Coating apparatus – Gas or vapor deposition
Reexamination Certificate
1997-02-21
2001-12-11
Jones, Deborah (Department: 1775)
Coating apparatus
Gas or vapor deposition
C118S663000, C118S050000
Reexamination Certificate
active
06328803
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to vacuum processes, such as dry etching and chemical vapor deposition particularly for semiconductor manufacture. More specifically, this invention relates to a method and apparatus for controlling a rate of pressure change in a vacuum process chamber during pump down and vent up cycles of a vacuum process.
BACKGROUND OF THE INVENTION
Various etching and deposition processes for semiconductor manufacture are performed in vacuum process chambers. For example, dry etching and chemical vapor deposition (CVD) processes utilize vacuum process chambers. Conventional dry etching processes include plasma etching and reactive ion etching (RIE). Conventional chemical vapor deposition processes include plasma enhanced chemical vapor deposition (PECVD) and low pressure chemical vapor deposition (LPCVD).
During these processes the process chamber can be evacuated from an initial pressure to an operating pressure. For example, the process chamber may initially be at atmospheric pressure for loading wafers, then evacuated to an operational pressure in the milli-torr range. The initial evacuation cycle for a process is sometimes referred to as a “pump down cycle”. Typically, a pump down cycle is accomplished using a vacuum pump in flow communication with the process chamber.
Subsequently, the pressure in the process chamber can be increased from the operating pressure back to the initial pressure (e.g., back to atmospheric pressure). The subsequent pressurization cycle is sometimes referred to as a “vent up cycle”. Typically, a vent up cycle is accomplished by injecting an inert gas into the process chamber to a desired pressure.
Recently, etching and deposition systems having more than one vacuum process chamber have been employed for semiconductor manufacture. These multi-chamber systems improve production rates and provide increased efficiency over single chamber systems. An example of a multi-chambered etching or deposition system is sold under the trademark “APPLIED MATERIALS 5000”, by Applied Materials, Inc., of Santa Clara, Calif.
Such a multi chambered system can include a wafer handler, a load lock chamber and multiple process chambers. The wafer handler can include cassettes for holding the wafers and cassette ports for loading the wafers. During an etching or deposition process, the wafers can be moved from the load lock chamber and into or out of the process chambers as required. The process chambers can be pumped down and vented up to different pressures during various cycles of the process.
One limitation of multi chamber systems is that wafer defects can sometimes occur more frequently in a particular process chamber relative to the other process chambers. For example, some types of wafer defects can be detected using optical detectors such as those manufactured by KLA Instruments Corporation, Santa Clara, Calif. These types of defects are sometimes termed “KLA defects”. The inventors have observed variations in KLA defects among wafers processed in different process chambers of multi chamber vacuum systems. In particular, some process chambers in multi chamber systems produce wafers with more defects.
One possible source of defect variation between the process chambers is that the rate of pressure change for the chambers during pump down and vent up cycles may not be the same. This difference in rate of pressure change can cause the pressures in the process chambers to be different for significant time increments. The pressure rate differences may be due to variations between conduction lines, pumps, valves and associated equipment for the different chambers. These variations can be caused by residue build up and other factors.
The same situation can occur among different single chamber systems adapted to perform the same process. Specifically, variations can occur between the different process chambers causing differences in the wafers. In this situation it would be advantageous to control the rate of pressure change during pump down and vent up in the process chambers in order to achieve process uniformity.
Prior art attempts to regulate pump down cycles in vacuum process chambers include “soft-start” valves, which open at a linear rate (i.e., at a certain percentage per second). Prior art attempts to regulate vent up cycles in vacuum process chambers include needle valves and mass flow controllers which control the flow rate into a particular chamber during vent up. However, these prior art systems do not compensate for system variables and are inherently linear in response. Accordingly, significant pressure differentials can still occur between different process chambers causing differences in the semiconductor wafers being processed.
The present invention provides a method and apparatus for achieving an optimal rate of pressure change in a vacuum process chamber during pump down and vent up cycles of a vacuum process. For multi chamber vacuum systems, the rate of pressure change between different process chambers can be matched such that one process variable can be eliminated and wafer uniformity can be improved. Similarly, for multiple single chamber systems adapted to perform the same process, one process variable can be eliminated and the uniformity of the wafers produced by the different vacuum process chambers can be improved.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method and apparatus for controlling the rate of pressure change in a process chamber during pump down and vent up cycles of a vacuum process are provided. The method, simply stated, comprises, determining a desired rate of pressure change for the process chamber, and then, controlling the gas flow out of, or into, the process chamber to achieve the desired rate of pressure change. The gas flow can be controlled using a flow control valve and programmed controller responsive to feed back from pressure sensors within the process chamber. The desired rate of pressure change can be determined empirically for a particular vacuum process, expressed mathematically, and then programmed into the controller.
An apparatus constructed in accordance with the invention, comprises: a pressure sensor for sensing pressure in the process chamber; a control valve in flow communication with the process chamber; and a programmed controller for controlling the control valve responsive to the pressure sensor. Separate controllers and control valves can be operably associated with the process chamber for the pump down and vent up cycles of a vacuum process. For controlling the pump down cycle, a control valve can be in flow communication with a vacuum pump. For controlling the vent up cycle, a control valve can be in flow communication with an inert gas supply.
A system constructed in accordance with the invention comprises multiple process chambers configured for a vacuum process such as depositing or etching layers of semiconductor wafers. The multiple process chamber can be contained on the same frame or can be contained on separate pieces of equipment configured to perform the same process. Each process chamber includes a pressure sensor, and separate control valves and controllers for controlling pump down and vent up cycles during the vacuum processes. The controllers and control valves can be configured to match the rates of pressure change in the process chambers during the pump down and vent up cycles. The matched rates permit more process uniformity between the process chambers so that excessive defects do not occur in any one process chamber.
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Wolf, S. and Tauber, R. N., Silicon Processing For T
Hochhalter Elton
Rolfson J. Brett
Gratton Stephen A.
Jones Deborah
McNeil Jennifer
Micro)n Technology, Inc.
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