ω·cm or less is generally referred to as a highly doped silicon wafer.

[0036] Highly doped silicon wafers are harder than typical single-crystal silicon substrates (e.g., resistivity greater than 0.1 Ω·cm and less than 40.0 Ω·cm), and therefore are more prone to defects during grinding (especially fine grinding) compared to grinding typical single-crystal silicon substrates.

[0037] Similarly, compound semiconductor single crystal substrates and single crystal sapphire substrates formed from compound semiconductor materials such as gallium nitride and silicon carbide are harder than ordinary silicon single crystal substrates. Therefore, they are more prone to defects during grinding (especially fine grinding) compared to grinding ordinary silicon single crystal substrates.

[0038] In contrast, wafers formed from lithium tantalate (LT) and lithium niobate (LN) (i.e., composite oxide single crystal substrates) are not harder than ordinary silicon single crystal substrates, but they are prone to clogging during grinding. Therefore, compared with grinding ordinary silicon single crystal substrates, they are more prone to defects during grinding (especially fine grinding).

[0039] On the front side 13a of the single-crystal substrate 13, multiple pre-defined dividing lines (spacers) 15 are arranged in a grid pattern, and devices such as ICs (Integrated Circuits) 17 are formed in each small area divided by the multiple pre-defined dividing lines 15. In addition, there are no restrictions on the type, number, shape, structure, size, and arrangement of the devices 17 in the workpiece 11.

[0040] In this embodiment, a defined area on the back side 13b, corresponding to the area on the front side 13a (i.e., the device area) where the plurality of devices 17 are formed, is ground to thin a portion of the workpiece 11. Furthermore, the defined area on the back side 13b is a circular area concentric with the outer periphery of the workpiece 11 and smaller than the outer diameter of the workpiece 11.

[0041] Before grinding the single-crystal substrate 13, a protective member 19 made of resin with approximately the same diameter as the single-crystal substrate 13 (see reference) is applied. Figure 2 ) Attached to the front side 13a. Figure 2 This is a perspective view of the workpiece 11, etc. The protective component 19 is, for example, a strip having a substrate layer and an adhesive layer, the adhesive layer of which is attached to the front side 13a of the single crystal substrate 13.

[0042] However, the protective component 19 may also have only a substrate layer and no adhesive layer. In this case, the protective component 19 is attached to the front side 13a by thermoforming. By attaching the protective component 19 to the front side 13a, the impact on the device 17 during grinding can be mitigated.

[0043] After attaching the protective component 19, the chuck table 4 of the grinding device 2 (see reference) is used. Figure 3 The protective component 19 side of the workpiece 11 is attracted and held (holding step S10). Figure 3 This is a diagram showing the holding step S10. Additionally, in... Figure 3 In the following figures, several dividing lines 15 and device 17 are omitted.

[0044] The chuck stage 4, for example, includes a disc-shaped frame 6 made of non-porous ceramic. A circular recess is formed on the upper surface of the frame 6. A disc-shaped porous plate 8 made of porous ceramic is fixed to this recess.

[0045] The upper surface of the porous plate 8 has a conical shape, with the central portion protruding more than the outer periphery. Furthermore, in... Figure 3 For ease of explanation, the shape of the porous plate 8 has been exaggerated. On the upper surface of the porous plate 8, the protrusion of the central portion relative to the outer periphery is, for example, 10 μm or more and 30 μm or less.

[0046] The upper surface of the porous plate 8 is approximately the same plane as the upper surface of the frame 6, and functions as a holding surface 4a for attracting and holding the workpiece 11 through the protective member 19. The porous plate 8 is connected to a suction source (not shown) such as a vacuum pump via a flow path, valve (not shown) etc. provided inside the frame 6.

[0047] Therefore, when the workpiece 11 is placed on the upper surface of the porous plate 8 with the protective member 19 in between, and then negative pressure from the attraction source is transmitted to the porous plate 8, the workpiece 11 is attracted and held by the holding surface 4a in a manner that exposes the back side 13b of the single crystal substrate 13 upwards.

[0048] A rotary drive source (not shown), such as an electric motor, is provided at the lower part of the frame 6 to rotate the chuck table 4. The chuck table 4 can rotate around the rotation axis 4b by the power of the rotary drive source.

[0049] The rotation axis 4b is tilted at a small angle relative to the Z-axis direction (vertical direction, up and down direction) in such a way that a portion of the holding surface 4a is approximately horizontal. Furthermore, the chuck table 4 is supported by a horizontal movement mechanism (not shown), which allows it to move in a horizontal direction perpendicular to the Z-axis.

[0050] After holding step S10, the specified area on the back side 13b corresponding to the device area is ground (first grinding step S20). Figure 4 This is a diagram illustrating the first grinding step S20. (See diagram below.) Figure 4 As shown, a rough grinding unit (first grinding unit) 10 is arranged above the chuck table 4.

[0051] The rough grinding unit 10 includes, for example, a cylindrical spindle housing (not shown). A Z-axis moving mechanism (not shown) is connected to the spindle housing, allowing the rough grinding unit 10 to move along the Z-axis. A portion of a cylindrical spindle 12 is rotatably housed in the space inside the spindle housing.

[0052] The spindle housing and spindle 12 are arranged along the Z-axis. A rotary drive source (not shown) such as an electric motor is provided on a portion of the upper side of the spindle 12. The lower end of the spindle 12 protrudes downwards beyond the lower end of the spindle housing.

[0053] A disc-shaped mounting base 14 with a diameter smaller than that of the workpiece 11 (e.g., having approximately half the diameter of the workpiece 11) is fixed to the lower end of the spindle 12. An annular roughing grinding wheel (first grinding wheel) 16 is fixed to the lower surface of the mounting base 14.

[0054] The rough grinding wheel 16 includes an annular grinding wheel base (first base) 18a formed of a metal such as aluminum alloy. A plurality of rough grinding tools (first grinding tools) 18b are arranged in a ring at approximately equal intervals along the circumference of the grinding wheel base 18a on the lower surface side of the grinding wheel base 18a.

[0055] The rough grinding wheel 18b comprises abrasive grains formed from cBN (cubic boron nitride), diamond, etc., and bonding materials such as ceramic binders and resin binders for fixing the abrasive grains. The abrasive grains of the rough grinding wheel 18b have a relatively large average grain size. For example, abrasive grains with a grit size of #240 to #1200 are used.

[0056] The particle size is specified in JIS R6001-2:2017 (Particle size of grinding materials for grinding wheels - Part 2: Micro powder), a JIS standard established by the Japanese Industrial Standards Committee. Furthermore, particle sizes not specified in JIS R6001-2:2017 shall conform to or be based on expressions commonly used in the industry for manufacturing and selling abrasives.

[0057] A grinding water supply nozzle (not shown) is provided near the rough grinding wheel 16 to supply grinding fluid (typically pure water) to the rough grinding tool 18b and the like. During grinding, this fluid is used to remove heat generated in the machining area and grinding chips.

[0058] When grinding the single-crystal substrate 13 using the coarse grinding wheel 16, the chuck stage 4 is first moved directly below the coarse grinding unit 10. Specifically, the chuck stage 4 is moved such that the coarse grinding wheel 16 (i.e., all the coarse grinding tools 18b) is located directly above the circular area where the device 17 is formed.

[0059] Then, as Figure 4 As shown, the chuck table 4 and the rough grinding wheel 16 are rotated in the specified directions, and while the grinding fluid is supplied from the nozzle, the rough grinding unit 10 is lowered at a specified speed (grinding feed speed) (upper machining step S22).

[0060] In the upper machining step S22, the rotational speed of the chuck table 4 is set to 100 rpm or more and 600 rpm or less (typically 300 rpm), the rotational speed of the rough grinding wheel 16 is set to 1000 rpm or more and 7000 rpm or less (typically 4500 rpm), and the grinding feed rate is set to 0.8 μm / s or more and 10 μm / s or less (typically 6.0 μm / s).

[0061] Figure 5 This is a schematic cross-sectional view showing a portion of the workpiece 11 after the upper processing step S22. In the upper processing step S22, the back side 13b side corresponding to the device area is ground using a rough grinding wheel 16, thereby forming a disk-shaped first thin plate portion 13c and an annular reinforcing portion 13d surrounding the outer periphery of the first thin plate portion 13c.

[0062] The first thin plate portion 13c and the annular reinforcing portion 13d constitute the first annular stepped difference portion 21a. The annular reinforcing portion 13d is the area that was not ground by the upper processing step S22, and it is located on the outermost side in the radial direction 11a of the workpiece 11.

[0063] The first thin plate portion 13c is the area that has been ground by the upper processing step S22. It is located inside the annular reinforcing portion 13d in the radial direction 11a and is thinner than the annular reinforcing portion 13d. A rough surface region 13e caused by grinding by the coarse grinding tool 18b is formed on the back side 13b of the first thin plate portion 13c.

[0064] The rough surface region 13e has a greater degree of roughness than the roughness formed on the ground surface of the workpiece 11 by the second grinding step S30 described later. In one example, the roughness is evaluated by arithmetic mean roughness Ra, maximum height Rz, etc.

[0065] After performing the upper side machining step S22 to form the first thin plate portion 13c and the annular reinforcing portion 13d, the inner side of the first thin plate portion 13c is then ground radially 11a using a rough grinding wheel 16, thereby forming a second thin plate portion 13f that is thinner than the first thin plate portion 13c (see reference). Figure 7 (Lower side processing step S24).

[0066] In the lower machining step S24, firstly, as Figure 6 As shown in (A), in order to grind the inner side of the first thin plate portion 13c in the radial direction using the rough grinding wheel 16, the chuck table 4 is moved in the horizontal direction. As a result, the outer side of the rough grinding tool 18b moves away from the inner peripheral side of the annular reinforcement portion 13d.

[0067] Figure 6 (A) is a partial cross-sectional side view showing the chuck table 4 and the rough grinding unit 10 moving relative to each other in the horizontal direction. When the chuck table 4 and the rough grinding wheel 16 are moving relative to each other, the chuck table 4 and the rough grinding wheel 16 can be kept rotating or their rotation can be stopped.

[0068] There are no strict restrictions on the speed or distance of movement. For example, the speed of movement can be set to be above 1.0 mm / s and below 2.0 mm / s, and the distance of movement can be set to be above 3.0 mm and below 6.0 mm.

[0069] After moving horizontally, as Figure 6 As shown in (B), the rough grinding unit 10 is lowered relative to the chuck table 4 to further perform rough grinding on the first thin plate portion 13c. Furthermore, in Figure 6 (A) and Figure 6 In (B), the rough surface region 13e is omitted for ease of observation. In subsequent figures, the rough surface region 13e is sometimes also omitted for convenience.

[0070] Figure 6 (B) is a partial cross-sectional side view showing the lower side machining step S24. Figure 7 This is a schematic cross-sectional view showing a portion of the workpiece 11 after the lower machining step S24. The rotational speed of the chuck table 4, the rotational speed of the rough grinding wheel 16, and the grinding feed rate in the lower machining step S24 are the same as those used in the upper machining step S22 described above.

[0071] As described above, in the lower processing step S24, the inner side of the first thin plate portion 13c is ground in the radial direction 11a to form the second thin plate portion 13f. At this time, a rough surface region 13e is also formed on the back side 13b of the second thin plate portion 13f, and a second annular stepped difference portion 21b composed of the first thin plate portion 13c and the second thin plate portion 13f is also formed.

[0072] Furthermore, in the next machining step S24, the descent speed of the rough grinding unit 10 can be changed accordingly to the grinding progress. Specifically, the grinding feed rate can be reduced as the grinding progresses.

[0073] For example, depending on the grinding progress, the grinding feed rate is gradually reduced to 6.0 μm / s, then to 3.0 μm / s, and then to 1.0 μm / s. By gradually reducing the grinding feed rate, the thickness of the second thin plate portion 13f can be adjusted with high precision.

[0074] After the first grinding step S20, the rough grinding unit 10 is raised and moves away from the workpiece 11. Then, a fine grinding unit (second grinding unit) 20, different from the rough grinding unit 10, is positioned above the workpiece 11 (see reference). Figure 8 (A) The first thin plate portion 13c and the second thin plate portion 13f are ground using the fine grinding unit 20 (second grinding step S30).

[0075] In this embodiment, the fine grinding unit 20 is mounted together with the rough grinding unit 10 in the grinding apparatus 2. However, the fine grinding unit 20 may also be mounted in a different grinding apparatus (not shown) than the grinding apparatus 2 which has the rough grinding unit 10.

[0076] The fine grinding unit 20 includes, for example, a cylindrical spindle housing (not shown). A Z-axis moving mechanism (not shown) is connected to the spindle housing, for example, allowing the fine grinding unit 20 to move along the Z-axis direction.

[0077] A portion of a cylindrical spindle 22 is housed within the space inside the spindle housing. The spindle housing and spindle 22 are arranged along the Z-axis. A rotary drive source (not shown) such as an electric motor is mounted on a portion of the upper side of the spindle 22.

[0078] The lower end of the spindle 22 protrudes downwards beyond the lower end of the spindle housing. A disc-shaped mounting base 24, approximately the same diameter as the aforementioned mounting base 14, is fixed to the lower end of the spindle 22.

[0079] A fine grinding wheel (second grinding wheel) 26, with a diameter approximately the same as that of the coarse grinding wheel 16 and in an annular shape, is fixed to the lower surface of the mounting base 24. The fine grinding wheel 26 includes an annular grinding wheel base (second base) 28a formed of a metal such as aluminum alloy.

[0080] On the lower surface of the grinding wheel base 28a, a plurality of fine grinding tools (second grinding tools) 28b are arranged in a ring at approximately equal intervals along the circumference of the grinding wheel base 28a. The fine grinding tool 28b contains abrasive grains formed from cBN (cubic boron nitride), diamond, etc., and bonding materials such as ceramic binders and resin binders for fixing the abrasive grains.

[0081] The average grain size of the abrasive grains contained in the fine grinding wheel 28b is smaller than the average grain size of the abrasive grains contained in the rough grinding wheel 18b. Regarding the average grain size, for example, when the size of one particle is expressed in terms of a specified grain size (i.e., length), it is determined based on the frequency distribution of the particle group expressed using that grain size.

[0082] In addition, there are known methods for representing particle size, such as geometric diameter and equivalent diameter. Geometric diameters include Feret diameter, maximum diameter in a given direction (i.e., Krummbein diameter), Martin diameter, sieve diameter, etc. Equivalent diameters include the equivalent diameter of a projected area circle (i.e., Heywood diameter), the equivalent diameter of a sphere with equal surface area, the equivalent diameter of a sphere with equal volume, Stokes diameter, light scattering diameter, etc.

[0083] Regarding particle swarms, when a frequency distribution is constructed with particle size (μm) on the horizontal axis and frequency on the vertical axis, for example, the average particle size is the average value under a weight-based or volume-based distribution. Alternatively, instead of the average particle size, the particle size can be determined based on the median particle size, which is the cumulative frequency of the particles in the frequency distribution of the particle swarm, or the mode particle size, which is the particle size with the highest frequency.

[0084] Even when based on the median or mode grit size, the abrasive grains contained in the finishing grinding wheel 28b have a smaller grit size than those contained in the coarse grinding wheel 18b. The finishing grinding wheel 28b of this embodiment uses abrasive grains with a grit size of #2000 to #10000, for example.

[0085] When grinding the first thin plate portion 13c and the second thin plate portion 13f using the fine grinding wheel 26, the chuck table 4 is first moved to a position directly below the fine grinding unit 20. Specifically, the position of the chuck table 4 is adjusted so that all the fine grinding tools 28b are located radially 11a further inward than the inner circumferential side of the annular reinforcement portion 13d (see reference). Figure 8 (A)).

[0086] Then, the chuck table 4 and the fine grinding wheel 26 are rotated in the specified directions, and while the grinding fluid is supplied from the nozzle, the fine grinding wheel 26 is lowered at the specified speed. Figure 8 (A) is a partial cross-sectional side view of the workpiece 11, etc., at the start of the second grinding step S30. Figure 8 (B) is a partial cross-sectional side view of the workpiece 11, etc., in the second grinding step S30.

[0087] In the second grinding step S30, the rotational speed of the chuck table 4 is set to 100 rpm or more and 600 rpm or less (typically 300 rpm), and the rotational speed of the fine grinding wheel 26 is set to 1000 rpm or more and 7000 rpm or less (typically 4000 rpm).

[0088] In the second grinding step S30, the fine grinding tool 28b is first dressed using the rough surface region 13e on the first thin plate portion 13c. Therefore, when the grinding feed progresses, the first thin plate portion 13c can be ground using the fine grinding tool 28b that has undergone the first dressing.

[0089] As the grinding feed progresses, the finishing grinding tool 28b is dressed a second time using the rough surface region 13e on the second thin plate portion 13f. Therefore, as the grinding feed progresses, the first thin plate portion 13c and the second thin plate portion 13f can be ground using the finishing grinding tool 28b that has undergone the second dressing.

[0090] In the second grinding step S30, multiple dressing operations can be performed at intervals through staged grinding. In this way, the condition of the fine grinding tool 28b can be restored at different times in the second grinding step S30, thus suppressing the defects that are prone to occur in fine grinding.

[0091] Especially when performing fine grinding on highly doped silicon wafers, compound semiconductor single crystal substrates, and single crystal sapphire substrates, the condition can be restored by performing multiple adjustments at time intervals during fine grinding, thus enabling appropriate fine grinding.

[0092] Furthermore, in the fine grinding of composite oxide single-crystal substrates formed from materials such as LT and LN, clogging is prone to occur during grinding. When clogging occurs, more heat is generated in the processing area compared to when no clogging occurs, and the heat-sensitive LT and LN are prone to cracking. However, by performing multiple dressings at time intervals during fine grinding, the condition can be restored, thus reducing heat generation and allowing for proper fine grinding.

[0093] Figure 9This is a schematic cross-sectional view showing a portion of the workpiece 11 after the second grinding step S30. Figure 9 In the image, a portion of each of the first thin plate portion 13c and the second thin plate portion 13f removed in the second grinding step S30 is shown with a double-dotted line.

[0094] like Figure 9 As shown, a disc-shaped third thin plate portion 13g, which is thinner and has a larger diameter than the second thin plate portion 13f, is formed inside the first thin plate portion 13c that remains unground in the radial direction 11a. In addition, the second annular stepped difference portion 21b is removed and replaced to form a third annular stepped difference portion 21c composed of the first thin plate portion 13c and the third thin plate portion 13g.

[0095] Furthermore, in the second grinding step S30, after grinding only the first thin plate portion 13c as described above, grinding is performed on both the first thin plate portion 13c and the second thin plate portion 13f. Since the area of ​​the surface to be ground is relatively small when only the first thin plate portion 13c is ground, the grinding feed rate of the fine grinding unit 20 can be increased compared to grinding both the first thin plate portion 13c and the second thin plate portion 13f.

[0096] For example, in the first half of the fine grinding process where only the first thin plate portion 13c is ground, the grinding feed rate is set to 0.8 μm / s or more and 5.0 μm / s or less (typically 1.6 μm / s). In the second half of the fine grinding process where both the first thin plate portion 13c and the second thin plate portion 13f are ground, the grinding feed rate is set to 0.1 μm / s or more and less than 0.8 μm / s (typically, the feed rate is reduced in two stages: initially 0.6 μm / s and then 0.3 μm / s).

[0097] Therefore, compared with the case where the grinding feed rate is fixed at a relatively low speed during the second half of the fine grinding process throughout the entire second grinding step S30, the grinding time required can be shortened and efficiency improved.

[0098] Furthermore, compared to the case where the grinding feed rate is fixed at a relatively high speed during the first half of the fine grinding process throughout the second grinding step S30, the amount of damage and strain formed on the third thin plate portion 13g can be significantly reduced.

[0099] (Second Implementation)

[0100] Next, the second embodiment will be described. Figure 10 This is a flowchart of the grinding method for the workpiece 11 in the second embodiment. In the second embodiment, in the first grinding step S20 after the holding step S10, as follows... Figure 11As shown in (A), the second thin plate portion 13f described above is first formed (inner processing step S26).

[0101] Figure 11 (A) is a schematic cross-sectional view showing a portion of the workpiece 11 after the inner processing step S26. In the inner processing step S26, the rough surface region 13e described above is formed on the back side 13b side of the second thin plate portion 13f.

[0102] Then, after the inner machining step S26, as... Figure 11 As shown in (B), the first thin plate portion 13c and the annular reinforcing portion 13d are formed (outer side processing step S28). Figure 11 (B) is a schematic cross-sectional view showing a portion of the workpiece 11 after the outer processing step S28.

[0103] After the outer machining step S28, a second grinding step S30 is performed using the fine grinding wheel 26. In the second embodiment, the condition of the fine grinding tool 28b can be restored by repeating the process multiple times at time intervals, thus suppressing defects that are prone to occur during fine grinding.

[0104] (Third Implementation)

[0105] Next, the third embodiment will be described. The third embodiment is basically the same as the first embodiment, except that in the lower side processing step S24, a cylindrical protrusion 13h is formed in the center of the back side 13b (see reference). Figure 13 (A, etc.).

[0106] In the order described, in the upper processing step S22 of the third embodiment, the first thin plate portion 13c is formed in the same manner as in the first embodiment. Figure 12 It is a schematic cross-sectional view showing a portion of the workpiece 11 after the upper processing step S22.

[0107] In the lower processing step S24 following the upper processing step S22, the lower processing step S24 of the first embodiment (see reference) is similar to that of the lower processing step S24 in the first embodiment. Figure 6 Compared to (B), the rotation center of the spindle 12 is moved toward the center of the radial direction 11a of the workpiece 11 (see reference). Figure 13 (A) and Figure 13 (B)

[0108] Figure 13 (A) is a top view of the lower side processing step S24 in the third embodiment. Wherein, in Figure 13 In (A), radial saw marks are shown formed in the rough surface region 13e of the first thin plate portion 13c, the second thin plate portion 13f, and the cylindrical protrusion 13h.

[0109] Figure 13 (B) is a partial cross-sectional side view of the lower side processing step S24 in the third embodiment. In the lower side processing step S24, the back side 13b of the single crystal substrate 13 is ground while the rotation trajectory of the plurality of rough grinding tools 18b does not pass through the extension line of the rotation axis 4b of the chuck table 4.

[0110] Thus, a cylindrical protrusion 13h is formed in the radial direction 11a, located inside the second thin plate portion 13f and having the same thickness as the first thin plate portion 13c. Figure 14 It is a schematic cross-sectional view showing a portion of the workpiece 11 after the lower processing step S24.

[0111] Next, in the second grinding step S30, the fine grinding unit 20 is used to first perform fine grinding on the first thin plate portion 13c and the cylindrical protrusion 13h, and then perform grinding feed to perform fine grinding on the second thin plate portion 13f.

[0112] Therefore, the cylindrical protrusion 13h is removed, and the third thin plate portion 13g is formed (see reference). Figure 14 (The dotted line). In the third embodiment, the condition of the fine grinding tool 28b can also be restored by repeating the process multiple times at time intervals, thus suppressing the adverse conditions that are prone to occur during fine grinding.

[0113] Furthermore, in the third embodiment, as the cylindrical protrusion 13h is formed by the first grinding step S20, the volume of the workpiece 11 to be removed by grinding in the second grinding step S30 increases compared to the first and second embodiments.

[0114] However, compared with the first embodiment, the area of ​​the rough surface region 13e is increased, and therefore has the following advantages: when grinding the first thin plate portion 13c and the cylindrical protrusion 13h using the fine grinding tool 28b, a higher finishing effect can be obtained.

[0115] (Fourth implementation)

[0116] Next, the fourth embodiment will be described. In the fourth embodiment, it is basically the same as the second embodiment, except that in the inner processing step S26, a cylindrical protrusion 13i is formed in the center of the back surface 13b (see reference). Figure 15 (A, etc.).

[0117] In the following description, in the inner processing step S26 of the fourth embodiment, the second thin plate portion 13f is formed in the same manner as in the second embodiment. However, in the inner processing step S26 of the fourth embodiment, compared with the inner processing step S26 of the second embodiment, the rotation center of the spindle 12 is moved toward the center of the radial direction 11a of the workpiece 11.

[0118] While the rotation trajectories of the multiple coarse grinding tools 18b do not pass through the extension line of the rotation axis 4b of the chuck table 4, the back side 13b of the single crystal substrate 13 is ground to form a cylindrical protrusion 13i located in the radial direction 11a inside the second thin plate portion 13f and having the same thickness as the single crystal substrate 13.

[0119] Figure 15 (A) is a schematic cross-sectional view showing a portion of the workpiece 11 after the cylindrical protrusion 13i has been formed by the inner processing step S26. In the inner processing step S26, a rough surface region 13e is also formed on the back side 13b side of the second thin plate portion 13f.

[0120] Figure 15 (B) is a schematic cross-sectional view showing a portion of the workpiece 11 after the outer processing step S28 in the fourth embodiment. In the outer processing step S28, the height of the cylindrical protrusion 13i is reduced, becoming... Figure 14 The cylindrical protrusion 13h shown has the same height. In addition, a rough surface region 13e is formed on the back surface 13b side of the first thin plate portion 13c and the cylindrical protrusion 13h.

[0121] Next, in the second grinding step S30, using the fine grinding unit 20, the first thin plate portion 13c and the cylindrical protrusion 13h are first finely ground, and then the second thin plate portion 13f is finely ground by grinding feed. Thus, the third thin plate portion 13g is formed (see reference). Figure 15 (The dashed line of (B)).

[0122] In the fourth embodiment, the condition of the fine grinding tool 28b can be restored by repeating the process multiple times at time intervals, thus suppressing defects that are prone to occur during fine grinding. Furthermore, in the fourth embodiment, the area of ​​the rough surface region 13e is increased, similar to the third embodiment, thus providing the advantage of achieving a higher level of finishing effect.

[0123] Furthermore, the structure and method of the above embodiments can be appropriately modified to implement them without departing from the purpose of the present invention. In the above embodiments, the chuck table 4 is moved in the horizontal direction, but the rough grinding unit 10 and the fine grinding unit 20 can also be moved in the horizontal direction relative to the chuck table 4.

[0124] In addition, in the first grinding step S20 of the first and second embodiments described above, two step differences, namely the first annular step difference portion 21a and the second annular step difference portion 21b, are formed, but three or more step differences may also be formed.

[0125] By creating more than three step differences, the processing time required for the first grinding step S20 may be slightly longer, but it has the following advantages: in the subsequent second grinding step S30, it is possible to set more opportunities to restore the condition of the fine grinding tool 28b.

[0126] Furthermore, the retaining surface 4a of the chuck table 4 is not limited to a conical shape. When the chuck table 4 is viewed in a cross-section along its radial direction, the retaining surface 4a can also be a double-concave shape with a recess between the radial center and both ends.

[0127] When the holding surface 4a is in a double concave shape, the workpiece 11 held by the holding surface 4a is ground sequentially by the rough grinding unit 10 and the fine grinding unit 20, and the grinding is also performed with the rotation axis 4b tilted appropriately.

Claims

1. A method for grinding a workpiece, comprising grinding the single-crystal substrate of the workpiece, wherein a thin plate portion and an annular reinforcing portion surrounding the outer periphery of the thin plate portion are formed on the workpiece, characterized in that, The single-crystal substrate is a silicon single-crystal substrate, a compound semiconductor single-crystal substrate, a single-crystal sapphire substrate, or a composite oxide single-crystal substrate with a resistivity of less than 0.1 Ω·cm. The grinding method for the workpiece comprises the following steps: The holding step involves using a chuck table to hold the workpiece. In the first grinding step, a first grinding wheel with a plurality of first grinding tools arranged in a ring along the circumference of the annular first base is used to form on the workpiece an annular reinforcement portion located on the outermost side in the radial direction of the workpiece, a first thin plate portion located on the inner side of the annular reinforcement portion in the radial direction and thinner than the annular reinforcement portion, and a second thin plate portion located on the inner side of the first thin plate portion in the radial direction and thinner than the first thin plate portion; as well as The second grinding step involves grinding the first thin plate portion and the second thin plate portion using a second grinding wheel with a plurality of second grinding tools arranged in a ring along the circumference of the annular second base. The plurality of second grinding tools each contain abrasive grains with an average grain size smaller than that of the abrasive grains of the first grinding tool.

2. The grinding method for a workpiece according to claim 1, characterized in that, The first grinding step has the following steps: The upper processing steps form the annular reinforcing portion and the first thin plate portion; and The lower processing step forms the second thin plate portion after the upper processing step.

3. The grinding method for a workpiece according to claim 1, characterized in that, The first grinding step has the following steps: The inner processing steps form the second thin plate portion; and The outer processing step, after the inner processing step, forms the first thin plate portion and the annular reinforcing portion.

4. The grinding method for a workpiece according to claim 2 or 3, characterized in that, In this first grinding step, The single-crystal substrate of the workpiece is ground while the rotation trajectory of the plurality of first grinding tools does not pass through the extension line of the rotation axis of the chuck table, thereby forming a cylindrical protrusion located radially inside the second thin plate portion and having the same thickness as the first thin plate portion. In this second grinding step, The first thin plate portion, the second thin plate portion, and the cylindrical protrusion are ground.

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