Polishing method

The present invention is relates to a polishing method for polishing a semiconductor wafer (W) by pressing the semiconductor wafer (W) against a polishing surface (10) with use of a top ring (23) for holding the semiconductor wafer (W). A pressure chamber (70) is defined in the top ring (23) by attaching an elastic membrane (60) to a lower surface of a vertically movable member (62). The semiconductor wafer (W) is polished while a pressurized fluid is supplied to the pressure chamber (70) so that the semiconductor wafer (W) is pressed against the polishing surface (10) by a fluid pressure of the fluid. The semiconductor wafer (W) which has been polished is released from the top ring (23) by ejecting the pressurized fluid from an opening (62a) defined centrally in the vertically movable member (62).

This application is a PCT/JP03/04894 Apr. 17, 2003.

TECHNICAL FIELD

The present invention relates to a polishing method, and more particularly to a polishing method for polishing a workpiece, such as a semiconductor wafer having a thin film formed on a surface thereof, to a flat mirror finish.

BACKGROUND ART

In recent years, semiconductor devices have become more integrated, and structures of semiconductor elements have become more complicated. Further, the number of layers in multilayer interconnections used for a logical system has been increased. Accordingly, irregularities on a surface of a semiconductor device become increased, so that step heights on the surface of the semiconductor device tend to be larger. This is because, in a manufacturing process of the semiconductor device, a thin film is formed on the semiconductor device, then micro machining processes, such as patterning or forming holes, are performed on the semiconductor device, and these processes are repeated many times to form subsequent thin films on the semiconductor device.

When the number of irregularities is increased on the surface of the semiconductor device, the following problems arise. The thickness of a film formed in a portion having a step is relatively small when a thin film is formed on the semiconductor device. An open circuit is caused by disconnection of interconnections, or a short circuit is caused by insufficient insulation between interconnection layers. As a result, good products cannot be obtained, and the yield tends to be reduced. Further, even if the semiconductor device initially works normally, the reliability of the semiconductor device is lowered after a long-term use. At the time of exposure in a lithography process, if the irradiation surface has irregularities, then a lens unit in an exposure system is locally unfocused. Therefore, if the irregularities of the surface of the semiconductor device are increased, then it becomes problematic that it is difficult to form a fine pattern itself on the semiconductor device.

Accordingly, in a manufacturing process of a semiconductor device, it increasingly becomes important to planarize a surface of the semiconductor device. The most important one of the planarizing technologies is CMP (Chemical Mechanical Polishing). In the chemical mechanical polishing, with use of a polishing apparatus, while a polishing liquid containing abrasive particles such as silica (SiO2) therein is supplied onto a polishing surface such as a polishing pad, a substrate such as a semiconductor wafer is brought into sliding contact with the polishing surface, so that the substrate is polished.

This type of polishing apparatus comprises a polishing table having a polishing surface constituted by a polishing pad, a top ring or a carrier head for holding a semiconductor wafer, and the like. When the semiconductor wafer is polished with use of such a polishing apparatus, the semiconductor wafer is held and pressed against the polishing table under a predetermined pressure by the top ring. At this time, the polishing table and the top ring are moved relatively to each other to bring the semiconductor wafer into sliding contact with the polishing surface, so that the surface of the semiconductor wafer is polished to a flat mirror finish.

In such a polishing apparatus, if a relative pressing force between the semiconductor wafer being polished and the polishing surface of the polishing pad is not uniform over an entire surface of the semiconductor wafer, then the semiconductor wafer may insufficiently be polished or may excessively be polished at some portions depending on the pressing force applied to those portions of the semiconductor wafer. Therefore, it has been attempted to form a surface, for holding the semiconductor wafer, of the top ring with use of an elastic membrane made of an elastic material such as rubber and to apply a fluid pressure such as an air pressure to a backside surface of the elastic membrane to uniform the pressing force applied to the semiconductor wafer over the entire surface of the semiconductor wafer.

Further, the polishing pad is so elastic that the pressing force applied to a circumferential edge portion of the semiconductor wafer being polished becomes non-uniform, and hence only the circumferential edge portion of the semiconductor wafer may excessively be polished, which is called “edge rounding”. In order to prevent such edge rounding, there has been used a top ring in which a semiconductor wafer is held at its circumferential edge portion by a guide ring or a retainer ring, and the annular portion of the polishing surface that corresponds to the circumferential edge portion of the semiconductor wafer is pressed by the guide ring or retainer ring.

When a semiconductor wafer is polished with use of such a top ring, it is necessary to attract and hold the semiconductor wafer which has been transferred to the top ring. Further, after the semiconductor wafer is polished, it is necessary to attract the semiconductor wafer again to the top ring and thereafter to release the semiconductor wafer from the top ring at a transfer position. However, the top ring using the above elastic membrane tends to fail in attracting and releasing the semiconductor wafer because of the presence of the elastic membrane.

DISCLOSURE OF INVENTION

The present invention has been made in view of the above drawbacks. It is an object of the present invention to provide a polishing method which can reliably attract and release a workpiece, to be polished, even if the workpiece is held and polished using an elastic membrane.

In order to solve the above drawbacks, according to a first aspect of the present invention, there is provided a polishing method for polishing a workpiece by pressing the workpiece against a polishing surface with use of a top ring for holding the workpiece, the polishing method comprising: defining a pressure chamber in the top ring by attaching an elastic membrane to a lower surface of a vertically movable member; polishing the workpiece while a pressurized fluid is supplied to the pressure chamber so that the workpiece is pressed against the polishing surface by a fluid pressure of the fluid; and releasing the workpiece which has been polished from the top ring by ejecting the pressurized fluid from an opening defined centrally in the vertically movable member.

When the pressurized fluid is ejected from the opening defined centrally in the vertically movable member, the pressurized fluid is delivered into the region where the elastic membrane and the workpiece are held in close contact with each other. Therefore, the workpiece can reliably be released.

In a preferred aspect of the present invention, a hole is provided in a surface, to be brought into close contact with the workpiece, of the elastic membrane which defines the pressure chamber; and the releasing comprises releasing the workpiece which has been polished from the top ring by ejecting the pressurized fluid not only from the opening defined centrally in the vertically movable member, but also from the hole provided in the elastic membrane.

Since the pressurized fluid is ejected not only from the opening defined centrally in the vertically movable member, but also from the hole in the elastic membrane, the workpiece can be released more reliably.

In a preferred aspect of the present invention, the pressurized fluid is ejected from the opening defined centrally in the vertically movable member after the pressurized fluid is ejected from the hole of the elastic membrane.

According to the present invention, it is possible to break the close contact between the elastic membrane and the workpiece, for thereby releasing the workpiece more reliably.

According to a second aspect of the present invention, there is provided a polishing method for polishing a workpiece by pressing the workpiece against a polishing surface with use of a top ring for holding the workpiece, the polishing method comprising: defining a pressure chamber in the top ring by attaching an elastic membrane to a lower surface of a vertically movable member; polishing the workpiece while a pressurized fluid is supplied to the pressure chamber so that the workpiece is pressed against the polishing surface by a fluid pressure of the fluid; when the polishing is finished, moving the vertically movable member downwardly so as to bring the workpiece into close contact with an attraction section provided on the vertically movable member; and attracting the workpiece to the top ring by the attraction section.

When the polishing process is finished, the workpiece and the vertically movable member may have occasionally been spaced from each other. In such a case, the attraction section fails to attract the workpiece even if the attraction section attempts to attract the workpiece. According to the present invention, when the polishing process is finished, the vertically movable member is moved downwardly to bring the workpiece into close contact with the attraction section, and thereafter the attraction section attracts and holds the workpiece. Consequently, it is possible to reliably attract the workpiece.

According to a third aspect of the present invention, there is provided a polishing method for polishing a workpiece by pressing the workpiece against a polishing surface with use of a top ring for holding the workpiece, the polishing method comprising: defining a pressure chamber in the top ring by attaching an elastic membrane to a lower surface of a vertically movable member; guiding the workpiece to the top ring while the vertically movable member is positioned upwardly with respect to a retainer ring which holds an outer circumferential edge of the workpiece; attracting the workpiece which has been guided to the top ring to the top ring by an attraction section provided on the vertically movable member; moving the workpiece which is held by the top ring onto the polishing surface; and polishing the workpiece while a pressurized fluid is supplied to the pressure chamber so that the workpiece is pressed against the polishing surface by a fluid pressure of the fluid.

If the vertically movable member projects downwardly from the retainer ring and the workpiece is attracted at a displaced position when the workpiece is transferred, then the workpiece tends to be caught by the retainer ring when the vertically movable member is moved upwardly in a subsequent motion, thus causing the workpiece to be dropped off and damaged. According to the present invention, since the vertically movable member is positioned upwardly with respect to the retainer ring in advance, the workpiece is transferred while the outer circumferential portion thereof is guided by the retainer ring. Therefore, the workpiece is not caught by the retainer ring when the vertically movable member is moved upwardly, and hence the workpiece can be prevented from being dropped off and damaged.

BEST MODE FOR CARRYING OUT THE INVENTION

A polishing method according to a first embodiment of the present invention will be described below in detail with reference toFIGS. 1 through 12.FIG. 1is a schematic plan view showing a polishing apparatus according to the first embodiment of the present invention. As shown inFIG. 1, in the polishing apparatus, a pair of polishing sections1a,1bare disposed at one side of a space on a floor having a rectangular shape so as to face each other. A pair of load/unload units for placing cassettes2a,2bthereon which accommodate semiconductor wafers are disposed at the other side. Two transfer robots4a,4bfor transferring the semiconductor wafer are disposed on a line connecting the polishing sections1a,1bto the load/unload units, thus forming a transfer line. Reversing devices5,6are disposed on each side of the transfer line, respectively, and cleaning devices7a,8aand cleaning devices7b,8bare disposed so as to interpose the respective reversing devices5,6therebetween.

The two polishing sections1a,1bhave basically the same specifications and are disposed symmetrically with respect to the transfer line. Each of the polishing sections1a,1bcomprises a polishing table11having a polishing pad attached to an upper surface thereof, a top ring unit12for holding a semiconductor wafer as a workpiece to be polished by vacuum suction and pressing the semiconductor wafer against the polishing pad on the polishing table11to polish the semiconductor wafer, a dressing unit13for dressing the polishing pad on the polishing table11. Each polishing sections1a,1balso has a pusher14positioned at a transfer-line side for transferring the semiconductor wafer to and from the top ring unit12.

Each transfer robots4a,4bhas an articulated arm which is bendable and stretchable in a horizontal plane and has upper and lower holding portions which are separately used as a dry finger and a wet finger. Since two robots are used in the present embodiment, the first transfer robot4ais basically responsible for a region from the reversing devices5,6to the cassettes2a,2b,and the second transfer robot4bis basically responsible for a region from the reversing devices5,6to the polishing sections1a,1b.

The reversing devices5,6serve to turn over the semiconductor wafer, and are disposed in such a position that hands of the transfer robots4a,4bcan reach the reversing devices5,6. In the present embodiment, the two reversing devices5,6are used separately for handling a dry substrate and for handling a wet substrate.

Each of the cleaning devices7a,7b,8aand8bmay be of any type. For example, the cleaning devices7a,7bat the side of the polishing sections1a,1bare of a type that wipes both surfaces of a semiconductor wafer with rollers having sponges, and the cleaning devices8a,8bat the side of the cassettes2a,2bare of a type that holds an edge of a semiconductor wafer and rotates the semiconductor wafer in a horizontal plane while supplying a cleaning liquid to the semiconductor wafer. The latter also has a function as a drier for centrifugally dehydrating and drying a semiconductor wafer. The cleaning devices7a,7bcan perform a primary cleaning process of the semiconductor wafer, and the cleaning devices8a,8bcan perform a secondary cleaning process of the semiconductor wafer after the primary cleaning process.

Next, the above polishing section will be described in detail.FIG. 2is a vertical cross-sectional view showing an essential part of the polishing section1ashown inFIG. 1. Although only the polishing section1awill be described below, the following description can be applied to the polishing section1b.

As shown inFIG. 2, the polishing section1acomprises a polishing table11having a polishing pad10attached to an upper surface thereof, a top ring unit12for holding a semiconductor wafer W as a workpiece to be polished by vacuum suction and pressing the semiconductor wafer W against the polishing table11to polish the semiconductor wafer W, and a dressing unit13for dressing the polishing pad10on the polishing table11. The polishing table11is coupled to a motor (not shown) disposed below the polishing table11through a table shaft11a,and hence the polishing table11is rotatable about the table shaft11ain a direction indicated by the arrow C inFIG. 2. A surface of the polishing pad10on the polishing table11serves as a polishing surface which is brought into sliding contact with a semiconductor wafer W as a workpiece to be polished.

Various kinds of polishing pads are commercially available. For example, some of these are SUBA800, IC-1000, and IC-1000/SUBA400 (two-layer cloth) manufactured by Rodel Inc., and Surfin xxx-5 and Surfin 000 manufactured by Fujimi Inc. SUBA800, Surfin xxx-5, and Surfin 000 are non-woven fabrics composed of fibers bound together by urethane resin, and IC-1000 is made of hard polyurethane foam (single layer). Polyurethane foam is porous and has a large number of fine recesses or holes formed in a surface thereof.

A polishing liquid supply nozzle15and a water supply nozzle16are disposed above the polishing table11. The polishing liquid supply nozzle15supplies pure water or a chemical liquid onto the polishing surface10on the polishing table11. The water supply nozzle16supplies a dressing liquid (e.g., water) for use in dressing onto the polishing surface10on the polishing table11. The polishing table11is surrounded by a frame17for recovering the polishing liquid and water, and a tub17ais formed in a lower portion of the frame.

The top ring unit12comprises a rotatable support shaft20, a top ring head21coupled to an upper end of the support shaft20, a top ring shaft22extending downwardly from a free end of the top ring head21, and a substantially disk-like top ring23connected to a lower end of the top ring shaft22. When the top ring head21is angularly moved by the rotation of the support shaft20, the top ring23is moved horizontally. Thus, the top ring23can be reciprocated between the pusher14and a polishing position on the polishing surface10, as indicated by the arrow A inFIG. 1. Further, the top ring23is coupled through the top ring shaft22to a motor (not shown) and a lifting/lowering cylinder (not shown) provided in the top ring head21, so that the top ring23is vertically movable and is rotatable about the top ring shaft22, as indicated by the arrows D, E inFIG. 2. The semiconductor wafer W to be polished is attracted to and held on the lower surface of the top ring23by vacuum suction. With the above mechanisms, the top ring23can press the semiconductor wafer W held on the lower surface thereof against the polishing surface10under a desired pressure while being rotated.

The dressing unit13serves to regenerate the polishing surface10that has been deteriorated by a polishing process. The dressing unit13is disposed at an opposite side of top ring unit12with respect to a center of polishing table11. The dressing unit13, as with the above top ring unit12, comprises a rotatable support shaft30, a dresser head31coupled to an upper end of the support shaft30, a dresser shaft32extending downwardly from a free end of the dresser head31, a dresser33coupled to a lower end of the dresser shaft32, and a dressing member34attached to a lower surface of the dresser33. When the dresser head31is angularly moved by the rotation of the support shaft30, the dresser33is moved horizontally, and thus can be reciprocated between a dressing position on the polishing surface10and a standby position located outwardly of the polishing table11, as indicated by the arrow B inFIG. 1.

FIG. 3is a schematic view showing the top ring unit12of the polishing section shown inFIG. 2together with a fluid passage arrangement, andFIG. 4is a vertical cross-sectional view showing the top ring23of the top ring unit12shown inFIG. 3. As shown inFIGS. 3 and 4, the top ring23is connected to the top ring shaft22through a universal joint40. The top ring shaft22is coupled to a top ring air cylinder111fixed to the top ring head21. The top ring23comprises a substantially disk-like top ring body42coupled to the lower end of the top ring shaft22, and the retainer ring43disposed on an outer circumferential portion of the top ring body42. The top ring body42is made of a material having high strength and rigidity, such as metal or ceramics. The retainer ring43is made of highly rigid synthetic resin, ceramics, or the like.

The top ring air cylinder111is connected to a pressure adjuster120through a regulator R1. The pressure adjuster120serves to adjust a pressure by supplying a pressurized fluid such as pressurized air from a compressed air source or developing a vacuum with a pump or the like. The pressure adjuster120can adjust an air pressure of the pressurized air or the like supplied to the top ring air cylinder111with the regulator R1. The top ring air cylinder111allows the top ring shaft22to move vertically, so that the whole top ring23is lifted or lowered and the retainer ring43mounted on the top ring body42is pressed against the polishing table11under a predetermined pressing force.

The top ring shaft22is coupled to a rotary sleeve112by a key (not shown). The rotary sleeve112has a timing pulley113disposed on an outer circumferential portion thereof. A top ring motor114is fixed to the top ring head21, and the above timing pulley113is connected to a timing pulley116mounted on the top ring motor114through a timing belt115. Therefore, when the top ring motor114is energized, the rotary sleeve112and the top ring shaft22are rotated together with each other through the timing pulley116, the timing belt115, and the timing pulley113, thus rotating the top ring23. The top ring head21is supported by the support shaft20which is rotatably supported by a frame (not shown).

As shown inFIG. 4, the top ring body42comprises a housing42ahaving a cylinder-vessel shape, an annular pressurizing-sheet support42bfitted in a cylindrical portion of the housing42a,and an annular seal42cfitted into an outer circumferential edge of an upper surface of the housing42a.The retainer ring43is fixed to a lower end of the housing42aof the top ring body42and has a lower portion projecting radially inwardly.

The top ring shaft22is disposed upwardly of the central portion of the housing42aof the top ring body42. The top ring body42and the top ring shaft22are coupled to each other through the universal joint40. The universal joint40has a spherical bearing mechanism for allowing the top ring body42and the top ring shaft22to be tilted with respect to each other, and a rotation transmitting mechanism for transmitting the rotation of the top ring shaft22to the top ring body42. The spherical bearing mechanism and the rotation transmitting mechanism transmit a pressing force and a rotating force from the top ring shaft22to the top ring body42while allowing the top ring body42and the top ring shaft22to be tilted with respect to each other.

The spherical bearing mechanism comprises a hemispherical concave recess22adefined centrally in the lower surface of the top ring shaft22, a hemispherical concave recess42ddefined centrally in the upper surface of the top ring body42, and a bearing ball52made of a highly hard material such as ceramics and interposed between the hemispherical concave recesses22aand42d.As shown inFIG. 4, a connecting bolt47is attached to the top ring body42in the vicinity of the top ring shaft22, and a coil spring48is interposed between the connecting bolt47and a spring retainer22bprovided on the top ring shaft22. With this structure, the top ring body42is held tiltably with respect to the top ring shaft22.

On the other hand, the rotation transmitting mechanism comprises engage pins49fixed to the top ring body42in the vicinity of the top ring shaft22, and engage holes22cformed in the top ring shaft22. Since each of the engage pins49is movable in each of the engage holes22c,even when the top ring body42is tilted, the engage pins49are held in engagement with the engage holes22cwhile a contact point is displaced, so that the rotating torque of the top ring shaft22is reliably transmitted to the top ring body42through the rotation transmitting mechanism.

The top ring body42and the retainer ring43have a space defined therein, which accommodates therein an elastic pad60which is brought into close contact with the semiconductor wafer W held by the top ring23, an annular holder ring61, and a substantially disk-shaped chucking plate (vertically movable member)62which is vertically movable in the space formed in the top ring body42. The elastic pad60has an outer circumferential portion which is clamped between the holder ring61and the chucking plate62fixed to the lower end of the holder ring61, and covers the lower surface of the chucking plate62. Thus, a pressure chamber70is formed between the elastic pad60and the chucking plate62. The elastic pad60is made of a rubber having excellent strength and durability such as ethylene propylene rubber (EPDM), polyurethane rubber, silicone rubber, or neoprene rubber.

The chucking plate62has an opening62adefined centrally therein. The opening62acommunicates with a fluid passage80comprising a tube, a connector, and the like, and is connected to the pressure adjuster120through a regulator R2provided on the fluid passage80. Specifically, the pressure chamber70formed between the elastic pad60and the chucking plate62is connected to the pressure adjuster120through the regulator R2provided on the fluid passage80. The elastic pad60has a central hole60ahaving a large diameter (e.g., a diameter of 12 mm) at a position corresponding to the opening62a.

A pressurizing sheet63comprising an elastic membrane is provided between the holder ring61and the top ring body42. One edge portion of the pressurizing sheet63is clamped by the pressurizing-sheet support42battached to the lower surface of the top ring body42, and other edge portion of the pressurizing sheet63is clamped between an upper portion61aof the holder ring61and a stopper61b.The top ring body42, the chucking plate62, the holder ring61, and the pressurizing sheet63define a pressure chamber71in the top ring body42. As shown inFIG. 4, a fluid passage81comprising a tube, a connector, and the like communicates with the pressure chamber71, and the pressure chamber71is connected to the pressure adjuster120through a regulator R3provided on the fluid passage81. The pressurizing sheet63is made of a rubber having excellent strength and durability such as ethylene propylene rubber (EPDM), polyurethane rubber, silicone rubber, or neoprene rubber, or made of a reinforced rubber containing fibers, very thin stainless (e.g., having a thickness of 0.2 mm), or the like.

Since a small gap is formed between the outer circumferential surface of the elastic membrane60and the retainer ring43, components such as the holder ring61and the chucking plate62can vertically be moved with respect to the top ring body42and the retainer ring43in a floating manner. The stopper61bof the holder ring61has a plurality of projections61cprojecting radially outwardly from the outer circumferential edge thereof. When the projections61cengage an upper surface of a radially inwardly projecting portion of the retainer ring43, a downward movement of the components such as the above holder ring61is restricted to a predetermined position.

In the case where the pressurizing sheet63is made of an elastic member such as a rubber, if the pressurizing sheet63is clamped between the retainer ring43and the top ring body42, then the pressurizing sheet63as an elastic member is elastically deformed. Consequently, a desired horizontal plane cannot be maintained on the lower surface of the retainer ring43. Therefore, in order to prevent such a problem from occurring, the pressurizing-sheet support42bis provided as a separate member in the present embodiment, so that the pressurizing sheet63is clamped between the housing42aof the top ring body42and the pressurizing-sheet support42b.The retainer ring43may vertically be movable with respect to the top ring body42, or the retainer ring43may have a structure capable of being pressed independently of the top ring body42. In such cases, the pressurizing sheet63is not necessarily fixed in the above manner.

The pressure chamber70between the chucking plate62and the elastic pad60, and the pressure chamber71positioned above the chucking plate62are supplied with a pressurized fluid such as pressurized air, or the atmospheric pressure or vacuum is produced in the pressure chambers70,71through the fluid passages80,81communicating respectively with the pressure chambers70,71. Specifically, as shown inFIG. 3, the pressures of the pressurized fluids supplied to the respective pressure chambers70,71can be adjusted by the regulators R2, R3provided on the fluid passages80,81communicating respectively with the pressure chambers70,71. Thus, it is possible to independently control the pressures in the pressure chambers70,71, or independently produce the atmospheric pressure or vacuum in the pressure chambers70,71.

The chucking plate62has an inner attraction section64and an outer attraction section65which project downwardly and are disposed outwardly of the opening62a.The inner attraction section64has a communication hole64adefined therein which communicates with a fluid passage82comprising a tube, a connector, and the like. The inner attraction section64is connected to the pressure adjuster120through a regulator R4provided on the fluid passage82. As with the inner attraction section64, the outer attraction section65has a communication hole65adefined therein which communicates with a fluid passage83comprising a tube, a connector, and the like. The outer attraction section65is connected to the pressure adjuster120through a regulator R5provided on the fluid passage83. The pressure adjuster120develops a negative pressure in open ends of the communication holes64a,65aof the attraction sections64,65, for thereby attracting the semiconductor wafer W to the attraction sections64,65. Elastic sheets such as rubber sheets or backing films are attached to the lower surfaces of the attraction sections64,65, respectively, so that the attraction sections64,65attract and hold the semiconductor wafer W softly.

The seal42cof the top ring body42has a cleaning liquid passage91as an annular groove defined in a lower surface thereof. The cleaning liquid passage91communicates with a fluid passage84. A plurality of communication holes92extend from the cleaning liquid passage91of the seal42cand pass through the housing42aand the pressurizing-sheet support42b.The communication holes92communicate with a small gap between the outer circumferential surface of the elastic pad60and the retainer ring43. A cleaning liquid (e.g., pure water) is supplied through the cleaning liquid passage91to the gap.

Operation of the polishing apparatus having such a structure will be described below. First, the first transfer robot4atakes a semiconductor wafer W from the cassette2aor2b,and the reversing device5or6reverses the semiconductor wafer W. Thereafter, the second transfer robot4btransfers and places the semiconductor wafer W onto the pusher14. In this state, the top ring head21of the top ring unit12is angularly moved to bring the top ring23to a position above the pusher14.

FIG. 5is a vertical cross-sectional view showing the state of the polishing apparatus at this time. As shown inFIG. 5, the pusher14comprises a guide stage141which is vertically movable by an air cylinder or the like, a wafer guide142disposed on an outer circumferential portion of the guide stage141, and a push stage143which is disposed above the guide stage141and is vertically movable independently of the guide stage141. The wafer guide142has a two-step structure having an upper step144and a lower step145. The upper step144of the wafer guide142serves to access the lower surface of the retainer ring43of the top ring23, and the lower step145serves to centrally align and hold the semiconductor wafer W. A taper146for guiding the retainer ring43is formed upwardly of the upper step144, and a taper147for guiding the semiconductor wafer W is formed upwardly of the lower step145. The semiconductor wafer W is placed on the lower step145of the wafer guide142in such a state that the semiconductor wafer W is centrally aligned by the taper147of the wafer guide142.

In the state shown inFIG. 5, the pressure chamber71in the top ring23is connected to the pressure adjuster120through the fluid passage81, so that a negative pressure is developed in the pressure chamber71. Therefore, as shown inFIG. 5, the chucking plate62is positioned upwardly with respect to the retainer ring43, and hence the semiconductor wafer W can be attracted reliably as described later.

Next, as shown inFIG. 6, the guide stage141of the pusher14is moved upwardly to guide the retainer ring43onto the upper step144of the wafer guide142by the taper146of the wafer guide142. When the upper step144of the wafer guide142is brought into contact with the lower surface of the retainer ring43, the upward movement of the guide stage141is finished.

In this state, as shown inFIG. 7, the push stage143of the pusher14is moved upwardly to hold a pattern surface of the semiconductor wafer W which has been placed on the lower step145of the wafer guide142, and bring the semiconductor wafer W into close contact with the elastic pad60of the top ring23. The communication holes64a,65aof the attraction sections64,65are connected to the pressure adjuster120through the fluid passages82,83, and the semiconductor wafer W is attracted to the lower surfaces of the attraction sections64,65by a sucking action of the communication holes64a,65a.

If the chucking plate62projects downwardly from the retainer ring43and the semiconductor wafer W is attracted at a displaced position when the semiconductor wafer W is transferred, then the semiconductor wafer W tends to be caught by the retainer ring43when the chucking plate62is moved upwardly in a subsequent motion, thus causing the semiconductor wafer W to be dropped off and damaged. In the present embodiment, since the negative pressure is developed in the pressure chamber71in the top ring23so as to position the chucking plate62upwardly with respect to the retainer ring43in advance, the semiconductor wafer W is transferred while the outer circumferential portion thereof is guided by the retainer ring43. Therefore, the semiconductor wafer W is not caught by the retainer ring43when the chucking plate62is moved upwardly, and hence the semiconductor wafer W can be prevented from being dropped off and damaged.

When the attraction of the semiconductor wafer W is completed, the pusher14is moved downwardly, and the top ring head21is moved angularly horizontally to a position above the polishing surface10while attracting the semiconductor wafer W. The outer circumferential edge of the semiconductor wafer W is held by the retainer ring43so that the semiconductor wafer W is not dislodged from the top ring23. The top ring23is moved downwardly while being rotated to press the semiconductor wafer W against the polishing surface10of the rotating polishing table11. Specifically, during the polishing process, the semiconductor wafer W is released from the attraction sections64,65, and is held on the lower surface of the top ring23. The top ring air cylinder111coupled to the top ring shaft22is operated to press the retainer ring43fixed to the lower end of the top ring23against the polishing surface10of the polishing table11under a predetermined pressing force. In this state, a pressurized fluid having a predetermined pressure is supplied to the pressure chamber70, thereby pressing the semiconductor wafer W against the polishing surface of the polishing table11. At this time, a polishing liquid is supplied from the polishing liquid supply nozzle15, and the semiconductor wafer W is polished in the presence of the polishing liquid between the surface to be polished (i.e., lower surface) of the semiconductor wafer W and the polishing surface10.FIG. 4shows the state in which the semiconductor wafer W is polished.

As described above, the pressing force applied by the top ring air cylinder111to press the retainer ring43against the polishing surface10and the pressing force applied by the pressurized air supplied to the pressure chamber70to press the semiconductor wafer W against the polishing surface10are appropriately adjusted to polish the semiconductor wafer W. When the pressurized fluid is supplied to the pressure chamber70, the chucking plate62is subjected to an upward force. In the present embodiment, the pressurized fluid is supplied to the pressure chamber71through the fluid passage81, thus preventing the chucking plate62from being lifted upwardly due to the force from the pressure chamber70.

When the polishing process is finished, as shown inFIG. 8, the supply of the pressurized fluid to the pressure chamber70is stopped, and the pressure in the pressure chamber70is released to the atmospheric pressure. Accordingly, the chucking plate62is moved downwardly and hence the lower ends of the attraction sections64,65are brought into contact with the semiconductor wafer W. The pressure in the pressure chamber71is released to the atmospheric pressure or the pressure chamber71is evacuated to develop a negative pressure therein. If the pressure chamber71is maintained at a high pressure, then the semiconductor wafer W is strongly pressed against the polishing surface only in portions which are brought into contact with the attraction sections64,65. The semiconductor wafer W is attracted again to the lower surfaces of the attraction sections64,65. In this manner, since the chucking plate62is moved downwardly when the polishing process is finished, the semiconductor wafer W can reliably be attracted to the attraction sections64,65.

The top ring23is moved to an overhanging position while the semiconductor wafer W is attracted to the top ring23. As shown inFIG. 9, the pressure chamber71is connected to the pressure adjuster120through the fluid passage81to develop a negative pressure in the pressure chamber71, thus positioning the chucking plate62upwardly with respect to the retainer ring43. In this state, the top ring23is moved upwardly, and the top ring head21is moved angularly horizontally to move the top ring23to a position above the pusher14again as shown inFIG. 10.

Next, as shown inFIG. 11, the guide stage141of the pusher14is moved upwardly to guide the retainer ring43onto the upper step144of the wafer guide142by the taper146of the wafer guide142. The upward movement of the guide stage141is finished when the upper step144of the wafer guide142is brought into contact with the lower surface of the retainer ring43.

In this state, as shown inFIG. 12, the opening62apositioned at the center of the chucking plate62and the attraction sections64,65are connected to the pressure adjuster120through the fluid passages80,82and83, respectively, and the pressurized fluid (e.g., a mixture of compressed air or nitrogen and pure water) is ejected downwardly from the opening62aand the attraction sections64,65at a pressure of 0.2 MPa, for example (water spout). The semiconductor wafer W is released from the lower surface of the elastic pad60by the ejection of the fluid. The semiconductor wafer W is centrally aligned by the taper147of the wafer guide142and is held by the lower step145of the wafer guide142.

In the present embodiment, the pressurized fluid is ejected from the large-diameter opening62adefined centrally in the chucking plate62and the attraction sections64,65. Therefore, the pressurized fluid is delivered into the region where the elastic pad60and the semiconductor wafer W are held in close contact with each other, and hence the semiconductor wafer W can be released reliably.

In this manner, the polished semiconductor wafer W is transferred from the top ring23to the pusher14. The semiconductor wafer W and the top ring23are cleaned by pure water or a cleaning liquid as needed. Thereafter, the top ring23receives a new semiconductor wafer W from the pusher14and is moved to a position above the polishing table10, and then a new polishing process is performed.

When the semiconductor wafer W is polished to a predetermined extent, the polishing process is finished. After the polishing process is performed, the characteristics of the polishing surface10are changed due to polishing, and the polishing capability thereof for a next polishing process is lowered. Therefore, the dressing unit13dresses the polishing surface10. In a dressing process, the dresser30and the polishing table11are rotated about their own axes independently of each other, and the dressing member34is brought into close contact with the polishing surface10with a predetermined pressing force. At the same time that or before the dressing member34is brought into contact with the polishing surface10, water is supplied from the water supply nozzle16to the upper surface of the polishing surface10, for thereby washing out the used polishing liquid remaining on the polishing surface10. When the dressing process is finished, the dresser33is returned to a standby position by the dressing head31, and is cleaned by a dresser-cleaning device18(seeFIG. 1) that is installed in the standby position.

The polished semiconductor wafer W which has been placed on the pusher14is transferred by the second transfer robot4bto the cleaning device7aor7bhaving, for example, roll sponges for cleaning both surfaces of the semiconductor wafer W. After both surfaces of the semiconductor wafer W are cleaned by the cleaning device7aor7b,the semiconductor wafer W is transferred to the reversing device5or6by the second transfer robot4b,and then the semiconductor wafer W is reversed by the reversing device5or6. Thereafter, the first transfer robot4areceives the semiconductor wafer W from the reversing device5or6, and transfers the semiconductor wafer W to the second cleaning device8aor8bhaving a pen sponge for cleaning the upper surface and a spin dry function. The semiconductor wafer W is cleaned and dried by the second cleaning device8aor8b,and returned to the cassette2aor2bby the first transfer robot4a.

Next, a second embodiment of a polishing method according to the present invention will be described in detail with reference toFIGS. 13 through 22. Those parts or elements of the second embodiment which have the same operation or function as those parts or elements of the first embodiment are denoted by identical reference numerals, and those which will not be described below are identical to those of the first embodiment. Other structural details other than the top ring are basically identical to those of the first embodiment.

FIG. 13is a vertical cross-sectional view showing a top ring according to the second embodiment of the present invention. In the present embodiment, a space defined in the top ring body42and the retainer ring43integrally fixed to the top ring body42houses therein an outer membrane160to be brought into contact with the outer circumferential portion of the semiconductor wafer W that is held by a top ring123. The elastic pad according to the first embodiment is not provided in the present embodiment.

An outer circumferential portion of the outer membrane160is interposed between the holder ring61and the chucking plate62which is fixed to the lower end of the holder ring61. The lower surface of the chucking plate62near the outer circumferential edge thereof is covered by the outer membrane160. The outer membrane160has a lower surface which is brought into contact with the upper surface of the semiconductor wafer W to be polished. The outer membrane160is made of a rubber material having excellent strength and durability, such as ethylene propylene rubber (EPDM), polyurethane rubber, or silicone rubber. The semiconductor wafer W has a recess, which is called a notch or an orientation flat, formed in the outer circumferential edge thereof for recognizing (specifying) the orientation of the semiconductor wafer W. It is preferable that the outer membrane160extends inwardly of the chucking plate62beyond such a notch or an orientation flat.

A ring tube170serving as a contact member which is brought into close contact with the semiconductor wafer W is disposed in a space defined between the chucking plate62and the semiconductor wafer W. In the present embodiment, as shown inFIG. 13, the ring tube170is disposed so as to surround the opening62apositioned at the center of the chucking plate62. In the present embodiment, only the outer attraction section65is provided outwardly of the ring tube170, and no inner attraction section is provided.

The ring tube170comprises an elastic membrane171which is brought into close contact with the upper surface of the semiconductor wafer W, and a ring tube holder172for detachably holding the elastic membrane171. The ring tube170has a pressure chamber72defined by the elastic membrane171and the ring tube holder172. The space between the chucking plate62and the semiconductor wafer W is divided into a plurality of spaces by the ring tube170. Specifically, a pressure chamber73is defined inwardly of the ring tube170, i.e., around the opening62apositioned at the center of the chucking plate62, and a pressure chamber74is defined outwardly of the ring tube170, i.e., around the attraction section65. The elastic membrane171of the ring tube170is made of a rubber material having high strength and durability, such as ethylene propylene rubber (EPDM), polyurethane rubber, or silicone rubber.

The elastic membrane171of the ring tube170has a hole171aformed in a surface thereof to be brought into close contact with the semiconductor wafer W. As shown inFIGS. 14A and 14B, the hole171amay have a shape of a combination of a plurality of ellipses or circles. Alternatively, as shown inFIG. 14C, the hole171amay have a shape of an ellipse with triangular recesses. Alternatively, as shown inFIG. 14D, the hole171amay have a large elliptical shape. Alternatively, as shown inFIG. 14E, the hole171amay have a square or rhombic shape, or as shown inFIGS. 14F and 14G, the hole171amay be a simple slit.

A pressure chamber72in the ring tube71communicates with a fluid passage85comprising a tube, a connector, and the like. The pressure chamber72is connected to the pressure adjuster120(seeFIG. 3) through a regulator provided on the fluid passage85. The pressure chamber73communicates with a fluid passage86comprising a tube, a connector, and the like. The pressure chamber73is connected to the pressure adjuster120through a regulator provided on the fluid passage86.

The pressure chamber71above the chucking plate62and the pressure chambers72,73and74are supplied with a pressurized fluid such as pressurized air, or the atmospheric pressure or vacuum is produced in the pressure chambers71,72,73and74through the fluid passages81,85,86and83. Specifically, the regulators provided on the fluid passages81,85,86and83of the pressure chambers71˜74can regulate the pressures of the pressurized fluids supplied to the pressure chambers71˜74, respectively. Thus, the pressures in the pressure chambers71˜74can be controlled independently or the atmospheric pressure or vacuum is produced in the pressure chambers71˜74. In this manner, the pressures in the pressure chambers71˜74are varied independently by the regulators, and hence the pressing force for pressing the semiconductor wafer W against the polishing pad10can be adjusted with respect to local areas of the semiconductor wafer W.

In this case, the pressurized fluid supplied to the pressure chambers72˜74and the atmospheric pressure may independently be controlled in temperature, for thereby directly controlling a temperature of a workpiece such as a semiconductor wafer from a backside of a surface thereof to be polished. Particularly, when each of the pressure chambers is independently controlled in temperature, the rate of chemical reaction can be controlled in the chemical polishing process of CMP.

Operation of the polishing apparatus according to the present embodiment will be described below. First, the first transfer robot4atakes a semiconductor wafer W from the cassette2aor2b,and the reversing device5or6reverses the semiconductor wafer W. Thereafter, the second transfer robot4btransfers and places the semiconductor wafer W onto the pusher14. In this state, the top ring head21of the top ring unit12is angularly moved to bring the top ring123to a position above the pusher14.

FIG. 15is a vertical cross-sectional view showing the state of the polishing apparatus at this time. In the state shown inFIG. 15, the pressure chamber71in the top ring123is connected to the pressure adjuster120through the fluid passage81, so that a negative pressure is developed in the pressure chamber71. As sown inFIG. 15, the chucking plate62is thus positioned upwardly with respect to the retainer ring43, and hence the semiconductor wafer W can be attracted reliably, as with the first embodiment.

Next, as shown inFIG. 16, the guide stage141of the pusher14is moved upwardly to guide the retainer ring43onto the upper step144of the wafer guide142by the taper146of the wafer guide142. The upward movement of the guide stage141is finished when the upper step144of the wafer guide142is brought into contact with the lower surface of the retainer ring43.

In this state, as shown inFIG. 17, the push stage143of the pusher14is moved upwardly to hold the pattern surface of the semiconductor wafer W which has been placed on the lower step145of the wafer guide142and bring the semiconductor wafer W into close contact with the outer membrane160and the ring tube170of the top ring123. The fluid passages85,86and83communicating respectively with the pressure chamber72in the ring tube170and the pressure chambers73,74are connected to the pressure adjuster120, so that negative pressures are developed in the fluid passages85,86and83to attract the semiconductor wafer W. For example, a pressure of −80 kPa is developed in the fluid passage83and a pressure of −20 kPa is developed in the fluid passages85,86so as to attract the semiconductor wafer W.

At this time, as described above, since the negative pressure is developed in the pressure chamber71in the top ring123so as to position the chucking plate62upwardly with respect to the retainer ring43in advance, the semiconductor wafer W is transferred while the outer circumferential portion thereof is guided by the retainer ring43. Therefore, the semiconductor wafer W is not caught by the retainer ring43when the chucking plate62is moved upwardly, and hence the semiconductor wafer W can be prevented from being dropped off and damaged.

When the attraction of the semiconductor wafer W is completed, the pusher14is moved downwardly, and the top ring head21is moved angularly horizontally to a position above the polishing surface10while attracting the semiconductor wafer W. The outer circumferential edge of the semiconductor wafer W is held by the retainer ring43so that the semiconductor wafer W is not dislodged from the top ring123. The top ring123is moved downwardly while being rotated to press the semiconductor wafer W against the polishing surface10on the rotating polishing table11. Specifically, during the polishing process, the semiconductor wafer W is released from the attraction, and is held by the lower surface of the top ring123. The top ring air cylinder111coupled to the top ring shaft22is operated to press the retainer ring43fixed to the lower end of the top ring123against the polishing surface10of the polishing table11under a predetermined pressing force. In this state, a pressurized fluid having a predetermined pressure is supplied to the pressure chambers72,73and74, thereby pressing the semiconductor wafer W against the polishing surface of the polishing table11. At this time, a polishing liquid is supplied from polishing liquid supply nozzle15, and the semiconductor wafer W is polished in the presence of the polishing liquid between the surface to be polished (i.e. lower surface) of the semiconductor wafer W and the polishing surface10.FIG. 13shows the state in which the semiconductor wafer W is polished.

As described above, the pressing force applied by the top ring air cylinder111to press the retainer ring43against the polishing surface10and the pressing forces applied by the pressurized air supplied to the pressure chambers72˜74to press the semiconductor wafer W against the polishing surface10are appropriately adjusted to polish the semiconductor wafer W. When the pressurized fluid is supplied to the pressure chambers72˜74, the chucking plate62is subjected to an upward force. In the present embodiment, the pressurized fluid is supplied to the pressure chamber71through the fluid passage81, thus preventing the chucking plate62from being lifted upwardly due to the force from the pressure chamber72.

When the polishing process is finished, as shown inFIG. 18, the supply of the pressurized fluid to the pressure chambers72˜74is stopped, and the pressures in the pressure chambers72˜74are released to the atmospheric pressure. Accordingly, the chucking plate62is moved downwardly and hence the lower end of the attraction section65is brought into contact with the semiconductor wafer W. The pressure in the pressure chamber71is released to the atmospheric pressure, or the pressure chamber71is evacuated to develop a negative pressure therein. If the pressure chamber71is maintained at a high pressure, then the semiconductor wafer W is strongly pressed against the polishing surface only in a portion which is brought into contact with the attraction section65. The semiconductor wafer W is attracted again to the lower surface of the attraction section65due to vacuum. When the polishing process is finished, the semiconductor wafer W and the chucking plate62may have occasionally been spaced from each other. In such a case, the attraction section65fails to attract the semiconductor wafer W even if the attraction section65attempts to attract the semiconductor wafer W. In the present embodiment, as described above, since the chucking plate62is moved downwardly when the polishing process is finished, the semiconductor wafer W can reliably be attracted to the attraction section65.

The top ring123is moved to an overhanging position while the semiconductor wafer W is attracted to the top ring123. As shown inFIG. 19, the pressure chamber71is connected to the pressure adjuster120through the fluid passage81to develop a negative pressure in the pressure chamber71in the top ring123, thus positioning the chucking plate62upwardly with respect to the retainer ring43. In this state, the top ring123is moved upwardly, and the top ring head21is moved angularly horizontally to bring the top ring123to a position above the pusher14again as shown inFIG. 20. At this time, it is preferable to supply the pressurized fluid to the pressure chamber72in the ring tube170to pressurize the pressure chamber72. In this manner, the semiconductor wafer W can easily be released from the outer membrane160and the ring tube170.

Then, as shown inFIG. 21, the guide stage141of the pusher14is moved upwardly to guide the retainer ring43onto the upper step144of the wafer guide142by the taper146of the wafer guide142. The upward movement of the guide stage141is finished when the upper step144of the wafer guide142is brought into contact with the lower surface of the retainer ring43.

In this state, as shown inFIG. 22, the opening62apositioned at the center of the chucking plate62and the attraction section65are connected to the pressure adjuster120through the fluid passages86,83, respectively, and a pressurized fluid (e.g., a mixture of compressed air or nitrogen and pure water (D. I. water, de-ionized water)) is ejected downwardly from the opening62aand the attraction section65(water spout). The pressure chamber72in the ring tube170is connected to the pressure adjuster120, and a pressurized fluid (e.g., a mixture of compressed air or nitrogen and pure water) is ejected downwardly from the hole171a(seeFIG. 13) defined in the elastic membrane171of the ring tube170(water spout). The semiconductor wafer W is released from the top ring123by the ejection of the fluid. The semiconductor wafer W is centrally aligned by the taper147of the wafer guide142and is held by the lower step145of the wafer guide142. For example, the fluid is ejected from the opening62aat a pressure of 0.03 MPa, from the attraction section65at a pressure of 0.2 MPa, and from the hole171aof the ring tube170at a pressure of 0.05 MPa. In order to easily break the close contact between the elastic membrane171of the ring tube170and the semiconductor wafer W, it is preferable to eject the fluid first from the hole171aof the ring tube170and then from the opening62aand the attraction section65.

In this manner, in the present embodiment, the pressurized fluid is ejected from the large-diameter opening62adefined centrally in the chucking plate62, the attraction section65, and the hole171adefined in the elastic membrane171of the ring tube170. Therefore, the pressurized fluid is delivered into the region where the outer membrane160and the elastic membrane171of the ring tube170are held in close contact with the semiconductor wafer W, and hence the semiconductor wafer W can be released more reliably. In the case where the hole171adefined in the elastic membrane171of the ring tube170has a shape shown inFIG. 14Cor14D, the semiconductor wafer W can be released more smoothly without producing noise at the time of releasing the semiconductor wafer W.

In the above embodiment, although the fluid passages80˜86are provided separately from each other, these fluid passages may be combined together, or the pressure chambers may communicate with each other, for example. In this manner, the embodiment may be freely modified depending on the magnitude of the pressing force to be applied to the semiconductor wafer W and the position where the pressing force is applied to the semiconductor wafer W. In the above embodiment, although the ring tube170is brought into direct contact with the semiconductor wafer W, the present invention is not limited to such an arrangement. For example, an elastic pad may be interposed between the ring tube170and the semiconductor wafer W to bring the ring tube170into indirect contact with the semiconductor wafer W.

In the above embodiments, although the polishing pad serves as the polishing surface, the present invention is not limited to the above structure. For example, the polishing surface may be constituted by a fixed abrasive. The fixed abrasive is formed into a flat plate comprising abrasive particles fixed by a binder. With the fixed abrasive for polishing, the polishing process is performed by abrasive particles that are self-generated from the fixed abrasive. The fixed abrasive comprises abrasive particles, a binder, and pores. For example, cerium dioxide (CeO2) having an average particle diameter of 0.5 μm or less is used as an abrasive particle, and epoxy resin is used as a binder. Such a fixed abrasive forms a harder polishing surface. The fixed abrasive includes a fixed abrasive pad having a two-layer structure formed by a thin layer of a fixed abrasive and an elastic polishing pad attached to a lower surface of the thin layer of the fixed abrasive. IC-1000 described above may be used for another hard polishing surface.

As described above, according to the present invention, when the pressurized fluid is ejected from the opening defined centrally in the vertically movable member, the pressurized fluid is delivered into the region where the elastic membrane and the workpiece to be polished are held in close contact with each other. Therefore, the workpiece can reliably be released. Further, the hole is formed in the surface, to be brought into contact with the workpiece, of the elastic membrane, so that the pressurized fluid is ejected not only from the opening defined centrally in the vertically movable member, but also from the above hole, thereby releasing the workpiece more reliably.

Furthermore, according to the present invention, because the workpiece is attracted after the vertically movable member is moved downwardly to bring the workpiece into close contact with the attraction section when the polishing process is finished, it is possible to attract the workpiece reliably.

INDUSTRIAL APPLICABILITY

The present invention is preferably applicable to a polishing method for polishing a workpiece, such as a semiconductor wafer having a thin film formed on a surface thereof, to a flat mirror finish.