POLISHING PROCESS

Abstract

Polishing method for polishing a wafer (11) using a polishing device (2) comprising a clamping table (6) rotatable in a position in which it holds the wafer (11) and a polishing unit (28) comprising a spindle (32) to which a polishing tool (40) is attached for polishing the wafer (11) held by a holding surface (6a) of the clamping table (6), wherein the polishing tool (40) has a disc-shaped base (42) and an annular polishing layer (46) which is attached to a surface of the base (42) and which has an opening section (46a) which is arranged on a central section in a diameter direction of the base (42) and has a predetermined diameter (46a1), a maximum width (44c) of an effective polishing area (44b) of the polishing layer (46) in a radial direction of the base (42) is smaller than a radius of the wafer (11) and the radius of the wafer (11) is smaller than the diameter (46a1) of the opening section (46a), the polishing process includes: a holding step of holding the wafer (11) by the holding surface (6a); and a polishing step of polishing the wafer (11), while the polishing tool (40) is rotated around the spindle (32) in a state in which the wafer (11) and the polishing tool (40) are positioned such that part of a circumferential edge of the wafer (11) protrudes from a circumference of the polishing layer (46) and that a center of the wafer (11) is arranged at the opening section (46a) of the polishing layer (46), wherein the wafer (11) is polished only in a state in which the center of the wafer (11) is positioned at the opening section (46a) of the polishing layer (46).

Description

TECHNICAL BACKGROUND Technical field

[0001] The present invention relates to a polishing method for polishing a wafer and a polishing tool used in polishing a wafer. Description of the state of the art

[0002] Semiconductor chips are used in electronic devices such as mobile phones and PCs. Chips are manufactured by processing a semiconductor wafer whose front surface is formed with multiple streets in a grid pattern, creating a component such as an integrated circuit (IC) or a large-scale integration (LSI) in each of the areas divided by the streets. Specifically, the side of a rear surface of the semiconductor wafer is ground to thin the wafer, and then the semiconductor wafer is cut along the streets to produce the semiconductor chips. A grinding machine is used to grind the semiconductor wafer.For example, the side of the rear surface of the semiconductor wafer is successively subjected to coarse and fine grinding, thereby thinning the semiconductor wafer to a predetermined thickness (see, for example, JP 2000 - 288 881 A).

[0003] However, grinding leaves grinding marks (or saw marks) on the machining surface. If the semiconductor wafer is cut into semiconductor chips while these grinding marks remain, the chip strength of the semiconductor chips is lower compared to when the grinding marks are absent. Therefore, after grinding, chemical-mechanical polishing (CMP) is performed to polish the side of the back surface of the semiconductor wafer and remove the saw marks (see, for example, JP H08-99265A). A polishing device used in CMP has a disc-shaped clamping table.

[0004] The clamping table has a holding surface for gripping the semiconductor wafer. A polishing unit, comprising a cylindrical spindle, is located on the upper side of the clamping table. The spindle is oriented substantially parallel to the vertical direction. A disc-shaped polishing wheel is attached to a lower end section of the spindle by a disc attachment (see, for example, JP 5 405 979 B2). The polishing wheel has a base formed with a hole extending from a central section of an upper surface to a central section of a lower surface. Several segmented polishing pads are arranged in an annular pattern around the hole on one surface of the base.Each of the segmented polishing pads has a polishing area with a width that is smaller than the diameter of the wafer held by the clamping table, but larger than the radius of the wafer in a radial direction of the disc base.

[0005] DE 100 57 998 A1 relates to a polishing device and a polishing method with which excessive polishing of a surface of an outer circumferential edge of a surface to be polished of an object to be polished can be suppressed due to elastic deformation of a polishing tool. PRESENTATION OF THE INVENTION

[0006] However, when polishing the wafer using the polishing wheel, the area around the center of the wafer's processing surface could be over-polished, leading to the formation of a depression near the center of the wafer. The present invention was developed in consideration of such a problem, and it is an objective of the present invention to prevent the formation of a depression near the center of the wafer's processing surface.

[0007] According to one aspect of the present invention, a polishing method for polishing a wafer is provided using a polishing device comprising a clamping table rotatable in a position in which it holds the wafer, and a polishing unit having a spindle to which a polishing tool for polishing the wafer held by a holding surface of the clamping table is attached, wherein the polishing tool has a disc-shaped base and an annular polishing layer attached to a surface of the base and having an opening section arranged at a central section in a diameter direction of the base and having a predetermined diameter, a maximum width of an effective polishing area of ​​the polishing layer in a radial direction of the base being less than a radius of the wafer, and the radius of the wafer being less than the diameter of the opening section.wherein the polishing process comprises: a holding step of holding the wafer by the holding surface; and a polishing step of polishing the wafer while the polishing tool is rotated around the spindle in a state in which the wafer and the polishing tool are positioned such that a portion of a circumferential edge of the wafer protrudes from a circumference of the polishing layer and that a center of the wafer is located at the opening portion of the polishing layer. The wafer is polished only in the state in which the center of the wafer is located at the opening portion of the polishing layer.

[0008] Preferably, in the polishing step, the polishing tool and the wafer are moved relative to each other along a diameter direction of the polishing tool that passes through the center of a surface of the wafer.

[0009] In the polishing method according to one embodiment of the present invention, the polishing tool is used, which has a disc-shaped base and an annular polishing layer attached to a surface of the base and which has an opening section arranged at a central section in the diameter direction of the base and having a predetermined diameter, wherein the maximum width of the effective polishing area of ​​the polishing layer in the radial direction of the base is smaller than the radius of the wafer, and the radius of the wafer is smaller than the diameter of the opening section. In the polishing step, the wafer is polished in a state in which the wafer and the polishing tool are positioned such that a portion of the wafer's circumferential edge projects from the circumference of the polishing layer and the center of the wafer is located at the opening section of the polishing layer.This prevents the formation of a depression near the center of the machining surface.

[0010] The polishing tool according to another embodiment of the present invention comprises a disc-shaped base and an annular polishing layer attached to a surface of the base. The annular polishing layer has an opening section arranged at a central section in the diameter direction of the base and having a predetermined diameter. In this polishing tool, the maximum width of the effective polishing area of ​​the polishing layer in the radial direction of the base is smaller than the diameter of the opening section. Thus, when polishing a wafer with a radius smaller than the diameter of the opening section, the formation of a depression near the center of the surface being processed can be prevented.

[0011] The above and further aims, features and advantages of the present invention and the way in which they are realized will become more apparent, and the invention itself will best be understood by studying the following description and the attached claims with reference to the attached drawings, which show preferred embodiments of the invention. SHORT FIGURE DESCRIPTION Fig. Figure 1 is a perspective view of a polishing device; Fig. 2 is a view from below of a polishing tool; Fig. Figure 3 is a flowchart of a polishing process; Fig. Figure 4 is a diagram illustrating one method of polishing a wafer; Fig. 5A is a general view from below, showing a positional relationship between the polishing tool and the wafer in a first embodiment; Fig. 5B is a general sectional view showing the wafer polished in a state where it is positioned at a front position; Fig. 5C is a general sectional view showing the wafer polished in a state where it is located in a rear position; Fig. Figure 6 is a graph representing the amount of distance the wafer is removed by polishing; Fig. Figure 7A is a general view from below, showing the positional relationship between the polishing tool and the wafer in a comparative example; Fig. 7B is a general sectional view showing the wafer polished in the state in which it is positioned at a front position; Fig. 7C is a general sectional view showing the wafer polished in the state in which it is positioned in a rear position; and Fig. Figure 8 is a bottom view of a polishing tool according to a second embodiment. DETAILED DESCRIPTION OF PREFERRED EXECUTION FORMS

[0012] An embodiment according to an embodiment of the present invention is described below with reference to the accompanying drawings. Fig. Figure 1 is a perspective view of a polishing device 2. Note that the X-axis, Y-axis, and Z-axis directions (vertical direction, machining feed direction) are orthogonal to each other. The polishing device 2 has a base 4 that supports components. An upper section of the base 4 has an opening 4a, the longitudinal direction of which lies in the Y-axis direction. A disc-shaped clamping table 6 is arranged in the opening 4a.

[0013] The clamping table 6 comprises a metallic frame and a porous plate made of porous ceramic. An upper surface 8a1 of the frame and an upper surface 8a2 of the porous plate are flush with each other, forming a substantially flat holding surface 6a. The frame is designed with a predefined flow channel (not shown), and a suction source (not shown), such as an ejector, is connected to the flow channel. A negative pressure generated in the suction source is transferred through the predefined flow channel to the upper surface 8a2 of the porous plate.

[0014] One side of a front surface 11a of a wafer 11 (see Fig. 4) The wafer 11, with a diameter substantially equal to that of the upper surface 8a2 of the porous plate, is held by suction against the holding surface 6a. In the present embodiment, the diameter of the wafer 11 is equal to or greater than the diameter of the upper surface 8a2 of the porous plate, but smaller than the outer diameter of the upper surface 8a1 of the frame body. The wafer 11 is a disk-shaped semiconductor wafer made of silicon or the like, and several streets (not shown) are defined in a grid pattern on the side of the front surface 11a. A device (not shown), such as an IC or LSI, is formed in each of the areas subdivided by the streets.At the time of polishing, the side of the front surface 11a faces the holding surface 6a, and one side of a rear surface 11b is exposed on the upper side, so that to reduce damage to the components, a protective strip 13 made of a plastic, having substantially the same diameter as the wafer 11, is attached to the side of the front surface 11a to form a wafer unit 15 (see . Fig. 4).

[0015] A rotary drive source (not shown), such as a motor, is provided on a lower section of the clamping table 6, and an output shaft of the rotary drive source is connected to one side of the lower surface of the clamping table 6. The clamping table 6 is rotatable about the output shaft. The rotary drive source is supported by a motion plate for the Y-axis (not shown). The Y-axis motion plate is slidably mounted on a pair of guide rails (not shown) that are arranged substantially parallel to the Y-axis direction. A nut section (not shown) is provided on one side of a lower surface of the Y-axis motion plate. A ball screw (not shown), which is arranged substantially parallel to the Y-axis direction, is rotatably connected to the nut section.A drive source (not shown), such as a pulse motor, is connected to an end section of the ball screw spindle.

[0016] The Y-axis motion plate, the pair of guide rails, the ball screw, the drive source, and the like form a Y-axis motion mechanism for moving the clamping table 6 and the rotary drive source in the Y-axis direction. As shown in Fig. As shown in Figure 1, a rectangular table base 10 is provided between the clamping table 6 and the rotary drive source. Bellows-like, expandable covers 12 are provided on both sides of the table base 10 in the Y-axis direction. The table base 10, together with the clamping table 6, is moved between an in / out conveying area A at the front (one side in the Y-axis direction) and a polishing area B at the rear (the other side in the Y-axis direction).

[0017] A prismatic column section 14 is provided at the rear of the polishing device 2. A pair of guide rails 16, arranged along the Z-axis direction, are attached to a side surface at the front of the column section 14. A Z-axis motion plate 18 is slidably mounted on the pair of guide rails 16. A nut section (not shown) is provided on a side surface at the rear of the Z-axis motion plate 18, and a ball screw 20 is rotatably connected to the nut section. The ball screw 20 is arranged substantially parallel to the Z-axis direction. A drive source 22, such as a pulse motor, is connected to an upper end section of the ball screw 20.

[0018] The pair of guide rails 16, the Z-axis motion plate 18, the ball screw 20, the drive source 22, and the like form a Z-axis motion mechanism 24. A support section 26 for attaching a polishing unit 28 is provided on a side surface at the front of the Z-axis motion plate 18. The polishing unit 28 has a cylindrical spindle housing 30, the vertical direction of which is essentially parallel to the Z-axis direction. A portion of a cylindrical spindle 32 is rotatably mounted in the spindle housing 30.

[0019] A motor 34 is provided at an upper end section of the spindle 32. A lower end section of the spindle 32 projects downward beyond the spindle housing 30, and one side of an upper surface of a disc-shaped attachment 36 is fastened to the lower end section of the spindle 32. A disc-shaped polishing tool 40 is attached to one side of a lower surface of the attachment 36 using fastening devices 38, such as screws. Based on Fig. Section 4 describes the polishing tool 40. The polishing tool 40 has a disc-shaped base 42. An upper surface 42a of the base 42 is attached to a lower surface of the attachment 36.

[0020] Several segmented polishing pads 44 are attached to a lower surface (a surface) 42b of the base 42. The segmented polishing pad 44 comprises, for example, a polishing material such as a non-woven fabric, abrasive grains embedded in the polishing material, and a binder such as lacquer for fixing the abrasive grains in the polishing material. The abrasive grains are made of diamond, cerium oxide, silicon dioxide, or the like and have, for example, a size on the order of 0.01 µm to 10.0 µm. It should be noted that the segmented polishing pad 44 could comprise a foamed plastic such as foamed polyurethane and abrasive grains embedded in the foamed plastic.

[0021] The multiple segmented polishing pads 44 are arranged in a ring-shaped pattern in a circumferential direction 42e (see Fig. 2) of the base 42 and form a polishing layer 46. A bottom surface of the polishing layer 46 is formed with a circular opening section 46a. The opening section 46a has a predetermined diameter and is arranged concentrically to the base 42 in a central section in a diameter direction of the base 42. Immediately above the opening section 46a, a cylindrical opening 42c formed in a central section in a diameter direction of the base 42, a cylindrical opening 36a formed in a central section in a diameter direction of the attachment 36, and a cylindrical opening 32a formed in a central section in a diameter direction of the spindle 32 are arranged concentrically (see Fig. 4) Openings 32a, 36a, and 42c serve as a supply line through which a base polishing fluid is supplied in the case of wet polishing. Additionally, openings 32a and the like serve as a wiring passage in which a temperature sensor for measuring the temperature of wafer 11 and connecting wires are arranged when dry polishing is performed.

[0022] The following refers to Fig. 2 the design of the segment polishing pads 44 is described. Fig. Figure 2 is a bottom view of the polishing tool 40. In the first embodiment, five segmented polishing pads 44 are arranged essentially rotationally symmetrically around a center 42d of the lower surface 42b of the base 42. Each segmented polishing pad 44 has a shape resembling a cherry blossom petal or a teardrop. The width of the segmented polishing pad 44 in a circumferential direction 42e of the lower surface 42b increases from the center 42d to a predetermined position, but decreases from the predetermined position to an outer circumferential end section by extending outwards in a radial direction 42f of the lower surface 42b.

[0023] On a circle (see double arrow 42g) that is concentric to the center 42d and extends through a first position 42p1 in the radial direction 42f, a segment polishing pad 44 is in contact with two segment polishing pads 44 that are adjacent in the circumferential direction 42e. In each segment polishing pad 44, an annular thin material section 44a is formed on the inside of a second position 42p2, which is located on the inside (i.e., on the side of the center 42d) compared to the first position 42p1 in the radial direction 42f. Fig. For the sake of simplicity, diagonal lines are applied to the thin material section 44a.

[0024] A circle concentric with the center 42d and passing through the second position 42p2 corresponds to the outer shape of the opening section 46a formed in the polishing layer 46. The thin material section 44a gradually thins from the second position 42p2 towards the center 42d. Note that an inner end section of the thin material section 44a is located on the outside compared to the opening 42c in the base 42. The thin material section 44a does not come into contact with the wafer 11 when the wafer 11 is polished by the polishing tool 40. Thus, an area on the outside, compared to the thin material section 44a of the segmented polishing pad 44, becomes an effective polishing area 44b, which contributes to the polishing of the wafer 11.In the present embodiment, the effective polishing area 44b has the property that the maximum width 44c in the radial direction 42f is smaller than the diameter 46a1 of the opening section 46a of the polishing layer 46 (i.e. maximum width 44c < diameter 46a1).

[0025] At this point, in order to Fig. Returning to Section 1, further components of the polishing device 2 are described. The polishing device 2 has a control unit 48, which controls the operation of the polishing unit 28, the Y-axis movement mechanism, the rotary drive source, and the like. The control unit 48 includes a computer, which, for example, has a processor (processing unit), represented by a central processing unit (CPU), a main memory unit such as dynamic main memory (DRAM), and an auxiliary memory unit such as flash memory. The auxiliary memory element stores software, including a predefined program. The functions of the control unit 48 are realized by operating the processing unit and the like according to the software.

[0026] Next, with reference to the Fig. 3, Fig. 4, Fig. 5 to Fig. 6 a polishing method of polishing the wafer 11 using the polishing device 2 according to the first embodiment is described. Fig. Figure 3 is a flowchart of a polishing process using the polishing device 2. Note that the diameter of the wafer 11 to be polished is 300 mm (12 inches) in the present embodiment. First, as shown in Fig. Figure 4 shows the side of the front surface 11a of the wafer unit 15 held by the holding surface 6a over the protective band 13 under suction (holding step S10). After holding step S10, a polishing step S20 is performed on the side of the rear surface (a surface) 11b that is exposed on the top side.

[0027] Fig. Figure 4 is a diagram illustrating the polishing process of wafer 11. In polishing step S20, the clamping table 6 is first rotated in a predetermined direction at a first rotational speed (e.g., 100 rpm), and the spindle 32 is rotated in a predetermined direction at a second rotational speed (e.g., 1600 rpm). With both the clamping table 6 and the spindle 32 rotating, and a predetermined load (e.g., 300 N) applied to the wafer 11 by the Z-axis motion mechanism 24, the side of the back surface 11b is polished for a predetermined time period (e.g., 100 seconds).

[0028] In particular, in the first embodiment, in a state in which the wafer 11 and the polishing tool 40 are positioned such that the center 11c of the rear surface 11b of the wafer 11 is located at the opening section 46a, the side of the rear surface 11b is polished while the polishing tool 40 is rotated. Fig. Figure 5A is a general view from below, showing the positional relationship between the polishing tool 40 and the wafer 11 in the first embodiment. Note that in Fig. 5A the polishing layer 46 is shown in a state where it is simplified to an annular region. However, the diameter 46a1 of the opening section 46a of the polishing layer 46 and the maximum width 44c of the effective polishing area 44b correspond to those in Fig. 2 (that is, maximum width 44c < diameter 46a1).

[0029] In the first embodiment, the maximum width 44c is smaller than the radius of the wafer 11, since the maximum width 44c is 125 mm and the radius of the wafer 11 is 150 mm. Furthermore, since the diameter 46a1 is 200 mm, the radius of the wafer 11 is smaller than the diameter 46a1 (i.e., maximum width 44c < radius of wafer 11 < diameter 46a1). It should be noted that the outer diameter of the base 42 and the polishing layer 46 is each 450 mm. Fig. 5B is a general sectional view showing the polished wafer 11 and the polishing layer 46 in the state in which it is positioned at a front position. The in Fig. Wafer 11 shown in 5B corresponds, in terms of positioning, to the one in Fig. 5A with a solid line representing wafer 11.

[0030] In the present embodiment, the polishing is carried out such that the center 11c of the rear surface 11b is exposed at the opening section 46a, and thus, when the wafer 11 is in a front position, the central axis of rotation of the wafer 11 is positioned slightly on the inner side as an end section of the opening section 46a. Additionally, when the wafer 11 is in the front position, the center 11c of the rear surface 11b is exposed at the opening section 46a, and an end section (a portion of an outer circumferential edge) 11d on the front side of the wafer 11 is not covered with the polishing layer 46 and projects beyond the circumference of the polishing layer 46.

[0031] Fig. 5C is a general sectional view of the polished wafer 11 and the polishing layer 46 in the state in which it is arranged in a rear position. The in Fig. Wafer 11, shown in Figure 5C, corresponds in its position to the one shown in Figure 5C. Fig. 5A wafer 11 indicated by a dashed line. Even though the wafer 11 is in the rear position, the center 11c of the rear surface 11b is exposed at the opening section 46a, and the end section 11d at the front side of the wafer 11 is not covered with the polishing layer 46 and protrudes slightly beyond the perimeter of the polishing layer 46.

[0032] In polishing step S20, the wafer 11 and the polishing tool 40 are moved relatively along a diameter direction 42h of the base 42, which passes through the center 11c of the rear surface 11b, so that the wafer 11 is positioned between the front position ( Fig. 5B) and the rear position ( Fig. 5C) is moved back and forth. For example, the wafer 11 is polished while the clamping table 6 is moved along the Y-axis direction at 0.1 mm / s to 0.2 mm / s by the operation of the Y-axis motion mechanism. Note that in the present example, where the maximum width 44c is 125 mm, the radius of the wafer 11 is 150 mm, and the diameter 46a1 is 200 mm, the wafer 11 is moved back and forth with an amplitude of less than 25 mm. This allows the rear surface 11b to be polished in a state where the center 11c is always aligned with the opening section 46a. Accordingly, excessive polishing near the center 11c of the wafer 11 can be prevented, and the formation of a depression near the center 11c can be limited.

[0033] However, in the case where the end section 11d on the front side of the wafer 11 does not project beyond the circumference of the polishing layer 46 (i.e., where the circumference of the polishing layer 46 projects beyond the end section 11d on the front side of the wafer 11), the polishing layer 46 protrudes slightly downwards below the rear surface 11b, thus forming a step on the polishing layer 46. This could create an irregular load on the polishing layer 46, promote deterioration of the polishing layer 46, or similar effects. On the other hand, in the present embodiment, even in the case where the wafer 11 is arranged in a rear position (see Fig. 5C), the end section 11d on the front side of the wafer 11 always extends beyond the circumference of the polishing layer 46, so that no step is formed on the polishing layer 46. In this way, irregular stress or the promotion of deterioration can be prevented.

[0034] Fig. Figure 6 is a graph showing the experimental results of a measurement of the material removal rate of wafer 11 when the wafer 11 is polished using the polishing method according to the first embodiment. The abscissa represents the measurement position (mm) of wafer 11 when the center 11c is the origin, and the ordinate represents the material removal rate (µm). In this experiment, using the polishing device 2, to which the polishing tool 40 is attached, the sides of the rear surface 11b of three wafers 11 with a diameter of 300 mm (12 inches) were polished successively. However, it should be noted that no component was formed on the side of the front surface 11a of each wafer 11.

[0035] Graphs C1, C2 and C3 show polishing results of the first, second and third wafers respectively. The processing conditions were as follows. Rotational speed of the clamping table: 300 rpm Spindle rotational speed: 1,500 rpm Load during polishing: 300 N Back-and-forth movement in the Y-axis direction: 0.1 mm / s to 0.2 mm / s Polishing time: 150 s Polishing fluid supply: Zero (dry polishing)

[0036] In each of graphs C1 to C3, the difference between the maximum and minimum polishing quantity was calculated, and the average of the differences was determined to be 0.364 µm. In other words, a comparatively high flatness was achieved. Furthermore, as in Fig. 6 shown, no depression is formed near the center of 11c (i.e. near the origin).

[0037] Next, a comparative example will be described. Fig. Figure 7A is a general view from below, showing the positional relationship between a polishing tool 60 and the wafer 11 in the comparative example. The polishing tool 60 corresponds to the polishing tool 40 according to the first embodiment and has a polishing layer 66 with the same outer diameter (450 mm) as the polishing layer 46. However, the diameter 66a1 of an opening section 66a of the polishing layer 66 is smaller than the aforementioned diameter 46a1. The diameter 66a1 in the comparative example is 150 mm, and a maximum width 64c of the effective polishing area is also 150 mm.

[0038] The in Fig. Wafer 11, represented by a solid line in Figure 7A, shows a case in which the end section 11d on the front side of the wafer 11 overlaps with an end section on the front side of the polishing layer 66. In this case, the center 11c of the rear surface 11b is located at an end section of the opening section 66a. On the other hand, the two in Fig. 7A Wafer 11 shown in dashed lines the wafer 11 ( Fig. 7B) which is located in a front position and represents wafer 11 ( Fig. 7C), which is positioned in a rear position.

[0039] Fig. 7B is a general sectional view of the polished wafer and polishing layer 66 in the state in which it is positioned at a front position. Fig. Figure 7C is a general sectional view of the polished wafer and the polishing layer 66 in the state in which it is positioned at a rear position. In the case of polishing the 300 mm (12 in) diameter wafer 11 using the polishing tool 60, if the polishing is performed while the polishing tool 60 and the wafer 11 are moved relatively in the Y-axis direction, the contact time of the effective polishing area and the area around the center 11c is prolonged, and a depression is created in the area around the center 11c (see the area shown in Figure 7C). Fig. 7B is surrounded by a dashed line), as in Fig. 7B is shown.

[0040] Furthermore, as stated in Fig. Figure 7C shows the perimeter of the polishing layer 66 extending beyond the end section 11d on the front side of the wafer 11, thus forming a step on the polishing layer 66. This exerts an irregular load on the polishing layer 66 and promotes its deterioration (see the area surrounded by a dashed line in Figure 7C). Fig. 7C). On the other hand, as described above, in the first embodiment, the side of the rear surface 11b is polished in a state in which the wafer 11 and the polishing tool 40 are positioned such that the center 11c of the rear surface 11b of the wafer 11 is located at the opening section 46a. Thus, excessive polishing near the center 11c of the wafer 11 can be prevented, and the formation of a depression near the center 11c can be limited. Furthermore, in the first embodiment, since the side of the rear surface 11b is polished in a state in which the end section 11d on the front side of the wafer 11 protrudes from the circumference of the polishing layer 46, no step is formed on the polishing layer 46, and the application of an irregular load to the polishing layer 46 and the promotion of deterioration can be prevented.

[0041] Next, a second embodiment will be described. Fig. Figure 8 is a bottom view of a polishing tool 50 according to a second embodiment. The polishing tool 50 corresponds to the polishing tool 40 and has a base 52 corresponding to the base 42 and a polishing layer 56 corresponding to the polishing layer 46. However, it should be noted that the base 52 is disc-shaped and does not have the opening 42c of the base 42, and that in a lower surface (a surface) 52b to which the polishing layer 56 is attached, a center 52d is not covered by the polishing layer 56 and is exposed.

[0042] Additionally, the polishing layer 56 does not have multiple segmented polishing pads 44, but rather a continuous annular polishing pad. The second embodiment differs from the first embodiment in these points, but is identical to the first embodiment in other points. In particular, the maximum width 54c of an effective polishing area 54b in a radial direction 52f of the base 52 is smaller than the diameter 56a1 of an opening section 56a of the polishing layer 56 (that is, maximum width 54c < diameter 56a1). For example, if the radius of the wafer 11 is 150 mm, the maximum width 54c in the radial direction 53f is 125 mm and the diameter 56a1 is 200 mm (that is, maximum width 54c < radius of the wafer 11 < diameter 56a1).

[0043] In the second embodiment, excessive polishing near the center 11c of the wafer 11 can also be prevented, and the formation of a depression near the center 11c can be inhibited. Furthermore, no step is formed on the polishing layer 56, since the rear surface 11b is polished in such a way that the end section 11d on the front side of the wafer 11 projects beyond the circumference of the polishing layer 56. Therefore, the application of an irregular load to the polishing layer 56 and the promotion of deterioration can be prevented. Structures, methods, and the like relating to the embodiments can be carried out with suitable modifications other than those described above, provided that the modifications do not deviate from the scope of the present invention.

[0044] The present invention is not limited to the details of the preferred embodiments described above. The scope of the invention is defined by the attached claims.

Claims

[1] Polishing method for polishing a wafer (11) using a polishing device (2) comprising a clamping table (6) rotatable in a position in which it holds the wafer (11) and a polishing unit (28) comprising a spindle (32) to which a polishing tool (40) for polishing the wafer (11) held by a holding surface (6a) of the clamping table (6) is attached, wherein the polishing tool (40) has a disc-shaped base (42) and an annular polishing layer (46) which is attached to a surface of the base (42) and which has an opening section (46a) which is arranged on a central section in a diameter direction of the base (42) and has a predetermined diameter (46a1), a maximum width (44c) of an effective polishing area (44b) of the polishing layer (46) in a radial direction of the base (42) is smaller than a radius of the wafer (11) and the radius of the wafer (11) is smaller than the diameter (46a1) of the opening section (46a), the polishing process includes: a holding step of holding the wafer (11) by the holding surface (6a); and a polishing step of polishing the wafer (11), while the polishing tool (40) is rotated around the spindle (32) in a state in which the wafer (11) and the polishing tool (40) are positioned such that part of a circumferential edge of the wafer (11) protrudes from a circumference of the polishing layer (46) and that a center of the wafer (11) is arranged at the opening section (46a) of the polishing layer (46), wherein the wafer (11) is polished only in a state in which the center of the wafer (11) is positioned at the opening section (46a) of the polishing layer (46). [2] Polishing method according to claim 1, wherein in the polishing step the polishing tool (40) and the wafer (11) are moved relative to each other along a diameter direction of the polishing tool (40) which passes through a center of a surface of the wafer (11). [3] Polishing device (2) for polishing a wafer (11), wherein the polishing device (2) comprises: a polishing tool (40), comprising: a disc-shaped base (42); and an annular polishing layer (46) which is attached to a surface of the base (24) and which has an opening section (46a) which is arranged on a central section in a diameter direction of the base (42) and has a predetermined diameter (46a1), wherein a maximum width (44c) of an effective polishing area (44b) of the polishing layer (46) in a radial direction of the base (42) is smaller than the diameter (46a1) of the opening section (46a), a control unit (48) configured to control the polishing device (2) to perform a polishing process, the polishing process comprising: a polishing step of polishing the wafer (11), while the polishing tool (40) is rotated about a spindle (32) in a state in which the wafer (11) and the polishing tool (40) are positioned such that a part of a circumferential edge of the wafer (11) protrudes from a circumference of the polishing layer (46) and that a center of the wafer (11) is arranged at the opening section (46a) of the polishing layer (46), wherein the wafer (11) is polished only in a state in which the center of the wafer (11) is positioned at the opening section (46a) of the polishing layer (46).

Images