Grinding method for workpiece

Abstract

To provide a method for grinding a work-piece that can suppress areas occupied by a grinding device from increasing, without deteriorating productivity of chips.SOLUTION: A rotation speed (a second rotation speed) of a grinding wheel at the time of grinding a second layer including a second material which is harder to grind than a first material is set to be lower than a rotation speed (a first rotation speed) of the grinding wheel at the time of grinding a first layer including the first material. This enables the second layer to be ground, without causing defect. Further, when the second layer is ground as described above, it is not necessary to utilize a grinding wheel with high grinding force or make a speed of grinding a work-piece lower. This can suppress areas occupied by a grinding device from increasing, without deteriorating productivity of chips.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for grinding a workpiece, in which the workpiece is ground to a predetermined finishing thickness. [Background technology]

[0002] Semiconductor device chips such as ICs (Integrated Circuits) or LSIs (Large Scale Integration) are essential components in various electronic devices such as mobile phones and personal computers. Such chips are manufactured by dividing a workpiece such as a wafer having many devices formed on its surface into regions containing individual devices.

[0003] Furthermore, the workpiece is often ground before being separated in order to thin the resulting chips or to expose the metal electrodes that are components of the device. Such grinding is performed, for example, by rotating a grinding wheel having multiple grinding wheels formed in an annular shape and bringing the multiple grinding wheels into contact with the workpiece held on a chuck table (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-90389 Summary of the Invention [Problem to be solved by the invention]

[0005] The workpieces used for grinding include a variety of materials. For example, when the workpiece includes a silicon (Si) wafer (silicon wafer), a silicon oxide (SiO2) film may be formed on one side of the wafer. In addition, the workpiece may have metal electrodes, which are components of the device, embedded in the silicon wafer.

[0006] The difficulty of grinding varies depending on the type of material being ground. For example, when grinding silicon oxide, the abrasive grains contained in the grinding wheel tend to fall off (drop out). This makes silicon oxide a more difficult-to-cut material than silicon. Also, because the metals used as electrodes are less hard than silicon, grinding metal electrodes tends to produce a large amount of fine grinding debris. In this case, the abrasive grains exposed on the underside of the grinding wheel are likely to become covered (clogging). This makes metal electrodes a more difficult-to-cut material than silicon.

[0007] In consideration of this, the workpiece may be ground under different conditions depending on the type of material being ground. For example, when grinding a layer containing a difficult-to-cut material, a grinding wheel with a high grinding power (e.g., a grinding wheel with multiple grinding stones each containing large abrasive grains formed in a ring) may be used, or the grinding speed of the workpiece (the speed at which the grinding wheel and chuck table are brought closer together) may be slowed down.

[0008] However, when a grinding wheel with high grinding power is used to grind a layer containing a difficult-to-cut material, it becomes necessary to change the grinding wheel or to use a grinding machine that can accommodate two or more types of grinding wheels. In this case, chip productivity may decrease or the grinding machine's footprint may increase. Similarly, chip productivity may decrease when the grinding speed of the workpiece is slowed to grind a layer containing a difficult-to-cut material.

[0009] In view of these points, an object of the present invention is to provide a method for grinding a workpiece that does not reduce chip productivity and that can suppress an increase in the area occupied by a grinding device. [Means for solving the problem]

[0010] According to the present invention, there is provided a method for grinding a workpiece having a first layer containing a first material and a second layer containing a second material that is more difficult to cut than the first material and that is laminated on the first layer, to a predetermined finishing thickness, the method comprising: a first grinding step of grinding the first layer of the workpiece held by a chuck table with a plurality of grinding wheels while rotating a grinding wheel having a plurality of grinding wheels arranged in an annular shape at a first rotational speed; Utilized in the first grinding step a second grinding step of grinding the second layer of the workpiece held by the chuck table with the plurality of grinding wheels while rotating the grinding wheel at a second rotational speed slower than the first rotational speed.

[0011] In the present invention, it is preferable to further include a separating step between the first grinding step and the second grinding step, in which the plurality of grinding wheels are separated from the workpiece.

[0012] In the present invention, it is also preferred that the first material is silicon and the second material is silicon oxide, and that the first grinding step is performed after the second grinding step is performed to remove the second layer.

[0013] Furthermore, when a layer containing silicon oxide (e.g., a silicon oxide film) is removed in the second grinding step, it is preferable that the second grinding step be completed when a predetermined time has elapsed since grinding of the second layer was started, while the grinding wheel and the chuck table are moved relatively to each other at a predetermined speed so that they approach each other.

[0014] Alternatively, in this case, the second grinding step is terminated when the thickness of the workpiece reaches a predetermined thickness, with the thickness of the workpiece being measured. wherein the predetermined thickness is a thickness of the first layer that is less than or equal to a thickness obtained by subtracting a thickness of the second layer from an original thickness of the workpiece. It is preferable that [Effects of the Invention]

[0015] In the present invention, the rotational speed (second rotational speed) of the grinding wheel when grinding a second layer including a second material that is more difficult to cut than the first material is set to be slower than the rotational speed (first rotational speed) of the grinding wheel when grinding a first layer including a first material.

[0016] When the grinding wheel rotates slowly during grinding, strong frictional forces act on each of the grinding wheels due to contact with the workpiece, making it easier for the grinding wheels to grind. In other words, in this case, self-sharpening is promoted in each of the grinding wheels. This makes it possible to grind the second layer without causing any problems.

[0017] Furthermore, when the second layer is ground in this manner, it is not necessary to use a grinding wheel with a high grinding force or to slow down the grinding speed of the workpiece, which prevents a decrease in chip productivity and reduces the area occupied by the grinding device. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a perspective view schematically showing an example of a grinding device. [Figure 2] FIG. 2(A) is a perspective view that schematically shows an example of a workpiece before grinding, and FIG. 2(B) is a cross-sectional view that schematically shows an example of a workpiece before grinding. [Figure 3] FIG. 3 is a side view schematically showing some of the components of the grinding unit. [Figure 4] FIG. 4 is a flow chart schematically illustrating an example of a method for grinding a workpiece, in which the workpiece is ground until it has a predetermined finishing thickness. [Figure 5] FIG. 5 is a flow chart schematically showing a specific example of the rough grinding step. [Figure 6] 6(A), 6(B), and 6(C) are each a partial cross-sectional side view that schematically shows the rough grinding step. DETAILED DESCRIPTION OF THE INVENTION

[0019] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a perspective view showing a schematic diagram of an example of a grinding device. Note that the X-axis direction (left-right direction) and the Y-axis direction (front-rear direction) shown in Fig. 1 are directions perpendicular to each other on a horizontal plane, and the Z-axis direction (up-down direction) is a direction (vertical direction) perpendicular to the X-axis direction and the Y-axis direction.

[0020] 1 includes a base 4 that supports or houses each of the components. An opening 4a is formed on the upper surface side of the front end of the base 4, and a transport unit 6 is provided inside this opening 4a. This transport unit 6 has, for example, a suction pad that sucks the upper surface side of the workpiece 11, which will be described later.

[0021] Further, cassette installation areas 8a and 8b are provided diagonally to the left and right of the transport unit 6. Cassettes 10a and 10b each capable of accommodating a plurality of workpieces are placed above the cassette installation areas 8a and 8b, respectively.

[0022] Cassette 10a accommodates, for example, workpieces to be ground in grinding device 2 (workpieces before grinding). Cassette 10b accommodates, for example, workpieces that have been ground in grinding device 2 (workpieces after grinding).

[0023] Fig. 2(A) is a perspective view showing an example of a workpiece before grinding, and Fig. 2(B) is a cross-sectional view showing an example of the workpiece before grinding. The workpiece 11 shown in Fig. 2(A) and Fig. 2(B) has a wafer (first layer) 13 made of silicon (first material) on the surface 11a side.

[0024] The silicon wafer 13 is divided into a plurality of regions by streets (planned dividing lines) 15 set in a grid pattern, and devices 17 such as ICs or LSIs are formed in each region. A thin film (silicon oxide film) (second layer) 19 made of silicon oxide (second material), which is harder to cut than silicon, is formed on the back surface 11b of the workpiece 11 so as to be stacked on the silicon wafer 13.

[0025] This silicon oxide film 19 is formed in association with a process (e.g., heating) performed on the workpiece 11 when forming a device. Furthermore, the workpiece 11 is made of a material that is more difficult to cut than silicon, and a metal electrode that is a component of the device 15 may be buried inside the silicon wafer 13.

[0026] Furthermore, a film-like tape for protecting the device 17 may be attached to the surface 11a of the workpiece 11. This tape has, for example, a circular film-like base material and an adhesive layer (glue layer) provided on the base material.

[0027] The base material is made of, for example, a polyolefin, polyvinyl chloride, or polyethylene terephthalate resin, and the adhesive layer is made of, for example, an epoxy or acrylic adhesive. Alternatively, the adhesive layer may be made of an ultraviolet-curable resin that hardens when irradiated with ultraviolet light.

[0028] There are no limitations on the material, shape, structure, size, etc. of the workpiece 11. For example, the workpiece 11 may include a wafer made of another semiconductor material, or a substrate made of a material such as ceramic, resin, or metal. Similarly, there are no limitations on the type, number, shape, structure, size, arrangement, etc. of the device 17.

[0029] 1, the workpiece 11 is accommodated with the back surface 11b on which the silicon oxide film 19 is formed facing upward. The transport unit 6 sucks the top surface (e.g., the back surface 11b) of the workpiece 11 with a suction pad, and transports the workpiece 11 out of the cassette 10a while the workpiece 11 is held by the transport unit 6.

[0030] Furthermore, an alignment mechanism 12 is provided diagonally to the rear left of the transport unit 6 and at a position where the workpiece 11 can be transported by the transport unit 6. When the workpiece 11 carried out from the cassette 10a by the transport unit 6 is carried into the alignment mechanism 12, the alignment mechanism 12 operates to sandwich the workpiece 11 and position it at a predetermined position.

[0031] Further, a transport unit 14 is provided behind the transport unit 6 and to the right of the alignment mechanism 12 to transport out the workpiece 11 that has been aligned by the alignment mechanism 12. This transport unit 14 has, for example, a suction pad that sucks the top surface side (for example, the back surface 11b side) of the workpiece 11.

[0032] Then, when the workpiece 11 that has been aligned by the alignment mechanism 12 is sucked by the suction pad of the transport unit 14 and held by the transport unit 14, the transport unit 14 operates to rotate the suction pad and transport the workpiece 11 backward.

[0033] A disk-shaped turntable 16 is provided behind the transport unit 14. The turntable 16 is connected to a rotation drive source (not shown) such as a motor that rotates the turntable 16 around a rotation axis that is roughly parallel to the Z-axis direction.

[0034] In addition, a plurality of chuck tables 18 are provided on the turntable 16, each capable of sucking and holding the lower surface side (e.g., the front surface 11a side) of the workpiece 11. Note that Fig. 1 shows an example in which three chuck tables 18 are arranged at approximately equal intervals along the circumferential direction of the turntable 16.

[0035] The chuck table 18 has a circular upper surface that is roughly parallel to the horizontal plane (XY plane), and this upper surface holds the workpiece 11. In other words, the upper surface of the chuck table 18 serves as a holding surface that holds the workpiece 11.

[0036] Moreover, the turntable 16 rotates, for example, clockwise in a plan view, and positions each chuck table 18 in the following order: transfer position A, first grinding position (rough grinding position) B, second grinding position (finish grinding position) C, and transfer position A. Then, the workpiece 11 transferred by the transfer unit 14 is loaded onto the chuck table 18 positioned at the transfer position A.

[0037] Furthermore, the holding surface of the chuck table 18 communicates with a suction source (not shown) such as an ejector via a flow path (not shown) and a valve (not shown) formed inside the chuck table 18. Then, when the suction source is operated and the valve is opened with the workpiece 11 loaded onto the chuck table 18, the lower surface side (for example, the front surface 11a side) of the workpiece 11 is sucked toward the chuck table 18. As a result, the workpiece 11 is held on the holding surface of the chuck table 18.

[0038] The chuck table 18 is also connected to a rotary drive source (not shown) such as a motor that rotates the chuck table 18 around a rotation axis that is generally parallel to the Z-axis direction. This rotary drive source rotates the chuck table 18 when the workpiece 11 is ground by a plurality of grinding stones 48 (see FIG. 3) of grinding wheels 44a and 44b, which will be described later.

[0039] Further, thickness gauges 20a and 20b for measuring the thickness of the workpiece 11 held by the chuck table 18 are provided near the first grinding position B and near the second grinding position C. Each of the thickness gauges 20a and 20b measures the change in the thickness of the workpiece 11 over time as the workpiece 11 is ground.

[0040] Specifically, each of the thickness measuring devices 20a and 20b has a pair of height gauges, one of which has a probe that comes into contact with the exposed upper surface (e.g., back surface 11b) of the workpiece 11 that is not covered by grinding wheels 44a and 44b (described later) when the workpiece 11 is ground.

[0041] The other of the pair of height gauges has a probe that comes into contact with the holding surface of the chuck table 18, which is exposed and not covered by the workpiece 11 and the grinding wheels 44a and 44b described later, when the workpiece 11 is ground.

[0042] Therefore, when the workpiece 11 is ground, the height of the upper surface (e.g., back surface 11b) of the workpiece 11 and the height of the holding surface of the chuck table 18 are measured by a pair of height gauges. Then, each of the thickness gauges 20a and 20b measures the difference between these heights as the thickness of the workpiece 11.

[0043] A pillar-shaped support structure 22a is disposed behind the first grinding position B, and a pillar-shaped support structure 22b is disposed behind the second grinding position C. Movement mechanisms 24a and 24b that move (raise and lower) moving plates 28a and 28b along the Z-axis direction are provided on the front side (surface side) of each support structure 22a and 22b.

[0044] Each of the movement mechanisms 24a, 24b has a pair of guide rails 26 extending along the Z-axis direction. Movement plates 28a, 28b are slidably connected to the front sides (surface sides) of the pair of guide rails 26. A screw shaft 30 extending along the Z-axis direction is disposed between the pair of guide rails 26.

[0045] A motor 32 for rotating the screw shaft 30 is connected to the upper end of the screw shaft 30. A nut portion (not shown) for accommodating balls that circulate in response to the rotation of the screw shaft 30 is provided on the outer circumferential surface of the screw shaft 30 on which the threads are formed, thereby forming a ball screw.

[0046] The nuts are fixed to the rear surfaces (back surfaces) of the movable plates 28a and 28b. Therefore, when the screw shaft 30 is rotated by the motor 32, the movable plates 28a and 28b move (move up and down) along the Z-axis direction together with the nuts.

[0047] A grinding unit 34a that performs rough grinding of the workpiece 11 is fixed to the front side (surface side) of the movable plate 28a. On the other hand, a grinding unit 34b that performs finish grinding of the workpiece 11 is fixed to the front side (surface side) of the movable plate 28b.

[0048] Therefore, when movable plate 28a moves up and down, grinding unit 34a also moves up and down, and when movable plate 28b moves up and down, grinding unit 34b also moves up and down. Each of grinding units 34a, 34b has a hollow cylindrical housing 36 extending along the Z-axis direction.

[0049] A motor 38 is provided on the upper part of the housing 36, and the motor 38 is connected to the base end (upper end) of a spindle that is rotatably accommodated in the housing 36. The spindle extends along the Z-axis direction, and its tip end (lower end) is exposed from the bottom of the housing 36.

[0050] 3 is a side view schematically showing the components of the grinding units 34a and 34b exposed from the bottom of the housing 36. A disk-shaped mount 42 made of metal or the like is fixed to the tip of the spindle 40 exposed from the bottom of the housing 36.

[0051] Furthermore, a grinding wheel 44a for rough grinding is attached to the underside of the mount 42 of the grinding unit 34a, and a grinding wheel 44b for finish grinding is attached to the underside of the mount 42 of the grinding unit 34b. Each of the grinding wheels 44a, 44b rotates around a rotation axis that is roughly parallel to the Z-axis direction by power transmitted from the motor 38 via the spindle 40 and the mount 42.

[0052] Each of the grinding wheels 44a, 44b has an annular wheel base 46 whose outer diameter is roughly equal to the diameter of the mount 42. The wheel base 46 is made of a metal such as aluminum or stainless steel. A plurality of grinding stones 48 are fixed to the underside of the wheel base 46.

[0053] Each of the plurality of grinding wheels 48 has, for example, a rectangular parallelepiped shape and is arranged at approximately equal intervals along the circumferential direction of the wheel base 46. Each of the plurality of grinding wheels 48 is formed by fixing abrasive grains made of diamond, cBN (cubic boron nitride), or the like with a binder such as a metal bond, a resin bond, or a vitrified bond.

[0054] However, a grinding stone suitable for rough grinding is used as the grinding stone 48 of the grinding wheel 44a, and a grinding stone suitable for finish grinding is used as the grinding stone 48 of the grinding wheel 44b. Therefore, the average particle size of the abrasive grains contained in the grinding stone 48 of the grinding wheel 44b is smaller than the average particle size of the abrasive grains contained in the grinding stone 48 of the grinding wheel 44a, for example.

[0055] Furthermore, a grinding fluid supply path (not shown) for supplying a liquid (grinding fluid) such as pure water is provided inside each of the grinding units 34a, 34b. Further, a nozzle for supplying the grinding fluid may be provided near each of the grinding units 34a, 34b instead of or in addition to the grinding fluid supply path.

[0056] When the workpiece 11 is ground by the grinding wheels 48 of the grinding wheels 44a and 44b, this grinding fluid is supplied to the contact interface (processing point) between the workpiece 11 and the grinding wheels 48. This cools the workpiece 11 and the grinding wheels 48, and also washes away chips (grinding chips) generated by grinding.

[0057] In the grinding unit 34a, each component is arranged so that the trajectory of the multiple grinding stones 48 when the grinding wheel 44a is rotated overlaps with the center of the holding surface of the chuck table 18 positioned at the first grinding position B.

[0058] Similarly, in the grinding unit 34b, each component is arranged so that the trajectory of the multiple grinding stones 48 when the grinding wheel 44b is rotated overlaps with the center of the holding surface of the chuck table 18 positioned at the second grinding position C.

[0059] Further, at a position adjacent to the transport unit 14 in the X-axis direction, a transport unit 50 is provided to transport the workpiece 11 placed on the chuck table 18 positioned at the transport position A. The transport unit 50 includes, for example, a suction pad that sucks the upper surface side (for example, the back surface 11b side) of the workpiece 11.

[0060] Then, when the ground workpiece 11 is sucked by the suction pad of the transport unit 50 and held by the transport unit 50, the transport unit 50 operates to rotate the suction pad and transport the workpiece 11 forward.

[0061] A cleaning unit 52 for cleaning the workpiece 11 is provided diagonally forward to the right of the transport unit 50 and at a position where the workpiece 11 can be transported by the transport unit 50. When the ground workpiece 11 is carried into the cleaning unit 52 by the transport unit 50, the cleaning unit 52 operates to clean the workpiece 11.

[0062] 4 is a flowchart schematically illustrating an example of a method for grinding a workpiece 11 to a predetermined finishing thickness in the grinding device 2. In this method, first, the workpiece 11 with the back surface 11b facing upward is held on the chuck table 18 positioned at the transfer position A (holding step: S1).

[0063] Next, the turntable 16 is rotated so that the chuck table 18 is positioned at the first grinding position B (first rotation step: S2). Next, the workpiece 11 held by the chuck table 18 is ground by the plurality of grinding stones 48 while the grinding wheel 44a for rough grinding is rotated (rough grinding step: S3).

[0064] FIG. 5 is a flowchart showing a specific example of the rough grinding step (S3), and each of FIGS. 6(A), 6(B), and 6(C) is a partially cross-sectional side view showing a schematic view of the rough grinding step (S3).

[0065] In this rough grinding step (S3), first, while rotating the grinding wheel 44a for rough grinding at a low speed, the silicon oxide film 19 of the workpiece 11 held by the chuck table 18 is ground by a plurality of grinding wheels 48 (first grinding step: S31).

[0066] Specifically, the motor 38 is operated so that the grinding wheel 44a rotates together with the spindle 40 and the mount 42 at a rotational speed (second rotational speed) of 700 rpm or more and less than 1500 rpm. Also, the rotational drive source connected to the chuck table 18 is operated so that the chuck table 18 rotates at a rotational speed of 100 rpm or more and less than 300 rpm.

[0067] Then, while both the grinding wheel 44a and the chuck table 18 are rotating, the moving mechanism 24a lowers the moving plate 28a and the grinding unit 34a at a predetermined speed so that the grinding wheel 44a and the chuck table 18 approach each other.

[0068] As a result, the plurality of grinding wheels 48 come into contact with the silicon oxide film 19 of the workpiece 11, and the silicon oxide film 19 is ground (see FIG. 6(A)). The first grinding step (S31) is continued until the silicon oxide film 19 is removed.

[0069] For example, the first grinding step (S31) ends when a predetermined time (specifically, a time equal to or greater than the time obtained by dividing the thickness of the silicon oxide film 19 by the descending speed of the grinding unit 34a) has elapsed since grinding of the silicon oxide film 19 began.

[0070] Alternatively, the first grinding step (S31) may be terminated when the thickness of the workpiece 11, measured by the thickness measuring device 20a, reaches a predetermined thickness (specifically, a thickness equal to or less than the thickness obtained by subtracting the thickness of the silicon oxide film 19 from the original thickness of the workpiece 11).

[0071] Next, the grinding wheels 48 are separated from the workpiece 11 (separating step: S32). Specifically, while both the grinding wheel 44a and the chuck table 18 are rotating, the moving mechanism 24a raises the moving plate 28a and the grinding unit 34a so as to separate the grinding wheels 48 from the workpiece 11 (see FIG. 6(B)).

[0072] Next, while the grinding wheel 44a for rough grinding is rotated at high speed, the silicon wafer 13 of the workpiece 11 held by the chuck table 18 is ground by the plurality of grinding stones 48 (second grinding step: S33).

[0073] Specifically, the motor 38 is operated so that the grinding wheel 44a rotates together with the spindle 40 and the mount 42 at a rotational speed (first rotational speed) of 1500 rpm or more and less than 6000 rpm.

[0074] Then, while both the grinding wheel 44a and the chuck table 18 are rotating, the moving mechanism 24a lowers the moving plate 28a and the grinding unit 34a at a predetermined speed (for example, a speed equal to the lowering speed of the moving plate 28a and the grinding unit 34a in the first grinding step (S31)) so as to bring the grinding wheel 44a and the chuck table 18 closer to each other.

[0075] As a result, the plurality of grinding wheels 48 come into contact with the silicon wafer 13 of the workpiece 11, and the silicon wafer 13 is ground (see FIG. 6(C)). The second grinding step (S33) may be ended when a predetermined time has elapsed since grinding of the silicon wafer 13 started, or when the thickness of the workpiece 11 reaches a predetermined thickness.

[0076] Next, the operation of the motor 38 and the rotational drive source connected to the chuck table 18 is stopped so as to stop the rotation of both the grinding wheel 44a and the chuck table 18. In addition, the moving mechanism 24a raises the moving plate 28a and the grinding unit 34a so as to separate the multiple grinding wheels 48 from the workpiece 11.

[0077] Next, the turntable 16 is rotated so that the chuck table 18 is positioned at the second grinding position C (second rotation step: S4). Next, the workpiece 11 held by the chuck table 18 is ground by the plurality of grinding stones 48 while rotating the grinding wheel 44b for finish grinding (finish grinding step: S5).

[0078] Specifically, the motor 38 is operated so that the grinding wheel 44b rotates at a predetermined rotational speed together with the spindle 40 and the mount 42. Also, the rotation drive source connected to the chuck table 18 is operated so that the chuck table 18 rotates at a predetermined rotational speed.

[0079] Then, while both the grinding wheel 44b and the chuck table 18 are kept rotating, the moving mechanism 24b lowers the moving plate 28b and the grinding unit 34b at a predetermined speed so that the grinding wheel 44b and the chuck table 18 approach each other.

[0080] As a result, the plurality of grinding wheels 48 come into contact with the silicon wafer 13 of the workpiece 11, grinding the silicon wafer 13. The finish grinding step (S5) continues until the thickness of the workpiece 11 measured by the thickness gauge 20b reaches a predetermined finish thickness. This completes the grinding method for the workpiece shown in FIG. 4.

[0081] In the above-mentioned rough grinding step (S3), the rotation speed of the grinding wheel 44a when grinding the thin film (silicon oxide film) 19 made of silicon oxide, which is a material that is more difficult to cut than silicon, is set to be slower than the rotation speed of the grinding wheel 44a when grinding the wafer (silicon wafer) 13 made of silicon.

[0082] Here, when the rotation speed of the grinding wheel 44a during grinding is low, a strong frictional force acts on each of the grinding stones 48 due to contact with the workpiece 11, making it easier to grind the grinding stones 48. In other words, in this case, self-sharpening is promoted in each of the grinding stones 48. This makes it possible to grind the silicon oxide film 19 without causing any problems.

[0083] Furthermore, when the silicon oxide film 19 is ground in this manner, it is not necessary to use a grinding wheel with a high grinding force or to slow down the grinding speed (the lowering speed of the grinding wheel 44a) of the workpiece 11. This makes it possible to prevent a decrease in productivity of chips manufactured by dividing the workpiece 11 and to suppress an increase in the area occupied by the grinding device 2.

[0084] The above-described grinding method of the workpiece is one aspect of the present invention, and the present invention is not limited to the above-described grinding method of the workpiece. For example, the grinding method of the present invention may be performed to expose a metal electrode, which is a material that is more difficult to cut than silicon and is a component of device 17, on back surface 11b of workpiece 11.

[0085] In this case, in the rough grinding step (S3), first, while rotating the grinding wheel 44a at high speed, the back surface 11b side of the workpiece 11 is ground by the plurality of grinding stones 48 until it reaches the vicinity of the metal electrode. Then, while rotating the grinding wheel 44a at low speed, the back surface 11b side of the workpiece 11 is further ground until a part of the layer including the metal electrode is ground away.

[0086] In this rough grinding step (S3), as described above, it is possible to grind a layer including a metal electrode, which is a material that is more difficult to cut than silicon. Also, as described above, it is possible to prevent a decrease in productivity of chips manufactured by dividing the workpiece 11 and to suppress an increase in the area occupied by the grinding device 2.

[0087] In the grinding method of the present invention, the finish grinding step (S5) may be omitted. That is, in the grinding method of the present invention, the workpiece 11 may be ground to a predetermined finish thickness in the second grinding step (S33).

[0088] In addition, in the grinding method of the present invention, the separating step (S32) may be omitted. That is, in the grinding method of the present invention, the rotation speed of the grinding wheel 44a may be changed while the plurality of grinding stones 48 and the workpiece 11 are in contact with each other.

[0089] Furthermore, in the grinding method of the present invention, grinding of the workpiece 11 may be performed while raising the chuck table 18 that holds the workpiece 11. In other words, the grinding device 2 is not limited to any particular structure as long as it is provided with a structure that allows the grinding wheels 44a, 44b and the chuck table 18 to move relative to each other.

[0090] In addition, the structures and methods according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0091] 2: Grinding equipment 4: Base (4a: opening) 6: Transport unit 8a, 8b: Cassette installation area 10a, 10b: cassette 11: Workpiece (11a: front side, 11b: back side) 12: Alignment mechanism 13: Wafer made of silicon (silicon wafer) 14: Transport unit 15: Street (planned division line) 16: Turntable 17: Device 18: Chuck table (18a: holding surface) 19: Thin film made of silicon oxide (silicon oxide film) 20: Thickness measuring instrument 22a, 22b: Support structure 24a, 24b: Movement mechanism 26: Guide rail 28a, 28b: Moving plates 30:Screw shaft 32: Motor 34a, 34b: Grinding unit 36: Housing 38: Rotation drive source 40:Spindle 42: Mount 44a, 44b: Grinding wheels 46: Wheel base 48: Grinding wheel 50:Transport unit 52: Cleaning unit

Claims

1. A method for grinding a workpiece, the method comprising: grinding a workpiece having a first layer containing a first material; and a second layer containing a second material that is more difficult to cut than the first material and laminated on the first layer, to a predetermined finishing thickness, the method comprising: a first grinding step of grinding the first layer of the workpiece held by a chuck table with a plurality of grinding stones while rotating a grinding wheel having a plurality of grinding stones arranged in an annular shape at a first rotational speed; a second grinding step in which the second layer of the workpiece held by the chuck table is ground with the plurality of grinding wheels while rotating the grinding wheel used in the first grinding step at a second rotational speed that is slower than the first rotational speed; A method for grinding a workpiece, comprising:

2. 2. The method for grinding a workpiece according to claim 1, further comprising a step of separating the plurality of grinding wheels from the workpiece between the first grinding step and the second grinding step.

3. the first material is silicon; the second material is silicon oxide; 3. The method for grinding a workpiece according to claim 1, wherein the first grinding step is carried out after the second grinding step is carried out to remove the second layer.

4. 4. The method for grinding a workpiece according to claim 3, wherein the second grinding step is completed when a predetermined time has elapsed since grinding of the second layer was started, while the grinding wheel and the chuck table are moved relative to each other at a predetermined speed so that the grinding wheel and the chuck table approach each other.

5. the second grinding step is terminated when the thickness of the workpiece reaches a predetermined thickness, with the thickness of the workpiece being measured; 4. The method for grinding a workpiece according to claim 3, wherein the predetermined thickness is a thickness of the first layer that is less than or equal to a thickness obtained by subtracting the thickness of the second layer from the original thickness of the workpiece.

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