CMP apparatus and load cup mechanism

In accordance with one embodiment of the invention, a load cup mechanism is provided for loading and unloading apparatus such as a CMP apparatus. The load cup mechanism, configured to load a work piece into and to unload a work piece from the apparatus, comprises a load cup arm configured to pivot about an axis between a load position aligned with the apparatus and an off-load position. A work piece platform is coupled to an end of the load cup arm and a plurality of lift fingers and a plurality of guide fingers, configured to support and center a work piece, are spaced about the work piece platform. A plurality of guide posts are spaced apart about the periphery of the work piece platform and are configured to align the work piece platform, in the load position, to the processing apparatus.

TECHNICAL FIELD

The present invention generally relates to a mechanism for loading and unloading a processing apparatus and more specifically, in one embodiment, to a chemical mechanical planarization (CMP) apparatus and to a load cup mechanism for loading and unloading a processing apparatus such as a CMP apparatus.

BACKGROUND

Many manufacturing processes require the automated loading and unloading of work pieces into and out of a processing apparatus. In the interest of reducing cost and increasing productivity, such movement of work pieces is often accomplished with the aid of a robotically controlled load and unload mechanism.

One example of such a manufacturing process is the planarization of a surface of a work piece, a process that finds application in the manufacture of many types of products such as semiconductor wafers, optical blanks, memory disks, and the like. Chemical mechanical planarization (CMP) is one accepted method for achieving a planar surface on such work pieces. The CMP method typically requires the work piece to be loaded into and mounted precisely on a carrier head in a manner such that the surface to be planarized is exposed. The exposed side of the work piece is then held against a polishing pad and relative motion is initiated between the work piece surface and the polishing pad in the presence of a polishing slurry. Typically the work pieces are processed in batches or lots that include a plurality of work pieces. For example, with the CMP processing of semiconductor wafers, each of the wafers in a lot must be sequentially loaded from a wafer cache onto the carrier head for planarization. Following the planarization, each wafer is unloaded from the carrier head and again placed in a wafer cache or is directly transferred to a subsequent processing apparatus such as a cleaning station.

Loading a work piece into a chemical mechanical planarization apparatus presents problems for conventional work piece handling mechanisms because of the nature of the CMP carrier head. The conventional CMP carrier head includes a flexible diaphragm against which the back surface (the surface that is not to be polished) is pressed. The flexible diaphragm is surrounded by an annular wear ring or retaining ring having an inner diameter only slightly greater than the diameter of the work piece to be polished. The diaphragm and the wear ring form a cavity into which the work piece must be loaded. To carry out the planarization operation, the work piece must be mounted against the diaphragm within the confines of the wear ring. In the CMP processing of a semiconductor wafer the recess into which the semiconductor wafer must be loaded has a depth on the order of the thickness of the wafer itself, or about 0.75 mm, and the clearance between the inner diameter of the wear ring and the outer diameter of the semiconductor wafer is typically less than 1 mm.

With many work pieces, and certainly with semiconductor device wafers, the surfaces of the work pieces can be easily damaged if the surfaces are contacted during the loading and unloading processes. Because of this, the loading and unloading should preferably be done in a manner such that only the edge of the work piece or, at most, the surface within a narrow distance from the edge is contacted during the process. With the CMP processing of semiconductor wafers this requirement is made even more significant by the current migration of the semiconductor industry from 200 mm to 300 mm wafers. As part of this change, the semiconductor industry has adopted new wafer-handling standards for 300 mm wafers that preclude all contact with the major portion of the surfaces of a wafer, and has tightened limitations on the extent of the wafer that may be contacted near the wafer edge. Thus no significant contact with the front surface of the wafer is permitted and even known vacuum type end-effectors, or other end-effectors that grip or touch the back surface of the wafer are not allowed. These requirements and restrictions place serious limitations on the mechanisms used to handle the wafers. In addition, 300 mm wafers are significantly heavier than 200 mm wafers, adding still more demands on the mechanical integrity, precision, and reliability of the load and unload mechanisms.

Other types of processing apparatus in addition to CMP apparatus also require a work piece to be loaded into a recessed space with a high degree of positional accuracy and without adversely contacting the surfaces of the work piece. Although there are existing load and unload mechanisms such as robotically controlled work piece wands to address such applications, such mechanisms are costly, have difficulty with large or heavy work pieces, and require frequent maintenance and calibration to retain the necessary positional accuracy. Accordingly, it is desirable to provide an improved work piece handling mechanism that can load work pieces into and unload work pieces from a work piece processing apparatus with a high degree of precision and without adversely contacting the critical surfaces of the work piece. In addition, it is desirable to provide an improved chemical mechanical planarization (CMP) apparatus that includes a precision load and unload mechanism. 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.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, or the following detailed description.

In accordance with one embodiment of the invention, a load cup mechanism is provided that facilitates the accurate loading of an unprocessed work piece into a processing apparatus and the unloading of a processed work piece from that apparatus following a processing operation. In accordance with a further embodiment of the invention, a multistage chemical mechanical planarization (CMP) apparatus that includes a plurality of load cup mechanisms is provided.

The drawing figures are intended to illustrate the general manner of construction of the inventive apparatus and are not necessarily to scale. In the description and in the claims, the terms such as up, down, downward, inward, upper, lower, top, bottom, and the like may be used for descriptive purposes. However, it is understood that the embodiments of the invention described herein are capable of operation in other orientations than as shown, and the terms so used are only for the purpose of describing relative positions and are interchangeable under appropriate circumstances. The term “chemical mechanical planarization” is also often referred to in the industry as “chemical mechanical polishing,” and it is intended to encompass herein both term by the use of “chemical mechanical planarization” and to represent each by the acronym “CMP.” For purposes of illustration only, the invention will be described as it applies to a CMP apparatus and to a CMP process and specifically as is applies to the CMP processing of a semiconductor wafer. It is not intended, however, that the invention be limited to these illustrative embodiments; instead, the invention is applicable to a variety of processing apparatus and to the processing and handling of many types of work pieces.

FIG. 1illustrates schematically, in top view, a multiple stage chemical mechanical planarization (CMP) apparatus20in accordance with one embodiment of the invention. CMP apparatus20includes a plurality of chemical mechanical planarization carrier heads22,23,24positioned about a centrally located work piece robot26. The work piece robot includes an extensible arm28with an end-effector30or other implement at the end of the extensible arm. The end-effector is capable of grasping a work piece31and transporting it, for example, from a work piece cache32to one of a plurality of load cups34,35,36. The load cups and the operation of the load cups will be described in detail below. Each of the CMP carrier heads is positioned over a polishing pad (not illustrated) in a manner well known to those of skill in the CMP art. Load cup34is coupled to a load cup arm38that is configured to a pivot about an axis40from an off-load position (as illustrated) to a load position aligned beneath carrier head22. The path traversed by load cup34as it pivots about axis40is indicated by double headed arrow41. In a similar manner, load cup35is coupled to a load cup arm42that is configured to pivot about an axis44from an off-load position to a load position aligned beneath carrier head23. The path traversed by load cup35as it pivots about axis44is indicated by double headed arrow45. And load cup36is coupled to a load cup arm46that is configured to pivot about an axis48from an off-load position to a load position aligned beneath carrier head24. The path traversed by load cup36as it pivots about axis48is indicated by double headed arrow49. Although three carrier heads are illustrated, CMP apparatus20can be configured with any number of carrier heads and with a proportionate number of load cups and associated elements.

In operation, robot26and end-effector30(or other grasping device) remove a work piece31from work piece cache32and transport it to a selected one of load cups34,35,36where it is transferred to the selected load cup. If the selected load cup is load cup34, for example, load cup34then pivots on load cup arm38about axis40to a position aligned beneath carrier head22. Once aligned beneath carrier head22, the work piece that had been transferred from the work piece cache32is transferred to carrier head22for processing. After the transfer is completed, load cup34pivots on load cup arm38to the off-load position and work piece31is processed by carrier head22pressing the surface of the work piece against a polishing pad. The CMP process is well known and will not be described herein. After the CMP process is completed, the carrier head is raised to a position above the polishing pad, load cup34again pivots on load cup arm38about axis40to the load position, and the now processed work piece is transferred from the carrier head to the load cup. Load cup34then pivots back to the off-load position where the work piece is removed from the load cup by end-effector30and work piece robot26. The work piece robot can then return the now processed work piece to the work piece cache or can transfer the work piece to another of the carrier heads for further processing or to another processing station (not illustrated).

FIG. 2illustrates, in perspective view, a load cup mechanism134in accordance with a further embodiment of the invention. Load cup mechanism134finds application, for example, in a multiple stage CMP apparatus20as illustrated inFIG. 1. Various elements of a load cup in accordance with one embodiment are more clearly seen inFIG. 3. Load cup134includes a work piece platform136which, in a preferred embodiment includes a substantially planar peripheral load ring138to which are coupled a plurality of spaced apart lift fingers140and a plurality of spaced apart guide fingers142. Load cup134also includes a plurality of spaced apart guide posts144. In accordance with this embodiment, load cup134includes four lift fingers, four guide fingers, and four guide posts, but a greater or lesser number could also be used depending on the particular application.

Lift fingers140are designed to support a work piece such as a semiconductor wafer in a position above the plane of peripheral load ring138. The lift fingers are positioned about the peripheral load ring along a circular path having a diameter slightly less than the diameter of the work piece to be handled by the load cup. For example, for a 300 mm diameter semiconductor wafer, the lift fingers are positioned along a circular path having a diameter of about 298 mm so that they contact only the outer 1 mm of the wafer. The lift fingers preferably have an upper surface146that slopes downwardly and inwardly with respect to the circumference of the peripheral load ring. The downwardly sloping surface of the lift fingers helps to insure that even if a work piece is initially misaligned with respect to the load cup mechanism, only the near peripheral edge of the work piece is contacted. Lift finger140is preferably coupled to the peripheral load ring by a leaf spring149that provides a “soft landing” for a work piece transferred to the load cup.

Guide fingers142act to position, preferably to center, a work piece on the load cup mechanism. The plurality of guide fingers are positioned about the peripheral load ring along a circular path having a diameter slightly greater than the diameter of the work piece to be handled by the load cup mechanism. For example, if the work piece is a 300 mm semiconductor wafer, the vertical surfaces148of the guide fingers can be placed along a circular path having a diameter of about 300.6 mm. As a work piece is transferred to the load cup mechanism, it is captured by vertical surfaces148of the guide fingers. If a work piece is slightly off center as it is transferred to the load cup mechanism, beveled edges150of the guide fingers guide the work piece to a centered position defined by vertical surfaces148. A work piece transferred to load cup mechanism134thus rests with its peripheral edge supported on lift fingers140and centered by vertical surfaces148of guide fingers142. Beveled surfaces150also serve an additional purpose as will be explained below. For reasons also explained below, guide finger142is preferably configured to pivot about a pin (not illustrated) to a recessed position. The pivot pin passes through holes formed in guide finger142and is retained in load/unload block156by a bracket or other mechanism which can be attached to the load/unload block. Guide finger142is biased to an upright position by a torsion spring155positioned about the pivot pin and captured by the load/unload block. Load/unload blocks156are coupled to peripheral load ring138.

Guide posts144are also coupled to peripheral load ring138. The guide posts serve to align the load cup mechanism to the processing apparatus such as a CMP carrier head as will be explained more fully below. Preferably one each of a guide post144, lift finger140, and guide finger142are positioned in proximity to each other. Preferably one each of the guide post, lift finger and guide finger are coupled together by a load/unload block156which, in turn, can be coupled to the peripheral load ring. The load/unload block can be coupled to the peripheral load ring, for example, by screw fasteners or the like.

FIGS. 4 and 5schematically illustrate, in cross section, operation of the load and unload elements of load cup mechanism134in accordance with an embodiment of the invention.FIGS. 4 and 5, which should be considered together withFIGS. 1-3, illustrate a portion of load cup mechanism134and its interaction with a processing apparatus and specifically its interaction with a carrier head122of a CMP apparatus as a work piece such as a semiconductor wafer126is loaded into the apparatus. Carrier head122, a portion of which is illustrated, includes a wear ring124and a diaphragm125. The diaphragm and wear ring form a recess into which a work piece such as a semiconductor wafer126must be inserted for processing. In the process of loading semiconductor wafer126into the recess in carrier head, the wafer is first transferred from a wafer cache to load cup mechanism134. The wafer may be transferred from the wafer cache to the load cup mechanism by an end-effector30or other grasping mechanism secured to the end of an extensible robot arm28. The robot and the end-effector transfer the wafer, process side down, to a load cup mechanism134that is pivoted to the off-load position. By “process side down” is meant that the side of the wafer that is to be planarized is down. The outer periphery of wafer126rests on surface146of lift fingers140and is centered on the load cup mechanism by vertical surfaces148of guide fingers142. Load cup mechanism134is then pivoted to the load position roughly aligned beneath carrier head122. The load cup mechanism is then raised vertically toward the carrier head so that guide posts144contact the edge of wear ring124or other alignment key on the carrier head. The interaction of the guide posts with the wear ring or other alignment key precisely aligns the load cup mechanism and the wafer it carries with respect to the recess in the carrier head as illustrated inFIG. 4. The ends of guide posts144are preferably chamfered to assist in the alignment. During the movement of the load cup mechanism, the guide fingers, touching only the edge of the wafer, maintain the wafer positioned on the lift fingers of the load cup mechanism.

After load cup mechanism134and wafer126are aligned with carrier head122, the load cup mechanism is further raised toward the carrier head. As the load cup mechanism is raised, the beveled ends150of guide fingers142contact the bottom surface of wear ring124and this contact with the beveled surface begins to cause the guide fingers to pivot about pivot pin152away from wafer126as illustrated inFIG. 5. Although not illustrated, the load cup mechanism continues to lift the wafer toward the recess in carrier head122, and as the load cup mechanism and wafer get closer to the carrier head, the guide fingers continue to pivot away from the wafer. The load cup mechanism thus continues to lift the wafer until it is secured within the recess in the carrier head. The load cup mechanism is then lowered to a plane beneath carrier head122and is pivoted to the off-load position. Processing of the wafer can then proceed in the normal manner. In the normal processing of wafer126the carrier head is lowered to place the lower or process side of the wafer in contact with a polishing pad and the CMP process is carried out.

Following the CMP process, the load process is reversed to unload the now processed wafer from the carrier head. -The load cup mechanism is pivoted from the off-load position to the load position under the carrier head. Load cup mechanism134is raised so that guide posts144align the load cup mechanism with the recess in carrier122. The load cup mechanism is raised further to cause guide fingers142to contact the lower surface of wear ring124and to pivot away from the recess. The now processed wafer is discharged from the recess in the carrier head and is supported on surfaces146of lift fingers140of load cup mechanism134. The load cup mechanism is lowered away from the carrier head and as the load cup mechanism is lowered, torsion springs155causes guide fingers142to pivot to a position centering wafer126on the load cup mechanism between surfaces148of the plurality of guide pins. The load cup mechanism is lowered further out of contact with the carrier head and then is pivoted to the off-load position. During this movement of the load cup mechanism, the guide fingers again maintain wafer126positioned on the lift fingers of the load cup mechanism. From the off-load position the now processed wafer can be removed from the load cup mechanism by the end-effector and work piece robot and can be returned to the wafer cache or can be moved to another process station or to another load cup mechanism associated with another carrier head.

Referring again toFIG. 2, there is illustrated a further embodiment of the invention. As illustrated, load cup arm238is coupled to a support ring240. Support ring240, in turn, is coupled to and supports peripheral load ring138. In a preferred embodiment, a plurality of radial spokes246are coupled at one end to support ring240and at the opposite end to a central hub248. During the processing of some work pieces, and specifically during the CMP processing of semiconductor wafers, it is desirable to maintain the surface of the wafer in a hydrophilic state because in that state the wafer is less susceptible to contamination. A semiconductor wafer that has just undergone CMP processing is generally hydrophilic, but rapidly becomes hydrophobic upon exposure to air. Accordingly, it is desirable to spray a fluid such as water or other liquid, especially a liquid containing a surfactant, onto the wafer surface before that surface becomes hydrophobic. In other applications, it is desirable for this or other reasons to maintain the surface of the work piece wetted with a fluid. In accordance with another embodiment of the invention the load cup mechanism is provided with a plurality of fluid spray nozzles250from which a fluid can be sprayed onto the surface of the work piece before and/or after processing. In accordance with one embodiment of the invention, the fluid spray nozzles are positioned on radial spokes246and the spokes are configured as a spray manifold for conveying fluid to spray nozzles250. A fluid coupling252can be fitted to the spray manifold through which fluid can be brought from a fluid reservoir and tubing (not illustrated) to the manifold.

FIG. 6illustrates, in a cross section of a portion of a load cup mechanism, a preferred embodiment of the invention for coupling support ring240and peripheral load ring138. It is desirable that the peripheral load ring be aligned with the carrier head and in a plane parallel to the wear ring and diaphragm of the carrier head when the load cup mechanism is in the load position. In accordance with this embodiment of the invention a plurality of springs254are positioned between the support ring and the peripheral load ring. The springs can be attached at one end to either the support ring or to the peripheral load ring with a screw or other fastener. InFIG. 6this attachment has been illustrated as being to the peripheral load ring. The other end of the spring can be attached to the other of the support ring or peripheral load ring with a threaded stud256that is integral with an end of the spring. The spacing between the support ring and the peripheral load ring can be adjusted by adjusting the distance the threaded stud is turned into the support ring. By so adjusting each of the plurality of springs, the plane of the peripheral load ring can be adjusted to keep it parallel to the plane of the wear ring. In addition to providing a height adjustment and an adjustment to the plane of peripheral load ring138, springs254allow for a lateral adjustment within the plane of the peripheral load ring as the load cup mechanism is aligned with processing apparatus such as a carrier head of a CMP apparatus. As guide posts144coupled to peripheral load ring138contact the wear ring or other alignment key of the carrier head, springs254allow the load cup mechanism to move in the plane defined by the peripheral load ring to align the semiconductor wafer or other work piece to be aligned with the recess in the bottom of the carrier head.

FIG. 7illustrates, in perspective view, when considered together withFIG. 2, a work piece gravity sensor258in accordance with a further embodiment of the invention. Work piece gravity sensor258is preferably coupled to peripheral load ring138and is configured to detect the presence of a work piece such as a semiconductor wafer positioned on the load cup mechanism. Work piece gravity sensor258includes a work piece sense finger260which is constrained to pivot about a pivot point within the sensor. The pivot point can be, for example, a pivot pin that passes through a bore formed in the work piece sense finger. At one extremity of the work piece sense finger is a work piece contact264. At the opposite extremity of the work piece sense finger is a sensor target266. The pivot point is positioned relative to the center of gravity of the work piece sense finger such that in the absence of a work piece on the load cup mechanism, the sense finger is biased with the work piece contact264in the “up” position. When a work piece such as a semiconductor wafer is placed on the load cup mechanism, the work piece contacts work piece contact264, moving the work piece contact to a “down” position and causing the sense finger to pivot about the pivot point. The work piece sensor also includes a magnetic, inductive, or other type of sensor268positioned proximate the extremity of the work piece sense finger that includes sensor target266. As the work piece contact moves from the “up” position when no work piece is present to the “down” position when a work piece is present, sensor target266moves relative to sensor268causing a sensor signal to be generated.

FIG. 8schematically illustrates, in perspective view, a load cup134, load cup arm238, and pivot mechanism300in accordance with one embodiment of the invention. Pivot mechanism300includes a shaft302about which load cup134can pivot from an off-load position to a load position. Shaft302is coupled to and moves up and down in response to an up/down air cylinder304. Shaft302is also coupled to and rotates in response to an in/out air cylinder306. The motion of shaft302is relative to a coupling308which is fixed relative to the position of the related carrier head. The up or down motion and the rotational motion of shaft302causes load cup134and an associated work piece positioned thereon to move up and down with respect to a processing apparatus and to pivot between a load and an off-load position. Load cup arm238can be coupled to shaft302, for example, by a clamp309that tightens when torque is applied to threaded fasteners310or other similar fasteners. The clamp provides an adjustment point for initial set up adjustment in both height and angular position of the load cup. Once tightened, the clamp acts as a rigid connection between the load cup arm and the shaft. Computer controls can be used to activate the two air cylinders to move the load cup at the desired time. Other mechanisms such as servo motors or the like could also be used to move and activate shaft302and hence the load cup and the work piece carried by the load cup.