JP2024066327A - Wafer polishing method - Google Patents

Abstract

[Problem] To provide a wafer polishing method capable of polishing the ground surface of a wafer with high precision. [Solution] The wafer polishing method is a method for polishing a circular recess of a wafer having a circular recess and an annular protrusion surrounding the circular recess on the back surface thereof, and includes a first polishing step 401 in which a polishing pad having a diameter equal to or smaller than the radius of the circular recess is positioned in a radial region extending from the center to the outer periphery of the circular recess, and the wafer and the polishing pad are rotated in the same direction to polish the circular recess, and a second polishing step 402 in which a polishing pad having a diameter equal to or smaller than the diameter of the circular recess and larger than the diameter of the polishing pad is positioned so that the entire surface of the polishing pad is in contact with the circular recess, and the wafer and the polishing pad are rotated in opposite directions to polish the circular recess. [Selected Figure] Figure 5

Description

The present invention relates to a method for polishing a wafer.

After grinding, polishing with a polishing pad or wet etching using a polishing liquid is performed to remove the grinding marks and increase strength (see, for example, Patent Document 1).

JP 2018-60873 A

In TAIKO (registered trademark) grinding, if an abrasive pad larger than the recess is pressed against it to perform grinding, as in the method shown in Patent Document 1, pressure is applied to the annular convex portion, making it difficult to press the abrasive pad evenly over the entire recess, which will become the grinding surface. Also, if an abrasive pad smaller than the recess is used, the contact time of the abrasive pad is shorter in the peripheral region of the recess than in the center, and the amount of polishing is less than in the center, resulting in poor thickness accuracy of the recess.

For this reason, polishing by wet etching is common, but the etching solution tends to accumulate around the annular protrusion, making the periphery of the annular protrusion thicker than the center, making it difficult to form a uniform thickness even with wet etching.

The object of the present invention is to provide a method for polishing a wafer that can polish the grinding surface of the wafer with high precision.

In order to solve the above problems and achieve the object, the wafer polishing method of the present invention is a method for polishing a recess of a wafer having a recess and an annular protrusion surrounding the recess on one side, and is characterized by comprising a first polishing step in which a small polishing pad having a diameter equal to or smaller than the radius of the recess and the wafer are rotated in the same direction to polish the recess, and a second polishing step in which a large polishing pad having a diameter equal to or smaller than the diameter of the recess and equal to or larger than the diameter of the small polishing pad is positioned so that the entire surface of the large polishing pad is in contact with the recess, and the wafer and the large polishing pad are rotated in opposite directions to polish the recess.

The present invention has the effect of enabling the grinding surface of the wafer to be polished with high precision.

FIG. 1 is a perspective view that illustrates a wafer to be polished in the wafer polishing method according to the first embodiment. FIG. 2 is a perspective view that illustrates a schematic configuration example of a polishing apparatus that performs the wafer polishing method according to the first embodiment. FIG. 3 is a side view, partially in section, showing a schematic configuration of the small polishing unit of the polishing apparatus shown in FIG. FIG. 4 is a side view, partially in section, showing a schematic configuration of the large polishing unit of the polishing apparatus shown in FIG. FIG. 5 is a flowchart showing the flow of the wafer polishing method according to the first embodiment. FIG. 6 is a plan view diagrammatically showing the rotation directions of the polishing pad and the holding table in the first polishing step of the wafer polishing method shown in FIG. FIG. 7 is a diagram showing the amount of polishing of the bottom surface of the circular recess of the wafer in the first polishing step of the wafer polishing method shown in FIG. FIG. 8 is a plan view diagrammatically showing the rotation directions of the polishing pad and the holding table in the second polishing step of the wafer polishing method shown in FIG. FIG. 9 is a diagram showing the amount of polishing of the bottom surface of the circular recess of the wafer in the second polishing step of the wafer polishing method shown in FIG. FIG. 10 is a cross-sectional view that illustrates a first polishing step of the wafer polishing method according to a modified example of the first embodiment. FIG. 11 is a cross-sectional view illustrating a second polishing step of the wafer polishing method according to the modified example of the first embodiment.

The following describes in detail the form (embodiment) for carrying out the present invention with reference to the drawings. The present invention is not limited to the contents described in the following embodiment. The components described below include those that a person skilled in the art can easily imagine and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Various omissions, substitutions, or modifications of the configuration can be made without departing from the spirit of the present invention.

[Embodiment 1]
A wafer polishing method according to a first embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a perspective view showing a wafer to be polished by the wafer polishing method according to the first embodiment. Fig. 2 is a perspective view showing a configuration example of a polishing apparatus for carrying out the wafer polishing method according to the first embodiment.

(wafer)
The wafer polishing method according to the first embodiment is a method for polishing a wafer 1 shown in Fig. 1. The wafer 1 shown in Fig. 1, which is to be polished by the wafer polishing method according to the first embodiment, is a wafer such as a disk-shaped semiconductor wafer or an optical device wafer having a substrate 2 made of silicon, sapphire, gallium, or the like. As shown in Fig. 1, the wafer 1 has a device region 4 on a surface 3 of the substrate 2, and a peripheral excess region 5 surrounding the device region 4.

The device region 4 has planned division lines 6 set in a grid pattern on the surface 3 of the substrate 2, and devices 7 formed in each region partitioned by the planned division lines 6.

The device 7 is, for example, an integrated circuit such as an IC (Integrated Circuit) or an LSI (Large Scale Integration), an image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), a MEMS (Micro Electro Mechanical Systems) or a semiconductor memory (semiconductor memory device). The peripheral excess region 5 surrounds the entire device region 4 and is a region on the surface 3 of the substrate 2 where no device 7 is formed.

In addition, in embodiment 1, the wafer 1 is a so-called TAIKO (registered trademark) wafer in which the back surface 8 (corresponding to one surface) of the device region 4 is ground by a known grinding device to form a circular recess 10 (corresponding to a recess) on the back surface 8 of the device region 4, as shown in FIG. 1, and the peripheral excess region 5 is formed into an annular protrusion 11 (corresponding to a protrusion) that is thicker than the device region 4.

The circular recess 10 is formed in a region that overlaps with the device region 4 of the back surface 8 in the thickness direction, and the annular protrusion 11 is formed in a region that overlaps with the peripheral surplus region 5 of the back surface 8 in the thickness direction. Note that in this specification, the region that overlaps with the device region 4 of the back surface 8 in the thickness direction is referred to as the device region 4 of the back surface 8, and the region that overlaps with the peripheral surplus region 5 of the back surface 8 in the thickness direction is referred to as the peripheral surplus region 5 of the back surface 8.

In this way, the back surface 8 of the wafer 1 has a circular recess 10 formed in the center and an annular protrusion 11 surrounding the circular recess 10, and a step 12 is formed between the device region 4 and the peripheral surplus region 5. The front surface 3 of the wafer 1 is formed on the same plane across the device region 4 and the peripheral surplus region 5. The bottom surface 13 of the circular recess 10 is a ground surface that has been subjected to grinding processing by a grinding device.

The wafer polishing method according to the first embodiment is carried out by the polishing apparatus 100 shown in FIG. 2. In the first embodiment, the polishing apparatus 100 is a processing device that polishes the bottom surface 13 of the circular recess 10 of the wafer 1 shown in FIG. 1.

(Polishing device)
Next, the polishing apparatus 100 will be described. Fig. 3 is a side view, partly in section, typically showing the configuration of a small polishing unit of the polishing apparatus shown in Fig. 2. Fig. 4 is a side view, partly in section, typically showing the configuration of a large polishing unit of the polishing apparatus shown in Fig. 2.

As shown in FIG. 2, the polishing apparatus 100 includes an apparatus main body 101, a small polishing unit 102, a large polishing unit 103, a polishing feed unit 104, a turntable 105, a plurality of holding tables 106 (three in the first embodiment) installed on the turntable 105, a cassette 107, an alignment unit 108, a carry-in unit 109, a cleaning unit 110, a carry-in/out unit 111, an unloading unit 114, and a control unit 200.

The turntable 105 is a disk-shaped table provided on the upper surface of the device body 101, and is rotatable around an axis parallel to the Z-axis direction in a horizontal plane, and is driven to rotate at a predetermined timing. On this turntable 105, for example, three holding tables 106 are arranged at equal intervals, for example at a phase angle of 120 degrees. These three holding tables 106 have a holding table structure in which the holding surface is equipped with a vacuum chuck connected to a suction source (not shown), and the front surface 3 side of the wafer 1 is placed on the holding surface and sucked by the suction source, so that the wafer 1 is suction-held on the holding surface.

During polishing, these holding tables 106 are rotated in a horizontal plane by a rotary drive mechanism around an axis parallel to the vertical direction, i.e., the Z-axis direction. By rotating the turntable 105, the holding tables 106 are moved sequentially to the loading/unloading area 301, the small polishing area 302, the large polishing area 303, and the loading/unloading area 301.

The loading/unloading area 301 is an area where the wafer 1 is loaded onto and unloaded from the holding table 106, the small polishing area 302 is an area where the small polishing unit 102 polishes the bottom surface 13 of the circular recess 10 of the wafer 1 held on the holding table 106, and the large polishing area 303 is an area where the large polishing unit 103 polishes the bottom surface 13 of the circular recess 10 of the wafer 1 held on the holding table 106.

The small polishing unit 102 is a polishing unit equipped with a disk-shaped polishing pad 120 (corresponding to a small polishing pad) for polishing the bottom surface 13 of the circular recess 10 of the back surface 8 exposed above the wafer 1 held on the holding table 106, and polishes the bottom surface 13 of the circular recess 10 of the wafer 1 held on the holding surface of the holding table 106 in the small polishing area 302. The large polishing unit 103 is a polishing unit equipped with a disk-shaped polishing pad 130 (corresponding to a large polishing pad) for polishing the bottom surface 13 of the circular recess 10 of the wafer 1 held on the holding surface of the holding table 106 in the large polishing area 303, and polishes the bottom surface 13 of the circular recess 10 of the wafer 1 held on the holding surface of the holding table 106.

As shown in Figures 3 and 4, the polishing units 102 and 103 have polishing pads 120 and 130 attached to the lower ends of spindles 122 and 132 that are rotated about their axes by motors 121 and 131. The polishing units 102 and 103 polish the bottom surface 13 of the circular recess 10 of the wafer 1 by rotating the polishing pads 120 and 130 about axes parallel to the Z-axis direction while moving the polishing pads 120 and 130 closer to the holding table 106 at a predetermined feed speed by the polishing feed unit 104.

The polishing units 102 and 103 are provided with a polishing feed unit 104 and are mounted on a movable block 115 that is movable in the radial direction of the holding table 106 of each area 302 and 303 by a moving mechanism (not shown). That is, the polishing pads 120 and 130 of the polishing units 102 and 103 are movable in the radial direction of the holding table 106 of each area 302 and 303.

The polishing pad 120 of the small polishing unit 102 shown in FIG. 3 has a diameter equal to or smaller than the radius of the circular recess 10. The polishing pad 120 has a diameter equal to or larger than 5 mm smaller than the radius of the circular recess 10. In the first embodiment, the diameter of the polishing pad 120 is the radius of the circular recess 10.

In the first embodiment, as shown in FIG. 3, the small polishing unit 102 is disposed at a position where the outer edge of the polishing pad 120 overlaps with the outer edge of the bottom surface 13 of the circular recess 10 and the center of the bottom surface 13 of the circular recess 10, and polishes the bottom surface 13 of the circular recess 10 of the wafer 1. When the diameter of the polishing pad 120 is smaller than the radius of the circular recess 10, the polishing pad 120 is moved in the radial direction of the holding table 106 of the small polishing region 302 by the moving unit between the position where the outer edge of the polishing pad 120 overlaps with the outer edge of the bottom surface 13 of the circular recess 10 and the position where the outer edge of the polishing pad 120 overlaps with the center of the bottom surface 13 of the circular recess 10, thereby polishing the bottom surface 13 of the circular recess 10 of the wafer 1.

If the diameter of the polishing pad 120 exceeds the radius of the circular recess 10, the center of the bottom surface 13 of the circular recess 10, which is constantly in contact with the polishing pad 120, will be over-polished in the first polishing step 401, and it will be difficult to compensate for the variation in the polishing distribution formed in the first polishing step 401 in the second polishing step 402 in which the polishing pad 130 is used to polish the wafer 1 and suppress the thickness variation and flatten the wafer 1. Therefore, it is preferable that the diameter of the polishing pad 120 is equal to or smaller than the radius of the circular recess 10. In addition, there is no particular lower limit for the diameter of the polishing pad 120, since it can be made smaller by increasing the width by which the polishing pad 120 is moved. However, the larger the width of the movement, the more complex the distribution of the polishing amount becomes, which is difficult to offset by the polishing pad 130, so it is preferable that the diameter of the polishing pad 120 is equal to or smaller than the radius of the circular recess 10.

The polishing pad 130 of the large polishing unit 103 has a diameter that is equal to or smaller than the diameter of the circular recess 10 and equal to or larger than the diameter of the polishing pad 120. In the first embodiment, the diameter of the polishing pad 130 is the diameter of the circular recess 10. In the first embodiment, the large polishing unit 103 is positioned such that the outer edge of the polishing pad 130 overlaps the outer edge of the bottom surface 13 of the circular recess 10 over the entire circumference, as shown in FIG. 4, and polishes the bottom surface 13 of the circular recess 10 of the wafer 1. In addition, when the diameter of the polishing pad 130 is smaller than the diameter of the circular recess 10, it is preferable that the diameter of the polishing pad 130 is at least 5 mm smaller than the diameter of the circular recess 10.

If the diameter of the polishing pad 130 exceeds the diameter of the circular recess 10, the polishing pad 130 will ride up onto the annular protrusion 11, and the polishing pad 130 will be less likely to come into contact with the circular recess 10 and the outer edge, making it impossible to polish the bottom surface 13 of the circular recess 10 with a uniform load. Therefore, it is preferable that the diameter of the polishing pad 130 is equal to or smaller than the diameter of the circular recess 10. In addition, it is preferable that the diameter of the polishing pad 130 is equal to or larger than the diameter of the polishing pad 120 in order to flatten the bottom surface 13 of the circular recess 10 of the wafer 1 by offsetting the amount of polishing by the polishing pad 120.

In addition, the closer the diameter of the polishing pad 120 is to the radius of the circular recess 10, and the closer the diameter of the polishing pad 130 is to the diameter of the circular recess 10, the more accurately the distribution of the polishing amount can be offset, and the flatness of the bottom surface 13 of the circular recess 10 will be increased. Taking into account the positioning accuracy of the polishing pads 120, 130, etc. of the polishing apparatus 100 and the generally desired thickness variation of the bottom surface 13 of the circular recess 10, it is preferable that the diameter of the polishing pad 120 is at least 5 mm smaller than the radius of the circular recess 10, and the diameter of the polishing pad 130 is at least 5 mm smaller than the diameter of the circular recess 10.

The polishing feed unit 104 is installed on a movable block 115, and moves the polishing units 102 and 103 in the Z-axis direction to move the polishing units 102 and 103 away from and toward the holding table 106. In the first embodiment, the movable block 115 on which the polishing feed unit 104 is installed is supported by a moving unit on an erected column 118 erected from one end of the device body 101 in the Y-axis direction parallel to the horizontal direction so as to be movable in the radial direction of the holding table 106. The polishing feed unit 104 is equipped with a well-known ball screw that is rotatable around its axis, a well-known motor that rotates the ball screw around its axis, and a well-known guide rail that supports the spindle housing of each polishing unit 102 and 103 so as to be movable in the Z-axis direction.

The cassette 107 has multiple slots and is a container for storing multiple wafers 1. As shown in FIG. 2, the cassette 107 stores multiple wafers 1 before and after polishing. In the first embodiment, a pair of cassettes 107 are provided, each of which is placed on a cassette installation table. The cassette installation table raises and lowers the cassette 107 in the Z-axis direction. The alignment unit 108 is a table on which the wafer 1 removed from the cassette 107 is temporarily placed and its center is aligned.

The carry-in unit 109 has a suction pad that adsorbs the wafer 1. The carry-in unit 109 adsorbs and holds the unpolished wafer 1 aligned by the alignment unit 108, and carries it onto the holding table 106 located in the carry-in/out area 301. The carry-out unit 114 has a suction pad that adsorbs the wafer 1. The carry-out unit 114 adsorbs and holds the polished wafer 1 on the holding table 106 located in the carry-in/out area 301, and carries it out of the holding table 106 and transports it to the cleaning unit 110. The cleaning unit 110 cleans the polished wafer 1 to remove contamination such as polishing debris.

The loading/unloading unit 111 removes the wafer 1 before polishing from the cassette 107 and transports the wafer 1 to the alignment unit 108, and also removes the wafer 1 after polishing from the cleaning unit 110 and transports it to the cassette 107. The loading/unloading unit 111 is, for example, a robot pick equipped with a U-shaped hand 119, and transports the wafer 1 by suction and holding it with the U-shaped hand 119.

The control unit 200 controls each of the above-mentioned constituent units that make up the polishing apparatus 100. In other words, the control unit 200 causes the polishing apparatus 100 to execute the polishing operation on the wafer 1. The control unit 200 is a computer that has an arithmetic processing device having a microprocessor such as a CPU (central processing unit), a storage device having a memory such as a ROM (read only memory) or RAM (random access memory), and an input/output interface device.

The arithmetic processing device of the control unit 200 performs arithmetic processing according to a computer program stored in the storage device, and outputs control signals for controlling the polishing apparatus 100 to the above-mentioned components of the polishing apparatus 100 via the input/output interface device. The control unit 200 is also connected to a display unit composed of a liquid crystal display device or the like that displays the status and images of the processing operation, an input unit that the operator uses to register processing content information, and a notification unit that notifies the operator. The input unit is composed of at least one of a touch panel provided on the display unit and a keyboard, etc. The notification unit notifies the operator by emitting at least one of sound, light, and a message on the touch panel.

(Wafer Polishing Method)
Next, a method for polishing a wafer according to the first embodiment will be described. Fig. 5 is a flow chart showing the flow of the method for polishing a wafer according to the first embodiment. The method for polishing a wafer according to the first embodiment is also a polishing operation of the polishing apparatus 100 having the above-mentioned configuration, in which the polishing apparatus 100 polishes the bottom surface 13 of the circular recess 10 of the wafer 1. The method for polishing a wafer according to the first embodiment includes a first polishing step 401 and a second polishing step 402, as shown in Fig. 5.

The polishing apparatus 100 having the above-mentioned configuration starts the polishing operation, i.e., the first polishing step 401, when the operator places the cassette 107 containing the wafer 1 with the circular recess 10 side facing upward on the cassette mounting table of the apparatus main body 101, the polishing conditions are registered in the control unit 190, and the control unit 190 receives an instruction from the operator to start the polishing operation.

(First polishing step)
Fig. 6 is a plan view showing the rotation direction of the polishing pad and the holding table in the first polishing step of the wafer polishing method shown in Fig. 5. Fig. 7 is a diagram showing the polishing amount of the bottom surface of the circular recess of the wafer in the first polishing step of the wafer polishing method shown in Fig. 5. The first polishing step 401 is a step in which a polishing pad 120 having a diameter equal to or smaller than the radius of the circular recess 10 is positioned in a radial region extending from the center to the outer periphery of the circular recess 10, and the wafer 1 and the polishing pad 120 are rotated in the same direction to polish the bottom surface 13 of the circular recess 10.

In the first polishing step 401, the polishing apparatus 100 rotates the spindles 122, 132 of each polishing unit 102, 103 at a rotation speed determined by the processing conditions around the axis, for example, in the direction of arrows 123, 133 (shown in Figures 3 and 4, in the same direction in embodiment 1), and causes the loading/unloading unit 111 to take out one wafer 1 from one of the cassettes 107 and transport it to the alignment unit 108. The polishing apparatus 100 causes the alignment unit 108 to align the center of the wafer 1, and transports the wafer 1 aligned in the loading unit 109 onto the holding table 106 located in the loading/unloading area 301.

In the first polishing step 401, the polishing apparatus 100 suction-holds the wafer 1 on the holding table 106 in the loading/unloading area 301, rotates the turntable 105, and moves the holding table 106 holding the wafer 1 in the loading/unloading area 301 to the small polishing area 302.

In the first polishing step 401, the polishing apparatus 100 rotates the holding table 106 of the small polishing area 302 around its axis in the same direction as the polishing pad 120 of the small polishing unit 102, as indicated by the arrow 116 in FIG. 6, and positions the outer edge of the polishing pad 120 in a radial region extending from the center of the circular recess 10 to the outer periphery, where the outer edge of the bottom surface 13 of the circular recess 10 overlaps with the center of the bottom surface 13 of the circular recess 10, and lowers the polishing pad 120 of the small polishing unit 102 by the polishing feed unit 104, so that the bottom surface 13 of the circular recess 10 of the wafer 1 is polished with the polishing pad 120, as shown in FIG. 3 and FIG. 6.

In the first polishing step 401, as shown in FIG. 6, the outer edge of the polishing pad 120 is positioned so that it overlaps with the outer edge of the bottom surface 13 of the circular recess 10 and the center of the bottom surface 13 of the circular recess 10, so the contact time of the bottom surface 13 with the polishing pad 120 becomes longer as it approaches the center of the circular recess 10. As a result, in the first polishing step 401, as shown in FIG. 7, the amount of polishing is greatest at the center of the bottom surface 13 of the circular recess 10, and the amount of polishing gradually decreases as it approaches the outer edge of the bottom surface 13 of the circular recess 10.

The amount of polishing indicates the thickness of the circular recess 10 that is thinned by the polishing process. The horizontal axis of FIG. 7 indicates each position on a line passing through the center of the circular recess 10, with both ends indicating the outer edge of the bottom surface 13 of the circular recess 10 and the center indicating the center of the bottom surface 13 of the circular recess 10. The vertical axis of FIG. 7 indicates the amount of polishing.

In the first polishing step 401, the polishing apparatus 100 polishes the bottom surface 13 of the circular recess 10 with the polishing pad 120 for a predetermined time, then raises the polishing pad 120 with the polishing feed unit 104, rotates the turntable 105, and moves the holding table 106 holding the wafer 1 after the first polishing step 401 to the large polishing area 303, and proceeds to the second polishing step 402. In the first polishing step 401, if the diameter of the polishing pad 120 is smaller than the radius of the circular recess 10, the polishing pad 120 is moved by the moving unit in the radial direction of the holding table 106 in the small polishing area 302 from a position where the outer edge of the polishing pad 120 overlaps with the outer edge of the bottom surface 13 of the circular recess 10 to a position where the outer edge of the polishing pad 120 overlaps with the center of the bottom surface 13 of the circular recess 10, while polishing the bottom surface 13 of the circular recess 10 of the wafer 1.

(Second polishing step)
Fig. 8 is a plan view showing the rotation direction of the polishing pad and the holding table in the second polishing step of the wafer polishing method shown in Fig. 5. Fig. 9 is a diagram showing the polishing amount of the bottom surface of the circular recess of the wafer in the second polishing step of the wafer polishing method shown in Fig. 5. The second polishing step 402 is a step in which the polishing pad 130, which has a diameter smaller than the diameter of the circular recess 10 and larger than the diameter of the polishing pad 120, is positioned so that the entire surface of the polishing pad 130 contacts the circular recess 10, and the wafer 1 and the polishing pad 130 are rotated in opposite directions to each other to polish the bottom surface 13 of the circular recess 10.

In the second polishing step 402, the polishing apparatus 100 rotates the holding table 106 of the large polishing area 303 around its axis in the direction of arrow 117, which is the opposite direction of arrow 133, which is the rotation direction of the polishing pad 130 of the large polishing unit 103, and positions the outer edge of the polishing pad 130 in a position overlapping with the outer edge of the bottom surface 13 of the circular recess 10. The polishing feed unit 104 lowers the polishing pad 130 of the large polishing unit 103, and as shown in Figures 4 and 8, the entire surface of the polishing pad 130 comes into contact with the bottom surface 13 of the circular recess 10, and the bottom surface 13 of the circular recess 10 of the wafer 1 is polished with the polishing pad 130.

In the second polishing step 402, as shown in FIG. 8, the polishing pad 130 is positioned so that the outer edge of the polishing pad 130 overlaps the outer edge of the bottom surface 13 of the circular recess 10 and the entire surface of the polishing pad 130 is in contact with the circular recess 10, and the polishing pad 130 and the holding table 106, i.e., the wafer 1, are rotated around the axis in opposite directions to polish the bottom surface 13 of the circular recess 10, so that the relative speed between the polishing pad 130 and the bottom surface 13 of the circular recess 10 becomes faster toward the outer edge of the circular recess 10. As a result, in the second polishing step 402, as shown in FIG. 9, the amount of polishing is the smallest at the center of the bottom surface 13 of the circular recess 10, and the amount of polishing gradually increases toward the outer edge of the bottom surface 13 of the circular recess 10.

The horizontal axis in FIG. 9 indicates each position on a line passing through the center of the circular recess 10, with both ends indicating the outer edge of the bottom surface 13 of the circular recess 10 and the center indicating the center of the bottom surface 13 of the circular recess 10. The vertical axis in FIG. 9 indicates the amount of polishing.

In the second polishing step 402, the polishing apparatus 100 polishes the bottom surface 13 of the circular recess 10 with the polishing pad 130 for a predetermined time, then raises the polishing pad 130 with the polishing feed unit 104, rotates the turntable 105, and moves the holding table 106 holding the wafer 1 after the second polishing step 402 to the loading/unloading area 301.

In the second polishing step 402, the polishing apparatus 100 transports the wafer 1 after the second polishing step 402 from the holding table 106 in the loading/unloading area 301 to the cleaning unit 110, cleans it in the cleaning unit 110, and then stores it in the cassette 107. In the polishing operation, the polishing apparatus 100 transports the wafer 1 from the holding table 106 in the loading/unloading area 301 that holds the wafer 1 after the second polishing step 402 to the cleaning unit 110 every time the turntable 105 rotates, and transports the wafer 1 before polishing to the holding table 106 in the loading/unloading area 301 that does not hold the wafer 1. When the polishing apparatus 100 performs the first polishing step 401 and the second polishing step 402 on all the wafers 1 in the cassette 107, the polishing operation is completed.

The wafer 1 that has been subjected to the first polishing step 401 and the second polishing step 402 has a metal film formed on the bottom surface 13 of the circular recess 10 on the back surface 8 by plating or the like. After the metal film is formed on the bottom surface 13 of the circular recess 10, the wafer 1 is divided into individual devices 7 along the planned division lines 6 and cut along the outer edge of the circular recess 10 to separate the device region 4 and the peripheral excess region 5, i.e., the circular recess 10 and the annular protrusion 11 are separated.

As described above, in the wafer polishing method according to embodiment 1, in the first polishing step 401, the amount of polishing is gradually increased toward the center of the bottom surface 13 of the circular recess 10, and in the second polishing step 402, the amount of polishing is gradually increased toward the outer edge of the bottom surface 13 of the circular recess 10, so that the thickness of the circular recess 10 of the wafer 1 after the second polishing step 402 can be maintained uniform.

As a result, the wafer polishing method according to the first embodiment has the effect of being able to precisely polish the bottom surface 13 of the circular recess 10, which is the ground surface of the so-called TAIKO wafer 1.

The present invention is not limited to the above embodiment. In other words, various modifications can be made without departing from the gist of the present invention. For example, the present invention may be implemented in a polishing device 100 equipped with only one polishing unit 126, as shown in Figures 10 and 11. In Figures 10 and 11, the same parts as those in embodiment 1 are denoted by the same reference numerals, and the description thereof will be omitted.

The polishing apparatus 100 shown in Figures 10 and 11 has a polishing pad 120 equivalent to a small polishing pad attached to the tip of a spindle 122 of a polishing unit 126, and an outer peripheral polishing pad 125 that moves up and down in the Z-axis direction by a cylinder unit 124 attached to the spindle 122. When the outer peripheral polishing pad 125 is raised by the cylinder unit 124, the lower surface is positioned above the lower surface of the polishing pad 120, as shown in Figure 10. When the outer peripheral polishing pad 125 is lowered by the cylinder unit 124, the lower surfaces of the polishing pads 120 and 120 are positioned on the same plane, as shown in Figure 11, and together with the polishing pad 120, it forms a polishing pad 130 equivalent to a large polishing pad.

In the first polishing step 401, the polishing apparatus 100 raises the outer polishing pad 125 by the cylinder unit 124, and as shown in FIG. 10, polishes the bottom surface 13 of the circular recess 10 using only the polishing pad 120, as in the first embodiment. In the second polishing step 402, the polishing apparatus 100 lowers the outer polishing pad 125 by the cylinder unit 124, and as shown in FIG. 11, polishes the bottom surface 13 of the circular recess 10 using the polishing pads 120, 125, i.e., the polishing pad 130 equivalent to the polishing pad, as in the first embodiment.

Note that FIG. 10 is a cross-sectional view that shows a schematic first polishing step of the wafer polishing method according to a modified example of embodiment 1. FIG. 11 is a cross-sectional view that shows a schematic second polishing step of the wafer polishing method according to a modified example of embodiment 1.

The present invention may also be implemented using a polishing apparatus having only the small polishing unit 102 and a polishing apparatus having only the large polishing unit 103 out of the polishing units 102 and 103. The present invention is also effective for normal wafers that do not have annular convex portion 11 and circular concave portion 10, but since normal wafers are designed to process only the radial region of the holding table whose holding surface is formed in a cone shape, the polishing distribution can be adjusted by changing the inclination of the holding surface, which is the processing area. On the other hand, TAIKO wafers are often designed to be held on a flat holding table 106, so it is difficult to adjust the polishing distribution by changing the inclination of the holding surface, and the present invention is particularly effective.

1 Wafer 8 Back side (one side)
10 Circular recess (recess)
11 Annular protrusion 120 Polishing pad (small polishing pad)
130 Polishing pad (large polishing pad)
401 First polishing step 402 Second polishing step

Claims (1)

A method for polishing a wafer, the method comprising the steps of: polishing a recess of a wafer having, on one surface thereof, a recess and an annular protrusion surrounding the recess;
a first polishing step in which a small polishing pad having a diameter equal to or smaller than the radius of the recess and the wafer are rotated in the same direction to polish the recess;
a second polishing step in which a large polishing pad having a diameter equal to or smaller than the diameter of the recess and equal to or larger than the diameter of the small polishing pad is positioned so that the entire surface of the large polishing pad is in contact with the recess, and the wafer and the large polishing pad are rotated in opposite directions to each other to polish the recess;
A method for polishing a wafer, comprising:

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