Method of processing a wafer

Abstract

The present invention provides a wafer processing method that stably performs so-called TAIKO grinding that forms a circular recess and a ring-shaped protrusion on the back surface of a wafer. The method has the following steps: a processing preparation step (1001) that holds the wafer with a chuck table and fixes a rough grinding wheel having a diameter corresponding to the radius of the wafer to the lower end of a spindle; a limited grinding step (1002) that grinds the back surface of the wafer held by the chuck table, excluding the central portion, with the rough grinding wheel to form a ring-shaped recess and a central protrusion; a position adjustment step (1003) that moves the rough grinding wheel away from the wafer and toward the outer periphery of the wafer; and a circular grinding step (1004) that grinds the back surface of the wafer, including the central protrusion, to remove the central protrusion and form a circular recess, and forms a ring-shaped protrusion on the back surface of the wafer corresponding to the outer peripheral remaining area.

Description

Technical Field

[0001] This invention relates to a method for processing wafers, and in particular a method for processing wafers subjected to so-called TAIKO (registered trademark) grinding. Background Technology

[0002] As semiconductor devices become thinner and smaller, the thickness of wafers on which semiconductor devices are formed is ground down to less than 100 μm. The ground wafer warps due to grinding deformation on the ground surface. It is very difficult to deposit metal or other materials on the back side of the warped wafer. Therefore, a so-called TAIKO grinding technique (see, for example, Patent Documents 1 and 2) is used, where only the area of ​​the wafer excluding the periphery is ground to form a circular recess corresponding to the device area and an annular protrusion corresponding to the remaining peripheral area on the back side of the wafer.

[0003] Patent Document 1: Japanese Patent No. 5390740

[0004] Patent Document 2: Japanese Patent No. 4758222

[0005] In TAIKO grinding, because a grinding wheel with a diameter smaller than the wafer is used, the amount of material removed per grinding wheel is relatively larger compared to a conventional grinding wheel with a diameter greater than or equal to that of the wafer, sometimes making it difficult to perform TAIKO grinding consistently. Furthermore, even when rotating at the same speed, the smaller diameter makes it difficult to increase the rotational speed.

[0006] In particular, oxide or nitride films formed on the back side are difficult to grind, and sometimes the load current of the spindle motor exceeds the specified value, making it impossible to perform TAIKO grinding stably. Furthermore, the same tendency exists with so-called highly doped wafers. Summary of the Invention

[0007] The object of the present invention is to provide a wafer processing method capable of stably performing so-called TAIKO grinding, which forms a circular recess corresponding to the device region and an annular protrusion corresponding to the remaining outer peripheral region on the back side of the wafer.

[0008] To solve the aforementioned problems and achieve the objective, the wafer processing method of the present invention provides a wafer processing method having a device region on the front side in which devices are formed in each region divided by multiple intersecting predetermined dividing lines, and a remaining peripheral region surrounding the device region. The wafer processing method is characterized by the following steps: a processing preparation step, in which the wafer is held using a chuck stage having a holding surface for holding the wafer and capable of rotation, and a grinding wheel with a diameter equivalent to the radius of the wafer is fixed to the lower end of a spindle having a rotation axis perpendicular to the holding surface; and a defining grinding step, in which the grinding wheel is used to grind the wafer held on the chuck stage, excluding the central portion. The back side of the wafer corresponding to the device area, excluding the device area, is ground to form an annular recess, and a central protrusion surrounded by the annular recess is formed on the back side of the wafer; a position adjustment step, after the defined grinding step is performed, after the grinding wheel is removed from the wafer, the grinding wheel is moved relative to the outer periphery of the wafer; and a circular grinding step, after the position adjustment step is performed, the grinding wheel is used to grind the back side of the wafer corresponding to the device area, including the central protrusion, to remove the central protrusion on the back side of the wafer corresponding to the device area and form a circular recess, and an annular protrusion is formed on the back side of the wafer corresponding to the remaining outer periphery area.

[0009] In the wafer processing method, the following fine grinding step may also be included: after the circular grinding step is performed, the circular recess is ground deeper using a fine grinding wheel, which is a grinding tool obtained by fixing abrasive grains finer than the grinding wheel using an adhesive.

[0010] In the wafer processing method, the circular recess formed in the circular grinding step is deeper than the annular recess formed in the defined grinding step.

[0011] The wafer processing method of this invention has the following effect: it can stably perform so-called TAIKO grinding, which forms a circular recess corresponding to the device area and an annular protrusion corresponding to the remaining outer peripheral area on the back of the wafer. Attached Figure Description

[0012] Figure 1 This is a perspective view of the wafer to be processed in the wafer processing method of Embodiment 1.

[0013] Figure 2 This is a perspective view showing a structural example of a grinding apparatus used in the wafer processing method of Embodiment 1.

[0014] Figure 3 Shown from below Figure 2 A perspective view of the rough grinding unit and the fine grinding unit of the grinding apparatus shown.

[0015] Figure 4 This is a flowchart illustrating the wafer fabrication method of Embodiment 1.

[0016] Figure 5 It is shown in Figure 4 The diagram shows a perspective view of the wafer's front side facing the protective component during the wafer fabrication preparation step of the wafer fabrication method.

[0017] Figure 6 It is shown in Figure 4 In the processing preparation step of the wafer processing method shown, a three-dimensional diagram of the state of the protective component is pasted on the front side of the wafer.

[0018] Figure 7 It is shown schematically. Figure 4 The diagram shows a top view of the wafer and the rough grinding wheel after the initial grinding step of the wafer processing method.

[0019] Figure 8 It is shown schematically using partial cross-sections. Figure 7 The side view shows the state in which the rough grinding wheel is in contact with the wafer.

[0020] Figure 9 It is shown schematically. Figure 4 The diagram shows a cross-sectional view of the rough grinding wheel and the wafer at the end of the defined grinding step in the wafer processing method.

[0021] Figure 10 It is shown schematically. Figure 9 The image shows a top view of the roughing grinding wheel and the wafer.

[0022] Figure 11 Shown in partial cross-section Figure 4 The side view of the wafer processing method shown is a state in which the rough grinding unit is raised and the rough grinding wheel is separated from the wafer during the position adjustment step.

[0023] Figure 12 Showing the partial cross-section Figure 11 The side view shown is of the coarse grinding wheel moving relative to the outer periphery of the wafer.

[0024] Figure 13 It is shown schematically. Figure 12 The image shows a top view of the roughing grinding wheel and the wafer.

[0025] Figure 14 It is shown schematically using partial cross-sections. Figure 4 The side view shows the state of the coarse grinding wheel in contact with the wafer after the circular grinding step of the wafer processing method has just begun.

[0026] Figure 15It is shown schematically using partial cross-sections. Figure 4 The image shows a side view of the roughing grinding wheel and the wafer at the end of the circular grinding step in the wafer processing method shown.

[0027] Figure 16 It is shown schematically. Figure 15 The image shows a top view of the roughing grinding wheel and the wafer.

[0028] Figure 17 This is a cross-sectional view schematically showing the state in which the annular recess and the central protrusion are first formed in the limited grinding step of the wafer processing method of the modified embodiment 1.

[0029] Label Explanation

[0030] 7: Chuck table; 32: Rough grinding wheel; 33: Spindle; 35: Outer diameter; 38: Rotation axis; 41: Grinding tool for fine grinding; 42: Fine grinding wheel; 71: Holding surface; 200: Wafer; 201: Back side; 203: Device area; 204: Remaining peripheral area; 205: Front side; 206: Pre-defined dividing line; 207: Device; 208: Radius; 211: Circular recess; 212: Annular protrusion; 214: Annular recess; 215: Central protrusion; 1001: Machining preparation step; 1002: Limiting grinding step; 1003: Position adjustment step; 1004: Circular grinding step; 1005: Fine grinding step. Detailed Implementation

[0031] The embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the contents described in the following embodiments. Furthermore, the constituent elements described below include substantially the same constituent elements readily conceived by those skilled in the art. In addition, the structures described below can be appropriately combined. Moreover, various omissions, substitutions, or modifications to the structure can be made without departing from the spirit of the present invention.

[0032] [Implementation Method 1]

[0033] The wafer processing method of Embodiment 1 of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a perspective view of the wafer to be processed in the wafer processing method of Embodiment 1. Figure 2 This is a perspective view of a structural example of a grinding apparatus used in the wafer processing method of Embodiment 1. Figure 3 Shown from below Figure 2 A perspective view of the rough grinding unit and the fine grinding unit of the grinding apparatus shown. Figure 4 This is a flowchart illustrating the wafer fabrication method of Embodiment 1.

[0034] The wafer processing method of Embodiment 1 is to... Figure 1 The method for processing the wafer 200 shown is described. The wafer 200, which is the object of processing in the wafer processing method of Embodiment 1, is a disc-shaped semiconductor wafer made of silicon or an optical device wafer made of sapphire, SiC (silicon carbide), or the like. In Embodiment 1, the disc-shaped raw material of the wafer 200 is made of silicon, and at least on the back side 201, a film 202 such as an oxide film or a nitride film is formed.

[0035] In Embodiment 1, a film 202 is formed on the back side 201 of the wafer 200. Compared with a wafer without a film 202, the wafer 200 becomes a wafer whose back side 201 is difficult to grind (i.e., a difficult-to-grind wafer) due to the formation of the film 202, compared with a wafer whose raw material is made of silicon and without a film 202.

[0036] like Figure 1 As shown, the wafer 200 has a device region 203 and a peripheral remaining region 204 surrounding the device region 203 on its front side 205. Devices 207 are formed in each region of the device region 203, which is divided by multiple intersecting predetermined dividing lines 206. The devices 207 are integrated circuits such as ICs (Integrated Circuits) or LSIs (Large Scale Integrations). The peripheral remaining region 204 is the area of ​​the front side 205 of the wafer 200 surrounding the device region 203 where no devices 207 are formed.

[0037] Next, the wafer processing method used in Embodiment 1 will be discussed. Figure 2 The grinding apparatus 1 shown will be described below. The grinding apparatus 1 is a processing apparatus for grinding (equivalent to machining) the back surface 201 of the wafer 200. For example... Figure 2 As shown, the grinding device 1 mainly includes a device body 2, a rough grinding unit 3 (equivalent to a grinding unit), a fine grinding unit 4 (equivalent to a grinding unit), a grinding feed unit 5, a rotary table 6, a chuck worktable 7 (three in embodiment 1) with multiple chuck worktables 7, boxes 8 and 9, an alignment unit 10, a conveying unit 11, a cleaning unit 12, a transfer-out and transfer-in unit 13, and a control unit 100.

[0038] The rotary table 6 is a disc-shaped worktable mounted on the upper surface of the main body 2, designed to rotate in the horizontal plane and driven to rotate at predetermined times. For example, three chuck worktables 7 are arranged on the rotary table 6 at equal intervals, with a phase angle of 120 degrees. These three chuck worktables 7 are chuck worktables with vacuum chucks on their holding surfaces 71, which hold the wafer 200 by attracting it. During grinding, these chuck worktables 7 are driven to rotate in the horizontal plane via a rotary drive mechanism about an axis parallel to the vertical direction, i.e., the Z-axis. Thus, the chuck worktables 7 have holding surfaces 71 that hold the wafer 200 and are capable of rotating about their axes.

[0039] The chuck table 7 moves sequentially to the loading / unloading area 301, the rough grinding area 302, the fine grinding area 303, and the loading / unloading area 301 through the rotation of the rotary table 6.

[0040] In addition, the loading and unloading area 301 is the area where the wafer 200 is loaded and unloaded relative to the chuck stage 7, the rough grinding area 302 is the area where the wafer 200 held in the chuck stage 7 is rough ground (equivalent to grinding) using the rough grinding unit 3, and the fine grinding area 303 is the area where the wafer 200 held in the chuck stage 7 is fine ground (equivalent to grinding) using the fine grinding unit 4.

[0041] The rough grinding unit 3 is a grinding unit that performs rough grinding on the back side 201 of the wafer 200 held on the holding surface 71 of the chuck table 7 in the rough grinding area 302, by mounting a rough grinding wheel 32 for rough grinding. The rough grinding wheel 32 has a grinding tool 31 for rough grinding. The fine grinding unit 4 is a grinding unit that performs fine grinding on the back side 201 of the wafer 200 held on the holding surface 71 of the chuck table 7 in the fine grinding area 303 by mounting a fine grinding wheel 42 for fine grinding. The fine grinding wheel 42 has a grinding tool 41 for fine grinding. Furthermore, since the structures of grinding units 3 and 4 are largely the same, the same reference numerals will be used for the same parts in the following description.

[0042] like Figure 3 As shown, the rough grinding unit 3 and the fine grinding unit 4 have grinding wheels 32 and 42 mounted on the lower end of the spindle 33. The grinding wheels 32 and 42 have an annular base 34 and multiple grinding tools 31 and 41 fixed on the lower surface 341 of the annular base 34. The grinding tools 31 and 41 are arranged circumferentially on the outer edge of the lower surface 341 of the annular base 34. The lower surfaces 311 and 411 of the multiple grinding tools 31 and 41 are formed in an annular shape. The grinding tools 31 and 41 are obtained by fixing the abrasive grains using an adhesive. The abrasive grains of the grinding tool 41 of the fine grinding wheel 42 are finer than those of the grinding tool 31 of the rough grinding wheel 32.

[0043] In Embodiment 1, the outer diameter 35 of the annular shape formed by the lower surfaces 311, 411 of the plurality of grinding tools 31, 41 of the grinding wheels 32, 42 (corresponding to the diameter of the grinding wheels 32, 42) is equal to the radius 208 of the wafer 200. In this invention, the fact that the outer diameter 35 of the annular shape formed by the lower surfaces 311, 411 of the plurality of grinding tools 32, 42 is equal to the radius 208 of the wafer 200 is referred to as the diameter of the grinding wheels 32, 42, i.e., the outer diameter is equivalent to the radius 208 of the wafer 200.

[0044] The spindle 33 is housed in the spindle housing 36 in a manner that allows it to rotate freely about a rotation axis 38 that is parallel to the Z-axis direction and perpendicular to the retaining surface 71. Figure 2 (As shown) Inside, via a spindle motor 37 mounted on the spindle housing 36 Figure 2 (As shown) The spindle 33 rotates around its axis. The spindle 33 is cylindrical, and a grinding wheel mounting base 39 for mounting grinding wheels 32 and 42 is provided at its lower end. The grinding wheel mounting base 39 protrudes circumferentially from the lower end of the spindle 33, and its outer circumferential surface is circular. The upper surface 342 of the annular base 34 of the grinding wheel mounting base 39 overlaps with its lower surface 391, and the grinding wheels 32 and 42 are fixed by bolts (not shown). The spindle 33 and the grinding wheel mounting base 39 are arranged coaxially.

[0045] Grinding units 3 and 4 rotate spindle 33 and grinding wheels 32 and 42 around rotation axis 38 via spindle motor 37, and while supplying grinding water to the back side 201 of wafer 200 held on chuck table 7 in grinding area 302 and 303, grinding tools 31 and 41 are brought close to chuck table 7 at a specified feed speed via grinding feed unit 5, thereby performing rough grinding or fine grinding on the back side 201 of wafer 200.

[0046] The grinding feed unit 5 moves the grinding units 3 and 4 in the Z-axis direction. In embodiment 1, the grinding feed unit 5 is mounted on a vertical column 21 erected at one end in the Y-axis direction parallel to the horizontal direction of the device body 2. The grinding feed unit 5 includes a known ball screw rotatably mounted about its axis, a known electric motor that rotates the ball screw about its axis, and a known guide rail that supports the spindle housing 36 of each grinding unit 3 and 4 so that it can move freely in the Z-axis direction.

[0047] Furthermore, in Embodiment 1, regarding the rough grinding unit 3 and the fine grinding unit 4, the rotation axis 38, which serves as the rotation center of the grinding wheels 32 and 42, is arranged parallel to each other in the horizontal direction at intervals. Within a range where the grinding tools 31 and 41 are held at or near the center 210 of the back surface 201 of the wafer 200 on the chuck table 7, and the grinding wheel mounting base 39 is coaxial with the chuck table 7 of the grinding areas 302 and 303, the grinding feed unit 5 and the upright column 21 are moved together in the horizontal direction via the sliding movement mechanism 16. The sliding movement mechanism 16 includes a known ball screw rotatably arranged about its axis, a known electric motor that rotates the ball screw about its axis, and a known guide rail that supports the upright column 21 supporting each grinding unit 3 and 4 so that it can move freely in the horizontal direction.

[0048] Boxes 8 and 9 are storage containers with multiple slots for storing wafers 200. Box 8 stores the wafer 200 before grinding, and box 9 stores the wafer 200 after grinding. Furthermore, the alignment unit 10 is a worktable for temporarily placing the wafer 200 taken from box 8 and performing center alignment of the wafer 200.

[0049] Two transfer units 11 are provided. Both transfer units 11 have adsorption pads for adsorbing the wafers 200. One transfer unit 11 adsorbs and holds the wafers 200 before grinding after alignment by the alignment unit 10 and transfers them onto the chuck stage 7 located in the transfer-in / transfer-out area 301. The other transfer unit 11 adsorbs and holds the ground wafers 200 held on the chuck stage 7 located in the transfer-in / transfer-out area 301 and transfers them to the cleaning unit 12.

[0050] The transfer unit 13 is, for example, a robotic arm with a U-shaped hand 131, which uses the U-shaped hand 131 to hold and transport the wafer 200. Specifically, the transfer unit 13 removes the wafer 200 from the cassette 8 before grinding and moves it to the alignment unit 10, and removes the ground wafer 200 from the cleaning unit 12 and moves it into the cassette 9. The cleaning unit 12 cleans the ground wafer 200, removing grinding debris and other contaminants adhering to the ground back surface 201.

[0051] The control unit 100 controls each of the aforementioned components constituting the grinding apparatus 1. That is, the control unit 100 causes the grinding apparatus 1 to perform grinding operations on the wafer 200. The control unit 100 is a computer that includes: an arithmetic processing unit having a microprocessor such as a CPU (central processing unit); a storage unit having a memory such as ROM (read-only memory) or RAM (random access memory); and an input / output interface device.

[0052] The arithmetic processing unit of the control unit 100 performs arithmetic processing according to a computer program stored in a storage device, and outputs control signals for controlling the grinding apparatus 1 to the aforementioned components of the grinding apparatus 1 via an input / output interface device. Furthermore, the control unit 100 is connected to a display unit, such as a liquid crystal display device, that displays the status and images of the machining operation, and to an input unit used by the operator to register machining information. The input unit consists of at least one of a touch panel and a keyboard provided on the display unit.

[0053] The wafer processing method of Embodiment 1 is a TAIKO grinding method for wafer 200. This TAIKO grinding refers to grinding the back surface 201 of wafer 200 corresponding to device region 203 using grinding wheels 32 and 42, forming a circular recess 211 on the back surface 201 of wafer 200 corresponding to device region 203. Figure 15 , 16 As shown), an annular protrusion 212 is formed on the back surface 201 of the wafer 200 corresponding to the remaining peripheral region 204. Figure 15 , 16 (As shown). In addition, the back surface 201 of the wafer 200 corresponding to the device region 203 refers to the region in the back surface 201 of the wafer 200 that overlaps with the device region 203 in the thickness direction of the wafer 200, and the back surface 201 of the wafer 200 corresponding to the peripheral remaining region 204 refers to the region in the back surface 201 of the wafer 200 that overlaps with the peripheral remaining region 204 in the thickness direction of the wafer 200.

[0054] like Figure 4 As shown, the wafer processing method of Embodiment 1 includes a processing preparation step 1001, a limiting grinding step 1002, a position adjustment step 1003, a circular grinding step 1004, a fine grinding step 1005, and a cleaning and storage step 1006.

[0055] (Processing preparation steps)

[0056] Figure 5 It is shown in Figure 4The diagram shows a perspective view of the wafer's front side facing the protective component during the wafer fabrication preparation step of the wafer fabrication method. Figure 6 It is shown in Figure 4 In the processing preparation step of the wafer processing method shown, a three-dimensional diagram of the state of the protective component is pasted on the front side of the wafer.

[0057] The processing preparation step 1001 is a step in which the wafer 200 is held by the chuck table 7 of the grinding apparatus 1 and the grinding wheels 32 and 42 are fixed to the lower end of the spindle 33. In Embodiment 1, in the processing preparation step 1001, as follows... Figure 5 As shown, after aligning the protective component 213 with the front surface 205 of the chip 200, as Figure 6 As shown, a protective member 213 is attached to the front side 205 of the wafer 200. In Embodiment 1, the protective member 213 is formed as a circular plate of the same size as the wafer 200 and is made of a flexible synthetic resin or a rigid substrate.

[0058] In Embodiment 1, in the processing preparation step 1001, the operator fixes the grinding wheels 32 and 42 to the lower end of the spindle 33 of each grinding unit 3 and 4 of the grinding apparatus 1, and stores the wafer 200 with the protective component 213 attached to its front surface 205 in the box 8 with the protective component 213 facing down. In the processing preparation step 1001, the operator registers the processing conditions in the control unit 100, and sets the box 8 containing the wafer 200 with the protective component 213 attached before grinding and the box 9 containing the wafer 200 without grinding in the main body 2 of the apparatus. In the processing preparation step 1001, when the control unit 100 of the grinding apparatus 1 receives the start instruction of the processing operation from the operator, the processing operation begins.

[0059] During the processing, the control unit 100 of the grinding device 1 rotates the spindles 33 of each grinding unit 3 and 4 around the rotation axis 38, causing the loading / unloading unit 13 to remove the wafers 200 one by one from the cassette 8 and move them out to the alignment unit 10. The control unit 100 causes the alignment unit 10 to center-align the wafers 200, and the transport unit 11 to move the aligned wafers 200 with their front side 205 side onto the chuck table 7 located in the loading / unloading area 301. At this time, the wafers 200 moved onto the chuck table 7 are positioned coaxially with the chuck table 7.

[0060] In the processing preparation step 1001, the control unit 100 of the grinding apparatus 1 attracts and holds the front 205 side of the wafer 200 on the chuck table 7 of the transfer-in-transfer area 301 through the protective member 213, and then proceeds to the limited grinding step 1002.

[0061] (Grinding steps are limited)

[0062] Figure 7 It is shown schematically. Figure 4 The diagram shows a top view of the wafer and the rough grinding wheel after the initial grinding step of the wafer processing method. Figure 8 It is shown schematically using partial cross-sections. Figure 7 The side view shows the state in which the rough grinding wheel is in contact with the wafer. Figure 9 It is shown schematically. Figure 4 The diagram shows a cross-sectional view of the rough grinding wheel and the wafer at the end of the defined grinding step in the wafer processing method. Figure 10 It is shown schematically. Figure 9 The image shows a top view of the roughing grinding wheel and the wafer.

[0063] The limited grinding step 1002 involves using a rough grinding wheel 32 to grind the back surface 201 of the wafer 200, which corresponds to the device region 203 and is held on the chuck stage 7, excluding the central portion, to form an annular recess 214. Figure 9 and Figure 10 As shown), and a central protrusion 215 surrounded by an annular recess 214 is formed on the back surface 201 of the wafer 200. Figure 9 and Figure 10 The steps are shown below. In the defined grinding step 1002, the control unit 100 of the grinding apparatus 1 rotates the turntable 6 so that the chuck table 7, which holds the wafer 200 in the loading and unloading area 301, moves to the coarse grinding area 302, exposing the back side 201 and using the turntable 6 to transport the wafer 200 to the coarse grinding area 302.

[0064] In the defined grinding step 1002, the control unit 100 of the grinding apparatus 1 uses the sliding movement mechanism 16 to move the rough grinding unit 3 in the horizontal direction, such as... Figure 7 As shown, the rotation axis 38 of the spindle 33 of the coarse grinding unit 3 and the axis of the rotary table 6, i.e., the center 210 of the wafer 200 held on the chuck table 7, are arranged horizontally at intervals (i.e., the wafer 200 and the coarse grinding wheel 32 are positioned in a non-coaxial position). Furthermore, in the defined grinding step 1002, the control unit 100 of the grinding apparatus 1, when viewed from above, positions the center 210 of the wafer 200 held on the chuck table 7 on the inner circumference of the grinding tool 31 of the coarse grinding wheel 32, and rotates the chuck table 7 about its axis. Additionally, in Embodiment 1, in the defined grinding step 1002, the control unit 100 of the grinding apparatus 1, when viewed from above, rotates the chuck table 7 and the coarse grinding wheel 32 of the coarse grinding unit 3 in the same direction.

[0065] In the defined grinding step 1002, the control unit 100 of the grinding apparatus 1 uses the grinding feed unit 5 to lower the rough grinding unit 3, such as... Figure 8As shown, the lower surface 311 of the grinding wheel 32 of the coarse grinding unit 3 abuts against the back surface 201 of the wafer 200, and the coarse grinding unit 3 decreases according to the grinding feed speed determined by the processing content information. Then, the grinding wheel 31 grinds the back surface 201 of the wafer 200, excluding the central portion, which corresponds to the device region 203, and sequentially grinds the film 202 and the raw material of the back surface 201 of the wafer 200 corresponding to the device region 203. In the defined grinding step 1002, as... Figure 9 As shown, when the control unit 100 of the grinding device 1 grinds from the back side 201 to the depth 216 determined by the processing content information using the coarse grinding unit 3, it enters the position adjustment step 1003.

[0066] Furthermore, in the defined grinding step 1002, the wafer 200 and the rough grinding wheel 32 are positioned in a non-coaxial position. When viewed from above, the center 210 of the wafer 200, held on the chuck table 7, is positioned on the inner circumferential side of the grinding tool 31 of the rough grinding wheel 32. Therefore, on the back surface 201 of the wafer 200 after the defined grinding step 1002, as shown... Figure 9 and Figure 10 As shown, an annular recess 214 is formed on the back surface 201 of the device region 203 of the wafer 200, and a central protrusion 215 is formed surrounding the annular recess 214. The planar shape of the annular recess 214 is annular, and the planar shape of the central protrusion 215 is circular. The annular recess 214 and the central protrusion 215 are formed at a position coaxial with the wafer 200. Furthermore, in this invention, since the raw material of the wafer 200 is made of silicon, in the defined grinding step 1002, the rough grinding wheel 32 only needs to be fed to grind to at least expose the bottom surface of the annular recess 214, that is, only the film 202 in contact with the lower surface 311 of the grinding tool 31 needs to be removed.

[0067] (Positioning steps)

[0068] Figure 11 Shown in partial cross-section Figure 4 The side view shows the state in which the rough grinding unit is raised and the rough grinding wheel leaves the wafer during the position adjustment step of the wafer processing method shown. Figure 12 Using partial cross-sections to show Figure 11 The side view shown is of the coarse grinding wheel moving relative to the outer periphery of the wafer. Figure 13 It is shown schematically. Figure 12 The image shows a top view of the roughing grinding wheel and the wafer.

[0069] Position adjustment step 1003 is a step performed after the defined grinding step 1002, whereby the rough grinding wheel 32 is moved relative to the outer periphery of the wafer 200 after it has left the wafer 200. In position adjustment step 1003, as... Figure 11 As shown, the control unit 100 of the grinding device 1 uses the grinding feed unit 5 to raise the coarse grinding unit 3, thereby causing the grinding wheel 32 of the coarse grinding wheel 32 to leave the wafer 200 held on the chuck table 7.

[0070] In the position adjustment step 1003, the control unit 100 of the grinding apparatus 1 uses the sliding movement mechanism 16 to move the coarse grinding wheel 32 of the coarse grinding unit 3 toward the outer periphery of the wafer 200 held on the chuck table 7 in the coarse grinding area 302. In Embodiment 1, in the position adjustment step 1003, as... Figure 12 and Figure 13 As shown, the control unit 100 of the grinding apparatus 1 positions the outer edge of a portion of the grinding wheel 32 on the boundary between the device region 203 and the remaining peripheral region 204 of the wafer 200, and positions the lower surface 311 of the other portion of the grinding wheel 31 on the center 210 of the wafer 200, and proceeds to the circular grinding step 1004.

[0071] (Circular grinding steps)

[0072] Figure 14 It is shown schematically using partial cross-sections. Figure 4 The side view shows the state of the coarse grinding wheel in contact with the wafer after the circular grinding step of the wafer processing method has just begun. Figure 15 It is shown schematically using partial cross-sections. Figure 4 The image shows a side view of the roughing grinding wheel and the wafer at the end of the circular grinding step in the wafer processing method shown. Figure 16 It is shown schematically. Figure 15 The image shows a top view of the roughing grinding wheel and the wafer.

[0073] The circular grinding step 1004 is as follows: After the position adjustment step 1003 is performed, the back surface 201 of the wafer 200, including the central protrusion 215, corresponding to the device region 203 is ground using a coarse grinding wheel 32. The central protrusion 215 of the back surface 201 of the wafer 200 corresponding to the device region 203 is removed and a circular recess 211 is formed, thereby forming an annular protrusion 212 on the back surface 201 of the wafer 200 corresponding to the outer peripheral remaining region 204.

[0074] In the circular grinding step 1004, the control unit 100 of the grinding device 1 uses the grinding feed unit 5 to lower the rough grinding unit 3, such as... Figure 14As shown, the lower surface 311 of the grinding wheel 32 of the coarse grinding unit 3 abuts against the region on the outer periphery of the annular recess 214 and the region on the central protrusion 215 of the back surface 201 of the wafer 200, and the coarse grinding unit 3 decreases according to the grinding feed speed determined by the processing content information. Thus, the grinding wheel 31 grinds and removes the region on the outer periphery of the annular recess 214 and the region on the central protrusion 215 of the back surface 201 of the wafer 200 corresponding to the device region 203.

[0075] In the circular grinding step 1004, at the start of grinding, the grinding wheel 31 abuts against the corners of the central protrusion 215 and the annular recess 214, and the grinding wheel 31 is dressed. In the circular grinding step 1004, when the control unit 100 of the grinding device 1... Figure 15 When the rough grinding unit 3 grinds from the back side 201 to a depth 217 determined by the processing content information that is deeper than the depth 216 of the limiting grinding step 1002, as shown, the process proceeds to the fine grinding step 1005.

[0076] Additionally, in the positioning adjustment step 1003, a portion of the outer edge of the grinding wheel 32 is positioned on the boundary between the device region 203 and the remaining peripheral region 204 of the wafer 200, while the lower surface 311 of the other portion of the grinding wheel 31 is positioned on the center 210 of the wafer 200. Therefore, on the back surface 201 of the wafer 200 after the circular grinding step 1004, as shown... Figure 15 and Figure 16 As shown, a circular recess 211 is formed on the entire back surface 201 of the device region 203 of the wafer 200, and an annular protrusion 212 is formed on the back surface 201 of the wafer 200 corresponding to the remaining peripheral region 204, leaving the back surface 201 un-ground. Thus, in the wafer processing method of Embodiment 1, the circular recess 211 formed in the circular grinding step 1004 is deeper than the annular recess 214 formed in the defined grinding step 1002. Furthermore, in Embodiment 1, during the defined grinding step 1002, the position adjustment step 1003, and the circular grinding step 1004, the chuck stage 7 positioned in the rough grinding region 302 rotates in the same direction.

[0077] (Fine grinding steps)

[0078] The fine grinding step 1005 is a step that grinds the circular recess 211 deeper using the fine grinding wheel 42 after the circular grinding step 1004. In the fine grinding step 1005, the control unit 100 of the grinding apparatus 1 rotates the turntable 6 and moves the chuck table 7, which holds the wafer 200 that has undergone the circular grinding step 1004 in the coarse grinding area 302, to the fine grinding area 303, exposing the back side 201 and using the turntable 6 to transfer the wafer 200 to the fine grinding area 303.

[0079] In Embodiment 1, in the fine grinding step 1005, the control unit 100 of the grinding apparatus 1 uses the sliding moving mechanism 16 to move the fine grinding unit 4 in the horizontal direction, positioning the outer edge of a portion of the grinding tool 41 of the fine grinding wheel 42 on the boundary between the device region 203 and the remaining peripheral region 204 of the wafer 200, and positioning the lower surface 411 of the other portion of the grinding tool 41 on the center 210 of the wafer 200. While rotating the chuck table 7 positioned in the fine grinding region 303 in the same direction as the fine grinding wheel 42, the fine grinding unit 4 is lowered using the grinding feed unit 5.

[0080] In the fine grinding step 1005, the control unit 100 of the grinding device 1 uses the fine grinding unit 4 to grind the bottom surface of the circular recess 211 to the depth determined by the processing content information. Then, the fine grinding unit 4 is raised by the grinding feed unit 5 to enter the cleaning and storage step 1006.

[0081] (Cleaning and storage steps)

[0082] The cleaning and storage step 1006 is the step of cleaning and storing the wafer 200 in the cassette 9 after the fine grinding step 1005. In the cleaning and storage step 1006, the control unit 100 of the grinding apparatus 1 rotates the turntable 6, moving the chuck table 7, which holds the wafer 200 after the fine grinding step 1005 in the fine grinding area 303, to the loading and unloading area 301, exposing the back side 201, and using the turntable 6 to move the wafer 200 to the loading and unloading area 301. In this way, the wafer processing method sequentially moves the wafer 200 to the rough grinding area 302, the fine grinding area 303, and the loading and unloading area 301 to sequentially perform the limited grinding step 1002, the position adjustment step 1003, the circular grinding step 1004, and the fine grinding step 1005. In addition, whenever the turntable 6 rotates 120 degrees, the control unit 100 of the grinding device 1 moves the wafer 200 before grinding into the chuck table 7 of the loading and unloading area 301.

[0083] In the cleaning and storage step 1006, the control unit 100 of the grinding apparatus 1 transports the ground wafer 200 into the cleaning unit 12 via the transfer unit 11, cleans it using the cleaning unit 12, and then uses the transfer pad of the transfer-out-transfer unit 13 to hold the cleaned wafer 200 from the protective member 213 side and transport it into the cassette 9. In addition, in Embodiment 1, whenever the turntable 6 rotates 120 degrees, the control unit 100 of the grinding apparatus 1 sequentially performs the limited grinding step 1002, the position adjustment step 1003, and the circular grinding step 1004 on the wafer 200 positioned in the coarse grinding area 302, and performs the fine grinding step 1005 on the wafer 200 positioned in the fine grinding area 303, and transports the ground wafer 200 from the chuck table 7 positioned in the transfer-in-transfer area 301 to the cleaning unit 12, and transports the unground wafer 200 to the chuck table 7. When all the wafers 200 in the box 8 have been ground, the control unit 100 of the grinding device 1 ends the processing operation, i.e., the wafer processing method.

[0084] As described above, in the wafer processing method of Embodiment 1, even for a difficult-to-grind wafer 200, after grinding in the limited grinding step 1002, which limits the ground area to a narrower extent than conventional TAIKO grinding and leaves a central protrusion 215 in the center, the back surface 201 of the wafer 200, including the central protrusion 215, which corresponds to the entire device region 203, is ground in the circular grinding step 1004. Therefore, the wafer processing method can make the grinding range of each of the limited grinding step 1002 and the circular grinding step 1004 narrower than conventional TAIKO grinding, and can reduce the load applied to the grinding tool 31. As a result, the wafer processing method has the following effect: it can suppress the load current value of the spindle motor 37 from exceeding the specified value, and can stably perform the so-called TAIKO grinding that forms a circular recess 211 corresponding to the device region 203 and an annular protrusion 212 corresponding to the remaining peripheral region 204 on the back surface 201 of the wafer 200.

[0085] Furthermore, in the wafer processing method, when the central protrusion 215 is ground in the circular grinding step 1004, the grinding tool 31 collides with the corners of the central protrusion 215 and the annular recess 214, thereby achieving a finishing effect and maintaining the grinding state well.

[0086] [Variation Example]

[0087] The wafer processing method of a modified embodiment 1 of the present invention will be described with reference to the accompanying drawings. Figure 17This is a schematic cross-sectional view showing the state in which the annular recess and central protrusion are first formed during the limited grinding step of the wafer processing method in a modified example of Embodiment 1. Furthermore, Figure 17 The same reference numerals are used for parts that are the same as in Implementation Method 1, and the description is omitted.

[0088] In the wafer processing method of the modified embodiment 1, while gradually changing the relative position of the rough grinding wheel 32 with respect to the wafer 200 from a position near the center 210 to the outer periphery, the limited grinding step 1002 is repeatedly performed to form an annular recess 214 and a central protrusion 215 on the back surface 201. Furthermore, Figure 17 An example is shown in which the rough grinding wheel 32 and the wafer 200 are positioned coaxially in the defined grinding step 1002, thereby first forming an annular recess 214 and a central protrusion 215. Furthermore, in this invention, the formation of the annular recess 214 and the central protrusion 215 is not limited to, for example... Figure 17 As shown, the coarse grinding wheel 32 and the wafer 200 are positioned coaxially. This can be achieved by repeatedly performing the limited grinding step 1002 while gradually changing the relative position of the coarse grinding wheel 32 with respect to the wafer 200 from a position near the center 210 to the outer periphery.

[0089] exist Figure 17 In the wafer processing method of the modified example shown, since the limited grinding step 1002 is repeatedly performed while gradually changing the relative position of the rough grinding wheel 32 with respect to the wafer 200 from a position near the center 210 to the outer periphery, the load applied to the grinding tool 31 can be further reduced compared with the embodiment.

[0090] Furthermore, the present invention is not limited to the embodiments described above. That is, it can be implemented with various modifications without departing from the spirit of the present invention. In the above embodiment 1, the raw material of the difficult-to-grind wafer 200 is made of silicon and a film 202 is formed on its outer surface, but the present invention is not limited to this. For example, in the present invention, the raw material of the difficult-to-grind wafer 200 can be made of sapphire or glass, or it can be a so-called highly doped wafer whose resistivity is adjusted to, for example, 0.001 Ωcm or more and 0.1 Ωcm or less by incorporating doping materials (e.g., boron: B; phosphorus: P; tin: Sn or arsenic: As). When circular recesses 211 and annular protrusions 212 are formed on these difficult-to-grind wafers 200, the wafer processing method of the present invention can be implemented by using at least one of the coarse grinding unit 3 and the fine grinding unit 4 to perform the defined grinding step 1002, the position adjustment step 1003, and the circular grinding step 1004.

Claims

1. A method for processing a wafer, the wafer having on its front side a device region in which devices are formed in regions divided by a plurality of intersecting predetermined dividing lines, and a remaining peripheral region surrounding the device region, wherein, The wafer fabrication method comprises the following steps: In the processing preparation step, the wafer is held by a chuck stage that has a holding surface for holding the wafer and is rotatable, and a grinding wheel with a diameter equivalent to the radius of the wafer is fixed at the lower end of a spindle having a rotation axis perpendicular to the holding surface. The grinding process involves using a grinding wheel to grind the back side of the wafer, excluding the central portion, which corresponds to the device area and is held on the chuck stage, to form an annular recess, and forming a central protrusion on the back side of the wafer surrounded by the annular recess. The position adjustment step involves moving the grinding wheel relative to the outer periphery of the wafer after the defined grinding step has been performed and after the grinding wheel has been removed from the wafer. as well as In the circular grinding step, after the position adjustment step is performed, the grinding wheel is used to grind the back side of the wafer corresponding to the device area, including the central protrusion, to remove the central protrusion on the back side of the wafer corresponding to the device area and form a circular concave portion, and to form an annular protrusion on the back side of the wafer corresponding to the remaining outer peripheral area.

2. The wafer processing method according to claim 1, wherein, The wafer processing method includes the following fine grinding step: after the circular grinding step, the circular recess is ground deeper using a fine grinding wheel, which is a grinding tool obtained by fixing abrasive grains finer than the grinding wheel using an adhesive.

3. The wafer processing method according to claim 1 or 2, wherein, The circular recess formed in the circular grinding step is deeper than the annular recess formed in the defined grinding step.

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