| 摘要 |
An improved method for specifying and reliably detecting endpoints in processes such as plasma etching, where the signal-to-noise ratio has been severely degraded due to factors such as "cloudy window" and low ratio of reactive surface area to non-reactive surface area. The improved method of the invention samples signals produced by photo sensitive equipment, digitally filters and cross-correlates the data, normalizes the data using an average normalization value, and provides further noise reduction through the use of three modes of endpoint specification and detection. The three modes of endpoint specification and detection require a pre-specified number of consecutive samples to exhibit a certain behavior before the endpoint is deemed detected and the process terminated as a result. The three modes of endpoint specification and detection also permit a very fine control of the etch time by permitting the user to adjust the specified endpoint by gradations of the sampling period. The improved method of the invention is capable of being implemented on known apparatus.
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