Pulsewidth modulated pressure control system for chemical vapor deposition apparatus
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United States of America Patent
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-
Mar 1, 1988
Issued Date -
N/A
app pub date -
Mar 27, 1986
filing date -
Dec 18, 1985
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A low pressure control system for chemical vapor deposition (CVD) apparatus, including a vacuum pressure chamber and an exhaust pump, is provided by a vacuum pump DC motor which is supplied power from a DC motor speed controller coupled to a DC control input signal from a pulsewidth modulation DC converter. The converter receives a single pulsewidth modulated pulse train having its percentage of modulation controlled in accordance with a DC to pulsewidth modulation controller which operates in accordance with the difference between a pair of DC input signals corresponding to the actual pressure inside the vacuum pressure chamber and a desired or set point pressure respectively. The vacuum pump motor speed and accordingly the exhaust pump is controlled with a high degree of precision, thereby providing improved coating uniformity of semiconductor wafers being fabricated by the CVD apparatus.
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