Refrigeration – Low pressure cold trap process and apparatus
Reexamination Certificate
1999-08-24
2001-07-10
Capossela, Ronald (Department: 3744)
Refrigeration
Low pressure cold trap process and apparatus
C062S125000, C062S129000
Reexamination Certificate
active
06257001
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to pumps generally, and more specifically to cryogenic vacuum pumps.
DESCRIPTION OF THE RELATED ART
Cryogenic vacuum pumps (also referred to herein as cryopumps) provide clean, reliable, high-speed pumping for critical vacuum process applications. Exemplary cryopumps are manufactured by the CTI Cryogenics division of Helix Technology Corp., Mansfield, Md. Cryopumps are also described in U.S. Pat. Nos. 4,918,930, 5,157,928, 5,343,708 and 5,450,316, which are expressly incorporated by reference herein in their entireties.
A common use for cryopumps is in ion implantation processes and sputtering which are frequently used in semiconductor fabrication. A cryopump can be used to achieve a vacuum on the order of 5×10
−6
Torr, which is important for implantation processes.
Cryopumps are typically designed to operate only at very low pressures, and do not operate properly under ambient conditions. Therefore, a cryopump is typically operated in conjunction with a roughing pump. The roughing pump reduces the pressure in the system to a pressure of about 3 to 4×10
−3
Torr, which is sufficiently low for the cryopump to operate.
In a typical semiconductor fabrication process, wafers are processed within a chamber. A valve connecting the cryopump to the chamber remains closed while the wafer is placed in the chamber. The chamber is closed and the roughing pump is used to reduce pressure within the chamber to a vacuum level suitable for operating the cryopump. The valve separating the cryopump from the chamber is then opened, to pump out the chamber to the degree of vacuum required for processing. The process may, for example, include the implantation of ions (e.g., arsenic, phosphorus, or boron) into the wafer. The ions are contained in a carrier gas, typically hydrogen.
In certain circumstances, the cryopump may be inadvertently exposed to atmospheric air. This may occur, for example, if a valve separating the cryopump from the chamber opens at the wrong time, or if the valve fails. When this occurs, the cryopump “dumps”. When the cryopump dumps, it can neither maintain the desired pressure or cryogenic temperature for its normal operation. Ice forms within the cryopump. Hydrogen from the carrier gas collects within the vacuum vessel of the cryopump. A significant risk exists that a spark may be introduced into the vessel and ignite the hydrogen.
For example, some cryopumps may have an ion tube in the vessel (either factory mounted, or installed by the user) for the purpose of measuring the vacuum pressure. Activating the ion tube when the cryopump dumps can cause a spark that ignites the hydrogen in the vacuum vessel of the cryopump. This results in an explosion within the vacuum vessel of the cryopump. This presents risk to personnel, and may result in substantial costs and processing schedule delays.
SUMMARY OF THE INVENTION
One aspect of the present invention is an assembly including a temperature sensor having an operating range that includes a normal operating temperature of a cryogenic vacuum pump and a temperature of the pump following a dump. A mounting bracket is capable of mounting the temperature sensor on the pump.
Another aspect of the invention is a semiconductor processing. apparatus including: a chamber containing a wafer; an ion source that provides ions to be implanted in the wafer; a cryogenic vacuum pump that maintains a vacuum in the chamber; and a temperature sensor having an operating range that includes a normal operating temperature of the pump and a temperature of the pump following a dump, the temperature sensor being mounted on the pump.
An additional aspect of the invention is a method including sensing a temperature of a cryogenic vacuum pump; and activating an alarm when the sensed temperature indicates that a dump condition exists.
Still another aspect of the invention is a semiconductor wafer produced by a method including: sensing a temperature of an exterior surface of a cryogenic vacuum pump; using the pump to form a vacuum in a semiconductor wafer processing apparatus for performing an implant operation on the wafer; and introducing an inert gas into the semiconductor wafer processing apparatus when the sensed temperature indicates that a dump condition exists.
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Muldowney Francis
Schall Eric Regis
Capossela Ronald
Duane Morris & Heckscher LLP
Koffs Steven E.
Lucent Technologies - Inc.
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