US20070066192A1

US20070066192A1 - Wafer-edge polishing system

Info

Publication number: US20070066192A1
Application number: US11/523,613
Authority: US
Inventors: Kenji Kumahara
Original assignee: Elpida Memory Inc
Current assignee: Micron Memory Japan Ltd
Priority date: 2005-09-21
Filing date: 2006-09-20
Publication date: 2007-03-22
Also published as: JP2007088143A

Abstract

A wafer-edge polishing device includes a buff member for polishing a semiconductor wafer, and a dresser for dressing the buff member, wherein the dresser opposes the buff member with an intervention of the semiconductor wafer. A wafer mount mounting thereon the semiconductor wafer and the dresser are respectively movable toward and from the buff member. The contact pressure between the wafer and the buff member as well as between the buff member and the dresser is fixed. The dresser performs in-situ dressing concurrently with polishing of the wafer by the buff member.

Description

BACKGROUND OF THE INVENTION

(a) Field of the Invention
The present invention relates to a wafer-edge polishing system and, more particularly, to the improvement of a wafer-edge polishing system for polishing the edge portion of a wafer.
(b) Description of the Related Art
Semiconductor devices are manufactured by using a wafer such as a single-crystal silicon wafer or compound semiconductor wafer, on which oxide films, nitride films, carbide films, polycrystalline films, metallic films etc. are formed by sputtering technique, CVD technique and the like. The materials configuring those films may be deposited on the edge of the semiconductor wafer and the vicinity thereof. The materials or films deposited on the edge portion of the wafer are unnecessary and often peeled off from the edge portion of the wafer during transportation of the wafer between different systems, such as between a cleaning system and a deposition system. If the deposited materials are peeled off from the wafer, the deposited materials may be a crucial contamination source against the product semiconductor devices. Thus, deposited materials should be removed using a wafer-edge polishing system at any time if desired.
The wafer-edge polishing system includes a cylindrical buff unit onto which a buff member such as made of polyurethane foam or rigid polyurethane resin is attached. Patent Publication JP-1995-40214A describes a wafer-edge polishing system, which is shown in FIG. 5. The wafer-edge polishing system may be referred to merely as “polishing system” hereinafter.
In FIG. 5, the polishing system includes a cylindrical buff member 31 which is rotatable with respect to the central axis 31 a thereof. A slurry supply nozzle not shown is provided in the vicinity of the buff member 31. A semiconductor wafer 40 is pressed against the cylindrical surface of the buff member 31 at the edge of the semiconductor wafer 40. The semiconductor wafer 40 is slanted upward and downward, with the edge of the semiconductor wafer 40 being fixed at the contact point of the cylindrical surface of the buff member 31, for polishing the entire edge portion of the semiconductor wafer 40.
Patent publication as described above also shows another buff member, which is shown in FIG. 6. FIG. 7 shows the enlarged sectional view of the vicinity of the contact portion of the buff member 32 shown in FIG. 6. The buff member 32 is rotated with respect to the central axis 32 a thereof, and a slurry supply nozzle 34 supplies a slurry or polishing agent onto the vicinity of a groove 32 b configuring the contact portion of the buff member 32. The groove 32 b has a shape fitted to the edge portion of the semiconductor wafer 40, thereby allowing the semiconductor wafer 40 not to be slanted during the polishing.
The slurry or polishing agent generally includes minute silica particles dispersed in an alkali or acidic liquid. The buff member configured by polyurethane foam or polyurethane resin has a large number of minute cells (blowholes) on and inside the buff member. The minute cells assist the buff unit to retain thereon the slurry, thereby improving the polishing efficiency of the buff member.
It is noted that polished particles peeled off from the wafer or contaminated slurry including the polished particles may enter the minute cells on the buff unit after an iterated polishing treatment, thereby clogging the minute cells. The clogging of the minute cells prevents new slurry from entering the minute cells to lower the polishing efficiency of the buff member. Thus, the buff unit should be replaced by a new buff unit having minute cells not clogged by the polished particles or contaminated slurry, to thereby improve the polishing efficiency. The replacement of the buff unit reduces the through-put of the polishing treatment however.

SUMMARY OF THE INVENTION

In view of the above problems in the conventional techniques, it is an object of the present invention to provide a wafer-edge polishing system which is capable of improving the polishing efficiency, by reducing the frequency of replacement of the buff unit in the polishing device to improve the through-put of manufacturing semiconductor devices and reduce the cost for the buff unit.
The present invention provides a wafer-edge polishing system including: a wafer mount for mounting thereon a wafer; a polishing device movable toward and from the wafer mount and having a buff member for polishing an edge portion of the wafer mounted on the wafer mount; a dresser movable toward and from the polishing device for dressing the buff member of the polishing device.
In accordance with the wafer-edge polishing system of the present invention, the buff member having thereon polished particles or contaminated slurry can be dressed by the dresser without replacement of the buff unit within the polishing system, thereby reducing the frequency of the replacement of the buff unit, improving the polishing efficiency of the polishing system and improving the through-put of manufacturing the semiconductor devices.
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 top plan view of a polishing system according to an embodiment of the present invention.
FIG. 2 is a side view of the polishing system of FIG. 1.
FIG. 3 is a side view of the buff unit in the polishing system shown in FIG. 1.
FIG. 4 is a perspective view showing the buff unit of FIG. 3 before being fixed onto the base pole.
FIG. 5 is a perspective view of a conventional polishing system.
FIG. 6 is a perspective view of another conventional polishing system.
FIG. 7 is an enlarged sectional view of a portion of the another conventional polishing system.

PREFERRED EMBODIMENT OF THE INVENTION

Now, the present invention is more specifically described with reference to accompanying drawings, wherein similar constituent elements are designated by similar or related reference numerals.
FIG. 1 shows a polishing system according to an embodiment of the present invention in a top plan view thereof, and FIG. 2 shows the polishing system in a side view thereof. The polishing system, generally designated by numeral 100, includes a wafer mount 15 for mounting thereon a semiconductor wafer 40, a pair of buff units 11 a, 11 b each having a buff member 18 for polishing the edge portion of the semiconductor wafer 40, a dresser 12 for dressing the buff members 18 of the buff units 11 a, 11 b, a pair of slurry supply nozzles 13 a, 13 b for supplying a slurry to the contact portion between the edge of the semiconductor wafer 40 and the buff members 18, and a pair of water nozzles 14 a, 14 b for supplying pure water to the contact portion between the buff members 18 and the dresser 12.
The buff members 18 are rotatably fixed onto the top of base poles 16 disposed for the buff units 11 a, 11 b. The dresser 12 is also rotatably fixed onto the top of a base pole 17 disposed for the dresser 12. As shown in FIG. 2, the semiconductor wafer 40 rotates in the clockwise direction, the buff units 11 a, 11 b rotate in the clockwise direction, and the dresser 12 rotates in the counter-clockwise direction.
In the polishing system 100, the edge portion of the semiconductor wafer 40 mounted on the wafer mount 15 is polished by the buff members 18, which are in turn dressed by the dresser 12 at the same time, whereby the dresser 12 assists the cylindrical buff members 18 to polish the edge portion of the semiconductor wafer 40.
The semiconductor wafer 40 is fixed onto the wafer mount 15 by using vacuum contact. The wafer mount 15 is associated with a displacement/rotation mechanism including an air cylinder, a stepping motor and a variable-speed motor, which are not specifically shown in the figure. Thus, the wafer mount 15 is movable in the X- and Z-directions shown in FIG. 2, and is rotatable with respect to the central axis thereof. The air cylinder is provided with a pressure sensor for detecting the internal pressure, based on which the contact pressure between the semiconductor wafer 40 and the buff members 18 is controlled at a fixed pressure.
The dresser 12 is made of a cylindrical stainless steel plate, onto which minute synthetic diamond particles are fixed by an electro-depositing technique. The dresser 12 is subjected to shaping for fixing the same onto the base pole 17 for the dresser 12. The base pole 17 for the dresser 12 is also associated with displacement/rotation mechanism including an air cylinder, a stepping motor and a variable-speed motor, similarly to the wafer mount 15, which are not specifically shown in the drawings. Thus, the base pole 17 for the dresser 12 is movable in X- and Z-directions and rotatable with respect to the central axis thereof. The air cylinder is provided with a pressure sensor for detecting the internal pressure, based on which the contact pressure between the dresser 12 and the buff members 18 is controlled at a fixed pressure.
The slurry supply nozzles 13 a, 13 b are disposed at the location and angle such that the slurry used as the polishing agent is directly supplied onto the contact portion between the wafer 40 and the buff members 18. Similarly, the water nozzle 14 a, 14 b are disposed at the location and angle such that the pure water is directly supplied onto the contact portion between the dresser 12 and the buff members 18.
Since the buff units 11 a, 11 b have similar structures, materials and dimensions, the configuration and function of buff unit 11 b alone will be described hereinafter with reference to FIG. 3. FIG. 3 is a side view of buff unit 11 b. Buff unit 11 b includes the buff member 18 having a substantially cylindrical shape, a strut 19 penetrating the buff member 18 at the central bore thereof, an insertion member 21 formed at the bottom of the strut 19, and a boss 20 protruding radially outside the insertion member 21.
The buff member 18 is of an axial symmetry. The buff member 18 is made of polyurethane foam having a hollow cylindrical shape, and the outer cylindrical surface of the buff member 18 has a depression at the central portion thereof as viewed in the axial direction. Thus, the buff member 18 has a U-shaped sidewall, as viewed in the horizontal direction. The U-shaped sidewall includes roughly a top flange-shaped portion, an upper curved portion 18 a of a truncated corn, a central depression, a lower curved portion 18 b of a truncated corn, and a bottom flange-shaped portion. The buff member 18 may be made of rigid polyurethane resin instead.
Polishing treatment of semiconductor wafers 40 abrades the surface of the buff member 18, thereby necessitating a regular replacement of the buff unit 11 b as an expendable part. FIG. 4 is a perspective view of buff unit 11 b before being mounted on top of the base pole 16. The buff unit 11 b is fixed onto the base pole 16 by the steps of aligning the boss 20 with a slot 22 of the base pole 16, inserting the insertion member 21 into a hole 23 of the base pole 16, and fixing buff unit 11 b on the base pole 16 by using thrust screws 24. Removal of buff unit 11 b is effected in the order reversed from the recited order.
Operation of the polishing system of FIG. 1 will be described hereinafter with reference to FIGS. 1 to 3 in separate steps. In a first step, a semiconductor wafer 40 is delivered from a wafer cassette etc. by a wafer transportation system onto top of the wafer mount 15. The bottom surface of the semiconductor wafer 40 is absorbed by the top of the wafer mount 15 using vacuum contact, whereby the semiconductor wafer 40 is fixed on the wafer mount 15. In a second step, the slurry supply nozzles 13 a, 13 b supply the slurry as a polishing agent in a specified amount, and the buff units 11 a, 11 b are rotated by the base poles 16 at a specified rotational speed.
In a third step, the dresser 12 is rotated by the base pole 17 at a specified rotational speed, and then moves in the X-direction to contact the buff members 18 of the buff units 11 a, 11 b. The contact pressure of the dresser 12 with respect to the buff members 18 is controlled by a pressure control mechanism including the air cylinder of the base pole 17. In a fourth step, the semiconductor wafer 40 is rotated with respect to the central axis of the wafer mount 15 and moved in the X-direction to contact the buff members 18 of the buff units 11 a, 11 b at the edge of the semiconductor wafer 40. The contact pressure of the edge of the semiconductor wafer 40 with respect to the buff members 18 is controlled by the pressure control mechanism including the air cylinder of the wafer mount 15. Thus, the semiconductor wafer 40, buff units 11 a, 11 b and dresser 12 are rotated by separate rotation mechanisms, and both the wafer 40 and dresser 12 are thrust or pressed against the buff members 18 at a specified contact pressure.
In a fifth step, the semiconductor wafer 40 is moved in the X- and Z-directions while being rotated, with the edge of the wafer 40 being moved along and polished by the U-shaped sidewall of the buff members 18. The top and bottom bevels of the edge of the wafer 40 are polished by the curved portions 18 a, 18 b of the U-shaped sidewall of the buff members 18. The dresser 12 is also moved in the X- and Z-directions while being rotated, with the edge of the dresser 12 moving along and abrading the U-shaped sidewall of the buff members 18. Abrasion of the buff members 18 by the dresser 12 allows the buff members 18 to expose a new surface thereof and removes the clogging of the minute cells by the polished particles or contaminated slurry, whereby the new surface of the buff members 18 is exposed at any time.
The semiconductor wafer 40 and dresser 12 periodically move in the Z-direction during polishing and dressing, wherein the periodical movement of he semiconductor wafer 40 in the Z-direction has a period same as that of the periodical movement of the dresser 12 in the Z-direction. In addition, the periodical movement of the semiconductor wafer 40 is deviated by half the period in the phase from the phase of the periodical movement of the dresser 12. For example, when the wafer 40 is located at the upper curved portion 18 a of the buff members 18, the dresser 12 is located at the lower curved portion 18 b of the buff members 18. On the other hand, when the wafer 40 is located at the lower curved portion 18 b of the buff members 18, the dresser 12 is located at the upper curved portion 18 a of the buff members 18.
Employment of such a locational relationship between the wafer 40 and the dresser 12 prevents the wafer 40 and the dresser 12 from being located at the same position of the buff members 18 as viewed in the Z-axis direction. This avoids the situation wherein the dresser 12 removes the new slurry from the buff members 18 in a period before the buff members 18 use the new slurry for polishing the wafer 40, the new slurry being supplied from the slurry supply nozzles 13 a, 13 b in the same period. Thus, the new slurry stays at any time between the wafer 40 and the buff members 18, thereby preventing reduction in the polishing efficiency.
After the edge of the semiconductor wafer 40 is polished, the polishing process advances to a sixth step, wherein the semiconductor wafer 40 is transferred by a wafer transportation system to a wafer cleaning system, wherein the remaining slurry is removed. Thereafter, the semiconductor wafer 40 is returned to the wafer cassette. A next semiconductor wafer is then supplied to the wafer mount 15, and the water nozzles 14 a, 14 b supply pure water to the contact portion between the buff members 18 and the dresser 12, whereby the buff members 18 are dressed by the dresser 12 for cleaning of the surface. Those first through sixth steps are iterated for polishing the edge portion of a number of semiconductor wafers 40.
In the present embodiment, the dresser is installed in the polishing system which polishes the edge of semiconductor wafers, whereby both the polishing and dressing are performed in a single process. This prevents clogging of the minute cells on the surface of the buff members, the clogging being caused by the polished particles or contaminated slurry and causing reduction in the polishing efficiency. Thus, the present embodiment achieves a higher polishing efficiency and thus a higher through-put in the polishing.
Removal of the clogging from minute cells on the surface of the buff members by the in-situ dressing eliminates necessity of the replacement of buff units caused by the clogging, thereby reducing the frequency of the replacement of the buff units. This improves the operation rate of the polishing system.
In the configuration of the present embodiment, dressing of the buff members gradually reduces the diameter of the buff members. However, the control of the contact pressure between the semiconductor wafer and the buff members as well as between the buff members and the dresser allows a continuous operation of the polishing and dressing irrespective of the reduction in the diameter of the buff members.
In the configuration of the present embodiment, the in-situ dressing treatment is used, wherein the dressing is concurrently performed with the polishing. The in-situ dressing treatment allows a plurality of semiconductor wafers to be polished in a continuous processing without replacement of buff units, thereby achieving a higher through-put in the polishing. However, this is not essential to the present invention, and an ex-situ dressing may be performed in the present invention. In this case, a single ex-situ dressing may be inserted at the interval between polishing of a wafer and polishing of another wafer, or between polishing of a plurality of wafers and polishing of another plurality of wafers.
Since the above embodiments are described only for examples, the present invention is not limited to the above embodiments and various modifications or alterations can be easily made therefrom by those skilled in the art without departing from the scope of the present invention. For example, the polishing system of the present invention may be used for polishing a wafer other than a semiconductor wafer. The term “wafer” as used herein means a relatively thin and flat object, such as a disk or disk-like plate.

Claims

1. A wafer-edge polishing system comprising:

a wafer mount for mounting thereon a wafer;

a polishing device movable toward and from said wafer mount and having a buff member for polishing an edge portion of the wafer mounted on said wafer mount;

a dresser movable toward and from said polishing device for dressing said buff member of said polishing device.

2. The wafer-edge polishing system according to claim 1, wherein said polishing by said polishing device and said dressing by said dresser are performed concurrently.

3. The wafer-edge polishing system according to claim 1, wherein said polishing by said polishing device and said dressing by said dresser are performed alternately.

4. The wafer-edge polishing device according to claim 1, wherein said wafer mount, said buff member and said dresser are capable of being rotated with respect to respective central axes thereof independently from one another.

5. The wafer-edge polishing device according to claim 4, wherein said buff member has a cylindrical surface capable of being in contact with said wafer and said dresser, said wafer mount and said dresser move periodically in a direction parallel to said central axes at least in a range wherein said wafer and said dresser are capable of being in contact with said cylindrical surface, and periodical movement of said wafer mount has a period same as a period of periodical movement of said dresser and a phase opposite with respect to a phase of said periodical movement of said dresser.

6. The wafer-edge polishing device according to claim 1, further comprising a pressure controller for controlling the contact pressure between the wafer and said buff member and/or the contact pressure between said dresser and said buff member.