Coating apparatus – Gas or vapor deposition
Reexamination Certificate
1999-04-19
2001-01-30
Lund, Jeffrie R. (Department: 1763)
Coating apparatus
Gas or vapor deposition
C137S625500, C251S129220
Reexamination Certificate
active
06179921
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to a semiconductor wafer processing system, and in particular, to a backside gas delivery system for a semiconductor wafer processing system.
2. Description of the Background Art
Electrostatic chucks (ESC) are used in many single-wafer processing systems for retaining wafers during processing. In order to improve heat conduction between the wafer and the chuck, a backside gas supplied between the wafer and the support surface of the chuck is often used as a heat transfer medium. The design of a backside gas delivery system may have significant impact on the performance of the wafer processing system, especially in cases where stringent pressure control is required. In many existing designs, when the wafer is removed from the chuck upon completion of processing, the backside gas is often allowed to enter the process chamber, resulting in a temporary yet undesirable pressure increase. For certain applications, the increased pumpdown time between wafers may have an adverse impact on the process throughput. An ion implanter, for example, is particularly susceptible to such inadvertent, pressure fluctuations because of the stringent requirement for a low operating pressure, typically in the range of about 10
−6
torr. Any increase in chamber pressure from the backside gas requires additional vacuum pumping and directly results in a decreased throughput. Maintaining a high process throughput is of special concern to a serial ion implanter. Furthermore, a transient pressure increase may result in other adverse effects—e.g., the ion beam may be neutralized, or be deflected onto the side of the flight tube, which may cause contaminants to be sputtered from surfaces within the equipment.
One solution involves a gas delivery system designed to rapidly remove the gas from the wafer backside with limited gas leakage into the process chamber. This is disclosed in a commonly-assigned U.S. patent application Ser. No. 08/154,509 entitled “Backside Gas Quick Dump Apparatus for a Semiconductor Wafer Processing System”, filed on May 12, 1997, and is herein incorporated by reference.
However, there is always an ongoing need for alternative backside gas delivery systems that provide a reliable gas shutoff and minimal pressure increase during wafer transfer. Additionally, a gas delivery system having simplified vacuum connections is also desirable.
SUMMARY OF THE INVENTION
The present invention is an apparatus for a semiconductor wafer processing system comprising a gas delivery system with a shutoff valve directly attached to a wafer support chuck (e.g., an electrostatic chuck).
The gas delivery system is used to deliver a gas between the backside of a wafer and the support surface of the wafer support chuck. The backside gas acts as a heat transfer medium for the wafer during processing, such as ion implant. By providing a shutoff valve in close proximity to the wafer chuck, the backside gas volume between the valve and the backside of the wafer can be minimized. Since the amount of trapped backside gas released into the process chamber from this volume during wafer transfer is negligible compared to the chamber volume, undesirable pressure increase inside the wafer processing system is avoided. Therefore, a high process throughput of the wafer processing system can be maintained.
The shutoff valve comprises two parts—a valve body and a valve seat, each having a narrow conduit to act as a passageway for the backside gas. The top of the valve seat, which has a top recess connected to its conduit, fits inside an opening of the chuck from the backside of the chuck. A batten (fastener), having a narrow conduit along its entire length, fits inside the center opening of the chuck and the top recess of the valve seat. As such, the batten acts as a fastener which secures the top of the valve seat inside the center opening of the chuck. In this configuration, a passageway is defined by the conduit of the batten, the top recess and the conduit of the valve seat. The conduit of the valve seat is connected to a bottom opening which is threaded to the top of the valve body.
A poppet, which has a top portion and a cylindrical shaft, is disposed towards the top of the valve body. The shaft fits through an opening of the valve body from the top such that the top portion of the poppet is located above the opening and the shaft is substantially inside the valve body.
The valve used in this embodiment is a normally closed solenoid valve. When the valve is closed, the top portion of the poppet is sealed against the conduit opening at the bottom of the valve seat, and provides a positive shutoff with a leak rate of less than about 10
−6
sccs. When the valve is actuated to its open position, the poppet retracts away from the valve seat, and a passageway is defined by the interiors of the batten and the valve seat. Thus, a backside gas can be delivered from the gas supply, through the pressure controller and the solenoid valve, to the support surface of the wafer chuck.
REFERENCES:
patent: 4527620 (1985-07-01), Pedersen et al.
patent: 5575311 (1996-11-01), Kingsford
Leeser Karl F.
Ruffell John
Applied Materials Inc.
Lund Jeffrie R.
MacArthur Sylvia R.
Thomason Moser & Patterson
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