Polishing apparatus

Abstract

The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer to form a flat surface thereon. The polishing apparatus includes a polishing table (20), a polishing tool (1) attached to an upper surface of the polishing table (20), and a fluid passage (40) having openings on the upper surface of the polishing table (20). The apparatus is operable to bring a workpiece (W) into sliding contact with the polishing tool (1) to polish the workpiece while supplying a polishing liquid onto the polishing tool (1). The polishing tool (1) is fixed to the polishing table (20) by a vacuum produced in the fluid passage (40).

Description

TECHNICAL FIELD

The present invention relates to a polishing apparatus, and more particularly to a polishing apparatus for polishing a workpiece such as a semiconductor wafer to form a flat surface thereon.

BACKGROUND ART

Planarizing a surface of a semiconductor device is becoming increasingly important in a semiconductor device fabrication process. One of the most important planarization techniques is chemical mechanical polishing (CMP). The chemical mechanical polishing is performed using a polishing apparatus. Specifically, a substrate, such a semiconductor wafer, is brought into sliding contact with a polishing surface while a polishing liquid containing abrasive particles such as silica (SiO₂) is supplied onto the polishing surface, so that the substrate is polished.

This kind of polishing apparatus comprises a polishing table having a cloth (polishing pad) attached to an upper surface thereof with an adhesive or the like, and a substrate holder, which is called a top ring or carrier head, for holding a semiconductor wafer. The polishing apparatus polishes a semiconductor wafer as follows. The substrate holder holds the semiconductor wafer and presses the semiconductor wafer against the polishing table at a predetermined pressure. At this time, a polishing liquid is supplied onto a polishing surface formed on an upper surface of the cloth, and the polishing table and the substrate holder are moved relative to each other to bring the semiconductor wafer into sliding contact with the polishing surface, whereby the semiconductor wafer is polished to have a flat and mirror-finished surface.

In the above-mentioned polishing apparatus, the cloth (polishing pad) on the turn table is replaced as follows. Firstly, the operation of the polishing apparatus is stopped, and the cloth is removed from the polishing table. Next, adhering substances, such as the adhesive, and the polishing liquid remaining on the polishing table are washed away, and then the polishing table is dried. Thereafter, a new cloth is attached directly to the upper surface of the polishing table with the adhesive or the like, whereby replacement of the cloth is completed.

Replacing the cloth in this manner is problematic because the cloth is replaced through various steps, which lower workability. Further, since the operation of the polishing apparatus should be stopped during replacement of the cloth, a longer replacement time results in a lower production lot per unit time.

In order to solve such drawbacks, there has been known a method in which a cloth cartridge, having a pedestal (base) made of metal or the like and a cloth (polishing cloth), is detachably fixed to a polishing table with bolts, as disclosed in Japanese laid-open patent publication No. 8-118231. According to this method, the cloth can be replaced simply by changing the cloth cartridge, and hence an operation time for replacing the cloth can be shortened. Therefore, the polishing apparatus is only stopped for a short time, thus increasing the production lot per unit time.

However, as the diameter of the semiconductor wafer, which is a workpiece to be polished, becomes large, the diameter of the cloth cartridge also becomes large, resulting in difficulty in handling the cloth cartridge.

DISCLOSURE OF INVENTION

The present invention has been made in view of the above drawbacks. It is, therefore, an object of the present invention to provide a polishing apparatus which can allow efficient replacement of the polishing pad to be disposed on the upper surface of the polishing table.

In order to achieve the above object, according to an aspect of the present invention, there is provided a polishing apparatus comprising a polishing table, a polishing tool attached to an upper surface of the polishing table, and a fluid passage having openings on the upper surface of the polishing table. The polishing apparatus is operable to bring a workpiece into sliding contact with the polishing tool to polish the workpiece while supplying a polishing liquid onto the polishing tool. The polishing tool is fixed to the polishing table by a vacuum produced in the fluid passage.

In a preferred aspect of the present invention, the polishing tool comprises a polishing pad, and a base on which the polishing pad is placed. The polishing tool is divided into a plurality of segments.

According to the present invention having such structure, the polishing tool can be easily removed from the polishing table by releasing the vacuum produced in the fluid passage. Further, because the segments can be removed and attached one by one, the polishing tool (i.e., the polishing pad and the base) can be easily replaced, and hence operation efficiency can be improved.

In a preferred aspect of the present invention, the base is made of resin or metal.

According to the present invention having such structure, the used polishing tool (i.e., the polishing pad and the base) can be discarded as it is. Accordingly, replacement operation, which is to be performed in a manner such that the used polishing pad is removed and a new polishing pad is attached to the base, can be eliminated. Such operation may cause distortions of the base.

In a preferred aspect of the present invention, the polishing pad and the base are made of the same material.

According to the present invention having such structure, the polishing pad and the base are not required to be separated when the polishing tool is discarded.

In a preferred aspect of the present invention, the polishing apparatus further comprises a gas-liquid separator for separating the polishing liquid and a gas from each other. The gas-liquid separator is disposed between the fluid passage and a vacuum source for producing the vacuum in the fluid passage.

As described above, the polishing tool comprising the plurality of segments is fixed to the polishing table by the vacuum produced in the fluid passage. In this structure, however, the polishing liquid may be sucked together with an ambient gas into the fluid passage and the vacuum source. According to the present invention, even in a case where the polishing liquid flows into the fluid passage, the polishing liquid is collected by the gas-liquid separator before being sucked into the vacuum source. Therefore, the polishing liquid can be prevented from entering the vacuum source.

In a preferred aspect of the present invention, the polishing apparatus further comprises a plurality of polishing liquid supply ports for supplying plural kinds of polishing liquids.

Generally, it is necessary to switch the polishing liquid when switching the polishing process, and to replace the polishing tool according to the polishing process for the purpose of preventing cross contamination. Therefore, it is difficult for the conventional polishing apparatus to perform plural polishing processes. According to the present invention having the above structure, the polishing pad can be easily replaced according to the polishing processes. Therefore, by supplying desirable polishing liquids onto the polishing tool through the polishing liquid supply ports, the polishing apparatus can perform plural polishing processes by itself.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a polishing apparatus according to a first embodiment of the present invention;

FIG. 2A is a plan view of a cloth cartridge shown in FIG. 1;

FIG. 2B is a cross-sectional view of segments shown in FIG. 2A;

FIG. 2C is an exploded perspective view of the cloth cartridge shown in FIG. 1;

FIG. 3 is a plan view showing a polishing table according to the first embodiment of the present invention;

FIG. 4 is a perspective view showing a storage bath for storing the cloth cartridge according to the first embodiment of the present invention;

FIG. 5 is a schematic view showing a gas-liquid separation vessel according to a second embodiment of the present invention; and

FIGS. 6A through 6C are views illustrating operation of the gas-liquid separation vessel according to the second embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing a polishing apparatus according to a first embodiment of the present invention. FIG. 2A is a plan view of a cloth cartridge shown in FIG. 1, FIG. 2B is a cross-sectional view of segments shown in FIG. 2A, and FIG. 2C is an exploded perspective view of the cloth cartridge shown in FIG. 1. FIG. 3 is a plan view showing a polishing table according to the first embodiment of the present invention.

As shown in FIG. 1, the polishing apparatus according to this embodiment comprises a polishing table 20 having an upper surface to which a cloth cartridge (polishing tool) 1 is attached, and a top ring 30 operable to hold a semiconductor wafer W, i.e., a workpiece to be polished, and press the semiconductor wafer W against an upper surface of the cloth cartridge 1. The cloth cartridge 1 basically comprises a cloth (polishing pad) 10 and a base (pedestal) 11. The upper surface of the cloth 10 serves as a polishing surface which comes into sliding contact with the semiconductor wafer W. An upper surface of a fixed abrasive plate which comprises fine abrasive particles (made of CeO₂ or the like) fixed by binder such as resin may be used to constitute the polishing surface.

The polishing table 20 is coupled to a motor (not shown) disposed therebelow so that the polishing table 20 is rotated about its own axis as indicated by an arrow. A first polishing liquid supply nozzle (polishing liquid supply port) 22A is disposed above the polishing table 20 so that a polishing liquid (i.e., slurry) Q is supplied onto the cloth 10 through the first polishing liquid supply nozzle 22A. Additionally, a second polishing liquid supply nozzle (polishing liquid supply port) 22B is disposed above the polishing table 20 so that a polishing liquid, which is different from the polishing liquid Q, is supplied onto the cloth 10 through the second polishing liquid supply nozzle 22B. The polishing liquid to be supplied onto the cloth 10 is appropriately selected according to the polishing process.

The top ring 30 is connected to a top ring shaft 32, and is coupled to a motor and a lifting/lowering cylinder (not shown) via the top ring shaft 32. With this structure, the top ring 30 is vertically moved and rotated about the top ring shaft 32 as indicated by arrows. The top ring 30 has an elastic mat 34 made of polyurethane or the like attached to a lower surface of the top ring 30. The semiconductor wafer W, i.e., a workpiece to be polished, is held by a lower surface of the elastic mat 34 due to a vacuum or the like.

With such structure, the top ring 30 can press the semiconductor wafer W held by the lower surface of the top ring 30 against the cloth 10 at a desired pressure while being rotated. A guide ring 36 is provided on the lower circumferential portion of the top ring 30 so that the semiconductor wafer W is not disengaged from the top ring 30.

The top ring 30 and the top ring shaft 32 are coupled via a flexible joint. The flexible joint comprises a spherical bearing mechanism 43 by which the top ring 30 and the top ring shaft 32 are tiltable with respect to each other, and a rotation transmitting mechanism 44 for transmitting the rotation of the top ring shaft 32 to the top ring 30. The spherical bearing mechanism 43 and the rotation transmitting mechanism 44 transmit a pressing force and a rotating force from the top ring shaft 32 to the top ring 30 while allowing the top ring 30 and the top ring shaft 32 to tilt with respect to each other.

In the polishing apparatus having the above structure, the semiconductor wafer W held by the lower surface of the top ring 30 is pressed against the cloth 10 disposed on the upper surface of the rotating polishing table 20. At this time, the polishing liquid Q is supplied from the polishing liquid supply nozzle 22A onto the cloth 10. In this manner, polishing of the semiconductor wafer W is performed in the presence of the polishing liquid Q between the surface to be polished (lower surface) of the semiconductor wafer W and the cloth 10.

As shown in FIGS. 2A through 2C, the cloth cartridge 1 is divided into four segments 1A, 1B, 1C and 1D. Specifically, the cloth cartridge 1 comprises four fan-shaped base pieces 11A, 11B, 11C and 11D, and fan-shaped cloth pieces 10A, 10B, 10C and 10D fixed respectively to upper surfaces of the base pieces 11A, 11B, 11C and 11D with an adhesive or the like. The base pieces 11A, 11B, 11C and 11D are made of hard resin (e.g., PVC (polyvinyl chloride)). Each of the cloth pieces 10A, 10B, 10C and 10D serves as a polishing cloth formed from a resin sheet or the like. The base pieces (base) may be made of metal such as stainless steel.

The respective base pieces 11A, 11B, 11C and 11D have through-holes 12 positioned at center-side tip ends thereof, and pins 13 are inserted respectively into the through-holes 12, as shown in FIG. 1. Lower end portions of the pins 13 are inserted into insertion holes (not shown) formed in the polishing table 20, and upper end portions of the pins 13 are fixed to a fixing member 14 detachably mounted on the polishing table 20. By inserting the pins 13 into the through-holes 12 and the insertion holes of the polishing table 20, the segments 1A, 1B, 1C and 1D are fixed in position relative to the polishing table 20.

As shown in FIG. 1, a fluid passage 40 is formed in the polishing table 20. The fluid passage 40 opens at the upper surface of the polishing table 20. Specifically, as shown in FIG. 3, the fluid passage 40 has a plurality of openings 40a uniformly formed over substantially the entire upper surface of the polishing table 20. The fluid passage 40 extends through the polishing table 20, and the lower end of the fluid passage 40 is coupled to a gas-liquid separation vessel (gas-liquid separator) 42. The gas-liquid separation vessel 42 serves to separate a liquid and a gas from each other, store the separated liquid therein, and allow only the gas to pass therethrough.

The gas-liquid separation vessel 42 is connected to a vacuum source 45 such as a vacuum pump, so that a vacuum (negative pressure) is produced in the fluid passage 40 through the gas-liquid separation vessel 42 by the operation of the vacuum source 45. With this structure, the cloth cartridge 1 is attracted to the upper surface of the polishing table 20 by the vacuum developed in the fluid passage 40.

Replacement of the cloth cartridge 1 having above-mentioned structure is performed as follows. Firstly, the top ring 30 is moved away from the polishing table 20, and the rotation of the polishing table 20 is stopped. Next, the operation of the vacuum source 45 is stopped to release the vacuum developed in the fluid passage 40, whereby a fixed state of the cloth cartridge 1 to the polishing table 20 is released. Thereafter, the fixing member 14 and the pins 13 are removed from the polishing table 20, and the cloth cartridge 1 is removed from the polishing table 20. Then, a new cloth cartridge (not shown) is placed onto the polishing table 20, and the pins 13 and the fixing member 14 are attached to the polishing table 20, so that the cloth cartridge (the segments) is fixed in position. Subsequently, the vacuum source 45 is driven to thereby fix the cloth cartridge to the upper surface of the polishing table 20.

As described above, since the cloth cartridge 1 comprises the four segments 1A, 1B, 1C and 1D which are detachably mounted on the polishing table 20, the segments 1A, 1B, 1C and 1D, i.e., the cloth cartridge 1, can be replaced one by one. Accordingly, replacement of the cloth cartridge 1 can be facilitated, and hence operation efficiency can be improved. Although the cloth cartridge comprises the four segments in this embodiment, it may comprise two or three segments.

In the above-mentioned structure, when the vacuum is produced in the fluid passage 40, the polishing liquid may be sucked together with an ambient gas into the fluid passage 40 through small gaps between the segments 1A, 1B, 1C and 1D of the cloth cartridge 1. The polishing liquid sucked into the fluid passage 40 is led to the gas-liquid separation vessel 42, where the polishing liquid and the gas are separated from each other. The separated polishing liquid is stored in the gas-liquid separation vessel 42, and only the gas is sucked from the gas-liquid separation vessel 42 into the vacuum source 45. In this manner, the gas-liquid separation vessel 42 prevents the polishing liquid from flowing into the vacuum source 45, and can thus prevent failure of the vacuum source 45 from occurring due to the entry of the polishing liquid.

Additionally, according to this embodiment, the polishing apparatus can perform plural processes by itself. Specifically, a semiconductor wafer is firstly polished while the polishing liquid Q is being supplied from the first polishing liquid supply nozzle 22A onto the cloth 10 (a first polishing process). Then, the cloth cartridge 1 is replaced with another cloth cartridge (not shown), and the semiconductor wafer is polished while a polishing liquid, which is different from the polishing liquid Q, is being supplied from the second polishing liquid supply nozzle 22B onto the cloth (a second polishing process). During the second polishing process, the cloth cartridge 1 used in the first polishing process is stored in a storage bath 46 shown in FIG. 4.

FIG. 4 is a perspective view showing the storage bath for storing the cloth cartridge according to the first embodiment of the present invention. As shown in FIG. 4, water 47 is retained in the storage bath 46. The segments 1A, 1B, 1C and 1D of the cloth cartridge 1, which were used in the first polishing process, are transferred to the storage bath 46, and are then immersed in the water 47, whereby the polishing liquid (i.e., slurry) adhering to the cloth 10 can be prevented from evaporating. Further, a running-in period can be shortened when the segments 1A, 1B, 1C and 1D are attached again to the polishing table 20.

Next, a second embodiment of the present invention will be described. FIG. 5 is a schematic view showing a gas-liquid separation vessel according to the second embodiment of the present invention. FIGS. 6A through 6C are views illustrating the operation of the gas-liquid separation vessel according to the second embodiment of the present invention. The polishing apparatus of this embodiment differs from the polishing apparatus of the first embodiment in that two gas-liquid separation vessels are provided. Components and functions which are identical to those of the polishing apparatus of the first embodiment will not be repetitively described below.

As shown in FIG. 5, a first gas-liquid separation vessel 42A and a second gas-liquid separation vessel 42B are arranged in parallel, and are connected to the fluid passage 40 (see FIG. 1) via a pipe 50. Check valves 52 and 52 are provided on the pipe 50, so that the vacuum, which is produced in the fluid passage 40, is maintained by the check valves 52 and 52. The first and second gas-liquid separation vessels 42A and 42B are connected to the vacuum source 45 via pipes 54 and 56, respectively. A first valve 58A is provided on the pipe 54 connected to the first gas-liquid separation vessel 42A, and a second valve 58B is provided on the pipe 56 connected to the second gas-liquid separation vessel 42B. With this structure, by operating the first and second valves 58A and 58B, the first and second gas-liquid separation vessels 42A and 42B can be independently controlled so as to communicate with the vacuum source 45.

Each of the first and second gas-liquid separation vessels 42A and 42B has a sensor 60 for detecting whether an amount of the polishing liquid stored therein exceeds a predetermined value. Drain pipes 62A and 62B are connected to lower ends of the first and second gas-liquid separation vessels 42A and 42B, respectively, so that the polishing liquid stored in the first and second gas-liquid separation vessels 42A and 42B is discharged through the drain pipes 62A and 62B. Communication pipes 64A and 64B are connected to upper ends of the first and second gas-liquid separation vessels 42A and 42B, respectively, so that the interior and the exterior of the first and second gas-liquid separation vessels 42A and 42B communicate with each other through the communication pipes 64A and 64B. First drain valves 66A and 66A are provided respectively on the drain pipe 62A and the communication pipe 64A which are connected to the first gas-liquid separation vessel 42A, and second drain valves 66B and 66B are provided respectively on the drain pipe 62B and the communication pipe 64B which are connected to the second gas-liquid separation vessel 42B. With this structure, by operating the first valves 66A and 66A and the second drain valves 66B and 66B, the polishing liquid in the first and second gas-liquid separation vessels 42A and 42B is discharged through the drain pipes 62A and 62B. Level sensors are preferably used as the sensors 60.

Next, operation of the gas-liquid separation vessel of this embodiment will be described with reference to FIGS. 6A through 6C. Arrows illustrated in FIGS. 6A through 6C indicate gas flow. Additionally, in FIGS. 6A through 6C, black-colored valves and black-colored drain valves indicate being in a closed state, and white-colored valves and white-colored drain valve indicate being in an open state.

As shown in FIG. 6A, the first valve 58A and the second drain valves 66B and 66B are closed, and the second valve 58B and the first drain valves 66A and 66A are opened (this state will be herein referred to as S1). Specifically, only the second gas-liquid separation vessel 42B communicates with the vacuum source 45. In this state, the polishing liquid stored in the first gas-liquid separation vessel 42A is discharged.

When the sensor 60 detects that an amount of the polishing liquid in the second gas-liquid separation vessel 42B reaches the predetermined value, the first drain valves 66A and 66A are closed, and the first valve 58A is opened, as shown in FIG. 6B. Specifically, the first and second drain valves 58A and 58B are opened, and the first drain valves 66A and 66A and the second drain valves 66B and 66B are closed (this state will be herein referred to as S2), whereby the first and second gas-liquid separation vessels 42A and 42B communicate with the vacuum source 45. In this state, the polishing liquid is not discharged.

After a given time has elapsed in the S2 state, the second valve 58B is closed, and the second drain valves 66B and 66B are opened, as shown in FIG. 6C. Specifically, the first valve 58A and the second drain valves 66B and 66B are opened, and the second valve 58B and the first drain valves 66A and 66A are closed (this state will be herein referred to as S3). In this state, the polishing liquid stored in the second gas-liquid separation vessel 42B is discharged.

When the sensor 60 detects that an amount of the polishing liquid in the first gas-liquid separation vessel 42A reaches the predetermined value, the second drain valves 66B and 66B are closed, and the second valve 58B is opened, whereby the state becomes S2. Further, after a predetermined time has elapsed, the state is switched to S1. In this manner, a cycle, which comprises S1, S2, S3, S2, and S1, is repeated to discharge the polishing liquid.

By alternately bringing the two gas-liquid separation vessels 42A and 42B into communication with the vacuum source 45 in this manner, the polishing liquid in the gas-liquid separation vessels 42A and 42B can be discharged without breaking the vacuum produced in the fluid passage 40. Therefore, the polishing apparatus is not required to stop its operation in order to discharge the polishing liquid from the gas-liquid separation vessels 42A and 42B.

As described above, according to the present invention, the polishing tool can be easily removed from the polishing table by releasing the vacuum developed in the fluid passage. Further, because the segments can be removed and attached one by one, the polishing tool (i.e., the polishing pad and the base) can be easily replaced, and hence operation efficiency can be improved.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a polishing apparatus for polishing a workpiece such as a semiconductor wafer to form a flat surface thereon.

Claims

1. A polishing apparatus comprising:

a polishing table;

a polishing tool attached to an upper surface of said polishing table, said polishing apparatus being operable to bring a workpiece into sliding contact with said polishing tool to polish the workpiece while supplying a polishing liquid onto said polishing tool; and

a fluid passage having openings on the upper surface of said polishing table,

wherein said polishing tool is fixed to said polishing table by a vacuum produced in said fluid passage.

2. The polishing apparatus according to claim 1, wherein:

said polishing tool comprises a polishing pad and a base on which said polishing pad is placed; and

said polishing tool is divided into a plurality of segments.

3. The polishing apparatus according to claim 2, wherein said base is made of resin or metal.

4. The polishing apparatus according to claim 2, wherein said polishing pad and said base are made of the same material.

5. The polishing apparatus according to claim 1, further comprising a gas-liquid separator for separating the polishing liquid and a gas from each other, said gas-liquid separator being disposed between said fluid passage and a vacuum source for producing the vacuum in said fluid passage.

6. The polishing apparatus according to claim 1, further comprising a plurality of polishing liquid supply ports for supplying plural kinds of polishing liquids.

7. The polishing apparatus according to claim 1, wherein:

said polishing tool comprises a first polishing tool for a first polishing process, and a second polishing tool for a second polishing process; and

said polishing apparatus further comprises a storage bath for storing said first polishing tool while performing the second polishing process.

8. The polishing apparatus according to claim 7, further comprising:

a first polishing liquid supply nozzle for supplying a first polishing liquid during the first polishing process; and

a second polishing liquid supply nozzle for supplying a second polishing liquid during the second polishing process.

9. The polishing apparatus according to claim 2, further comprising a gas-liquid separator for separating the polishing liquid and a gas from each other, said gas-liquid separator being disposed between said fluid passage and a vacuum source for producing the vacuum in said fluid passage.

10. The polishing apparatus according to claim 3, further comprising a gas-liquid separator for separating the polishing liquid and a gas from each other, said gas-liquid separator being disposed between said fluid passage and a vacuum source for producing the vacuum in said fluid passage.

11. The polishing apparatus according to claim 4, further comprising a gas-liquid separator for separating the polishing liquid and a gas from each other, said gas-liquid separator being disposed between said fluid passage and a vacuum source for producing the vacuum in said fluid passage.

12. The polishing apparatus according to claim 2, further comprising a plurality of polishing liquid supply ports for supplying plural kinds of polishing liquids.

13. The polishing apparatus according to claim 3, further comprising a plurality of polishing liquid supply ports for supplying plural kinds of polishing liquids.

14. The polishing apparatus according to claim 4, further comprising a plurality of polishing liquid supply ports for supplying plural kinds of polishing liquids.

15. The polishing apparatus according to claim 5, further comprising a plurality of polishing liquid supply ports for supplying plural kinds of polishing liquids.

16. The polishing apparatus according to claim 9, further comprising a plurality of polishing liquid supply ports for supplying plural kinds of polishing liquids.

17. The polishing apparatus according to claim 10, further comprising a plurality of polishing liquid supply ports for supplying plural kinds of polishing liquids.

18. The polishing apparatus according to claim 11, further comprising a plurality of polishing liquid supply ports for supplying plural kinds of polishing liquids.