JP7596031B2 - Method and apparatus for polishing workpiece - Google Patents

Description

The present invention relates to a method and apparatus for polishing a workpiece.

The various devices installed in electronic devices are generally manufactured using wafers. Furthermore, devices may be manufactured by bonding two wafers together to achieve high integration of devices, etc.

For example, when manufacturing a back-side illuminated (BSI (Back Side Illumination)) CMOS (Complementary Metal Oxide Semiconductor) sensor, first, a wafer with a photodiode formed on its surface and a wafer with wiring and the like formed on its surface are prepared, and the front sides of both wafers are bonded together.

Next, the back side of the wafer with the photodiodes formed on the front side is ground and removed. The back side of the wafer is then polished to remove damage from this grinding and to make the thickness of the photodiodes uniform. The back side of the wafer is polished so that the difference between the maximum and minimum thickness values (TTV: Total Thickness Variation) is 0.3 μm or less, for example.

If the thickness of the photodiode varies, the amount of light received by the photodiode also varies. In this case, the performance of the back-illuminated CMOS sensor also varies. For this reason, high precision is required for grinding and polishing the two wafers bonded together in this way (bonded wafers).

As an apparatus for grinding a workpiece such as a bonded wafer, a grinding apparatus having a grinding wheel with a plurality of grinding stones arranged in a circularly spaced pattern is known. As an apparatus for polishing a workpiece, a polishing apparatus for polishing a workpiece by a CMP (Chemical Mechanical Polishing) method is known (see, for example, Patent Document 1).

However, it is not easy to completely eliminate in-plane thickness variations by polishing a workpiece having in-plane thickness variations using CMP. In view of this, a polishing device has been proposed that includes a polishing head equipped with a zone pressing section that locally presses the workpiece (see, for example, Patent Document 2).

In this polishing device, the pressure distribution on the polished surface of the workpiece can be changed when the workpiece is polished. This makes it easier to reduce the in-plane variation in thickness on the polished surface of the workpiece by grinding or the like. In other words, it makes it easier to flatten the polished surface of the workpiece.

JP 2011-206881 A JP 2013-115381 A

In the polishing device described above, the workpiece is polished by rotating both the workpiece and the polishing head while they come into contact with each other. Therefore, all areas of the polished surface of the workpiece that come into contact with the polishing head are polished to the same degree.

However, the polished surface of the workpiece may have irregular (asymmetric) in-plane variations in thickness. In other words, the concentric regions of the workpiece may include multiple parts with different thicknesses. In such cases, it is not easy to flatten the polished surface of the workpiece even with a polishing device equipped with a polishing head provided with the above-mentioned zone pressing portion.

In view of this, the object of the present invention is to provide a method and apparatus for polishing a workpiece that can precisely polish a workpiece having a polishing surface with irregular (asymmetric) in-plane variations in thickness to a predetermined finished shape (e.g., a flat plate shape).

According to one aspect of the present invention, there is provided a method for polishing a workpiece, comprising: a measuring step for measuring the thickness of each of a plurality of regions of the workpiece; a calculation step for calculating, for each of the plurality of regions, the amount of polishing required to polish the workpiece to the predetermined finished shape by comparing the thickness of each of the plurality of regions in the predetermined finished shape of the workpiece with the thickness of each of the plurality of regions measured in the measuring step; a setting step for setting the power of the laser beam irradiated to each of the plurality of regions by referring to the amount of polishing in each of the plurality of regions after the calculation step, so that the area with the smaller amount of polishing is irradiated with a laser beam having a higher power; a laser beam irradiation step for irradiating the workpiece with a laser beam whose power has been adjusted according to the setting step after the setting step; and a polishing step for polishing the workpiece while supplying an alkaline liquid-containing polishing liquid to the surface of the workpiece irradiated with the laser beam after the laser beam irradiation step.

Furthermore, in the polishing method of the present invention, the polishing step preferably includes at least one of a first polishing step in which the workpiece is polished while supplying only an alkaline liquid to the surface of the workpiece irradiated with the laser beam, and a second polishing step in which the workpiece is polished while supplying a slurry in which an alkaline liquid and abrasive grains are mixed to the surface of the workpiece irradiated with the laser beam.

In the polishing method of the present invention, the workpiece is preferably a bonded wafer formed by stacking and bonding silicon wafers. In addition, the polishing liquid preferably contains abrasive grains having a particle size of 50 nm or less.

According to another aspect of the present invention , a polishing apparatus for polishing a workpiece includes a chuck table for rotatably holding the workpiece, a measurement unit for measuring thicknesses of each of a plurality of regions of the workpiece held on the chuck table, a laser beam irradiation unit for irradiating a laser beam onto the workpiece, a polishing unit equipped with a polishing pad for polishing the workpiece held on the chuck table, a polishing liquid supply unit for supplying a polishing liquid containing an alkaline liquid to the workpiece held on the chuck table, and a control unit for controlling each of the components, wherein the control unit measures thicknesses of the plurality of regions in a predetermined finished shape of the workpiece. A polishing apparatus is provided which has a memory unit which stores each thickness, a calculation unit which compares the thickness of each of the plurality of regions stored in the memory unit with the thickness of each of the plurality of regions measured by the measurement unit, and calculates, for each of the plurality of regions, the amount of polishing required to polish the workpiece to bring the shape of the workpiece into the specified finished shape, and a processing condition setting unit which sets the irradiation conditions of a laser beam by referring to the amount of polishing for each of the plurality of regions, wherein the processing condition setting unit sets the power of the laser beam to be irradiated to each of the plurality of regions such that the area with the lesser amount of polishing is irradiated with a laser beam with a stronger power.

In addition, in the polishing apparatus of the present invention, the polishing liquid supply unit includes a liquid supply source that stores an alkaline liquid, and a slurry supply source that stores a slurry, which is a suspension mixture of an alkaline liquid and abrasive grains, and it is preferable that the supply of the alkaline liquid from the liquid supply source to the polishing unit and the supply of the slurry from the slurry supply source to the polishing unit are controlled independently of each other.

In the present invention, prior to polishing the workpiece, a laser beam is irradiated onto the workpiece such that the smaller the difference between the workpiece shape and a predetermined finished shape (e.g., a flat plate shape) is, the stronger the power of the laser beam is irradiated onto the area.

For example, the laser beam is irradiated to areas (the former areas) that are slightly different from the predetermined finished shape (e.g., a flat plate shape), whereas the laser beam is not irradiated to areas (the latter areas) that are significantly different from the predetermined finished shape (e.g., a flat plate shape) (the power of the laser beam irradiated to the latter areas is set to 0).

In this case, the former area is significantly altered compared to the latter area. Specifically, the material in the former area is oxidized or its crystal structure is destroyed. In the present invention, the workpiece is polished while an alkaline liquid is supplied to the surface of the workpiece irradiated with the laser beam.

At this time, the chemical polishing action in the former region is weaker than that in the latter region. This causes the polishing speed in the former region to be slower than the polishing speed in the latter region. As a result, even if the polished surface of the workpiece has irregular (asymmetric) in-plane variations in thickness, the workpiece can be polished to a predetermined finished shape with high precision.

FIG. 1 is a perspective view showing a schematic example of a polishing apparatus. FIG. 2A is a perspective view that shows a schematic example of a workpiece, and FIG. 2B is a cross-sectional view that shows a schematic example of the workpiece. FIG. 3 is a perspective view showing an example of a structure around a chuck table for holding a workpiece and a polishing unit. FIG. 4 is a block diagram illustrating an example of the polishing liquid supply unit. FIG. 5 is a diagram illustrating an example of a laser beam irradiation unit. FIG. 6 is a diagram illustrating an example of a measurement unit. FIG. 7 is a diagram illustrating an example of a control unit. FIG. 8 is a flow chart illustrating an example of a polishing method.

An embodiment of the present invention will be described with reference to the attached drawings. FIG. 1 is a perspective view showing a schematic example of a polishing apparatus. Note that the X-axis direction (front-back direction) and the Y-axis direction (left-right 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 and Y-axis directions.

The polishing apparatus 2 shown in FIG. 1 has a base 4 that supports each of the components. Cassette mounting tables 6a and 6b are provided on the upper surface of the front part of the base 4. For example, a cassette 8a containing a workpiece before polishing is placed on the cassette mounting table 6a, and for example, a cassette 8b for containing a workpiece after polishing is placed on the cassette mounting table 6b.

Figure 2(A) is a perspective view showing an example of a workpiece stored in cassettes 8a and 8b, and Figure 2(B) is a cross-sectional view showing an example of the workpiece. The workpiece 1 shown in Figures 2(A) and 2(B) is a bonded wafer formed by stacking and bonding wafers 3 and 5.

Wafers 3 and 5 are, for example, silicon wafers. Furthermore, for example, wiring, etc. are formed on the upper surface side of wafer 3, and for example, photodiodes, etc. are formed on the lower surface side of wafer 5.

There are no limitations on the material, shape, structure, size, etc., of the wafers 3 and 5. The wafers 3 and 5 may be made of materials such as other semiconductors such as silicon carbide, ceramics, resin, or metal. In addition, the peripheral portions of the wafers 3 and 5 may be formed with a V-shaped notch or flat portion (orientation flat) indicating the crystal orientation.

As shown in FIG. 1, an opening 4a is formed between the cassette mounting tables 6a and 6b, and a transport mechanism 10 for transporting the workpiece 1 is provided within the opening 4a. The transport mechanism 10 is, for example, a robot arm with multiple joints, and can also turn the workpiece 1 upside down.

A position adjustment mechanism 12 is provided behind the cassette placement table 6a to adjust the position of the workpiece 1 so that it contacts a corner located at one end of the rear side of the opening 4a. The position adjustment mechanism 12 includes, for example, a disk-shaped table and multiple pins arranged around the periphery of the table.

The conveying mechanism 10, for example, carries the workpiece 1 out of the cassette 8a and carries it onto the table of the position adjustment mechanism 12. Then, multiple pins move along the radial direction of the table, so that the center of the workpiece 1 is aligned to a predetermined position in the X-axis and Y-axis directions.

A cleaning unit 14 is provided behind the cassette mounting table 6b to clean the workpiece 1 that has been ground so as to contact the corner located at the other end of the rear side of the opening 4a. The cleaning unit 14 includes, for example, a spinner table that rotates while holding the underside of the workpiece 1, a cleaning nozzle that sprays a cleaning liquid such as water onto the upper surface side of the workpiece 1 held on the spinner table, and a drying nozzle that sprays a drying gas such as air onto the upper surface side of the cleaned workpiece 1.

The cleaning unit 14 cleans the top side of the workpiece 1, thereby washing away, for example, polishing debris adhering to the top surface of the polished workpiece 1. The cleaned workpiece 1 is then dried in the cleaning unit 14, and then transported by the transport mechanism 10 out of the cleaning unit 14 and into the cassette 8b.

A transport mechanism (loading arm) 16a is provided on the side of the position adjustment mechanism 12 behind the opening 4a to hold the workpiece 1 and transport it rearward. The transport mechanism 16a includes a holding pad that holds the top side of the workpiece 1 by suction, and an arm connected to this holding pad. The transport mechanism 16a then rotates the holding pad with the arm, thereby transporting the workpiece 1, whose position has been adjusted by the position adjustment mechanism 12, rearward.

A transport mechanism (unloading arm) 16b that holds the workpiece 1 and transports it forward is provided on the side of the cleaning unit 14 behind the opening 4a. The transport mechanism 16b has a holding pad that holds the top side of the workpiece 1 by suction, and an arm connected to this holding pad. The transport mechanism 16b then transports the polished workpiece 1 forward by rotating the holding pad with the arm.

An opening 4b is formed behind the transport mechanisms 16a and 16b, and an X-axis moving table 18 is provided inside the opening 4b. A disk-shaped chuck table 20 is rotatably mounted on the top surface of the X-axis moving table 18.

The chuck table 20 has a disk-shaped frame made of a metal material such as stainless steel. A recess with a circular opening at the top end is formed on the upper surface of the frame, and a disk-shaped porous plate made of ceramics or the like is fixed in the recess. The circular upper surface of the chuck table 20 serves as a holding surface 20a that holds the workpiece 1.

The X-axis moving table 16 is also connected to an X-axis direction moving mechanism (not shown) provided below the X-axis moving table 18. This X-axis direction moving mechanism has, for example, a ball screw and a motor. When this X-axis direction moving mechanism operates, the X-axis moving table 18 and the chuck table 20 move along the X-axis direction.

By operating the X-axis direction movement mechanism in this manner, the chuck table 20 is positioned in either the loading/unloading area 22 where the workpiece 1 can be loaded and unloaded, or the processing area 24 where the workpiece 1 can be polished.

The porous plate of the chuck table 20 is connected to a suction source via suction paths provided in the frame and the X-axis moving table 18. This suction source has, for example, an ejector. When the suction source operates, negative pressure is generated on the upper surface side of the chuck table 20, and the workpiece 1 placed on the holding surface 20a is sucked into the chuck table 20.

The chuck table 20 is also connected to a rotary drive source (not shown) provided below it. This rotary drive source has, for example, a motor. When this rotary drive source operates, the chuck table 20 rotates in the direction of arrow a shown in FIG. 1, with a straight line passing through the center of the holding surface 20a along the Z-axis direction as the rotation axis.

A plate-shaped support structure 26 is erected on the rear end side of the opening 4b. A pair of guide rails 28 that are roughly parallel to the Z-axis direction are provided on the front side of the support structure 26, and a Z-axis moving plate 30 is attached to the guide rails 28 in a manner that allows it to slide along the Z-axis direction.

A nut (not shown) that constitutes a ball screw is fixed to the rear (back) surface of the Z-axis moving plate 30, and a screw shaft 32 that is generally parallel to the guide rail 28 is rotatably connected to this nut. A motor 34 is connected to one end of the screw shaft 32. By rotating the screw shaft 32 with the motor 34, the Z-axis moving plate 30 moves along the guide rail 28.

A fixture 36 is provided on the front (surface) side of the Z-axis moving plate 30. The fixture 36 supports a polishing unit 38 for polishing the workpiece 1. Figure 3 is a perspective view showing the structure around the chuck table 20 that holds the workpiece 1 and the polishing unit 38. For convenience, some of the components of the polishing device 2 are depicted as blocks in Figure 3.

The polishing unit 38 includes a spindle housing 40 that is fixed to the fixture 36. A spindle (not shown) that serves as a rotation axis generally parallel to the Z-axis direction is housed in the spindle housing 40 in a rotatable manner. The upper end of the spindle is connected to a motor 42, and the lower end is exposed from the spindle housing 40 and fixed to a disk-shaped mount 44.

A polishing pad 46 made of a resin such as polyurethane foam or a nonwoven fabric is attached to the underside of the mount 44. When a rotary drive source connected to the upper end of the spindle is operated, the polishing pad 46 rotates around a straight line passing through the center of the spindle along the Z-axis direction as the rotation axis.

The diameter of the polishing pad 46 is equal to or smaller than the radius of the holding surface 20a of the chuck table 20. Therefore, when the polishing pad 46 is brought into contact with the workpiece 1 to polish the workpiece 1, a part of the upper surface of the workpiece 1 is exposed. However, the diameter of the polishing pad 46 may be longer than the radius of the holding surface 20a of the chuck table 20. For example, the diameter of the polishing pad 46 may be longer than the diameter of the holding surface 20a of the chuck table so that the workpiece 1 is polished with the entire upper surface of the workpiece 1 in contact with the polishing pad 46.

The polishing unit 38 is further connected to a polishing liquid supply unit 48. The polishing liquid supply unit 48 supplies polishing liquid to the upper surface of the workpiece 1 when the upper surface is polished through a supply path (not shown) provided inside the spindle, mount 44, and polishing pad 46 housed in the spindle housing 40.

Figure 4 is a block diagram showing a schematic of the polishing liquid supply unit 48. The polishing liquid supply unit 48 has a liquid supply source 50 that stores an alkaline liquid, and a slurry supply source 52 that stores a slurry, which is a suspension mixture of the alkaline liquid and abrasive grains.

Examples of alkaline liquids include potassium hydroxide solution or tetramethylammonium hydroxide (TMAH) solution with a pH of 9 to 11. The alkaline liquid stored in the liquid supply source 50 and the alkaline liquid contained in the slurry stored in the slurry supply source 52 may be the same or different.

The material of the abrasive grains is appropriately selected according to the material of the workpiece 1. For example, the material of the abrasive grains may be silicon carbide, cBN (cubic boron nitride), diamond, or oxide fine particles. Examples of the oxide fine particles include fine particles made of silica (silicon oxide), ceria (cerium oxide), zirconia (zirconium oxide), and alumina (aluminum oxide).

However, it is preferable that the particle size of the abrasive grains be 50 nm or less. If the particle size of the abrasive grains contained in the slurry exceeds 50 nm, there is a risk that the area of the workpiece that is irradiated with the laser beam and the area that is not irradiated with the laser beam will be polished in the same way.

Furthermore, the polishing liquid supply unit 48 has a pump 54a that supplies the liquid stored in the liquid supply source 50 to the polishing unit 38, a valve 56a provided between the pump 54a and a supply path provided inside the polishing unit 38, a pump 54b that supplies the slurry stored in the slurry supply source 52 to the polishing unit 38, and a valve 56b provided between the pump 54b and a supply path provided inside the polishing unit 38.

In the polishing liquid supply unit 48, the supply of alkaline liquid from the liquid supply source 50 to the polishing unit 38 and the supply of slurry from the slurry supply source 52 to the polishing unit 38 are controlled independently of each other.

For example, the polishing liquid supply unit 48 can supply only alkaline liquid to the polishing unit 38 by operating the pump 54a with the valve 56a open and the valve 56b closed. Similarly, the polishing liquid supply unit 48 can supply a slurry, which is a suspension mixture of alkaline liquid and abrasive grains, to the polishing unit 38 by operating the pump 54b with the valve 56a closed and the valve 56b open.

The polishing liquid supply unit 48 can also supply a slurry with a reduced abrasive grain density to the polishing unit 38 by operating the pumps 54a and 54b with the valves 56a and 56b open. The polishing liquid supply unit 48 may also have a stirring mechanism for stirring the liquid supplied from the liquid supply source 50 and the slurry supplied from the slurry supply source 52.

Also, as shown in FIG. 3, a laser beam irradiation unit 58 configured to selectively irradiate each of a plurality of regions of the workpiece 1 with a laser beam is disposed upstream of the polishing unit 38 (polishing pad 46) along the direction in which the chuck table 20 rotates (the direction of arrow a).

Figure 5 is a schematic diagram of the laser beam irradiation unit 58. For convenience, some of the components of the laser beam irradiation unit 58 are depicted as blocks in Figure 5. The laser beam irradiation unit 58 includes a laser oscillator 60 capable of generating a laser beam A.

As the laser oscillator 60, for example, a laser oscillator capable of generating a laser beam A having a wavelength of 355 nm is used. The laser oscillator 60 may also be configured to generate laser beams of other wavelengths.

The mode of laser oscillation performed by the laser oscillator 60 may be either continuous wave (CW) oscillation or pulse oscillation. An adjuster 62 such as an attenuator that can adjust the power of the laser beam A is disposed adjacent to the laser oscillator 60. The laser beam A whose power has been adjusted by the adjuster 62 is incident on the galvano scanner 64.

The galvanometer scanner 64 includes a first mirror 66 and a second mirror 68. The first mirror 66 is connected to a rotary drive source (not shown) such as a motor, and rotates around a first axis. Similarly, the second mirror 68 is connected to a rotary drive source (not shown) such as a motor, and rotates around a second axis perpendicular to the first axis.

The laser beam A reflected by the first mirror 66 and the second mirror 68 is irradiated onto the top surface 1a of the workpiece 1 through the condenser 70. The condenser 70 includes an fθ lens 72, and focuses the laser beam A onto a specific plane regardless of its traveling direction. The diameter of the laser beam A on the top surface 1a of the workpiece 1 is, for example, about 3 μm to 1000 μm (typically, 4 μm to 15 μm).

The condenser 70 further includes an adjustment mechanism (not shown) that adjusts the vertical position (height) of the plane on which the laser beam A is focused. This adjustment mechanism includes, for example, a ball screw and a motor, and the motor operates the ball screw to adjust the vertical position of the fθ lens 72.

In the laser beam irradiation unit 58, the direction of travel of the laser beam A is controlled by adjusting the angle of the first mirror 66 and the angle of the second mirror 68. In other words, the laser beam irradiation unit 58 can selectively irradiate the laser beam A to each of multiple areas of the workpiece 1 by adjusting the angles of the first mirror 66 and the second mirror 68.

In addition, in the laser beam irradiation unit 58, the height of the plane on which the laser beam A is focused is adjusted by adjusting the vertical position of the fθ lens 72. In other words, the laser beam irradiation unit 58 can position the focusing point of the laser beam A at any height by adjusting the vertical position of the fθ lens 72.

The structure of the laser beam irradiation unit 58 may be any structure as long as it is possible to selectively irradiate the laser beam A to each of the multiple regions of the workpiece 1.

For example, the laser beam irradiation unit 58 may be equipped with an acousto-optical deflector or the like instead of the galvanometer scanner 64. Alternatively, the laser beam irradiation unit 58 may be connected to a horizontal movement mechanism that moves the laser beam irradiation unit 58 in the horizontal direction without the galvanometer scanner 64.

Also, as shown in FIG. 3, downstream of the polishing unit 38 (polishing pad 46) along the direction in which the chuck table 20 rotates, a non-contact measuring unit (thickness gauge) 74 configured to measure the thickness (thickness distribution) of multiple regions of the workpiece 1 is disposed.

Figure 6 is a diagram showing a schematic of the measurement unit 74. Note that in Figure 6, for convenience, some of the components of the measurement unit 74 are depicted as blocks. The measurement unit 74 includes a white light source 76 that can generate white light that includes light in the visible range.

The white light source 76 is, for example, an SLD (Super Luminescent Diode) light source, an ASE (Amplified Spontaneous Emission) light source, an SC (Super Continuum) light source, an LED (Light Emitting Diode) light source, a halogen lamp, a xenon lamp, a mercury lamp, or a metal halide lamp.

A spectroscopic unit 78 capable of separating the white light emitted from the white light source 76 into light of each wavelength is disposed adjacent to the white light source 76. The spectroscopic unit 78 includes, for example, an optical fiber with large wavelength dispersion, and utilizes the different light propagation speeds according to wavelength to emit the light of each wavelength that constitutes the white light at different times for each wavelength.

For example, when pulsed white light is incident on the spectroscopic unit 78, the wavelength of the light emitted from the spectroscopic unit 78 changes over time from short wavelengths to long wavelengths. Light B emitted from the spectroscopic unit 78 is incident on the beam splitter 82, for example, through the lens 80.

The beam splitter 82 is typically a half mirror that reflects a portion of the light B passing through the lens 80 at the reflecting surface 82a to change its direction of travel. The light B reflected by the beam splitter 82 passes through the telecentric lens 84 and is irradiated onto the upper surface 1a and the lower surface 1b of the workpiece 1.

Light B reflected by each of the upper surface 1a and the lower surface 1b of the workpiece 1 enters the beam splitter 82 again through the telecentric lens 84, and a part of it passes through the reflecting surface 82a. Light B that passes through the reflecting surface 82a is collimated by the lens 86 and the like, and enters the two-dimensional imaging unit 88.

The two-dimensional imaging unit 88 includes an imaging element such as a CCD image sensor or a CMOS image sensor, and when it receives light with a two-dimensional intensity distribution, it generates an electrical signal that reflects the intensity distribution of the light. In other words, the two-dimensional imaging unit 88 can obtain information on the two-dimensional intensity distribution that occurs due to the overlap (interference) of the light reflected from the upper surface 1a and the light reflected from the lower surface 1b of the workpiece 1.

As described above, the spectroscopic unit 78 emits light of each wavelength that constitutes the white light emitted from the white light source 76 at different times for each wavelength. Therefore, light of different wavelengths is incident on the two-dimensional imaging unit 88 at different times. In other words, the two-dimensional imaging unit 88 can obtain information on multiple two-dimensional intensity distributions caused by each wavelength. As a result, the thicknesses (thickness distribution) of multiple regions of the workpiece 1 are measured.

The operation of each component of the polishing apparatus 2 is controlled by a control unit built into the polishing apparatus 2. FIG. 7 is a block diagram showing a schematic example of a control unit built into the polishing apparatus 2. The control unit 90 shown in FIG. 7 has, for example, a processing unit 92 that generates signals for controlling the components of the polishing apparatus 2, and a memory unit 94 that stores various information (data, programs, etc.) used in the processing unit 92.

In addition, the memory unit 94 may store information regarding the thickness of the predetermined finished shape of the workpiece 1 prior to polishing the workpiece 1. For example, if the predetermined finished shape of the workpiece 1 is a flat plate shape, the memory unit 94 may store the thickness in the predetermined finished shape.

Alternatively, if the predetermined finish shape of the workpiece 1 includes multiple regions with different thicknesses, the memory unit 94 may store in advance a link between the regions with the same thickness in the predetermined finish shape and the thickness of the regions. In other words, the workpiece 1 may be partitioned into multiple regions according to the thickness in the predetermined finish shape, and the memory unit 94 may store in advance the thickness of each of the multiple regions in the predetermined finish shape.

The functions of the processing unit 92 are realized by a CPU (Central Processing Unit) that reads and executes programs stored in the memory unit 94. The functions of the memory unit 94 are realized by at least one of semiconductor memories such as DRAM (Dynamic Random Access Memory), SRAM (Static Random Access Memory), and NAND flash memory, and magnetic storage devices such as HDD (Hard Disk Drive).

The processing unit 92 includes a calculation unit 96 and a processing condition setting unit 98. The calculation unit 96, for example, compares the thickness of each of the multiple regions of the workpiece 1 in a predetermined finish shape stored in the memory unit 94 with the thickness of each of the multiple regions of the workpiece 1 measured by the measurement unit 74. The calculation unit 96 then calculates the amount of polishing required for each of the multiple regions of the workpiece 1 to polish the workpiece 1 to change the shape of the workpiece 1 to the predetermined finish shape.

The processing condition setting unit 98, for example, sets the irradiation conditions of the laser beam for the workpiece 1 by referring to the amount of polishing calculated by the calculation unit 96 for each of the multiple regions of the workpiece 1. Specifically, the processing condition setting unit 98 sets the power of the laser beam to be irradiated to each of the multiple regions so that the area with the smaller amount of polishing is irradiated with a laser beam with a stronger power.

The power of the laser beam irradiated to the workpiece 1 is adjusted, for example, by adjusting the power of the laser beam A irradiated from the laser beam irradiation unit 58. Alternatively, the power of the laser beam A irradiated to the workpiece 1 may be adjusted by adjusting the height of the focal point of the laser beam A irradiated from the laser beam irradiation unit 58.

Figure 8 is a flow chart showing an example of a polishing method for polishing the workpiece 1 using the polishing device 2. In this method, the measurement unit 74 first measures the thickness (thickness distribution) of each of multiple regions of the workpiece 1 (measurement step: S1).

Then, the thickness of each of the multiple regions in the predetermined finish shape of the workpiece 1 is compared with the thickness of each of the multiple regions measured in the measurement step (S1), and the calculation unit 96 calculates the amount of polishing required for each of the multiple regions to polish the workpiece 1 to obtain the predetermined finish shape (calculation step: S2).

Next, by referring to the amount of polishing calculated for each of the multiple regions in the calculation step (S2), the processing condition setting unit 98 sets the power of the laser beam to be irradiated to each of the multiple regions so that the area with the smaller amount of polishing is irradiated with a laser beam with a stronger power (setting step: S3).

Next, the laser beam irradiation unit 58 irradiates the workpiece 1 with the laser beam A, the power of which has been adjusted according to the settings made in the setting step (S3) (laser beam irradiation step: S4).

Next, the polishing unit 38 polishes the workpiece 1 while supplying an alkaline liquid to the surface (polished surface) of the workpiece 1 irradiated with the laser beam A (polishing step: S5). The polishing step (S5) may be performed in a state where the alkaline liquid is supplied to the polishing unit 38 only from the liquid supply source 50, or in a state where the slurry is supplied to the polishing unit 38 only from the slurry supply source 52.

Furthermore, the polishing step (S5) may include a first polishing step in which the workpiece 1 is polished while supplying only the alkaline liquid, and a second polishing step in which the workpiece 1 is polished while supplying a slurry. In this case, for example, the polishing surface of the workpiece 1 can be planarized to a certain extent in the first polishing step so as to reduce the in-plane variation in thickness on the polishing surface of the workpiece 1, and then the entire polishing surface of the workpiece 1 can be polished in the second polishing step.

In the method of polishing the workpiece 1 using the polishing device 2, a laser beam is irradiated onto the workpiece 1 so that the more powerful the laser beam A is irradiated, the smaller the difference between the workpiece 1 and the predetermined finished shape (e.g., a flat plate shape) (areas requiring less polishing) (laser beam irradiation step (S4)).

For example, laser beam A is irradiated onto areas that require less polishing, whereas no laser beam is irradiated onto areas that require more polishing (the power of the laser beam irradiated onto areas that require more polishing is set to 0).

In this case, the area requiring less polishing is significantly altered compared to the area requiring more polishing. Specifically, the material in the area requiring less polishing is oxidized or its crystal structure is destroyed. In this method, the workpiece 1 is polished while an alkaline liquid is supplied to the surface of the workpiece 1 irradiated with the laser beam A.

At this time, the chemical polishing action in the area where the required amount of polishing is small is weaker than the chemical polishing action in the area where the required amount of polishing is large. This makes the polishing speed in the area where the required amount of polishing is small slower than the polishing speed in the area where the required amount of polishing is large. As a result, even if the polished surface of the workpiece 1 has irregular (asymmetric) in-plane variations in thickness, the workpiece can be finished to a specified shape with high precision.

The structures and methods of the above-described embodiments can be modified as appropriate without departing from the scope of the present invention.

1: Workpiece (1a: top surface, 1b: bottom surface)
3, 5: Wafer 2: Polishing device 4: Base 4a, 4b: Opening 6a, 6b: Cassette placement table 8a, 8b: Cassette placement table 10: Transport mechanism 12: Position adjustment mechanism 14: Cleaning unit 16a: Transport mechanism ( Loading arm)
16b: Transport mechanism (unloading arm)
18: X-axis moving table 20: Chuck table (20a: holding surface)
22: Loading/unloading area 24: Processing area 26: Support structure 28: Guide rail 30: Z-axis moving plate 32: Screw shaft 34: Motor 36: Fixture 38: Polishing unit 40: Spindle housing 42: Motor 44: Mount 46: Polishing pad 48: Polishing liquid supply unit 50: Liquid supply source 52: Slurry supply source 54a, 54b: Pump 56a, 56b: Valve 58: Laser beam irradiation unit 60: Laser oscillator 62: Adjuster 64: Galvano scanner 66: First Mirror 68: Second mirror 70: Condenser 72: fθ lens 74: Measurement unit (thickness gauge)
76: White light source 78: Spectroscopic unit 80: Lens 82: Beam splitter 84: Telecentric lens 86: Lens 88: Two-dimensional imaging unit 90: Control unit 92: Processing unit 94: Storage unit 96: Calculation unit 98: Processing condition setting unit

Claims (6)

A method for polishing a workpiece, comprising the steps of:
measuring a thickness of each of a plurality of regions of the workpiece;
a calculation step of comparing, after the measurement step, the thickness of each of the plurality of regions in a predetermined finished shape of the workpiece with the thickness of each of the plurality of regions measured in the measurement step, and calculating, for each of the plurality of regions, a polishing amount required to polish the workpiece to change the shape of the workpiece to the predetermined finished shape;
a setting step of setting the power of the laser beam to be irradiated to each of the plurality of regions by referring to the amount of polishing in each of the plurality of regions after the calculation step, such that the area having a smaller amount of polishing is irradiated with a laser beam having a stronger power;
a laser beam irradiation step of irradiating the workpiece with a laser beam whose power has been adjusted according to the setting in the setting step after the setting step;
a polishing step of polishing the workpiece while supplying a polishing liquid containing an alkaline liquid to the surface of the workpiece irradiated with the laser beam after the laser beam irradiation step;
A method for polishing a workpiece, comprising the steps of: The polishing step comprises:
a first polishing step of polishing the workpiece while supplying only an alkaline liquid to the surface of the workpiece irradiated with the laser beam;
a second polishing step of polishing the workpiece while supplying a slurry, which is a mixture of an alkaline liquid and abrasive grains, to the surface of the workpiece irradiated with the laser beam;
2. The method for polishing a workpiece according to claim 1, comprising at least one of the steps of: The method for polishing a workpiece according to claim 1 or 2, characterized in that the workpiece is a bonded wafer formed by stacking and bonding silicon wafers. The method for polishing a workpiece according to any one of claims 1 to 3, characterized in that the polishing liquid contains abrasive grains having a particle size of 50 nm or less. A polishing apparatus for polishing a workpiece, comprising:
a chuck table that rotatably holds the workpiece;
a measuring unit for measuring thicknesses of each of a plurality of regions of the workpiece held on the chuck table;
a laser beam irradiation unit that irradiates the workpiece with a laser beam;
a polishing unit equipped with a polishing pad for polishing the workpiece held on the chuck table;
a polishing liquid supply unit that supplies a polishing liquid containing an alkaline liquid to the workpiece held on the chuck table;
A control unit for controlling each of the components,
The control unit
A memory unit that stores thicknesses of the respective regions in a predetermined finish shape of the workpiece;
a calculation unit that compares the thicknesses of the plurality of regions stored in the memory unit with the thicknesses of the plurality of regions measured by the measurement unit, and calculates, for each of the plurality of regions, a polishing amount required to polish the workpiece so that the shape of the workpiece is the predetermined finish shape;
a processing condition setting unit that sets a laser beam irradiation condition by referring to the amount of removal in each of the plurality of regions,
The polishing apparatus is characterized in that the processing condition setting unit sets the power of the laser beam to be irradiated to each of the plurality of regions such that the region having the smaller amount of polishing is irradiated with a laser beam having a stronger power. The polishing liquid supply unit includes:
a liquid source for storing an alkaline liquid;
a slurry supply source for storing a slurry, which is a suspension of an alkaline liquid and abrasive grains;
6. The polishing apparatus according to claim 5, wherein the supply of the alkaline liquid from the liquid supply source to the polishing unit and the supply of the slurry from the slurry supply source to the polishing unit are controlled independently of each other .

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