Patent Application
20050112279
1. Field of the Invention
The invention generally relates to a gripping mechanism to hold a workpiece during workpiece fabrication and, more particularly, to gripping mechanisms and a method of use which reduces process variations and contamination during wafer fabrication processing.
2. Background Description
To fabricate microelectronic devices such as an integrated circuit (IC), many different processes are used to achieve the final product. By way of example, in fabrication processes, it is known to use processing fluids such as, for example, chemicals, plating solutions, photoresists and the like on the wafer. To accomplish these processes, the wafer is typically held on a rotating chuck by grips that locate a wafer on its edges. But, it is known that these grips disrupt the uniform flow of processing fluids radially outward. This leads to inconsistencies in the processing near the areas of contact with the grips. This can also result in the accumulation of particulate contamination due to the stagnation of flow in the vicinity of grips, as well as shadowing effects.
Being more specific, in a single wafer application, the single wafer is placed on a rotating chuck of a processing machine. The wafer is held in place by three stationary gripping mechanisms, which contact an edge of the wafer about a radial edge. The grips allow the wafer to be rotated on the rotating chuck during fabrication thus ensuring that the wafer remains stationary. During the rotation of the chuck, processes are performed on the wafer to reach a final product. These processes may include, for example, the application of photoresists in order to form, for example, channels, isolation features and the like. Other chemicals are also used during the fabrication processes such as, for example, etching solutions, plating solutions and the like.
However, during the application of these fluids, it is known that the grips interfere with the processing of the wafer. That is, since the stationary grips are always in contact with the wafer, the wafer process suffers from process variations and or contamination around the grips. This is due to physical obstruction by the grips or, in some instances, capillary trapping. In either case, this results in yield deficiencies, higher manufacturing costs and other known problems.
Another problem arises during the acceleration phase of the workpiece, depending on a particular processing stage. For example, during a drying stage, rotational speeds of the workpiece may be about 2500 RPM. However, to obtain such speeds, there are accelerations that are applied to the workpiece. During these accelerations, certain forces, i.e., tangential forces, act on the workpiece such that the workpiece may shift from the rotating chuck. In known systems, however, stationary gripping mechanisms are used to maximize the contact area and thus maximize any frictional issues. But, in such systems there is a compromise between the grip area and impedance to flow of the process fluid; namely, the more contact area required to hold the workpiece stationary the more impedance to flow exists. Also, it is known that these grips may not by sufficient to prevent the shifting of the workpiece during the acceleration phase.
In a first aspect of the invention, a method for processing a workpiece is provided. The method includes providing a plurality of contacts for holding the workpiece and processing a surface of the workpiece. During the processing step, the method includes releasing at least one of the contacts.
In embodiments, the plurality of contacts comprises a first set of three contacts and a second set of three contacts.
The first set remains in contact with the workpiece and the second set are released from the workpiece. The first set holds the workpiece and during the processing step processing fluids are unimpeded to flow off a surface of the workpiece at the locations on the workpiece where the second set of contacts is released therefrom. This similar situation occurs for the first set when released from the workpiece. In embodiments, the contacts are released for a predetermined amount of time and then moved into engagement with the workpiece for holding the workpiece.
In another aspect of the invention, a method for processing a workpiece includes rotating a workpiece at a predetermined speed and providing a plurality of gripping mechanisms for holding the workpiece. The surface of the workpiece is processed with processing fluids. At least one of the plurality of gripping mechanisms is released from the workspace during the processing step and then moved into contact. Also, another of the plurality of gripping mechanisms is released from the workpiece during the processing step.
In still another aspect of the invention, the method for processing a workpiece includes moving alternately gripping mechanisms of the plurality of gripping mechanisms away from and into contact with the workspace during processing to allow processing fluids to freely flow, unimpeded, from a surface of the workpiece at previous locations of the released gripping mechanisms. In this aspect, in embodiments, the moving step includes moving alternately non-adjacent gripping mechanisms.
In yet another aspect of the invention, a system is provided for processing a workpiece. The system includes a plurality of moveable gripping mechanisms being moveable between a holding position and a releasable position with respect to a workpiece and a mechanism for controlling alternating movement of the moveable gripping mechanisms away from and into contact with the workspace during processing. This system allows processing fluids to freely flow, unimpeded, from a surface of the workpiece at previous locations of the released gripping mechanisms.
This invention is directed to a gripping mechanism to hold a workpiece during fabrication and, more particularly, to gripping mechanisms and a method of use which reduces process variations and contamination during wafer fabrication. In the invention, the gripping mechanisms are used to grip the workpiece, and in one implementation, a wafer on a rotating chuck. During the fabrication processes and more particularly during the application of processing fluids, each individual gripping mechanism is designed to radially move outward to release from the workpiece. Likewise, the individual gripping mechanisms also move radially inward to grip the workpiece during the fabrication processes. In the invention, during the fabrication processes, some of the gripping mechanisms will always remain in contact with the workpiece to hold the workpiece (e.g., wafer) to the rotating chuck, while other gripping mechanisms are released from the wafer to prevent contamination problems. Thus, by using the invention, accumulation of particulate contamination due to the stagnation of flow in the vicinity of the gripping mechanisms can be eliminated. Also, shadows (e.g., under etching or failure to remove the photoresist) in the areas of the gripping mechanisms, themselves, are also eliminated using the invention.
In one example, the gripping mechanisms are alternated between an engaged and disengaged position, i.e., moved toward and away from the workpiece to hold and release the workpiece, respectively, during fabrication or other processing. The movement of the gripping mechanisms toward and away from the workspace can be accomplished in many different ways, as contemplated by the invention. In one such configuration, by example, six gripping mechanisms may be used with the invention. During the fabrication of the workpiece, three gripping mechanisms may be used to hold the workpiece while three gripping mechanisms may be released or disengaged from the workpiece. Thereafter, the three released gripping mechanisms may be moved to hold the workpiece, at which time, the other three gripping mechanisms are moved away or disengaged from the workpiece. But, now the processing fluids will no longer accumulate on the workpiece causing contaminations since the gripping mechanisms alternately are released or disengaged from the workpiece. Thus, by this process, there is an increase in the device yield as well as reduction of overall costs, including manufacturing and material costs.
Referring to
Still referring to
The control may be implemented by computer program code in combination with the appropriate hardware. This computer program code may be stored on storage media such as a diskette, hard disk, CD-ROM, DVD-ROM or tape, as well as a memory storage device or collection of memory storage devices such as read-only memory (ROM) or random access memory (RAM). Additionally, the computer program code can be transferred to a workstation over the Internet or some other type of network.
In one implementation, a minimum of three movable gripping mechanisms are required to locate and hold the workpiece at any one time. For example, as controlled by the control “C”, as the workpiece is processed, the grip-ping mechanisms 2a, 2b and 2c may be used to grip the workpiece. At this time, the gripping mechanisms 3a, 3b and 3c are released or disengaged from the workpiece. During the fabrication process, the processing fluids, which normally are prevented from moving radially off of the workpiece surface, either by physical obstruction or capillary trapping, can now flow off the surface of the workpiece in the areas where the movable gripping mechanisms 3a, 3b and 3c are disengaged or released from the workpiece. This is because the movable gripping mechanisms 3a, 3b and 3c will no longer provide any interference with the processing fluids.
In another stage, during the same fabrication process, the movable gripping mechanisms 2a, 2b and 2c may be released from the workpiece while the movable gripping mechanisms 3a, 3b and 3c are moved into engagement with the workpiece. The movable gripping mechanisms 3a, 3b and 3c are now used to hold the workpiece to the chuck. But, in this manner, processing fluids that are typically prevented from moving radially off of the workspace can now freely move off of the surface during the rotation of the chuck, or otherwise, at the locations of the movable gripping mechanisms 2a, 2b and 2c. It should now be understood by those of ordinary skill in the art, though, that some of the movable gripping mechanisms are always holding the workpiece to the chuck. Thus, there is no possibility that the workpiece will shift or be released from the chuck during rotation or other fabrication processes.
In other implementations, each of the movable gripping mechanisms or other combinations of gripping mechanisms may be moved to release and hold the workpiece onto the chuck, depending on the processing stage and processing fluids being used by the system. This may be controlled by the control “C”, which is preprogrammed with a sequence of the processing. By way of example, the gripping mechanisms 2a, 2b, 2c, 3a and 3b may be used to grip or hold the workspace during a fabrication stage. During this stage, the gripping mechanism 3c may be released or disengaged from the workpiece. Then, in order, the gripping mechanism 3b may be released or disengaged while the gripping mechanism 3c is moved to engage and hold the workpiece with the remaining gripping mechanisms. Alternatively, the gripping mechanism 3c may remain disengaged from the workpiece and will be moved toward the holding position, as shown in
In a more definite example, it is contemplated by the invention that all movable gripping mechanisms will be used, initially, during the acceleration of the chuck. Once the rotation of the chuck has reached a desired speed, then the gripping mechanisms may be released, depending on variables such as time of processing, type of processing fluid and the like, as implemented by the control “C”. In one implementation, the following may be used for a fabrication process:
It should be understood, though, that the above is provided for illustration and that other configurations, depending on, for example, the properties of the fluid, may affect the processing times and sequential or alternating release of the movable gripping mechanisms. For example, a photoresist, which is a more viscous material, may be used as a processing fluid. In this example, the workpiece may be rotated at about 500 RPM. In this implementation, the movable gripping mechanisms may each or a set of move in an alternated manner about every five to ten seconds since the photoresist has a tendency to dry on the surface of the workpiece. In any scenario, the control “C” will be programmed with the desired parameters, known to those implementing the system and method of the invention, for ensuring that the processing fluids freely flow from the surface of the workpiece, unimpeded.
At step 300, the fabrication process begins. This process may include, for example, the application of processing fluids such as photoresists, chemical polishers, and the like. At first, in one implementation, all of the movable gripping mechanisms engage or hold the workpiece during the acceleration of the chuck. Once a desired speed is achieved, at step 305, one or more of the movable gripping mechanisms are released from the workpiece during the application of the processing fluids. During the rotation, the processing fluids are evenly distributed on the workpiece due to the rotational forces generated by the rotating chuck. Also, the processing fluids are able to freely flow off the surface of the workpiece. At step 310, the movable gripping mechanisms are all alternated so that some are engaged while others are removed from the workpiece.
At step 315, a next processing phase begins by, for example, accelerating the workpiece. At this stage, all of the movable gripping mechanism may be used to hold the workpiece to the chuck. At step 320, steps 305 and 310 are repeated. At step 325, a determination is made as to whether the fabrication process has ended. If not, then step 315 and step 320 is repeated. If the fabrication is completed, then the process ends at “E”.
The system and method of the invention ensures that some of the movable gripping mechanisms also hold the workpiece during the rotation of the chuck. This may be accomplished by, for example,
Of course, a check can be implemented by the system to ensure that there are movable gripping mechanisms holding the workpiece to the chuck, preferably three in one implementation.
Depending on each implementation, the logic of the system may be preprogrammed with the order and time periods for moving the movable gripping mechanisms into engagement with the workpiece and releasing the movable gripping mechanism from the workpiece. In one implementation, at some time, each of the movable gripping mechanism are to be released from the workpiece to ensure that the processing fluids are free to flow off of the surface of the workpiece, unimpeded.
It should also be recognized by those of ordinary skill in the art that the movable gripping mechanisms may be moved in a number or sequences. For example, the control “C” may be programmed to:
While the invention has been described in terms of embodiments, those skilled in the art will recognize that the invention can be practiced with modifications and in the spirit and scope of the appended claims.
