Method and apparatus for detecting optimal endpoints in plasma etch processes
First Claim
1. A method of detecting an endpoint for terminating a chemical process involving one or more chemical species, the process taking place in a chamber, said method comprising the steps of:
- defining the endpoint in the form of a mode, a minimum value of a delay count and a threshold;
initiating the chemical process;
detecting intensity of light emitted during the chemical process by one or more of the one or more species in the form of an analog signal representing the intensity of each of the detected species;
sampling each analog signal at a rate and at the beginning of a current sampling period defined by the rate to produce a set of raw data samples for the current sampling period;
pre-filtering each of the set of raw data samples of the current sampling period;
normalizing each of the set of pre-filtered data samples;
auto-correlating the set of normalized data samples to produce a multichannel value for the current sampling period;
post-filtering the multichannel value;
incrementing the delay count when the threshold has been exceeded by the post-filtered multichannel value and the mode is met, otherwise setting the delay count equal to zero; and
repeating said pre-filtering, normalizing, auto-correlating, post-filtering, and incrementing steps for each set of raw data samples until the delay count reaches or exceeds the minimum value; and
terminating the process when the delay count reaches or exceeds the minimum value.
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Abstract
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.
29 Citations
26 Claims
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1. A method of detecting an endpoint for terminating a chemical process involving one or more chemical species, the process taking place in a chamber, said method comprising the steps of:
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defining the endpoint in the form of a mode, a minimum value of a delay count and a threshold; initiating the chemical process; detecting intensity of light emitted during the chemical process by one or more of the one or more species in the form of an analog signal representing the intensity of each of the detected species; sampling each analog signal at a rate and at the beginning of a current sampling period defined by the rate to produce a set of raw data samples for the current sampling period; pre-filtering each of the set of raw data samples of the current sampling period; normalizing each of the set of pre-filtered data samples; auto-correlating the set of normalized data samples to produce a multichannel value for the current sampling period; post-filtering the multichannel value; incrementing the delay count when the threshold has been exceeded by the post-filtered multichannel value and the mode is met, otherwise setting the delay count equal to zero; and repeating said pre-filtering, normalizing, auto-correlating, post-filtering, and incrementing steps for each set of raw data samples until the delay count reaches or exceeds the minimum value; and terminating the process when the delay count reaches or exceeds the minimum value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An apparatus for detecting an endpoint at which to terminate a chemical process involving one or more chemical species, the process taking place in a chamber, said apparatus comprising:
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means for defining the endpoint in the form of a mode, a minimum value of a delay count and a threshold; means for initiating the chemical process; means for detecting intensity of light emitted during the chemical process by one or more of the one or more species in the form of an analog signal representing the intensity of each of the detected species; means for sampling each analog signal at a rate and at the beginning of a current sampling period defined by the rate to produce a set of raw data samples for the current sampling period; means for pre-filtering each of the set of raw data samples of the current sampling period; means for normalizing each of the set of pre-filtered data samples; means for auto-correlating the set of normalized data samples to produce a multichannel value for the current sampling period; means for post-filtering the multichannel value; means for incrementing the delay count when the threshold has been exceeded by the post-filtered multichannel value and the mode is met, otherwise setting the delay count equal to zero; and means for terminating the process when the delay count reaches or exceeds the minimum value. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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Specification