Grinding method and grinding tool

Abstract

This invention provides a polishing method and polishing tool to suppress the formation of depressions near the center of the polished surface. The polishing method uses a polishing apparatus to polish a wafer. The polishing apparatus includes: a chuck stage capable of rotating while holding the wafer; and a polishing unit having a spindle on which a polishing tool is mounted. The polishing tool has: a circular plate-shaped base; and an annular polishing layer fixed to one surface of the base and including an opening of a predetermined diameter located at the center of the base in the diametrical direction. The maximum width of the effective polishing area of ​​the polishing layer in the radial direction of the base is less than the radius of the wafer, and the radius of the wafer is less than the diameter of the opening. The polishing method includes the following steps: a holding step, in which the wafer is held using a holding surface; and a polishing step, in which the wafer and the polishing tool are positioned such that a portion of the outer periphery of the wafer protrudes from the outer periphery of the polishing layer, and the center of the wafer is located in the opening of the polishing layer, to polish the wafer.

Description

Technical Field

[0001] This invention relates to a grinding method for grinding wafers and grinding tools used in grinding wafers. Background Technology

[0002] Semiconductor device chips are incorporated into electronic devices such as mobile phones and personal computers. Semiconductor device chips are manufactured by processing semiconductor wafers, for example, in which multiple predetermined dividing lines are arranged in a grid pattern on the front side, and devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integrations) are formed in the areas divided by these multiple predetermined dividing lines.

[0003] Specifically, after thinning the back side of a semiconductor wafer by grinding, the semiconductor wafer is cut along predetermined dividing lines to manufacture a semiconductor device chip. A grinding apparatus is used in the grinding of the semiconductor wafer. For example, coarse grinding and fine grinding are performed sequentially on the back side of the semiconductor wafer, thereby thinning the semiconductor wafer to a predetermined thickness (see, for example, Patent Document 1).

[0004] However, due to grinding, grinding marks (i.e. saw marks) are formed on the ground surface. When a semiconductor wafer is divided into semiconductor device chips with grinding marks remaining on the ground surface, the bending strength of the semiconductor device chips is reduced compared to the case without grinding marks.

[0005] Therefore, after grinding, CMP (Chemical Mechanical Polishing) is performed to remove saw marks by polishing the back side of the semiconductor wafer (see, for example, Patent Document 2). The polishing apparatus used in CMP has a disc-shaped chuck stage.

[0006] The chuck stage has a holding surface for attracting and holding semiconductor wafers. A grinding unit with a cylindrical spindle is positioned above the chuck stage. The spindle is configured to be approximately parallel to the vertical direction.

[0007] A circular grinding wheel is mounted at the lower end of the spindle, for example, by means of a grinding wheel mounting base (see, for example, Patent Document 3). The grinding wheel has a grinding wheel base in which a hole is formed, extending from the center of the upper surface to the center of the lower surface.

[0008] Multiple segmented polishing pads are arranged in a ring around the hole on one side of the grinding wheel base. Each segmented polishing pad has a polishing area in the radial direction of the grinding wheel base that is narrower than the diameter of the wafer held by the chuck stage and larger than the radius of the wafer.

[0009] Patent Document 1: Japanese Patent Application Publication No. 2000-288881

[0010] Patent Document 2: Japanese Patent Application Publication No. 8-99265

[0011] Patent Document 3: Japanese Patent No. 5405979

[0012] However, when using this grinding wheel to grind the wafer, sometimes the center of the surface being ground is over-ground, resulting in a depression near the center of the wafer. Summary of the Invention

[0013] The present invention was made in view of this problem and its purpose is to suppress the formation of depressions near the center of the polished surface of the wafer.

[0014] According to one aspect of the present invention, a polishing method is provided, which polishes a wafer using a polishing apparatus comprising: a chuck stage capable of rotating while holding the wafer; and a polishing unit having a spindle on which a polishing tool is mounted, the polishing tool polishing the wafer held by the holding surface of the chuck stage, wherein the polishing tool comprises: a circular plate-shaped base; and an annular polishing layer fixed to one surface of the base and including an opening located at the center of the base in the diametrical direction and having a predetermined diameter, the maximum width of the effective polishing area of ​​the polishing layer in the radial direction of the base being less than the radius of the wafer, and the radius of the wafer being less than the diameter of the opening, the polishing method comprising the following steps: a holding step, in which the wafer is held using the holding surface; and a polishing step, in which the wafer and the polishing tool are positioned such that a portion of the outer periphery of the wafer protrudes from the outer periphery of the polishing layer and the center of the wafer is located in the opening of the polishing layer, and the wafer is polished while the polishing tool is rotated about the spindle.

[0015] Preferably, in this polishing process, the polishing tool and the wafer are moved relative to each other along the diametrical direction of the polishing tool passing through the center of one face of the wafer.

[0016] According to another aspect of the invention, a polishing tool is provided for use when polishing a wafer, wherein the polishing tool has: a circular plate-shaped base; and an annular polishing layer fixed to one surface of the base and including an opening located at the center of the base in the diametrical direction 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 diameter of the opening.

[0017] In one aspect of the polishing method of the present invention, a polishing tool is used, the polishing tool having: a circular plate-shaped base; and an annular polishing layer fixed to one surface of the base and including an opening located at the center of the base in the diametrical direction 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 less than the radius of the wafer, and the radius of the wafer is less than the diameter of the opening.

[0018] In the polishing process, the wafer is polished while the wafer and polishing tool are positioned such that a portion of the wafer's outer periphery protrudes from the outer periphery of the polishing layer and the center of the wafer is located within an opening in the polishing layer. Therefore, the formation of depressions near the center of the polished surface can be suppressed.

[0019] Another aspect of the polishing tool of the present invention includes: a circular plate-shaped base; and an annular polishing layer fixed to one surface of the base, and including an opening located at the center of the base in the diametrical direction 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. Therefore, when polishing a wafer having a radius smaller than the diameter of the opening, the formation of depressions near the center of the polished surface can be suppressed. Attached Figure Description

[0020] Figure 1 This is a three-dimensional view of the grinding device.

[0021] Figure 2 This is a bottom view of the grinding tool.

[0022] Figure 3 This is a flowchart of the grinding method.

[0023] Figure 4 This is a diagram showing the process of grinding a wafer.

[0024] Figure 5 (A) is a schematic bottom view showing the positional relationship between the polishing tool and the wafer in the first embodiment. Figure 5 (B) is a schematic cross-sectional view showing a wafer being ground in the forward position. Figure 5 (C) is a schematic cross-sectional view showing a wafer being ground in a rear position.

[0025] Figure 6 It is a graph showing the amount of material removed from the wafer based on grinding.

[0026] Figure 7 (A) is a schematic bottom view showing the positional relationship between the grinding tool and the wafer in the comparative example. Figure 7(B) is a schematic cross-sectional view showing a wafer being ground in the forward position. Figure 7 (C) is a schematic cross-sectional view showing a wafer being ground in a rear position.

[0027] Figure 8 This is a bottom view of the grinding tool according to the second embodiment.

[0028] Label Explanation

[0029] 2: Grinding device; 4: Base; 4a: Opening; 6: Chuck stage; 6a: Holding surface; 8a1, 8a2: Upper surface; 10: Stage base; 12: Telescopic cover; 14: Column; 11: Wafer; 11a: Front side; 11b: Back side (one side); 11c: Center; 11d: End (part of the outer perimeter); 13: Protective belt; 15: Wafer unit; 16: Guide rail; 18: Z-axis moving plate; 20: Ball screw; 22: Drive source; 24: Z-axis direction moving mechanism; 26: Support; 28: Grinding unit; 30: Spindle housing; 32: Spindle; 32a: Opening; 34: Motor; 36: Mounting base; 36a: Opening; 38: Fixing element; 40: Grinding tool; 42: Base; 42a: Upper surface; 42b: Lower surface (one side); 42c: Opening; 42 d: Center; 42e: Circumferential; 42f: Radial direction; 42g: Double arrow; 42h: Diameter direction; 42p1: Position 1; 42p2: Position 2; 44: Segmented grinding pad; 44a: Thin-walled portion; 44b: Effective grinding area; 44c: Maximum width; 46: Grinding layer; 46a: Opening; 46a1: Diameter; 48: Control unit; 50: Grinding tool; 52: Base; 52b: Lower surface (one face); 52d: Center; 52f: Radial direction; 54b: Effective grinding area; 54c: Maximum width; 56: Grinding layer; 56a: Opening; 56a1: Diameter; 60: Grinding tool; 64c: Maximum width; 66: Grinding layer; 66a: Opening; 66a1: Diameter; A: Loading / unloading area; B: Grinding area; C1, C2, C3: Curves. Detailed Implementation

[0030] An embodiment of one aspect of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a perspective view of the grinding device 2. Additionally, Figure 1 The X-axis, Y-axis, and Z-axis directions (vertical direction and grinding feed direction) shown are perpendicular to each other.

[0031] The grinding apparatus 2 has a base 4 that supports the constituent elements. An opening 4a with a length portion in the Y-axis direction is formed on the upper part of the base 4. A circular plate-shaped chuck worktable 6 is arranged in the opening 4a.

[0032] The chuck stage 6 has a metal frame and a porous plate made of porous ceramic. The upper surface 8a1 of the frame and the upper surface 8a2 of the porous plate are on the same plane, forming a generally flat holding surface 6a.

[0033] A defined flow path (not shown) is formed within the frame, and an attraction source (not shown) such as an ejector is connected to this flow path. The negative pressure generated by the attraction source is transmitted to the upper surface 8a2 of the porous plate via the defined flow path.

[0034] A wafer 11 having a diameter approximately the same as the upper surface 8a2 of a porous plate (see reference). Figure 4 The front side 11a of the wafer is attracted and held on the holding surface 6a. In this embodiment, the diameter of the wafer 11 is greater than or equal to the diameter of the upper surface 8a2 of the porous plate and smaller than the outer diameter of the upper surface 8a1 of the frame.

[0035] The wafer 11 is a disc-shaped semiconductor wafer formed of silicon or the like, with multiple pre-defined dividing lines (not shown) arranged in a grid pattern on the front side 11a. ICs, LSIs, and other devices (not shown) are formed within the regions defined by each pre-defined dividing line.

[0036] During polishing, the front side 11a faces the holding surface 6a, while the back side 11b is exposed upwards. Therefore, to reduce damage to the device, a resin protective tape 13 of approximately the same diameter as the wafer 11 is attached to the front side 11a to form the wafer unit 15 (see reference). Figure 4 ).

[0037] A rotary drive source (not shown) such as an electric motor is provided at the lower part of the chuck table 6, and the output shaft of the rotary drive source is connected to the lower surface of the chuck table 6. The chuck table 6 can rotate around this output shaft.

[0038] The rotary drive source is supported on a Y-axis moving plate (not shown). The Y-axis moving plate is slidably mounted on a pair of guide rails (not shown) arranged approximately parallel to the Y-axis direction. A nut portion (not shown) is provided on the lower surface of the Y-axis moving plate.

[0039] A ball screw (not shown) arranged approximately parallel to the Y-axis is rotatably connected to the nut section. A drive source such as a pulse motor (not shown) is connected to one end of the ball screw.

[0040] The Y-axis moving plate, a pair of guide rails, a ball screw, and a drive source constitute the Y-axis moving mechanism that moves the chuck table 6 and the rotary drive source in the Y-axis direction. For example... Figure 1 As shown, a rectangular worktable base 10 is provided between the chuck worktable 6 and the rotary drive source.

[0041] A corrugated telescopic cover 12 is provided on both sides of the worktable base 10 in the Y-axis direction. The worktable base 10 and the chuck worktable 6 move together between the loading and unloading area A on the front (one side in the Y-axis direction) and the grinding area B on the rear (the other side in the Y-axis direction).

[0042] A prism-shaped column 14 is provided at the rear of the grinding device 2. A pair of guide rails 16 arranged along the Z-axis are fixed on the side of the column 14 at the front. A Z-axis moving plate 18 is slidably mounted on the pair of guide rails 16.

[0043] A nut portion (not shown) is provided on the side of the rear side of the Z-axis moving plate 18, and a ball screw 20 arranged approximately parallel to the Z-axis direction is rotatably connected to the nut portion. A drive source 22 such as a pulse motor is connected to the upper end of the ball screw 20.

[0044] A pair of guide rails 16, a Z-axis moving plate 18, a ball screw 20, a drive source 22, etc. constitute a Z-axis moving mechanism 24. A support part 26 for fixing the grinding unit 28 is provided on the side of the front side of the Z-axis moving plate 18.

[0045] The grinding unit 28 has a cylindrical spindle housing 30 arranged approximately parallel to the Z-axis in the height direction. A portion of a cylindrical spindle 32 is rotatably housed within the spindle housing 30.

[0046] A motor 34 is provided at the upper end of the spindle 32. The lower end of the spindle 32 protrudes to a position lower than the spindle housing 30, and a circular plate-shaped mounting base 36 is fixed to the upper surface of the lower end of the spindle 32.

[0047] A circular grinding tool 40 is mounted on the lower surface of the mounting base 36 using screws or other fasteners 38. (See reference here.) Figure 4 The grinding tool 40 is described below. The grinding tool 40 has a circular plate-shaped base 42. The upper surface 42a of the base 42 is fixed to the lower surface of the mounting base 36.

[0048] Multiple segmented abrasive pads 44 are fixed on the lower surface (one side) 42b of the base 42. The segmented abrasive pads 44 may include, for example, abrasive cloth such as non-woven fabric; abrasive grains disposed in the abrasive cloth; and a bonding material such as varnish for fixing the abrasive grains in the abrasive cloth.

[0049] The abrasive grains are formed from materials such as diamond, cerium oxide, and silicon oxide, and have a size of approximately 0.01 μm to 10.0 μm. Additionally, the segmented abrasive pad 44 may contain foamed plastic such as polyurethane foam and abrasive grains fixed within the foamed plastic.

[0050] Multiple segmented grinding pads 44 are located circumferentially 42e of the base 42 (see reference). Figure 2 The polishing layer 46 is formed by the ring arrangement of the base plate 42. A circular opening 46a is formed on the lowest surface of the polishing layer 46. The opening 46a has a predetermined diameter and is arranged concentrically with the base plate 42 at the center of the diameter direction of the base plate 42.

[0051] Above the opening 46a, concentrically arranged are: a cylindrical opening 42c formed at the center of the base 42 in the diameter direction; a cylindrical opening 36a formed at the center of the mounting base 36 in the diameter direction; and a cylindrical opening 32a formed at the center of the main shaft 32 in the diameter direction (see reference). Figure 4 ).

[0052] Openings 32a, 36a, and 42c function as pathways for providing alkaline slurry during wet polishing. Additionally, openings 32a, etc., function as wiring channels for configuring temperature sensors for measuring the temperature of the wafer 11 and for lead wires during dry polishing.

[0053] Here, refer to Figure 2 The structure of the segmented abrasive pad 44 is described. Figure 2 This is a bottom view of the polishing tool 40. In the first embodiment, five segmented polishing pads 44 are arranged in a substantially rotationally symmetrical manner around the center 42d of the lower surface 42b of the base 42. Each segmented polishing pad 44 has a shape similar to a cherry blossom petal or a teardrop.

[0054] Regarding the width of the segmented abrasive pad 44 on the circumferential direction 42e of the lower surface 42b, it expands from the center 42d to a specified position and narrows from that specified position to the outer peripheral end, towards the outer side of the radial direction 42f of the lower surface 42b.

[0055] On a circle concentric with center 42d and passing through the first position 42p1 in the radial direction 42f (refer to double arrow 42g), a segmented abrasive pad 44 contacts two adjacent segmented abrasive pads 44 in the circumferential direction 42e.

[0056] In each segmented abrasive pad 44, an annular thin-walled portion 44a is formed from the second position 42p2, located inside the first position 42p1 (i.e., the center 42d side), along the radial direction 42f. Figure 2 For ease of explanation, the thin-walled portion 44a is marked with a slash.

[0057] The circle concentric with the center 42d and passing through the second position 42p2 corresponds to the shape of the opening 46a formed in the polishing layer 46. The thin-walled portion 44a gradually thins from the second position 42p2 toward the center 42d. In addition, the inner end of the thin-walled portion 44a is located on the outer side of the opening 42c of the base 42.

[0058] When the wafer 11 is polished using the polishing tool 40, the thin-walled portion 44a does not contact the wafer 11. Therefore, the area on the outer side of the segmented polishing pad 44, which is outside the thin-walled portion 44a, becomes the effective polishing area 44b that helps polish the wafer 11.

[0059] The effective grinding area 44b of this embodiment has the following characteristics: the maximum width 44c in the radial direction 42f is smaller than the diameter 46a1 of the opening 46a of the grinding layer 46 (i.e., the maximum width 44c < the diameter 46a1).

[0060] Here, return Figure 1 The other components of the grinding apparatus 2 will be described below. The grinding apparatus 2 has a control unit 48 that controls the operation of the grinding unit 28, the Y-axis moving mechanism, the rotary drive source, etc.

[0061] The control unit 48 is, for example, a computer, which includes: a processor (processing device) represented by a CPU (Central Processing Unit); a main storage device such as DRAM (Dynamic Random Access Memory); and an auxiliary storage device such as flash memory.

[0062] The auxiliary storage device stores software containing a prescribed program. The processing device and other components are operated according to this software, thereby realizing the function of the control unit 48.

[0063] Next, refer to Figures 3 to 6 The polishing method for polishing the wafer 11 using the polishing apparatus 2 of the first embodiment will be described. Figure 3 This is a flowchart of the polishing method using polishing apparatus 2. Additionally, in this embodiment, the diameter of the wafer 11 being polished is 300 mm (12 inches).

[0064] First, such as Figure 4 As shown, the front side 11a of the wafer unit 15 is attracted and held by the holding surface 6a through the protective strip 13 (holding process S10). After the holding process S10, a polishing process S20 is performed to polish the back side (one surface) 11b side that will be exposed upward.

[0065] Figure 4This diagram illustrates the grinding process of wafer 11. In the grinding process S20, the chuck stage 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).

[0066] While rotating the chuck stage 6 and spindle 32 together and applying a specified load (e.g., 300 N) to the wafer 11 using the Z-axis moving mechanism 24, the back side 11b is ground for a specified time (e.g., 100 seconds).

[0067] In particular, in the first embodiment, while the wafer 11 and the polishing tool 40 are positioned such that the center 11c of the back surface 11b of the wafer 11 is located in the opening 46a, the back surface 11b side is polished while the polishing tool 40 is rotated.

[0068] Figure 5 (A) is a schematic bottom view showing the positional relationship between the polishing tool 40 and the wafer 11 in the first embodiment. Additionally, in Figure 5 In (A), the polishing layer 46 is simplified as an annular region. However, the diameter 46a1 of the opening 46a of the polishing layer 46 and the maximum width 44c of the effective polishing area 44b are different from those of the polishing layer 46. Figure 2 Corresponding to (i.e., maximum width 44c < diameter 46a1).

[0069] In the first embodiment, the maximum width 44c is 125 mm, and the radius of the wafer 11 is 150 mm, therefore the maximum width 44c is smaller than the radius of the wafer 11. Additionally, the diameter 46a1 is 200 mm, therefore the radius of the wafer 11 is smaller than the diameter 46a1 (i.e., maximum width 44c < radius of wafer 11 < diameter 46a1). Furthermore, the outer diameters of both the substrate 42 and the polishing layer 46 are 450 mm.

[0070] Figure 5 (B) is a schematic cross-sectional view showing the wafer 11 and the polishing layer 46 being polished in the forward position. Figure 5 The wafer 11 shown in (B) and Figure 5 The position of the wafer 11 shown by the solid line in (A) corresponds to that of the wafer 11.

[0071] In this embodiment, grinding is performed such that the center 11c of the back surface 11b is exposed at the opening 46a. Therefore, when the wafer 11 is in the front position, the central axis of rotation of the wafer 11 is located slightly inside the end of the opening 46a.

[0072] In addition, when the wafer 11 is in the front position, the center 11c of the back surface 11b is exposed in the opening 46a, and the end (part of the outer periphery) 11d of the front side of the wafer 11 is not covered by the polishing layer 46 and protrudes from the outer periphery of the polishing layer 46.

[0073] Figure 5 (C) is a schematic cross-sectional view showing the wafer 11 and the polishing layer 46 being polished in a rear position. Figure 5 The chip 11 shown in (C) and Figure 5 The position of the wafer 11 shown by the dashed line in (A) corresponds to that of the wafer 11.

[0074] When the wafer 11 is in the rear position, the center 11c of the back surface 11b is also exposed at the opening 46a, and the front end 11d of the wafer 11 is not covered by the polishing layer 46 but protrudes slightly from the outer periphery of the polishing layer 46.

[0075] In the polishing process S20, according to the position of the wafer 11 in the front ( Figure 5 (B) and the rear position ( Figure 5 The reciprocating movement between the wafer 11 and the polishing tool 40 causes them to move relative to each other along the diametrical direction 42h of the base 42 through the center 11c of the back surface 11b.

[0076] For example, the Y-axis moving mechanism is activated, causing the chuck stage 6 to move along the Y-axis at a speed of 0.1 mm / s to 0.2 mm / s while grinding the wafer 11. Furthermore, in this 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 reciprocating movement is performed with an amplitude of less than 25 mm.

[0077] Therefore, the back surface 11b side can be ground while the center 11c is always positioned in the opening 46a. Thus, excessive grinding near the center 11c of the wafer 11 can be prevented, and the formation of depressions near the center 11c can be suppressed.

[0078] Furthermore, if the front end 11d of the wafer 11 does not protrude beyond the outer periphery of the polishing layer 46 (i.e., the outer periphery of the polishing layer 46 protrudes beyond the front end 11d of the wafer 11), the polishing layer 46 protrudes to a position slightly below the back surface 11b, creating a step difference on the polishing layer 46. This results in abnormal load on the polishing layer 46 and accelerated degradation of the polishing layer 46.

[0079] In contrast, in this embodiment, even when the chip 11 is positioned at the rear (see reference 11) Figure 5In the case of (C), the front end 11d of the wafer 11 always protrudes from the outer periphery of the polishing layer 46, so no step difference is formed on the polishing layer 46. Therefore, abnormal load and deterioration promotion can be prevented.

[0080] Figure 6 This is a graph showing the experimental results of measuring the amount of material removed from the wafer 11 when the wafer 11 is polished using the polishing method of the first embodiment. The horizontal axis shows the measurement position (mm) of the wafer 11 with the center 11c as the origin, and the vertical axis shows the amount of material removed (μm).

[0081] In this experiment, a grinding apparatus 2 equipped with a grinding tool 40 was used to grind the back side 11b of three wafers 11 with a diameter of 300 mm (12 inches) in sequence. However, no device was formed on the front side 11a of each wafer 11.

[0082] Curves C1, C2, and C3 represent the grinding results of the first, second, and third wafers 11, respectively. The processing conditions are as follows.

[0083] Chuck table speed: 300 rpm

[0084] Spindle speed: 1500 rpm

[0085] Grinding load: 300N

[0086] Reciprocating movement in the Y-axis direction: 0.1mm / s~0.2mm / s

[0087] Grinding time: 150s

[0088] Slurry supply: None (dry grinding)

[0089] The differences between the maximum and minimum grinding amounts were calculated for curves C1 to C3, and the average of these differences was then calculated, yielding a result of 0.364 μm. This indicates that a relatively high flatness can be achieved. Additionally, as... Figure 6 As shown, no depression is formed near the center 11c (i.e., near the origin).

[0090] Next, the comparative examples will be explained. Figure 7 (A) is a schematic bottom view showing the positional relationship between the polishing tool 60 and the wafer 11 in the comparative example. The polishing tool 60 corresponds to the polishing tool 40 of the first embodiment and has a polishing layer 66 with the same outer diameter (450 mm) as the polishing layer 46.

[0091] However, the diameter 66a1 of the opening 66a of the polishing layer 66 is smaller than the diameter 46a1 mentioned above. In the comparative example, the diameter 66a1 is 150 mm, and the maximum width 64c of the effective polishing area is also 150 mm.

[0092] Figure 7 In (A), the wafer 11 shown by the solid line is arranged such that the front end 11d of the wafer 11 overlaps with the front end of the polishing layer 66. At this time, the center 11c of the back surface 11b is located at the end of the opening 66a.

[0093] In contrast, Figure 7 The two wafers 11 shown by the dashed lines in (A) indicate the wafer 11 in the front position. Figure 7 (B) and the chip 11 located at the rear Figure 7 (C)).

[0094] Figure 7 (B) is a schematic cross-sectional view showing the wafer 11 and the polishing layer 66 being polished in the forward position. Figure 7 (C) is a schematic cross-sectional view showing the wafer 11 and the polishing layer 66 being polished in a rear position.

[0095] When using the polishing tool 60 to polish a wafer 11 with a diameter of 300 mm (12 inches), polishing is performed while the polishing tool 60 and the wafer 11 are moved relative to each other in the Y-axis direction, such as Figure 7 As shown in (B), the contact time between the effective grinding area and the vicinity of center 11c becomes longer, resulting in a depression near center 11c (refer to...). Figure 7 (The area enclosed by the dashed line in (B)).

[0096] In addition, such as Figure 7 As shown in (C), the outer periphery of the polishing layer 66 protrudes from the front end 11d of the wafer 11, thus forming a step difference on the polishing layer 66. Therefore, applying an abnormal load to the polishing layer 66 promotes its degradation (see Figure 1). Figure 7 (The area enclosed by the dashed line of (C)).

[0097] In contrast, as described above, in the first embodiment, the wafer 11 and the polishing tool 40 are positioned such that the center 11c of the back surface 11b of the wafer 11 is located in the opening 46a, and polishing is performed on the back surface 11b side. Therefore, excessive polishing near the center 11c of the wafer 11 can be prevented, and the formation of depressions near the center 11c can be suppressed.

[0098] Furthermore, in the first embodiment, the back side 11b side is polished while the front end 11d of the wafer 11 protrudes from the outer periphery of the polishing layer 46. Therefore, no step difference is formed on the polishing layer 46, and abnormal loads in the polishing layer 46 and deterioration are prevented.

[0099] Next, the second embodiment will be described. Figure 8 This is a bottom view of the polishing tool 50 according to the 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.

[0100] However, the base 52 is a circular plate without the opening 42c in the base 42, and the center 52d is exposed on the lower surface (one face) 52b of the fixed grinding layer 56, which is not covered by the grinding layer 56.

[0101] Furthermore, the polishing layer 56 does not have multiple segmented polishing pads 44, but is instead composed of annular polishing pads connected together. This aspect differs from the first embodiment, while other aspects are the same as the first embodiment.

[0102] Specifically, the maximum width 54c of the base 52 of the effective grinding area 54b in the radial direction 52f is smaller than the diameter 56a1 of the opening 56a of the grinding layer 56 (i.e., maximum width 54c < diameter 56a1).

[0103] For example, when the radius of wafer 11 is 150mm, the maximum width 54c of the radial direction 53f is 125mm and the diameter 56a1 is 200mm (i.e., the maximum width 54c < the radius of wafer 11 < the diameter 56a1).

[0104] In the second embodiment, excessive polishing near the center 11c of the wafer 11 can also be prevented, and the formation of depressions near the center 11c can be suppressed. In addition, the back surface 11b is polished in such a way that the front end 11d of the wafer 11 protrudes from the outer periphery of the polishing layer 56, thereby preventing the formation of step differences on the polishing layer 56, thus preventing the application of abnormal loads and the promotion of deterioration in the polishing layer 56.

[0105] In addition, the structure and method of the above embodiments can be appropriately modified and implemented as long as they do not depart from the scope of the purpose of the present invention.

Claims

1. A polishing method, comprising polishing a wafer using a polishing apparatus. The grinding device has the following features: A chuck stage that can rotate while holding the wafer; and The grinding unit has a spindle on which a grinding tool is mounted, which grinds the wafer held by the retaining surface of the chuck stage. Its features are, This grinding tool has the following features: A circular, plate-shaped base; and An annular abrasive layer is fixed to one surface of the base and includes an opening located at the center of the base in the diametrical direction and having a predetermined diameter. The maximum width of the effective polishing area of ​​the polishing layer in the radial direction of the substrate is smaller than the radius of the wafer, and the radius of the wafer is smaller than the diameter of the opening. The grinding method has the following steps: The holding process utilizes this holding surface to hold the wafer; and In the polishing process, the wafer and the polishing tool are positioned such that a portion of the wafer's outer periphery always protrudes from the outer periphery of the polishing layer and the center of the wafer is always located within the opening of the polishing layer. The polishing tool is rotated around the spindle while the wafer is polished. The maximum width of the effective grinding area is less than the diameter of the opening in the grinding layer.

2. The grinding method according to claim 1, characterized in that, In this polishing process, the polishing tool and the wafer are moved relative to each other along the diameter direction of the polishing tool passing through the center of one face of the wafer.

3. A polishing tool, used when polishing a wafer, characterized in that, This grinding tool has the following features: A circular, plate-shaped base; and An annular abrasive layer is fixed to one surface of the base and includes an opening located at the center of the base in the diametrical direction and having a predetermined diameter. The maximum width of the effective grinding area of ​​the grinding layer in the radial direction of the base is smaller than the diameter of the opening. When polishing the wafer using the polishing tool, the wafer and the polishing tool are positioned such that a portion of the outer periphery of the wafer always protrudes from the outer periphery of the polishing layer and the center of the wafer is always located in the opening of the polishing layer, while the polishing tool is rotated to polish the wafer.

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