Dynamic polishing fluid delivery system for a rotational polishing apparatus

Methods and apparatus are provided for performing a chemical-mechanical process on a workpiece surface. The apparatus includes a platen having a top surface and at least one inlet configured to receive a polishing fluid, a plurality of holes formed in the top surface, a manifold system in fluid communication with the at least one inlet and each of the holes, a controller adapted to supply valve command signals, and a plurality of valves, each valve being disposed in one of the holes and coupled to the controller to receive the valve command signals and being operable, in response thereto, to selectively move between an open and a closed position. The method includes the steps of supplying the valve command signals, and selectively opening and closing the valves in response to the valve command signals.

TECHNICAL FIELD

The present invention relates to chemical-mechanical polishing devices. More particularly, the present invention relates to wafer planarization enhancement through improved polishing fluid distribution on a polishing pad.

BACKGROUND OF THE INVENTION

Chemical-mechanical polishing (CMP) is the process of removing projections and other imperfections from a semiconductor wafer to create a smooth planar surface. The wafer is the basic substrate material in the semiconductor industry for the manufacture of integrated circuits. Wafers are typically created by growing an elongated cylinder or boule of single crystal silicon and then slicing individual wafers from the cylinder. Slicing causes both faces of the wafer to be somewhat rough. Planarization is desirable because the front face of the wafer on which integrated circuitry is to be constructed must be substantially flat in order to facilitate reliable semiconductor junctions with subsequent layers of material applied to the wafer. Composite thin film layers comprising metals for conductors or oxides for insulators must also be made of a uniform thickness if they are to be joined to the semiconductor wafers or to other composite thin film layers.

Planarization is typically completed before performing lithographic processing steps that create integrated circuitry or interconnects on the wafer. Non-planar surfaces result in poor optical resolution of subsequent photolithographic processing steps which in turn hinders high-density features from being adequately printed. If a metallization step height is too large, open circuits will likely be created. Consequently, CMP tools are continually being improved upon with an aim toward controlling wafer planarization.

In a conventional CMP assembly the wafer is secured in a carrier connected to a shaft. The shaft is typically connected to a transporter that moves the carrier between a load or unload station and a position adjacent to a polishing pad. One side of the polishing pad has a polishing surface thereon, and an opposite side is mounted to a rigid platen. Pressure is exerted on a wafer back surface by the carrier in order to press a wafer front surface against the polishing pad. Polishing fluid is introduced onto the polishing surface while the wafer and/or polishing pad are moved in relation to each other by means of motors connected to the shaft and/or platen. The above combination of chemical and mechanical stress results in removal of material from the wafer front surface. One requisite for removing wafer material at a high rate (“removal rate”) and for forming a wafer with high surface uniformity is a uniform distribution of polishing fluid about the polishing surface.

In the case of CMP tools that use a rotating polishing platen and pad, one way that the polishing fluid is supplied to the polishing surface is through one or more delivery outlets that deposit the polishing fluid onto the polishing pad near the wafer leading edge. However, polishing fluid is not efficiently utilized with this type of delivery system. Due to the centrifugal force from the rotating platen the polishing fluid is quickly evacuated from the pad surface and the wasted polishing fluid must be continuously replaced. Visual examination of the polishing pad also reveals that the polishing fluid accumulates at the pad outer edge during polishing. As mentioned above, non-uniform polishing fluid distribution causes poor wafer planarization, and this problem alone necessitates an improved polishing fluid supply mechanism.

Another way that the polishing fluid is supplied to the polishing surface is through a plurality of through-holes distributed about the polishing pad. The polishing pad through-holes are in communication with a supply source via holes or passageways extending through the platen. This “through-the-pad” polishing fluid delivery system is known to provide improved polishing fluid uniformity during polishing. Through-the-pad polishing fluid delivery systems have been successfully used on “non-rotational” type CMP tools having a polishing surface not much larger than the wafer, and which moves in an orbital or reciprocating motion. However through-the-pad fluid delivery has not been shown to provide improved polishing fluid uniformity when used in conjunction with the type of CMP tool incorporating a rotating polishing pad. This is due at least in part to the relative mismatch in wafer and platen diameter. Because the polishing surface is necessarily substantially larger than the wafer in a rotating polishing pad CMP tool, usually more than twice the wafer diameter, some polishing pad through-holes are covered by the wafer that is being polished, while others are left uncovered. The uncovered holes are naturally passages of lesser resistance, and consequently, little if any polishing fluid is delivered directly to the wafer-pad interface during polishing, while large amounts of slurry is wasted through the uncovered holes.

Accordingly, it is desirable to provide a CMP polishing fluid supply mechanism that enables substantially uniform polishing fluid distribution about a pad-wafer interface during polishing on a rotating platen type polishing apparatus. In addition, it is desirable to provide a CMP polishing fluid supply mechanism that efficiently utilizes the polishing fluid. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

BRIEF SUMMARY

An apparatus is provided for performing a chemical-mechanical process on a workpiece surface. The apparatus comprises a platen having a top surface and at least one inlet configured to receive a polishing fluid, a plurality of holes formed in the top surface, a manifold system in fluid communication with the at least one inlet and each of the holes, a controller adapted to supply valve command signals, and a plurality of valves, each valve being disposed in one of the holes and coupled to the controller to receive the valve command signals and being operable, in response thereto, to selectively move between an open and a closed position.

A platen is also provided for performing a chemical-mechanical polishing process on a workpiece surface. The platen comprises a top surface having a plurality of holes formed therein, at least one inlet configured to receive a polishing fluid, a manifold system in fluid communication with the at least one inlet and each of the holes, and a plurality of valves, each valve being disposed in one of said holes and being adapted to receive the valve command signals and operable, in response thereto, to selectively move between an open and a closed position.

A method is also provided for distributing a polishing fluid to a workpiece surface using a chemical-mechanical polishing platen having a top surface, a plurality of holes formed in the top surface, and a plurality of valves, each valve being disposed in one of said holes. The method comprises the steps of supplying valve command signals from a controller to the valves, and selectively opening and closing the valves in response to the valve command signals to control fluid distribution to the workpiece surface.

DETAILED DESCRIPTION

FIG. 1illustrates a top cutaway view of a CMP polishing apparatus100. The apparatus100depicted is suitable for polishing or planarizing material from the surface of a workpiece and can incorporate the fluid distribution system of the present invention. The apparatus100includes a multi-station polishing system102, a clean system104, and a wafer load/unload station106. In addition, the apparatus100includes a cover (not shown) that surrounds the apparatus100to isolate the apparatus100from the surrounding environment. The apparatus100may be any machine capable of removing material from a workpiece surface.

Although the present invention may be used to remove or polish material from the surface of a variety of workpieces such as magnetic disks, optical disks, and the like, the invention is conveniently described below in connection with removing material from the surface of a wafer. In the context of the present invention, the term “wafer” shall mean semiconductor substrates, which may include layers of insulating, semiconductor, and conducting layers or features formed thereon and used to manufacture microelectronic devices.

An exemplary polishing system102includes four polishing stations,108,110,112, and114, that operate independently; a buff station116; a stage118; a robot120; and optionally, a metrology station122. Polishing stations108-114may be configured as desired to perform specific functions.

The polishing system102also includes polishing surface conditioners140and142. The configuration of the conditioners140and142generally depends on the type of polishing surface to be conditioned. For example, when the polishing surface comprises a polyurethane polishing pad, conditioners140and142may include a rigid substrate coated with diamond material. Various other surface conditioners may also be used in accordance with the present invention.

The clean system104is generally configured to remove debris such as polishing fluid residue and material from the wafer surface during polishing. In accordance with the illustrated embodiment, the system104includes clean stations124and126, a spin rinse dryer128, and a robot130configured to transport the wafer between the clean stations124and126and the spin rinse dryer128. Alternatively, the clean station104may be separate from the remainder of the planarization apparatus. In this case, the load station106is configured to receive dry wafers for processing, but the wafers may remain in a wet (e.g., deionized water) environment until the wafers are transferred to the clean station. In operation, cassettes132, including one or more wafers, are loaded onto apparatus100at station106. The wafers are then individually transported to a stage134using a dry robot136. A wet robot138retrieves a wafer at the stage134and transports the wafer to metrology station122for film characterization or to the stage118within the polishing system102. The robot120picks up the wafer from the metrology station122or the stage118and transports the wafer to one of the polishing stations108-114for wafer surface planarization. After a desired amount of material has been removed, the wafer may be transported to another polishing station.

After material has been removed from the wafer surface, the wafer is transferred to the buff station116to further polish the surface of the wafer. After the polishing and/or buff process, the wafer is transferred to the stage118which is configured to maintain one or more wafers in a wet (e.g. deionized water) environment.

After the wafer is placed on the stage118, the robot138picks up the wafer and transports it to the clean system104. In particular, the robot138transports the wafer to the robot130, which in turn places the wafer in one of the clean stations124,126. The wafer is there cleaned and then transported to the spin rinse dryer128to rinse and dry the wafer prior to transporting it to the load/unload station106using the robot136.

FIG. 2illustrates a top cut away view of another exemplary polishing apparatus200, configured to planarize a wafer. The apparatus200is suitably coupled to a carousel300illustrated inFIG. 3to form an automated polishing system. The system in accordance with this embodiment may also include a removable cover (not shown) overlying the apparatus200and the carousel300.

The apparatus200includes three polishing stations,202,204, and206, a wafer transfer station208, a center rotational post210that is coupled to carousel300and which operatively engages carousel300to cause carousel300to rotate, a load and unload station212, and a robot214configured to transport wafers between stations212and208. Furthermore, the apparatus200may include one or more rinse washing stations216to rinse and/or wash a surface of a wafer before or after a polishing, process. Although illustrated with three polishing stations, the apparatus200may include any desired number of polishing stations, and one or more such polishing stations may be used to buff a surface of a wafer. Furthermore, the apparatus200may include an integrated wafer clean and dry system similar to the system104described above. The wafer station208is generally configured to stage wafers before or between polishing and/or buff operations and may be further configured to wash and/or maintain the wafers in a wet environment.

The carousel300includes polishing heads, or carriers,302,304,306, and308, each configured to hold a single wafer and urge the wafer against the polishing surface (e.g., a polishing surface associated with one of stations202-206). Each carrier302-308is suitably spaced from post the210such that each carrier aligns with a polishing station or the wafer station208. In accordance with one embodiment of the invention, each carrier302-308is attached to a rotatable drive mechanism that allows the carriers302-308to cause a wafer to rotate (e.g., during a polishing process). In addition, the carriers may be attached to a carrier motor assembly that is configured to cause the carriers to translate as, for example, along tracks310. Furthermore, each carrier302-308may rotate and translate independently of the other carriers.

In operation, wafers are processed using the apparatus200and carousel300by loading a wafer onto the station208from the station212using the robot214. When a desired number of wafers are loaded onto the carriers, at least one of the wafers is placed in contact with the polishing surface. The wafer may be positioned by lowering a carrier to place the wafer surface in contact with the polishing surface, or a portion of the carrier (e.g., a wafer holding surface) may be lowered to position the wafer in contact with the polishing surface. After polishing is complete, one or more conditioners218may be employed to condition the polishing surfaces.

During a polishing process, a wafer may be held in place by a carrier400, illustrated in FIG.4. The carrier400comprises a retaining ring406and a receiving plate402including one or more apertures404. The apertures404are designed to assist retention of a wafer by the carrier400by, for example, allowing a vacuum pressure to be applied to the backside of the wafer or by creating enough surface tension to retain the wafer. The retaining ring406limits the movement of the wafer during the polishing process.

FIG. 5illustrates another polishing system500in accordance with the present invention. It is suitably configured to receive a wafer from a cassette502and return the wafer to the same or to a predetermined different location within the cassette in a clean common dry state. The system500includes polishing stations504and506, a buff station508, a head loading station510, a transfer station512, a wet robot514, a dry robot516, a rotatable index table518, and a clean station520. The dry robot516unloads a wafer from the cassette502and places the wafer on the transfer station512. The wafer then travels to the polishing stations504-508for polishing and returns to the station510for unloading by the wet robot514and the transfer station512. The wafer is then transferred to the clean system520to clean, rinse, and dry the wafer before the wafer is returned to the load and unload station502using the dry robot516.

Turning now to the polishing fluid delivery system of the present invention,FIG. 6illustrates a rotatable platen10having a pattern of polishing fluid delivery holes therein. Although not shown, a CMP pad is provided on top of the platen10during use. It should be noted that the term “CMP pad” is used here purely for convenience, and is intended to more broadly cover any type of polishing, electropolishing, buffing, or cleaning pad disposed on a platen and used in conjunction with a suitable polishing, buffing, or cleaning fluid or slurry. The CMP pad includes a polishing surface for polishing a wafer or other workpiece, hereinafter generally referred to as a “wafer.” The CMP pad also includes through holes that are arranged in a pattern that matches the platen hole pattern so that the platen polishing fluid delivery holes are in fluid communication with the CMP through holes.

FIG. 6illustrates with shading an area13that is covered by the wafer at some time as the wafer is being polished. When the area13is covered, polishing fluid delivery holes11within the area13are open and deliver polishing fluid to the CMP pad top surface. All holes12that are not disposed within the area13are closed and consequently do not deliver polishing fluid to the CMP pad top surface. Consequently, the open holes11covered by the wafer form the only polishing fluid pathways to the CMP pad top surface.

The selectively opening and closing polishing fluid delivery holes11,12function to create an even polishing fluid distribution along the CMP pad/wafer interface during wafer polishing. The even polishing fluid distribution is a result of the polishing fluid pathways through each of the open holes11having substantially equal amounts of flow resistance since the wafer covering the holes11is essentially flat. Also, because the platen10rotates, all of the holes11,12are covered by the wafer at some time during a single rotation of the platen, thereby utilizing the entire polishing surface of the CMP pad.

FIG. 8depicts the coordinated elements within a polishing station designated108, although the illustrated polishing station108may be representative of any of the above mentioned polishing stations110,112,114,202,204,206or other conventional polishing stations to the extent that the polishing station features are commonly known in the art. As discussed above, a wafer20is secured in a carrier400that rotates during a polishing process as designated by arrow16and also oscillates in a radial direction relative to the platen as designated by arrow15. The platen10also rotates during a polishing process as designated by arrow14. The platen10is disposed on top of a rotary union25and houses a manifold distribution system30. Polishing fluid is introduced to the manifold system30via a supply port17that extends through the rotary union25that rotatably supports the platen10. The manifold system30distributes the polishing fluid about the platen interior. The manifold system30includes the platen holes11,12through which the polishing fluid flows from the platen interior to the platen top surface18. A CMP pad40is disposed on top of the platen top surface18, and includes through-holes42that are contiguous with the platen holes11,12and extend to a CMP pad top surface41.

As illustrated inFIG. 8, only the platen holes11that are covered by the wafer20are open. Valves (not shown) are disposed proximate to or inside of each of the holes11,12to regulate polishing fluid passage to the platen top surface18. Electronic components automatically control valve openings and closings.FIG. 7is a schematic of a valve control system50and the valves19it controls according to one embodiment of the invention. In an exemplary embodiment, valves19open as soon as it is determined that the wafer20entirely covers holes in which the valves19are disposed. The wafer20only momentarily covers any given hole due to the constant motion of the platen10and carrier400, so it is preferred that polishing fluid be quickly distributed to the CMP pad/wafer interface by disposing the valves19as close as possible to the platen top surface18. Valve opening and closing commands may be delayed or progressed as needed in order to allow the polishing fluid to always exist at the pad-wafer interface. For example, if polishing fluid will not reach the pad-wafer interface approximately at the instant that the wafer covers a hole11,12, the valves19may be commanded to open momentarily before the wafer20covers the hole11,12.

The valve control system50depicted inFIG. 7produces control signals53that regulate valve openings and closings. The valve control system50can be placed in any convenient location for communication with the valves11,12, but is preferably disposed within the platen10. The command signals53can be based on such factors as the hole configuration data52for the platen, and feedback data regarding the platen's angular position relative to the wafer20. In some cases it may be necessary to also base the command signals on data regarding the time required for polishing fluid to travel from the valves19to the wafer surface during polishing. The data regarding the polishing fluid travel time is a function of such determinants as the polishing fluid consistency, the depth at which the valves19are disposed in the platen10, the CMP pad thickness, and the pressure exerted on the polishing fluid. The angular position and wafer position can be provided for example by a rotary encoder51or other conventional clocking device.

A rotary encoder51is positioned on an external surface or inside a cavity of the rotary union25in an exemplary embodiment of the invention. In another exemplary embodiment of the invention the rotary encoder51is positioned on an external surface or inside a cavity of the platen10. Conventionally known optical, magnetic, or capacitive techniques can be employed to produce an electrical signal that is converted to rotary position data, and to input the data into the control system50. The inputted data from the encoder and pertaining to the platen hole configuration and, if necessary, the distance between the valves19and the CMP pad top surface41enables the control system50to select a specific configuration of holes to be opened and closed at any moment and to thereby provide a uniform distribution of polishing fluid across the surface of the wafer20that is being polished during a polishing process.

While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. For example, in addition to a CMP polishing process, the present invention is equally applicable to an electro-polishing process for electrochemically polishing a metal layer such as copper on a substrate using a suitable pad and electro-active chemistry, to a wafer buffing process for buffing scratches from a polished wafer using a buffing pad and suitable buffing fluid, or to a wafer cleaning process using a suitable cleaning pad in the presence of a cleaning, etching, or rinsing solution. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.