US20070197144A1

US20070197144A1 - Wafer polishing apparatus

Info

Publication number: US20070197144A1
Application number: US11/702,148
Authority: US
Inventors: Kenji Kumahara
Original assignee: Elpida Memory Inc
Current assignee: Micron Memory Japan Ltd
Priority date: 2006-02-06
Filing date: 2007-02-05
Publication date: 2007-08-23
Also published as: JP2007208184A

Abstract

A wafer polishing apparatus includes a wafer mount mounting thereon a wafer for rotation, a pair of bell-shaped buff units opposing each other and rotated to polish the periphery of the wafer. The buff units each have an edge-surface polishing section having a shape adapted to half the edge surface of the wafer periphery as divided in the thickness direction of the wafer, and a notch polishing section having a shape corresponding to half the edge surface of a notch of the wafer as divided in the thickness direction.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a wafer polishing apparatus and, more particularly, to a wafer polishing apparatus that polishes a wafer periphery including a notch.
2. Description of the Related Art
In manufacture of a semiconductor device, a variety of films, such as an oxide film, a nitride film, a carbide film, a polycrystalline film or a metallic film are deposited on a semiconductor wafer (hereinafter, referred to merely as “wafer”) configuring the substrate of the semiconductor device. The above films are deposited inadvertently at the periphery or edge surface of the wafer. The portion of the film deposited on the edge surface of the wafer is easily peeled-off from the wafer to generate undesirable particles. The undesirable particles generated in the process for manufacturing the semiconductor device may be adhered onto a device area formed on the wafer surface to cause a short-circuit failure between interconnect lines, for example, resulting in degradation of the product yield in the manufacture of the semiconductor device. Therefore, after the filming process, the, edge surface of the wafer is polished to remove the film formed on the edge surface.
FIG. 6A shows a typical wafer in a top plan view. A V-character shaped or circular-arc-shaped notch 62 is formed on an edge portion of the wafer by cutting the wafer 60 from the circumference of the wafer 60 toward the inner circumference thereof In manufacture of the semiconductor chips on the wafer, the notch 62 is used as a reference point for detecting the position or direction of the wafer 60. A peel-off of the film deposited on the, wafer periphery may easily occur, especially at the notch 62. Therefore, a polishing process for the wafer periphery should be applied onto the circumferential edge surface of the wafer including the notch 62. FIG. 6B is a sectional view taken along line b-b in FIG. 6A. As shown in FIG. 6B, the wafer 60 has a symmetric structure in the thickness direction thereof, and has a bulge where the central portion of the wafer 60 in the thickness direction moderately protrudes from the top-side and bottom-side portions of the wafer periphery 61 including the notch 62.
Patent Publication JP-2000-317790A describes a conventional wafer polishing apparatus that polishes the wafer periphery including the notch 62. FIG. 7 is a side view showing the configuration of the wafer polishing apparatus described in this publication. The wafer polishing apparatus, generally designated at numeral 70, includes a wafer mount 71 that mounts thereon a wafer and rotates the wafer, an edge-surface polishing device 72 that polishes the edge surface of the wafer periphery 61, and a notch polishing device 73 that polishes the edge surface of the notch 62 of the wafer 60. The wafer mount 71 includes a wafer suction pad 74 that fixes the wafer 60 by suction, a wafer rotation unit 75 that rotates the wafer suction pad 74, and a wafer tilting unit 76 that tilts the wafer rotation unit 75.
The edge-surface polishing device 72 has a cylindrical abrasive cloth (buff) 78 that rotates about the rotational axis 77 which is perpendicular to the plane including the wafer 60. A groove 79 having a cross section corresponding to the section of the wafer periphery 61 is formed on the surface of the buff unit 78. In a process of polishing the wafer periphery 61, the wafer 60 and buff unit 78 are rotated at respective predetermined rotational speeds, and the buff unit 78 is pressed against the wafer periphery 61 at the groove 79 thereof, while abrasive slurry is supplied onto the groove 79, to polish the wafer 60 along the circumferential direction thereof. In this state, the wafer 60 is tilted with respect to the groove 79 by the operation of the wafer tilting unit 76, to thereby polish the wafer periphery 61 along the thickness direction from the top-side edge toward the bottom-side edge of the wafer periphery.
The notch polishing device 73 has a disk-shaped buff unit 80 that rotates in a vertical plane, which extends perpendicular to the plane including the wafer 60 and in the radial direction of the wafer 60. The buff unit 80 has an edge portion adapted to the shape of the notch 62. In a process of polishing the notch 62, while the slurry is supplied, the buff unit 80 is rotated and pressed against the notch 62 without rotating the wafer 60. In this state, the wafer 60 is tilted by the operation of the wafer tilting unit 76 to thereby polish the notch 62 along the thickness direction thereof from the top-side edge to the bottom-side edge of the wafer.
By reducing the occupied area of individual semiconductor manufacturing apparatuses used for the process for manufacturing the semiconductor device, it is possible to reduce the time length required for transferring the wafer 60 to thereby improve the production efficiency. However, in the case of the conventional wafer polishing apparatus as described above, the edge-surface polishing device 72 that polishes the wafer periphery 61 and notch polishing device 73 that polishes the notch 62 have to be separately arranged in the area adjacent to the wafer 60, with the result that the size of the entire apparatus is inevitably increased. Thus, it is difficult to reduce the, occupied area for the wafer polishing apparatus in the conventional technique.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention to provide a wafer polishing apparatus that polishes the wafer periphery including a notch thereof and is capable of reducing the occupied area for the wafer polishing apparatus for improving the production efficiency.
The present invention provides a wafer polishing apparatus including: a wafer mount for mounting thereon a wafer and rotating the wafer about a rotational axis; at least one buff unit having a rotational symmetry and rotating in a rotational axis parallel to the rotational axis of the wafer mount; and a moving unit for moving the wafer relative to the buff unit, the buff unit including a edge-surface polishing section having a shape adapted to polishing an edge surface of the wafer and a notch polishing section having a shape adapted to polishing a notch of the wafer.
In accordance with the wafer polishing apparatus of the present invention, the buff unit including the edge-surface polishing section and the notch polishing section allows the polishing apparatus to have a smaller occupied area. It is to be noted that the moving unit may move any of the wafer and the buff unit.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the configuration of a wafer polishing apparatus according to an embodiment of the present invention;
FIG. 2 is an exploded perspective view showing the configuration of the buff unit and buff fixing members shown in FIG. 1;
FIG. 3 is a sectional view of the buff unit taken along the direction in which the fitting groove shown in FIG. 2 extends;
FIG. 4 is a flowchart showing the procedure of a wafer polishing process using the wafer polishing apparatus of FIG. 1;
FIGS. 5A to 5D are side views showing the positional relationship between the wafer and the buff unit during polishing the wafer at respective positions thereof;
PIG. 6A is a top plan view of a typical wafer, and FIG. 6B is a sectional view of the typical wafer taken along line b-b in FIG. 6A; and
FIG. 7 is a side view showing the configuration of a conventional wafer polishing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a sectional view showing the configuration of a wafer polishing apparatus according to an embodiment of the present invention. The wafer polishing apparatus, generally designated at numeral 10, includes a wafer mount 11 for mounting and rotating thereon a wafer 60 in a horizontal plane (XY-plane), and a polishing section 12 including a pair of bell- shaped buff units 21 a and 21 b opposing each other in the Z-axis direction for polishing the periphery of the wafer 60. The buff units 21 a and 21 b configure a body of the polishing section 12 in the present embodiment.
The wafer mount 11 includes a wafer holding unit that holds the wafer 60, a rotation unit that rotates the wafer holding unit about a rotational axis 13 extending parallel to the Z-axis, a Z-axis movement unit that moves the wafer holding unit in the Z-axis direction, and an X-axis movement unit that moves the wafer holding unit in the X-axis direction, i.e., direction from the wafer mount 11 to the polishing section 12. The wafer holding unit mounts the wafer 60 by utilizing a suction force, and holds the wafer 60 at the bottom surface of the wafer 60.
The rotation unit, Z-axis movement unit, and X-axis movement unit are driven by an adjustable-speed motor, a stepping motor, and an air cylinder, respectively. The X-axis movement unit includes a pressure sensor that detects the pressure in the air cylinder and a pressure control member that controls the pressure in the air cylinder based on the pressure detected by the pressure sensor. By controlling the pressure in the air cylinder, a pressing force pressing the wafer 60 against the buff units 21 a, 21 b in the X-direction can be adjusted.
In the polishing section 12, the pair of buff units 21 a and 21 b are disposed in a plane symmetry with respect to each other and outside the area of the wafer 60 in the radial direction thereof. The buff units 21 a and 21 b each have a rotational symmetry with respect to the rotational axis 14 thereof. The buff units 21 a and 21 b each include a buff body 22 a, 22 b and a buff- body support 23 a, 23 b tat supports the buff body 22 a, 22 b. The buff body 22 a, 22 b is made of polyurethane foam shaped by integral molding, and the surface thereof serves as a polishing surface. The buff body 22 a, 22 b has a bell-like, or dome-like shape including a narrow tip portion 25 a, 25 b, a middle curved portion 24 a, 24 b, and a substantially cylindrical bottom end. The middle curved portion 24 a, 24 b extends from the narrow tip portion 25 a, 25 b in a smoothly stepped fashion and has a radius larger than the radius of the narrow tip portion 25 a, 25 b and smaller than the radius of the substantially cylindrical bottom end. The substantially cylindrical bottom end of the buff body 22 a, 22 b supports the middle curved portion 24 a, 24 b and is supported by the buff-body support 23 a) 23 b. The narrow tip portions 25 a, 25 b of both the buff bodies 22 a and 22 b are disposed opposite to each other with an intervention of the plane including the wafer 60.
The middle curved portion 24 a, 24 b of the buff body 22 a, 22 b is used as an edge polishing section for polishing the periphery of the wafer 60, and the narrow tip portion 25 a, 25 b of the buff body 22 a, 22 b is used as a notch polishing section for polishing the notch of he wafer 60. The edge polishing section 24 a, 24 b has a shape adapted to the shape of the half portion of the edge of the wafer 60 as divided in the thickness direction. The notch polishing section 25 a, 25 b has a shape adapted to the half portion of the notch of the wafer 60 as divided in the thickness direction. The notch polishing section 25 a, 25 b has a small diameter and is adapted to the top-side or bottom-side edge of the notch of the wafer.
The buff units 21 a and 21 b are fixed, at the bottom portion of the buff-body supports 23 a and 23 b, onto the buff fixing members 26 a and 26 b. The buff fixing members 26 a and 26 b are rotatably supported by a supporting unit 28 by way of bearings 27 a and 27 b. Further, the buff fixing members 26 a and 26 b are coupled to rotating units 29 a and 29 b that rotate the buff fixing members 26 a and 26 b, respectively, about the rotational axis 14. The rotating units 29 a and 29 b are configured by a pulse motor, and control the rotational direction and rotational speed of the buff units 21 a and 21 b independently of each other.
Four nozzles 30 for supplying slurry or pure water to the buff units 21 a and 21 b are provided to oppose the wafer 60 with an intervention of the buff units 21 a and 21 b, extending from and being supported by the supporting unit 28 of the polishing section 12. The four nozzles 30 are arranged so as to correspond to the edge polishing sections 24 a and 24 b and notch polishing sections 25 a and 25 b of the buff units 21 a and 21 b. A slurry supply system for supplying slurry, a pure water supply system for supplying pure water, and a supply system switching section for switching the supply system to be coupled to the nozzles 30 are provided in the supporting unit 28.
FIG. 2 is an enlarged perspective view of the buff unit 21 a (and 21 b) and the buff fixing member 26 a (26 b). Formed at the top portion of the buff fixing members 26 a is a protrusion 43 including a rectangular prism portion 41 having a substantially rectangular solid shape and a cylindrical portion 42 having a substantially circular cylindrical shape and formed on the rectangular prism portion 41 and around the rotational axis 14. A fitting grove 44 to be fitted to the protrusion 43 is formed in the bottom portion of the buff-body support 23 a. The rectangular prism portion 41 and part of the fitting portion 44 (rectangular solid slot 47) to be fitted to the rectangular prism portion 41 are formed for preventing idle running of the buff unit 21 a.
Three screw holes 45 are formed in the buff-body support 23 a. The screw holes 45 penetrate from the surface of the buff-body support 23 a to the fitting groove 44 formed at the center of the buff-body support 23 a along the radial direction thereof. The three screw holes 45 are formed at an interval of 120° with respect to the rotational axis 14.
After the polishing apparatus is used for polishing a specific number of wafers or polishing for a specific time length, the surface of the buff body 22 a, 22 b is clogged with foreign matter such as polished particles or has a larger roughness, with the result that the polishing capability is deteriorated. Therefore, the buff body 22 a, 22 b has to be replaced with a new one periodically. In the present embodiment, replacement of the buff body 22 a, 22 b can be achieved by replacement of the buff units 21 a and 21 b.
As shown in FIG. 2, when the buff unit 21 a (21 b) is fitted to the buff fixing members 26 a (26 b), positioning is performed such that the side portion of the fitting groove 44 of the buff opposes the cylindrical portion 42 of the buff fixing members, and buff unit 21 a is moved toward the buff fixing members 26 a to allow the protrusion 43 to be inserted into the fitting groove 44. After the insertion is completed so that the rotational axis 14 of the buff unit 21 a is aligned with the rotational axis 14 of the buff fixing members 26 a, the buff unit 21 a is pressed against the buff fixing members 26 a along the rotational axis 14 to allow the protrusion 43 to be fitted to the fitting groove 44.
Thereafter, screws 46 are inserted into the screw holes 45 to press the cylindrical portion 42 for fixing. The reverse procedure may be used to remove the buff unit 21 a (21 b) from the buff fixing members 26 a (26 b). According to the above procedure, there is no need to disassemble parts of the polishing section 12 such as the buff fixing member 26 a, 26 b when the buff units 21 a and 21 b are replaced with new ones, whereby the replacement of the buff units 21 a and 21 b can be performed efficiently.
FIG. 3 shows a sectional view of the buff unit 21 a (21 b) taken along the direction in which the fitting groove 44 shown in FIG. 2 extends. The fitting groove 44 is configured by a rectangular solid slot 47 that receives therein the rectangular prism portion 41 of the buff fixing member 26 a (26 b) and a cylindrical slot 48 that receives therein the cylindrical portion 42 of the buff fixing member 26 a(26 b).
Formed on the surface of the buff-body support 23 a is a protrusion 53 including a cylindrical portion 51 having a center aligned with the rotational axis 14 and a rectangular prism portion 52 having a substantially rectangular solid shape that protrudes outward from the side surface of the cylindrical portion 51. A fitting grove 56 including a cylindrical slot 54 to be fitted to the cylindrical portion 51 and a rectangular prism slot 55 to be fitted to the rectangular prism portion 52 is formed at the bottom portion of the buff body 22 a. The rectangular prism portion 52 and rectangular prism slot 55 are formed for preventing idle running of the buff body 22 a.
FIG. 4 is a flowchart showing the procedure of a wafer polishing process using the wafer polishing apparatus 10 of FIG. 1. The wafer 60 received in a wafer cassette is transferred onto the wafer mount 11 by way of a wafer transfer system. The wafer mount 11 mounts thereon the wafer 60 by sucking the bottom surface of the wafer 60 to fix the position thereof onto the wafer mount 11 (step S11).
Thereafter, slurry is supplied from the nozzles 30 at a specific flow rate, and buff units 21 a and 21 b are rotated in a predetermined. rotational direction and at a predetermined rotational speed by way of the rotating units 29 a and 29 b (step S12). Subsequently, the wafer mount 11 moves the wafer 60 in the X-axis direction while rotating the wafer 60 to allow the wafer periphery 61 to be in contact with the edge-surface polishing section 24 b, as shown in FIG. 5A. In this state, the wafer 60 is moved along the contour of the edge-surface polishing section 24 b in the X-axis and Z-axis directions, and the edge surface of the wafer periphery 61 is polished from the top-side edge toward the middle-portion edge in the thickness direction of the wafer 60 (step S13).
Thereafter, the wafer mount 11 moves the wafer 60 in the X-axis and Z-axis directions while rotating the wafer 60 to allow the wafer periphery 61 to be in contact with the edge-surface polishing section 24 a, as shown in FIG. 5B. In this state, the wafer 60 is moved along the contour of the edge-surface polishing section 24 a in the X-axis and Z-axis directions, and the edge surface of the wafer periphery 61 is polished from the bottom-side edge toward the middle-portion edge of the wafer (step S14). The pressing force for pressing the wafer 60 against the edge- surface polishing sections 24 a and 24 b can be controlled by the pressure control member of the X-axis movement unit in steps S13 and S14.
Then, the rotation of the wafer 60 is stopped once, and an optical position sensor (not shown) is used to perform positioning of the notch 62 by rotating the wafer 60 such that the center of the, notch 62 is aligned with the rotational axis 14 of the buff units 21 a and 21 b (step S15).
Subsequently, the wafer mount 11 moves the wafer 60 in the X-axis and Z-axis directions to allow the notch 62 to be in contact with the notch polishing section 25 b, as shown in FIG. 5C. In this state the wafer 60 is moved in the X-axis and Z-axis directions step by step, and the edge surface of the notch 62 is polished from the top-side edge toward the middle-portion edge of the notch 62 in the thickness direction (step S16).
Thereafter, the wafer mount 11 moves the wafer 60 in the X-axis and Z-axis directions to allow the notch 62 to be in contact with the notch polishing section 25 a, as shown in FIG. 5D. In this state, the wafer 60 is moved the in X-axis and Z-axis directions step by step, and the edge surface of the notch 62 is polished from the bottom-side edge toward the middle-portion edge of the notch 62 in the thickness direction (step S17). The pressing force for pressing the wafer 60 against the notch polishing sections 25 a and 25 b can be controlled by the pressure control member of the X-axis movement unit in steps S16 and S17.
Subsequently, the supply of slurry from the nozzle 30 is stopped, and the wafer 60 is moved in the X-axis direction away from the buff units 21 a and 21 b. Subsequently, the rotation of the wafer 60 is stopped, and fixation of the wafer 60 by the wafer mount 11 is released (step S18). Thereafter, the wafer transfer system moves the wafer 60 to a wafer cleaning system in the wafer polishing apparatus and performs a cleaning treatment to remove the attached slurry (step S19). Subsequently, the wafer 60 is received in the wafer cassette by the wafer transfer system, and a series of processing steps are completed.
After the buff units 21 a and 21 b are released from the wafer 60, pure water is supplied from the nozzles 30 to the surface of the buff units 21 a and 21 b until the polishing for the next wafer 60 is started to thereby perform dressing of the surface of the buff units 21 a and 21 b. The procedure shown in FIG. 4 is only an example, and various modifications may be made as desired.
In the wafer polishing apparatus 10 according to the present embodiment, the buff units 21 a and 21 b each include the edge polishing section 24 a, 24 b having a shape corresponding to the edge surface of the wafer periphery 61 and the notch polishing section 25 a, 25 b having a shape corresponding to the edge surface of the notch 62. The X-axis movement unit and Z-axis movement unit move the wafer 60 relative to the buff units 21 a and 21 b, thereby polishing the wafer periphery including the notch 62 along the edge surface thereof In the conventional polishing apparatus, the edge-polishing device and the notch polishing device are separately provided in the wafer polishing apparatus, whereby the wafer polishing apparatus has a large occupied area. In contrast, in the wafer polishing apparatus according to the above embodiment the configuration wherein the edge-surface polishing section and notch polishing section are provided as an integrated device allows the wafer polishing apparatus to have a smaller occupied area.
Further, in the polishing treatment along the thickness direction of the wafer periphery, the wafer 60 need not be tilted, differently from the case of the conventional wafer polishing apparatus 70 of FIG. 7. This eliminates the need to provide a wafer tilting unit that requires a large torque, thereby reducing the power dissipation of the wafer-edge polishing apparatus. Since it is not necessary to separately provide the edge-surface polishing buff and the notch polishing buff and since the pair of buff units 21 a and 21 b have the same design shape, it is possible to reduce the cost required for replacement of consumable supplies.
Although the buff unit is configured by the pair of buff units 21 a and 21 b in the above embodiment, the polishing section may be configured by a single buff unit so long as the buff unit has an edge-surface polishing section having a shape corresponding to the edge surface of the wafer periphery 61 and a notch polishing section having a shape corresponding to the edge surface of the notch 62. Further, the buff body 22 a, 22 b may be made of rigid urethane resin instead of the foam polyurethane.
Although the present invention has been described based on the preferred embodiment, the configuration of the wafer polishing apparatus according to the present invention is not limited to that described in the above embodiment, and various modification and alternation may be made without departing from the spirit and scope of the invention. Thus, any wafer polishing apparatuses obtained by such modification and alternation are also included in the scope of the invention.

Claims

1. A wafer polishing apparatus comprising:

a wafer mount for mounting thereon a wafer and rotating the wafer about a rotational axis;

at least one buff unit having a rotational symmetry and rotating in a rotational axis parallel to said rotational axis of said wafer mount; and

a moving unit for moving the wafer relative to said buff unit,

said buff unit including a edge-surface polishing section having a shape adapted to polishing an edge surface of the wafer, and a notch polishing section having a shape adapted to polishing a notch of the wafer.

2. The waver polishing apparatus according to claim 1, wherein said at least one buff unit include a pair of buff units disposed in a plane symmetry with each other.

3. The wafer polishing apparatus according to claim 2, wherein said edge-surface polishing section has a shape adapted to polishing half said edge surface of the wafer in the thickness direction thereof and said notch polishing section has a shape adapted to half the surface of the notch in the thickness direction thereof.

4. The wafer polishing apparatus according to claim 1, wherein said moving unit moves the wafer in a first direction parallel to said rotational axis of said wafer mount and in a second direction normal thereto.

5. The wafer polishing apparatus according to claim 4, wherein said moving unit includes a stepping motor for moving said wafer in said first direction.

6. The wafer polishing apparatus according to claim 4, wherein said moving unit includes a pressing means for pressing the wafer against said buff unit at a controlled pressure.

7. The wafer polishing apparatus according to claim 1, wherein said buff unit includes a buff body made of polyurethane foam or rigid urethane.

8. The wafer polishing apparatus according to claim 1, further comprising a nozzle, opposing the wafer with an intervention of said buff unit, for supplying slurry onto a contact surface between the wafer and said buff unit.