Grinding method and method for manufacturing ground wafers

Abstract

The present invention provides a grinding method and a method for manufacturing a ground wafer that can achieve a more suitable surface shape in a workpiece after grinding. [Solution] The method includes a holding step of holding a workpiece on the holding surface of a holding table; a grinding step of rotating the holding table and the spindle so that the orientations of their respective rotation axes are aligned with each other, and while the workpiece and the grinding wheel are in contact, a moving unit brings the holding table and the spindle closer together in line with the orientation of the rotation axis of the spindle, thereby grinding the workpiece held on the holding surface; and a retraction and movement step after the grinding step, stopping the grinding feed by the moving unit, and while rotating the holding table and the spindle, moving the holding table and the spindle relative to each other in a direction intersecting the rotation axis of the spindle.

Description

Technical Field

[0001] The present invention relates to a method for grinding a workpiece such as a semiconductor wafer and a method for manufacturing a wafer that has been ground.

Background Art

[0002] Device chips mounted on electronic devices such as mobile phones and personal computers are manufactured by processing semiconductor wafers.

[0003] On one surface of a disk-shaped semiconductor wafer, a plurality of division planned lines (streets) are set in a grid pattern, and devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integration) are formed in each rectangular region partitioned by the division planned lines. By cutting the semiconductor wafer on which the devices are formed along each division planned line, the semiconductor wafer is divided into a plurality of device chips.

[0004] In recent years, in the manufacture of such device chips, the wafer has been thinned for chip miniaturization and weight reduction. For example, in the manufacturing process of the device chips as described above, the entire wafer is thinned by grinding the back surface of the wafer on which the devices are formed on the surface.

[0005] As a document describing a technique related to such wafer grinding, for example, Patent Document 1 can be cited.

[0006] By the way, in wafer grinding, it is desirable that the thickness of the wafer as the workpiece is as uniform as possible and that its surface is as close to a flat surface as possible. However, depending on conditions such as the shape and type of the grinding wheel used for grinding, the material and shape of the wafer, the shape of the holding table for holding the wafer, and the magnitude and distribution of the force applied between the grinding wheel and the wafer during grinding, unevenness that is not preferable may be formed on the surface of the wafer during grinding.

Prior Art Documents

[0007] [Patent Document 1] Japanese Patent Publication No. 2019-130637 [Overview of the project] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide a grinding method and a method for manufacturing a ground wafer that can achieve a more suitable surface shape in a workpiece after grinding. [Means for solving the problem]

[0009] According to one aspect of the present invention, a grinding method for grinding a workpiece using a grinding apparatus comprising: a holding table having a conical holding surface and rotatable about an axis intersecting the holding surface; a grinding unit having a spindle to which a grinding wheel is attached, which grinds a workpiece held on the holding surface of the holding table by rotating the grinding wheel in contact with the workpiece while forming a grinding surface oriented along the holding surface; and a moving unit for moving the holding table and the grinding wheel relative to each other, the method comprising a holding step of holding the workpiece on the holding surface of the holding table, and the holding table and the grinding wheel A grinding method is provided which includes a grinding step in which the spindle and the holding table are rotated such that the orientations of their respective rotation axes are aligned with each other, and the workpiece and the grinding wheel are in contact, and the holding table and the spindle are brought closer together by the moving unit in the direction of the rotation axis of the spindle, thereby grinding the workpiece held on the holding surface; and a retraction movement step in which, after the grinding step, the grinding feed by the moving unit is stopped, and the holding table and the spindle are rotated while the holding table and the spindle are moved relative to each other in a direction intersecting the rotation axis of the spindle.

[0010] Preferably, in the grinding step, a portion of the trajectory of the grinding wheel is located at the apex of the workpiece, which is held in a conical shape on the holding surface of the holding table.

[0011] Preferably, in the retraction step, the spindle and the holding table are moved relative to each other in a direction along the grinding surface of the grinding wheel.

[0012] Preferably, in the retraction step, the spindle and the holding table are moved relative to each other in a direction along the grinding surface of the grinding wheel, while being separated in a direction along the rotation axis of the spindle.

[0013] Preferably, the grinding wheel contains a resin bond as a bonding agent.

[0014] According to another aspect of the present invention, a method for manufacturing a ground wafer is provided, in which the workpiece is a plate-shaped wafer and the ground wafer is manufactured using the grinding method described above. [Effects of the Invention]

[0015] According to the grinding method and manufacturing method for ground wafers relating to each aspect of the present invention, after the grinding step, the grinding feed by the moving unit is stopped, and a retraction movement step is performed in which the holding table and spindle rotate while the holding table and spindle move relative to each other in a direction intersecting the rotation axis of the spindle. By doing so, a more suitable surface shape can be achieved in the workpiece. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a perspective view showing an example of the configuration of a grinding machine. [Figure 2] Figure 2 is a cross-sectional view showing the grinding process of a workpiece (wafer) using the grinding apparatus shown in Figure 1. [Figure 3] Figure 3 is a flowchart illustrating an example of the procedure for grinding a workpiece (wafer) and manufacturing a ground wafer using the grinding apparatus shown in Figure 1. [Figure 4] FIG. 4 is a cross-sectional view schematically showing the state of a grinding wheel and a workpiece (wafer) during grinding. [Figure 5] FIG. 5 is a cross-sectional view schematically showing, as a reference example, an example of the state of a grinding wheel and a workpiece (wafer) at the time of spark out. [Figure 6] FIG. 6 is a cross-sectional view schematically showing, as a reference example, an example of the state of a grinding wheel and a workpiece (wafer) at the time of escape cut. [Figure 7] FIG. 7 is a photograph showing, as a reference example, an example of the state of the surface of a workpiece (grinded wafer) after completion of a grinding step and a retraction movement step. [Figure 8] FIG. 8 is a diagram showing the result of measuring the shape of the surface of the workpiece (grinded wafer) shown in FIG. 7. [Figure 9] FIG. 9 is a flowchart for explaining another example of a procedure for grinding a workpiece (wafer) using the grinding apparatus of FIG. 1 and manufacturing a grinded wafer. [Figure 10] FIG. 10 is a cross-sectional view schematically showing another example of the state of a grinding wheel and a workpiece (wafer) at the time of spark out. [Figure 11] FIG. 11 is a cross-sectional view schematically showing another example of the state of a grinding wheel and a workpiece (wafer) at the time of escape cut. [Figure 12] FIG. 12 is a photograph showing another example of the state of the surface of a workpiece (grinded wafer) after completion of a grinding step and a retraction movement step. [Figure 13] FIG. 13 is a diagram showing the result of measuring the shape of the surface of the workpiece (grinded wafer) shown in FIG. 1E. [Figure 14] FIG. 14 is a photograph showing yet another example of the state of the surface of a workpiece (grinded wafer) after completion of a grinding step and a retraction movement step. [Figure 15] FIG. 15 is a diagram showing the result of measuring the shape of the surface of the workpiece (grinded wafer) shown in FIG. 14. [Figure 16] Figure 16 is a flowchart illustrating yet another example of the procedure for grinding a workpiece (wafer) and manufacturing a ground wafer using the grinding apparatus shown in Figure 1. [Figure 17] Figure 17 is a schematic cross-sectional view showing yet another example of the state of the grinding wheel and workpiece (wafer) during escape cutting. [Figure 18] Figure 18 is a photograph showing yet another example of the surface condition of the workpiece (ground wafer) after the completion of the grinding step and the retraction step. [Figure 19] Figure 19 is a diagram showing the results of measuring the surface shape of the workpiece (ground wafer) shown in Figure 18. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described with reference to the attached drawings. Figure 1 is a perspective view showing the configuration of the grinding apparatus 2 according to this embodiment. Figure 2 is a cross-sectional view showing the grinding of a workpiece (wafer) 4 by the grinding apparatus 2.

[0018] In Figures 1 and 2, the X, Y, and Z directions represent the orientations of three mutually orthogonal axes in three-dimensional space. The X direction (front-back direction) and the Y direction (left-right direction) are mutually orthogonal horizontal directions. The Z direction (up-down direction) is orthogonal to the X and Y directions and is the vertical direction.

[0019] In this specification, expressions such as "along the Z direction" or "along the XY plane" are used, but these do not necessarily mean that the orientation of the members or surfaces strictly coincides with or is parallel to these axes or planes. These expressions also include cases where, for example, they are at a slightly oblique angle to each other but are generally facing the same direction, or where the angle of the members, axes, or direction of motion has a component in that direction.

[0020] The wafer 4, which is the workpiece to be ground in the grinding apparatus 2, is a disc-shaped wafer formed from, for example, silicon, and has devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integrations) formed on one side.

[0021] There are no restrictions on the type, material, shape, structure, or size of the wafer 4, which is the workpiece. For example, wafer 4 may be a substrate (wafer) made of semiconductors other than silicon (GaAs, InP, GaN, SiC, etc.), sapphire, glass, ceramics, resin, metal, etc. There are also no restrictions on the type, number, shape, structure, size, or arrangement of devices formed on wafer 4. It is even possible for no devices to be formed on wafer 4.

[0022] The grinding device 2 comprises a holding table 6, a grinding unit 12, and moving units (X-moving unit 22, Z-moving unit 24).

[0023] The holding table 6 is a mechanism for holding a wafer 4, which is a plate-shaped workpiece, and is, for example, a chuck table. The holding table 6, which is a chuck table, has a disc-shaped table base 8 made of a material such as ceramics or metal, and a suction plate 10 attached to the table base 8.

[0024] The suction plate 10 is a disc-shaped member made of, for example, porous ceramics. A disc-shaped recess corresponding to the dimensions of the suction plate 10 is formed on the upper part of the table base 8, and the suction plate 10 is fixed by fitting into this recess. A flow channel (not shown) is formed inside the table base 8, and one end of the flow channel is connected to the lower surface of the suction plate 10.

[0025] The other end of the flow path provided within the table base 8 is connected to a suction source (not shown), such as an ejector. When the suction source is operated, the negative pressure supplied to the flow path acts on an object such as a wafer 4 placed on the upper surface 10a of the suction plate 10. In this way, the upper surface 10a of the suction plate 10 functions as a holding surface for the wafer 4, which is the workpiece. The suction plate 10 may be, for example, a plate-shaped member of metal or the like with multiple holes that penetrate vertically through it.

[0026] The upper surface of the suction plate 10, which forms the holding surface 10a of the holding table 6, is formed in a conical shape with the central part slightly protruding outward (opposite to the table base 8; upward). The bottom surface of the suction plate 10 (the surface facing the table base 8) is substantially flat.

[0027] Note that in Figure 2, the inclination of the holding surface (top surface) 10a is exaggerated for illustrative purposes, but in reality, this inclination can be so small that it is not visible to the naked eye. To give an example of specific values, if the diameter of the suction plate 10 is about 200 mm, the height difference between its center and outer edge is about 20 μm.

[0028] When the disc-shaped wafer 4 is attracted to the conical holding surface 10a, it takes on a conical shape along the holding surface 10a, as shown in Figure 2, with its center forming the apex of the cone and slightly protruding upward.

[0029] In the space above the holding table 6, a grinding unit 12 is positioned to grind the wafer 4 held by the holding table 6.

[0030] The grinding unit 12 comprises a spindle housing 14 and a spindle 16, which is a rotating body housed in the spindle housing 14. The cylindrical spindle 16 is rotatably supported relative to the spindle housing 14 around an axis provided along the vertical direction (Z direction).

[0031] The lower end of the spindle 16 is exposed to the outside of the spindle housing 14, and a disc-shaped wheel mount is fixed to the tip of the lower end of the spindle 16. A disc-shaped grinding wheel 18, which has approximately the same diameter as the wheel mount, is mounted on the lower surface of the wheel mount. Multiple grinding wheels 20 are fixed around the entire circumference of the lower surface of the grinding wheel 18. In this way, the grinding wheels 20 are attached to the spindle 16 as components of the grinding wheel 18.

[0032] Each grinding wheel 20 attached to the grinding wheel 18 is, for example, a grinding wheel in which abrasive grains are embedded in a bonding material. The bonding material is, for example, a resin bond, a vitrified bond, a metal bond, etc. Abrasive grains such as diamond and cubic boron nitride are dispersed in the bonding material.

[0033] A rotational drive source (not shown), such as a motor, is connected to the upper end of the spindle 16, causing the spindle 16 to rotate together with the grinding wheel 18. When the spindle 16 rotates due to the operation of the rotational drive source, the grinding wheel 20 attached to the lower surface of the grinding wheel 18 rotates in an annular trajectory around the rotation axis, and the lower end of the grinding wheel 20 forms an annular grinding surface. As the grinding surface of the grinding wheel 20 rotates, it aligns with the orientation of the holding surface 10a of the holding table 6.

[0034] Furthermore, the grinding surface formed by the lower end of the grinding wheel 20 is a plane approximately perpendicular to the rotation axis of the spindle 16, while the holding surface 10a of the holding table 6 is conical as described above. Therefore, the orientation of the grinding surface of the grinding wheel 20 and the orientation of the holding surface 10a of the holding table 6 do not strictly coincide.

[0035] The holding table 6 and the grinding unit 12 are designed to move relative to each other via the movement units, the X-movement unit 22 and the Z-movement unit 24.

[0036] In the grinding apparatus 2 of this embodiment, the X-movement unit 22 moves the holding table 6 along the X direction. The Z-movement unit 24 moves the grinding unit 12 along the Z direction.

[0037] The X-movement unit 22 includes a guide rail 26, a movable table 28, a ball screw 30, and a rotary drive source 32.

[0038] The guide rails 26 are a pair of rod-shaped members fixed to the upper surface of the base of the grinding device 2 and extending parallel to each other along the X-axis direction. Figure 2 shows only one of the pair of guide rails 26. A movable table 28, which forms a surface along the horizontal plane (XY plane), is slidably mounted on the upper surface of the pair of guide rails 26 along the longitudinal direction of the guide rails 26.

[0039] Between a pair of guide rails 26 that extend parallel to each other, a ball screw 30 is positioned parallel to the guide rails 26 and along the X-axis direction. A nut portion 34 is provided on the underside of the movable table 28, and the ball screw 30 is rotatably connected to the nut portion 34 via a ball (not shown).

[0040] A rotational drive source 32, such as a pulse motor, is connected to one end of the ball screw 30. The operation of the rotational drive source 32 causes the ball screw 30 to rotate around its axis, thereby moving the movable table 28 in the longitudinal direction (along the X direction) of the guide rail 26.

[0041] A rotating unit 36 ​​and a tilt adjustment unit 38 are mounted on the upper surface of the movable table 28, along with the holding table 6. The rotating unit 36 ​​is a mechanism for rotating the holding table 6. The tilt adjustment unit 38 is a mechanism for adjusting the angle of the holding table 6.

[0042] A rotating shaft is provided at the lower part of the table base 8 of the holding table 6, extending downward from the bottom surface of the table base in a direction perpendicular to the holding surface 10a. The rotating unit 36 ​​comprises a rotational drive source such as a motor, a drive pulley fixed to the output shaft of the rotational drive source, a driven pulley fixed to the rotating shaft of the holding table 6, and an endless belt (not shown) wrapped around the drive pulley and the driven pulley.

[0043] When the rotational drive source of the rotation unit 36 ​​is activated, its rotational force is transmitted to the holding table 6 via the output shaft, drive pulley, endless belt, and driven pulley, causing the holding table 6 to rotate around the axis of the conical surface formed by the holding surface 10a. The orientation of the axis of rotation of this rotation is along the vertical direction (Z direction), but the exact angle of the axis of rotation is adjusted by the tilt adjustment unit 38, which will be described next.

[0044] The holding table 6 is supported on the upper surface of the moving table 28 by a tilt adjustment unit 38. The tilt adjustment unit 38 has one fixed shaft 38a and multiple movable shafts 38b, each extending along the Z direction. Note that only one movable shaft 38b is shown in Figure 2.

[0045] The movable axis 38b is configured to extend and retract along the Z direction, thereby allowing the holding table 6 to tilt on the moving table 28 and to adjust its angle.

[0046] On the base of the grinding device 2, a projection is provided that extends upward from the top surface of the base at the rear (right side in Figure 2) of the X-movement unit 22 and the holding table 6. The grinding unit 12 is attached to the front of this projection via the Z-movement unit 24.

[0047] The Z-movement unit 24 includes a guide rail 40, a movable table 42, a ball screw 44, and a rotary drive source 46.

[0048] The guide rails 40 are a pair of rod-shaped members fixed to the front surface of the protrusion on the base and extending parallel to each other along the Z-axis direction. In Figure 2, only one of the pair of guide rails 40 is shown. A movable table 42, which forms a surface along the vertical plane (YZ plane), is slidably mounted along the longitudinal direction of the guide rails 40 on the front surface of the pair of guide rails 40 (the surface opposite to the surface attached to the protrusion on the base).

[0049] Between a pair of guide rails 40 that extend parallel to each other, a ball screw 44 is positioned parallel to the guide rails 40 and along the Z-axis direction. A nut portion 48 is provided on the back (rear) side of the movable table 42, and the ball screw 44 is rotatably connected to the nut portion 48 via a ball (not shown).

[0050] A rotary drive source 46, such as a pulse motor, is connected to one end of the ball screw 44. The operation of the rotary drive source 46 causes the ball screw 44 to rotate around its axis, thereby moving the movable table 42 in the longitudinal direction (along the Z-direction) of the guide rail 40.

[0051] The X-movement unit 22 and the Z-movement unit 24 are mechanisms that move the holding table 6 and the grinding unit 12 relative to each other, respectively. The type of movement performed by each movement unit may be set as appropriate, as long as it can suitably perform the movement of each part necessary for the grinding process.

[0052] For example, the X-movement unit 22 may move the grinding unit 12 relative to the holding table 6 by moving the grinding unit 12 instead of the holding table 6. Alternatively, the X-movement unit 22 may move both the holding table 6 and the grinding unit 12.

[0053] Similarly, the Z-movement unit 24 may move the holding table 6 relative to the grinding unit 12 by moving the holding table 6 instead of the grinding unit 12. Alternatively, the Z-movement unit 24 may move both the holding table 6 and the grinding unit 12.

[0054] The grinding apparatus 2 is further equipped with a processing fluid supply unit (not shown). The processing fluid supply unit is, for example, a nozzle that discharges water as the processing fluid, and supplies water to the wafer 4 and the grinding wheel 20 when the wafer 4 is being ground. The discharge port of the processing fluid supply unit, which is a nozzle, is provided, for example, above the holding surface 10a of the holding table 6. The grinding apparatus 2 may also be equipped with a processing fluid supply unit that supplies the processing fluid through the grinding unit 12.

[0055] Each component of the grinding apparatus 2 (holding table 6, grinding unit 12, moving units (X-moving unit 22, Z-moving unit 24), rotating unit 36, tilt adjustment unit 38, etc.) is connected to the controller 50 shown in Figure 1. In this embodiment, the controller 50 is a mechanism that monitors and controls the operation of each component of the grinding apparatus 2, and is configured, for example, by a computer.

[0056] The computer comprising the controller 50 includes, for example, an information processing unit that performs various information processing and a storage device that stores information. The information processing unit is, for example, a CPU (Central Processing Unit). The storage device includes, for example, a main memory such as DRAM (Dynamic Random Access Memory) and an auxiliary storage device such as a hard disk drive or flash memory. The functions of the controller 50 are realized, for example, by the operation of the information processing unit according to a program (software) stored in the storage device.

[0057] The controller 50 displays various information regarding the operation of the grinding machine 2, and is also connected to an input / output unit 52 for inputting operations for each part.

[0058] The input / output unit 52 is, for example, a touch panel display. The input / output unit 52 displays, for example, an operation screen for inputting various information and commands to each part of the grinding machine 2, and the operator can input information to the controller 50 by touching the operation screen. Note that the device for displaying various information and the device for inputting operations are provided separately from each other, and the input / output unit 52 may be equipped with, for example, a liquid crystal display connected to the controller 50 and an input device such as a mouse or keyboard also connected to the controller 50.

[0059] The procedure for grinding wafer 4 using the grinding apparatus 2 described above will now be explained. Figure 3 is a flowchart illustrating an example of the procedure for grinding the workpiece (wafer) 4 and manufacturing the ground wafer using the grinding apparatus shown in Figure 1.

[0060] The procedure for grinding wafer 4 and manufacturing the ground wafer includes, for example, a holding step S10, a grinding step S20, and a retraction and movement step S30, as shown in Figure 3.

[0061] In the holding step S10, as shown in Figure 2, the wafer 4 is held on the holding surface 10a of the holding table 6. The wafer 4 is placed on the holding surface 10a, which is the upper surface of the suction plate 10, and negative pressure is supplied to the suction plate 10 from a suction source (not shown), causing the wafer 4 to be attracted to the holding surface 10a.

[0062] Next, grinding step S20 is performed. As shown in Figure 2, the holding surface 10a of the holding table 6 is conical in shape, and the upper side of the wafer 4 held there (the side opposite to the side that is attracted to the holding surface 10a) is also conical in shape.

[0063] The holding table 6 and grinding unit 12 are moved by the moving units (X-moving unit 22, Z-moving unit 24), and the holding table 6 and grinding unit 12 are positioned relative to each other such that a portion of the annular trajectory formed by the grinding wheel 20 as the spindle 16 rotates coincides with the vertex of the conical surface formed by the holding surface 10a and the wafer 4 in a plan view (viewpoint from the Z direction; more precisely, a view along the relative direction of movement between the holding table 6 and the grinding unit 12 by the Z-moving unit 24).

[0064] From this state, the holding table 6 and the spindle 16 rotate independently and move closer to each other along the Z direction due to the operation of the Z movement unit 24. When the grinding wheel 20 of the grinding wheel 18 attached to the spindle 16 of the grinding unit 12 comes into contact with the upper surface of the wafer 4 held by the holding table 6, grinding of the wafer 4 begins. During grinding, water is supplied as the processing liquid from the processing liquid supply unit (not shown).

[0065] During grinding, as indicated by the arrows in Figure 4, the grinding unit 12 is gradually moved downward along the Z direction by the Z-movement unit 24 so that the holding table 6 and the spindle 16 move closer to each other (grinding feed). Figure 4 is a schematic cross-sectional view showing the state of the grinding wheel 20 and wafer 4 during grinding.

[0066] Here, "grinding feed" as used herein refers to a feed operation performed during grinding, which involves bringing the holding table 6 and the spindle 16 closer together so that the workpiece (wafer) 4 held on the holding table 6 and the grinding wheel 20 of the grinding wheel 18 attached to the spindle 16 of the grinding unit 12 are pressed against each other.

[0067] During grinding, the rotation axis of the holding table 6 and the rotation axis of the spindle 16 are in a relative position with their respective orientations aligned with each other (however, the rotation axis of the holding table 6 is slightly inclined with respect to the Z axis, so the two rotation axes are not strictly parallel). During grinding feed, as the wafer 4 and grinding wheel 20 wear down, the holding table 6 and the spindle 16 are moved relative to each other by the Z-movement unit 24 so that they approach the orientation aligned with the rotation axis of the spindle 16 (or the Z-direction).

[0068] In the case of the grinding apparatus 2 described above, the spindle 16 moves along the Z direction, causing the spindle 16 and the holding table 6 to move relative to each other in a direction along the Z direction. However, the holding table 6 may move instead of the spindle 16, or both the holding table 6 and the spindle 16 may move.

[0069] The trajectory of the lower end of the rotating grinding wheel 20 forms an annular grinding surface along the horizontal plane (XY plane) with a width equal to the width of the grinding wheel 20 (the radial dimension of the grinding wheel 18). One point of the annular trajectory is located at the apex of the wafer 4, which is held in a conical shape on the holding surface 10a of the holding table 6. In other words, the lower end of the rotating grinding wheel 20 contacts the wafer 4 at least at the apex of the conical surface formed by the wafer 4.

[0070] The wafer 4 and grinding wheel 20, which are in contact with each other, are pressed against each other in the Z-direction by the grinding feed, which generates stress inside both the wafer 4 and the grinding wheel 20. The grinding wheel 20, which is made of a bonding material in which abrasive grains are embedded, is pressed against the surface of the wafer 4 while deforming as if being crushed by the force it receives from the surface of the wafer 4. In particular, if the bonding material contained in the grinding wheel 20 is a resin such as a resin bond, the deformation that occurs in the grinding wheel 20 is large.

[0071] Once the wafer 4 has been ground to the desired thickness by the grinding step S20, the retraction and movement step S30 is performed. In the retraction and movement step S30, the grinding feed is stopped so that the holding table 6 and the spindle 16 move closer to each other, and then the holding table 6 and the grinding unit 12 move away from each other so that the wafer 4 and the grinding wheel 20 move away from each other.

[0072] At this time, operations generally referred to as spark-out (step S31) and escape cut (step S32) are performed. Spark-out is an operation in which, after grinding with grinding feed (grinding step S20), the wafer 4 and grinding wheel 20 are rotated while the grinding feed is stopped. Escape cut is an operation in which, while the wafer 4 and grinding wheel 20 are rotating, both are moved in the opposite direction to the grinding feed, thereby moving them apart.

[0073] Figure 5 is a schematic cross-sectional view illustrating an example of the state of the grinding wheel 20 and wafer 4 during spark-out.

[0074] In the spark-out (step S31), the grinding feed (movement of the spindle 16 along the Z direction) is stopped, but the rotation of the wafer 4 and the grinding wheel 20 continues. Even though the grinding feed is stopped, the positions of the wafer 4 and the grinding wheel 20 have not moved from the end of grinding step S20. Therefore, the state in which the grinding wheel 20 is deformed as if being crushed when pressed against the wafer 4 continues, and the grinding wheel 20 presses the abrasive grains against the wafer 4 due to the force trying to restore itself from the crushed state.

[0075] In this state, as the wafer 4 and grinding wheel 20 rotate, the wafer 4 is slightly ground, and the grinding wheel 20 is also worn down little by little. As a result, the shape of the material of the grinding wheel 20, which had been deformed as if being crushed, is gradually restored, and the stress that had been generated in the grinding wheel 20 is released.

[0076] Furthermore, although not shown in Figure 5, if a flexible protective material such as BG tape (backgrind tape) is attached to the back surface of the wafer 4 (the surface facing the holding table 6), the protective material is also compressed by the grinding feed in grinding step S20. In sparkout, as the wafer 4 is ground as described above with the grinding feed stopped, the force compressing the protective material is also released.

[0077] Thus, after the spark-out (step S31) is performed over an appropriate period of time, the escape cut (step S32) is then performed.

[0078] Figure 6 is a schematic cross-sectional view illustrating an example of the state of the grinding wheel 20 and wafer 4 during escape cutting.

[0079] In the escape cut (step S32), the wafer 4 and grinding wheel 20 continue to rotate, but the wafer 4 and grinding wheel 20 are moved in the opposite direction to the grinding feed. In other words, in this embodiment, the spindle 16 is moved upward along the Z direction.

[0080] For a short time after the escape cut begins, the wafer 4 and the grinding wheel 20 remain in contact with each other. However, when the material of the grinding wheel 20 and the protective material on the back of the wafer 4, which were compressed by the grinding feed, are released from the compressive force, the wafer 4 and the grinding wheel 20 separate, and the grinding of the wafer 4 is completely finished. In this way, a ground wafer 4' is produced.

[0081] The above is a description of the general spark-out and escape-cut operations in the retraction movement step S30. When the retraction movement step S30 is performed using such operations, shapes such as those shown in Figures 7 and 8 may appear on the surface of the wafer 4 after grinding.

[0082] Figure 7 is a micrograph showing an example of the surface condition of the workpiece (ground wafer) 4' after the completion of grinding step S20 and retraction step S30. In the figure, the point indicated by the symbol T is the apex of the wafer 4 that was held in a conical shape on the holding table 6. A circular groove-like shape (indicated by the symbol C in the figure; hereinafter referred to as the "circular groove") is visible around the apex T.

[0083] Figure 8 is a diagram showing the results of measuring the surface shape of the workpiece (ground wafer) 4' shown in Figure 7. The surface shape of wafer 4 after grinding is measured by a laser sensor installed on the top surface of wafer 4. Measurement light is shone vertically from the laser sensor onto the top surface of wafer 4, which is positioned horizontally, and the distance between the laser sensor and the surface of wafer 4 is measured as the position of the laser sensor moves along the radial direction of wafer 4.

[0084] In the graph in Figure 8, the horizontal axis represents the distance from the center (vertex T) of wafer 4 (position in the X direction), and the vertical axis represents the distance from the laser sensor to the surface of wafer 4 (distance in the Z direction).

[0085] In the figure, a downward-pointing peak can be seen at the location indicated by the arrow (approximately 2.5 mm from the center), which corresponds to the location of the circular groove C shown in Figure 7. Furthermore, the location where this circular groove C is engraved corresponds to the part of the wafer 4 surface where the edge of the grinding wheel 20 contacts the wafer 4 between the grinding step S20 and the retraction step S30, that is, the part where the radially inner edge (hereinafter referred to as the "inner edge E") of the annular grinding surface formed by the rotation of the grinding wheel 20 contacts the wafer 4 (see Figures 4 to 6).

[0086] In the grinding method described above (called infeed grinding), in which the wafer 4 and the grinding wheel 20 rotate and come into contact with each other, radial saw marks appear on most of the surface of the wafer 4. However, under certain conditions, a shape like the circular groove C shown in Figures 7 and 8 may appear specifically in the center of the wafer 4. This is especially likely to occur when the grinding wheel 20, which contains an elastic material such as a resin bond as a bonding agent, is used for grinding.

[0087] The inventors of the present invention have found that the occurrence of such circular saw marks (circular grooves C) can be reduced by modifying the operation during spark-out and escape cut. Such a method will be explained with reference to Figures 9 and 10-13.

[0088] Figure 9 is a flowchart illustrating another example of the procedure for grinding a workpiece (wafer) 4 using the grinding apparatus shown in Figure 1 and for manufacturing a ground wafer. In the procedure shown in Figure 9, the holding step S10 and grinding step S20 are performed in the same way as in the procedure shown in Figure 3, but the actions performed in the retraction and movement step S40 (spark out (step S41) and escape cut (step S42)) differ from those in the retraction and movement step S30 in the procedure shown in Figure 3.

[0089] Figure 10 is a schematic cross-sectional view showing an example of the state of the grinding wheel and workpiece (wafer) at the time of spark-out (step S41) in the procedure shown in Figure 9. Figure 11 is a schematic cross-sectional view showing an example of the state of the grinding wheel and workpiece (wafer) at the time of escape cut (step S42) in the procedure shown in Figure 9.

[0090] In the spark-out (step S41) during the retraction movement step S40 of the procedure in Figure 9, as indicated by the arrows in Figure 10, the holding table 6 moves along the horizontal direction (X direction), causing the spindle 16 and the holding table 6 to move relative to each other in a direction aligned with the grinding surface of the grinding wheel 20.

[0091] At this time, the relative direction of movement between the spindle 16 and the holding table 6 is such that the intersection point between the holding table 6 and the grinding surface of the rotation axis of the wafer 4 and the intersection point between the spindle 16 and the grinding surface of the rotation axis of the grinding wheel 20 are moving closer to each other in a plan view (viewpoint from a direction along the rotation axis), and the inner edge E of the portion of the grinding wheel 20's grinding surface that is in contact with the apex of the wafer 4, which is cone-shaped, is moving closer to the apex of the wafer 4.

[0092] In the case of the grinding apparatus 2 described above, the holding table 6 moves along the X direction, causing the spindle 16 and the holding table 6 to move relative to each other in a direction aligned with the grinding surface of the grinding wheel 20. However, the spindle 16 may move instead of the holding table 6, or both the holding table 6 and the spindle 16 may move. Alternatively, the holding table 6 and the spindle 16 may move relative to each other in a direction intersecting the X direction (along the Y direction) in a direction aligned with the grinding surface of the grinding wheel 20.

[0093] Next, as shown in Figure 11, an escape cut (step S42) is performed. In the previous spark-out, the positions of the wafer 4 and the grinding wheel 20 are offset from each other in the X direction. In the escape cut of step S42, the spindle 16 moves upward along the Z direction (opposite to the grinding feed) from this position, and the wafer 4 and the grinding wheel 20 are separated in the Z direction. In this way, the ground wafer 4' is manufactured.

[0094] Figures 12 and 13 show an example of the surface condition of wafer 4 after grinding according to the above procedure. Figure 12 is a micrograph showing an example of the surface condition of the workpiece (ground wafer) 4' after completion of the retraction movement step S40 according to the procedure shown in Figure 9. Figure 13 is a diagram showing the results of measuring the surface shape of the workpiece (ground wafer) 4' shown in Figure 12, and was created using the same method as the diagram shown in Figure 8.

[0095] In the photograph in Figure 12, it can be seen that the diameter of the circular groove C is smaller compared to the photograph in Figure 7. In the diagram in Figure 13, compared to the diagram in Figure 8, the position of the downward peak corresponding to the circular groove C (indicated by the arrow in the figure) is closer to the top of wafer 4.

[0096] In the procedure shown in Figures 9 to 11, during the spark-out (step S41), the holding table 6 and the spindle 16 move relative to each other in the X direction, causing a displacement between the wafer 4 and the grinding wheel 20. At the end of the spark-out, the inner edge E of the grinding surface formed by the grinding wheel 20 approaches the apex of the wafer 4, as shown in Figure 11. The position of the circular groove C shown in Figures 12 and 13 corresponds to the position of the inner edge E of the grinding surface at the end of the spark-out.

[0097] Based on the above, it is considered that if the holding table 6 and the spindle 16 are moved relative to each other during spark-out, and the inner edge E of the grinding surface formed by the grinding wheel 20 approaches the apex of the cone-shaped wafer 4, the diameter of the circular groove C will be reduced, and the range of the region in which the circular groove C is formed will be narrowed.

[0098] Furthermore, it is conceivable that the formation of noticeable circular grooves can be suppressed if the inner edge E of the grinding surface coincides with the position of the apex of the wafer 4 at the end of the spark-out process, or if the inner edge E of the grinding surface crosses over the position of the apex of the wafer 4 during the spark-out process.

[0099] Therefore, in the procedure shown in Figure 9, the relative movement amount between the holding table 6 and the spindle 16 during spark-out was adjusted so that the inner edge E of the grinding surface coincided with the position of the apex of the wafer 4 at the end of spark-out (step S41). The results of grinding are shown in the photographs and diagrams in Figures 14 and 15. Figure 14 is a micrograph showing an example of the surface state of the workpiece (ground wafer) 4' after completion of the retraction movement step S40 by such a procedure. Figure 15 is a diagram showing the results of measuring the surface shape of the workpiece (wafer 4) shown in Figure 14, and was created using the same method as the diagram shown in Figure 8.

[0100] In the photograph in Figure 14, a circular shape due to saw marks can be seen around the vertex T of wafer 4, but it is thinner than the circular groove C in Figures 7 and 12, and a distinct groove-like shape is not formed. In the diagram in Figure 15, no significant downward-pointing peak can be observed in the region near the vertex compared to other regions.

[0101] Thus, in the procedure shown in Figures 9 to 11, by moving the wafer 4 and the grinding wheel 20 relative to each other along the grinding surface during spark-out, the area in which the circular groove C appears can be narrowed, or the circular shape can be made thinner.

[0102] Figure 16 is a flowchart illustrating yet another example of the procedure for grinding a workpiece (wafer) 4 using the grinding apparatus shown in Figure 1 and for manufacturing a ground wafer. In the procedure shown in Figure 16, the spark-out step (step S31) of the holding step S10, grinding step S20, and retraction / movement step S50 is performed in the same way as in the procedure shown in Figure 3, but the content of the escape cut (step S51) that follows the spark-out is different from the escape cut (step S32) in the procedure in Figure 3.

[0103] Figure 17 is a schematic cross-sectional view showing an example of the state of the grinding wheel 20 and the workpiece (wafer) 4 during the escape cut (step S51) in the procedure shown in Figure 16.

[0104] In the escape cut (step S51) in the retraction movement step S50 of the procedure shown in Figure 16, as indicated by the arrows in Figure 17, the holding table 6 moves along the horizontal direction (X direction) and the spindle 16 moves along the vertical direction (Z direction). As a result, the spindle 16 and the holding table 6 move relative to each other in a direction aligned with the grinding surface of the grinding wheel 20, while separating in a direction aligned with the rotation axis of the spindle 16. In this way, the ground wafer 4' is manufactured.

[0105] In this case, the relative direction of movement between the spindle 16 and the holding table 6 along the X direction is such that the intersection point of the holding table 6 and the rotation axis of the wafer 4 with the grinding surface and the intersection point of the spindle 16 and the rotation axis of the grinding wheel 20 are moving closer to each other in a plan view (viewpoint from the direction along the rotation axis), and the inner edge E of the portion of the grinding wheel 20's grinding surface that is in contact with the apex of the wafer 4, which forms a conical surface, is moving closer to the apex of the wafer 4. In addition, the relative direction of movement between the spindle 16 and the holding table 6 along the Z direction is such that the holding table 6 and the wafer 4, and the spindle 16 and the grinding wheel 20 are moving away from each other.

[0106] In the case of the grinding apparatus 2 described above, in the escape cut shown in Figure 17, the relative movement between the holding table 6 and the spindle 16 is such that the holding table 6 is moved by the X-movement unit 22 in the horizontal direction (X direction) (movement along the grinding surface of the grinding wheel 20), and the spindle 16 is moved by the Z-movement unit 24 in the vertical direction (Z direction) (movement along the rotation axis of the holding table 6 and the spindle 16). However, the spindle 16 may be moved in the horizontal direction, or the holding table 6 may be moved in the vertical direction.

[0107] Furthermore, both the holding table 6 and the spindle 16 may move in the horizontal direction, or both the holding table 6 and the spindle 16 may move in the vertical direction.

[0108] Alternatively, the grinding device 2 may be equipped with a mechanism that moves at least one of the holding table 6 or the spindle 16 in an oblique direction intersecting both the horizontal and vertical directions, so that movement along the horizontal and vertical directions can be achieved by a single mechanism.

[0109] Figures 18 and 19 show an example of the surface condition of the workpiece (ground wafer) 4' after grinding according to the above procedure. Figure 18 is a micrograph showing an example of the surface condition of the workpiece (ground wafer) 4' after completion of the retraction movement step S50 according to the procedure shown in Figure 16. Figure 19 is a diagram showing the results of measuring the surface shape of the workpiece (ground wafer) 4' shown in Figure 18, and was created using the same method as the diagram shown in Figure 8.

[0110] On the surface of wafer 4 (ground wafer 4') shown in Figures 18 and 19, there is almost no circular shape around vertex T, and as shown in Figure 18, only radial saw marks centered on vertex T are observed.

[0111] Thus, in the procedure shown in Figure 16, the occurrence of circular saw marks can be suppressed by moving the wafer 4 and the grinding wheel 20 relative to each other in a direction along the grinding surface and along the rotation axis during escape cutting.

[0112] As described above, in the grinding process of the workpiece (wafer) 4, in the retraction and movement steps S40 and S50 after the grinding step S20, the grinding feed by the movement units 22 and 24 is stopped, and while rotating the holding table 6 and the spindle 16, the holding table 6 and the spindle 16 are moved in directions that intersect each other with the rotation axis of the spindle 16, thereby enabling a more favorable surface shape to be achieved in the workpiece (ground wafer) 4'.

[0113] It is also possible to perform the grinding process of wafer 4 by combining the procedure shown in Figure 9 and the procedure shown in Figure 16. For example, in the spark-out stage, wafer 4 and the grinding wheel 20 may first move relative to each other along the grinding surface, and then in the escape cut stage, the moving units 22 and 24 may operate so that wafer 4 and the grinding wheel 20 move relative to each other in a direction along the grinding surface, while also moving relative to each other in a direction intersecting the grinding surface (in a direction along the axis of rotation).

[0114] Furthermore, the structures, methods, etc., according to the embodiments described above are not limited to those embodiments and may be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of Symbols]

[0115] 2: Grinding machine, 4: Workpiece (wafer), 4': Grinded wafer 6: Holding table, 8: Table base, 10: Suction plate, 10a: Holding surface (top surface) 12: Grinding unit, 14: Spindle housing, 16: Spindle 18: Grinding wheel, 20: Grinding wheel 22: Movement unit (X movement unit), 24: Movement unit (Z movement unit) 26: Guide rail, 28: Mobile table, 30: Ball screw 32: Rotary drive source, 34: Nut section 36: Rotation unit, 38: Tilt adjustment unit, 38a: Fixed axis, 38b: Movable axis 40: Guide rail, 42: Mobile table, 44: Ball screw 46: Rotary drive source, 48: Nut section 50: Controller, 52: Input / Output section C: Circular groove, E: Inner edge, T: Vertex

Claims

1. A grinding method for grinding a workpiece using a grinding apparatus comprising: a holding table having a conical holding surface and rotatable about an axis intersecting the holding surface; a grinding unit having a spindle to which a grinding wheel can be attached, which grinds a workpiece held on the holding surface of the holding table by rotating the grinding wheel in contact with the workpiece while forming a grinding surface oriented along the holding surface; and a moving unit for moving the holding table and the grinding wheel relative to each other. A holding step of holding the workpiece on the holding surface of the holding table, A grinding step in which the holding table and the spindle are rotated so that the orientation of their respective rotation axes is aligned with each other, and with the workpiece and the grinding wheel in contact, the moving unit is used to bring the holding table and the spindle closer together along the orientation of the spindle's rotation axis, thereby grinding the workpiece held on the holding surface, After the grinding step, the grinding feed by the moving unit is stopped, and a retraction movement step is performed in which the holding table and the spindle are moved relative to each other in a direction intersecting the rotation axis of the spindle while the holding table and the spindle are rotated. A grinding method that includes [a specific type of grinding method].

2. The grinding method according to claim 1, wherein in the grinding step, a portion of the trajectory of the grinding wheel is located at the apex of the workpiece held in a conical shape on the holding surface of the holding table.

3. The grinding method according to claim 1, wherein in the retraction movement step, the spindle and the holding table are moved relative to each other in a direction along the grinding surface of the grinding wheel.

4. The grinding method according to claim 1, wherein in the retraction movement step, the spindle and the holding table are moved relative to each other in a direction along the grinding surface of the grinding wheel, while being separated in a direction along the rotation axis of the spindle.

5. The grinding method according to any one of claims 1 to 4, wherein the grinding wheel contains a resin bond as a bonding agent.

6. A method for manufacturing a ground wafer, wherein the workpiece is a plate-shaped wafer, and the ground wafer is manufactured using the grinding method described in claim 1.

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