Handling: hand and hoist-line implements – Grapple – Fixed and moveable jaw
Reexamination Certificate
2001-11-16
2004-01-27
Kramer, Dean J. (Department: 3652)
Handling: hand and hoist-line implements
Grapple
Fixed and moveable jaw
C294S116000, C414S744500, C414S941000
Reexamination Certificate
active
06682113
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a clamping mechanism for securing a semiconductor wafer during wafer handling. More particularly, the present invention is directed to a clamping mechanism that securely clamps a semiconductor wafer near the distal end of a robot arm.
BACKGROUND OF THE INVENTION
A wafer is the base material, usually silicon, used in semiconductor chip or integrated circuit fabrication. Typically, the wafer is a thin slice of base material cut from a silicon ingot or “boule.” Each 8 inch (200 mm) production wafer is approximately {fraction (1/30)} inch (0.85 mm) thick and has a diameter of approximately 8 inch (200 mm). Because of the nature of the base material and the thinness of each slice, the wafer can easily be damaged through mishandling.
Wafers are typically processed into semiconductor chips by sequentially exposing each wafer to a number of individual processes, such as photo masking, etching and implantation. Modern semiconductor processing systems include cluster tools that aggregate multiple process chambers together, where one or more of the individual processes are performed in each chamber. These process chambers may include, for example, degas chambers, substrate pre-conditioning chambers, cool down chambers, transfer chambers, chemical vapor deposition chambers, physical vapor deposition chambers, etch chambers, or the like.
Typically, these process chambers surround a central chamber housing a central wafer handling robot, which manipulates the individual wafers. The cluster tool also typically includes a cassette in which multiple wafers are stacked before and after semiconductor fabrication. The wafer handling robot has access to the multiple process chambers and the cassette through load ports coupling each chamber and cassette to the central chamber. During operation the wafer handling robot repetitively transports wafers from one chamber to another, or to and from the cassette. Processing times can range from a few seconds to a few minutes, depending on the specific type of process that is required. Furthermore, the cluster tool forms a sealed environment, generally at vacuum, that is controlled to limit potential contamination of the wafers and to ensure that optimal processing conditions are maintained. Examples of cluster tools can be found in U.S. Pat. Nos. 5,292,393; 5,764,012; 5,447,409; 5,469,035; and 5,955,858, all of which are incorporated herein by reference.
The high costs associated with manufacturing semiconductor devices together with the demand for lower consumer prices has brought about a push to increase fabrication efficiency. In order to increase fabrication efficiency, equipment makers now seek to reduce processing equipment footprint, cost of ownership, and power consumption, while increasing cluster tool reliability and throughput.
The throughput for a particular cluster tool is mainly dependent on the number of process chambers and the time required for a process chamber to service each wafer. Ideally, the maximum throughput for which a cluster tool is capable is:
Maximum
ideal
cluster
tool
throughput
=
N
·
(
60
t
)
wph
where
N=number of process chambers;
t=time required to process one wafer in minutes; and
wph is the number of wafers per hour that a cluster tool is capable of processing.
In order to calculate the actual throughput, the material handling issues must also be considered. The actual cluster tool throughput will always be less than the ideal throughput because of time lost in wafer transfers through the central chamber. For example, once a process chamber completes a process sequence on a wafer, it may take as much as 30 seconds for the central wafer-handling robot to replace the processed wafer with another unprocessed wafer. Since the time required for the robot to swap wafers detracts from the time in which the process chamber is actually processing wafers, minimizing the wafer swap or handling time at each process chamber will have a direct positive impact on the total throughput of the cluster tool.
A high throughput can be achieved in a number of ways. First, duplicate chambers can be provided. This, however, substantially increases the cost and complexity of each cluster tool. Second, additional wafer handling robots can be provided in each cluster tool. Again, this increases the cost and complexity of each cluster tool. Third, the speed of any individual process can be increased. However, although each process is always being improved upon, each process is typically completed in as short a time as is currently possible. Finally, the handling speed of each wafer by the wafer handling robot can be increased, i.e., the wafer handling robot must rotate and extend as fast as possible without causing the clamped wafer to slip during transport. Slip occurs when the robot accelerates the wafer such that its inertia overcomes the coefficient of static friction between the wafer and the blade material, causing undesired wafer movement and resulting in wafer misalignment and possibly the generation of unwanted particles.
Increasing the handling speed, however, is subject to a number of constraints, such as: each wafer must be securely grasped or clamped by the wafer handling robot in the minimum amount of time; the clamping of the wafer must be firm, but not overly so, so as not to damage the fragile wafer; the clamping and placement of each wafer must be precise and accurate, any misplacement might negatively impact the process and/or damage the wafer; transfer between chambers, or into or out of the cassette, must be smooth so that the wafer does not undergo any unnecessary stress, or in the worst case dislodge from the clamping mechanism; the clamping mechanism must be heat resistant, as some of the processes may expose the clamping mechanism to high temperatures; the clamping mechanism must not introduce into the closed environment any particulates or contaminants that can ultimately damage the wafer or semiconductors (it has been found that particulates as small as the critical dimension or line width of a semiconductor device, currently 0.18 &mgr;m, can damage the integrity of an integrated circuit formed on a wafer); the wafer clamping mechanism should be able to automatically center a misplaced wafer; and finally, the wafer clamping mechanism must not apply a static electric field to the wafer, which might discharge and damage the semiconductor devices being fabricated.
Of the abovementioned ways of increasing wafer throughput, increasing the handling speed of each wafer is the most practical and cost effective. Therefore, to address the above criteria, a more robust and better designed wafer clamping mechanism is required.
Currently, in order to minimize the time required to move a silicon wafer from one place to another, many atmospheric wafer-handling robots employ vacuum or electrostatic chucks to hold wafers firmly in place on the robot end-effector during transport. However, since vacuum chucks rely on a pressure differential to create the chucking force to hold the wafer in place, they typically cannot be used in vacuum robot applications. In addition, electrostatic chucks are difficult to incorporate in vacuum robots for a number of reasons including vacuum feed-through design complexities, limited performance, reliability, and cost. As a result, vacuum robots typically rely only on frictional forces between the wafer and robot end-effector to prevent relative motion during transport; and a robot must therefore move slowly enough that the wafer does not move relative to the end-effector. This can significantly impact wafer swap time.
Alternatively, some vacuum robot end-effectors or wafer carrying blades, such as those disclosed in U.S. Pat. No. 5,746,460, are designed with deep wafer carrying pockets or blades that are just slightly larger in diameter than the wafer itself. These tight pockets prevent the wafer from moving on the end-effectors or blades during tran
Cox Damon Keith
Menon Venugopal
Applied Materials Inc.
Kramer Dean J.
Pennie & Edmonds LLP
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