Method and apparatus for detecting optimal endpoints in plasma etch processes

• US 6,190,927 B1
• Filed: 10/27/1997
• Issued: 02/20/2001
• Est. Priority Date: 06/30/1995
• Status: Expired due to Term

• Current Assignee: Lam Research Corporation
• Original Assignee: Lam Research Corporation
• Inventors: Liu, Alexander F.
• Primary Examiner(s): Booth, Richard
• Assistant Examiner(s): LINDSAY JR, WALTER LEE
• Application Number:
  US08/958,611
• Time in Patent Office: 1,212 Days
• Field of Search: 438/8, 438/9, 216/60, 156/345, 204/192.33
• US Class Current: 438/8
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge
• CPC Class Codes: H01J 37/32963 End-point detection
• CPC Class Codes: H01J 37/32972 Spectral analysis

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.

Claims

1. A method of detecting an endpoint for terminating a process, 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;

producing a set of samples;

processing the samples;

incrementing the delay count when the threshold has been exceeded by a predefined number and the mode is met, otherwise setting the delay count equal to zero;

repeating said processing step for each set of 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.

2. The method of claim 1, wherein the process is a chemical process involving at least one chemical species.

3. The method of claim 1, wherein the process takes place in a chamber.

4. The method of claim 1, wherein the step of processing the samples further comprises the step of:

prefiltering each of the set of samples of a current sampling period.

5. The method of claim 4, wherein the step of processing the samples further comprises the step of:

normalizing each of the set of pre-filtered samples.

6. The method of claim 5, wherein the step of processing the samples further comprises the step of:

auto-correlating the set of normalized samples to produce the value for the current sampling period.

7. The method of claim 6, wherein the step of processing the samples further comprises the step of:

post-filtering the value.

8. The method of claim 1, wherein the step of producing a set of samples further comprises the steps of:

initiating the process;

detecting an intensity emitted during the process in the form of a signal representing the intensity; and

sampling each signal at a rate and at a beginning of a current sampling period defined by the rate to produce the set of samples for the current sampling period.

9. The method of claim 7, wherein the step of producing a set of samples further comprises the steps of:

initiating the process;

detecting an intensity emitted during the process in the form of a signal representing the intensity; and

sampling each signal at a rate and at a beginning of a current sampling period defined by the rate to produce the set of samples for the current sampling period.

10. The method claimed in claim 9 wherein the step of normalizing each of the set of pre-filtered samples further comprises the steps of:

determining an average normalization value corresponding to each of the sampled signals; and

dividing each of the set of pre-filtered samples by the average normalization value corresponding to the signal from which each of the pre-filtered samples was taken.

22. The method of claim 1, further comprising the steps of:

determining a first parameter associated with an immediately preceding samples set; and

determining a second parameter associated with a current sample set.

23. The method of claim 22, wherein the mode is met when the first parameter is less than the second parameter.

24. The method of claim 22, wherein the mode is met when the first parameter is greater than the second parameter.

25. The method of claim 22, wherein the mode is met when the first parameter is less than the threshold and is less than the second parameter.

11. An apparatus for detecting an endpoint for terminating a process, comprising:

means for defining the endpoint in the form of a mode, a minimum value of a delay count, and a threshold;

means for producing a set of samples;

means for processing the samples;

means for incrementing the delay count when the threshold has been exceeded by a predefined number and the mode is met, otherwise setting the delay count equal to zero;

means for repeating said processing step for each set of samples until the delay count reaches or exceeds the minimum value; and

means for terminating the process when the delay count reaches or exceeds the minimum value.

12. The apparatus claimed in claim 11, wherein the process is a chemical process involving at least one chemical species.

13. The apparatus claimed in claim 11, wherein the process takes place in a chamber.

14. The apparatus claimed in claim 11, wherein the means for processing the samples further comprises:

means for prefiltering each of the set of samples of a current sampling period.

15. The apparatus claimed in claim 14, wherein the means for processing the samples further comprises:

means for normalizing each of the set of pre-filtered samples.

16. The apparatus claimed in claim 15, wherein the means for processing the samples further comprises:

means for auto-correlating the set of normalized samples to produce the value for the current sampling period.

17. The apparatus claimed in claim 16, wherein the means for processing the samples further comprises:

means for post-filtering the value.

18. The apparatus claimed in claim 11, wherein the step of producing a set of samples further comprises:

means for initiating the process;

means for detecting an intensity emitted during the process in the form of a signal representing the intensity; and

means for sampling each signal at a rate and at a beginning of a current sampling period defined by the rate to produce the set of samples for the current sampling period.

19. The apparatus claimed in claim 11, wherein the means for producing a set of samples further comprises:

means for initiating the process;

means for detecting an intensity emitted during the process in the form of a signal representing the intensity; and

means for sampling each signal at a rate and at a beginning of a current sampling period defined by the rate to produce the set of samples for the current sampling period.

20. The apparatus claimed in claim 19 wherein the means for normalizing each of the set of pre-filtered samples further comprises:

means for determining an average normalization value corresponding to each of the sampled signals; and

means for dividing each of the set of pre-filtered samples by the average normalization value corresponding to the signal from which each of the pre-filtered samples was taken.

21. The apparatus claimed in claim 11, wherein the derivative of the value is used to determine whether the threshold has been exceeded and whether the mode has been met.

29. The apparatus claimed in claim 11, further comprising:

means for determining a first parameter associated with an immediately preceding sample set; and

means for determining a second paragraph associated with a current sample set.

30. The apparatus claimed in claim 29, wherein the mode is met when the first parameter is less than the second parameter.

31. The apparatus claimed in claim 29, wherein the mode is met when the first parameter is greater than the second parameter.

32. The apparatus claimed in claim 29, wherein the mode is met when the first parameter is less than the threshold and is less than the second parameter.

26. A method of detecting an endpoint for terminating a process, 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;

producing a set of samples;

processing the samples;

determining a first parameter associated with an immediately preceding sample set;

determining a second parameter associated with a current sample set;

incrementing the delay count when the threshold has been exceeded by a predefined number and the mode is met, otherwise setting the delay count equal to zero, wherein the mode is met when the first parameter is less than the second parameter;

repeating said processing step for each set of 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.

27. A method of detecting an endpoint for terminating a process, 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;

producing a set of samples;

processing the samples;

determining a first parameter associated with an immediately preceding sample set;

determining a second parameter associated with a current sample set;

incrementing the delay count when the threshold has been exceeded by a predefined number and the mode is met, otherwise setting the delay count equal to zero, wherein the mode is met when the first parameter is greater than the second parameter;

repeating said processing step for each set of 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.

28. A method of detecting an endpoint for terminating a process, 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;

producing a set of samples;

processing the samples;

determining a first parameter associated with an immediately preceding sample set;

determining a second parameter associated with a current sample set;

incrementing the delay count when the threshold has been exceeded by a predefined number and the mode is met, otherwise setting the delay count equal to zero, wherein the mode is met when the first parameter is less than the threshold and is less than the second parameter;

repeating said processing step for each set of 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.

33. An apparatus for detecting an endpoint for terminating a process, comprising:

means for defining the endpoint in the form of a mode, a minimum value of a delay count, and a threshold;

means for producing a set of samples;

means for processing the samples;

means for determining a first parameter associated with an immediately preceding sample set;

means for determining a second paragraph associated with a current sample set;

means for incrementing the delay count when the threshold has been exceeded by a predefined number and the mode is met, otherwise setting the delay count equal to zero, wherein the mode is met when the first parameter is less than the second parameter;

means for repeating said processing step for each set of samples until the delay count reaches or exceeds the minimum value; and

means for terminating the process when the delay count reaches or exceeds the minimum value.

34. An apparatus for detecting an endpoint for terminating a process, comprising:

means for defining the endpoint in the form of a mode, a minimum value of a delay count, and a threshold;

means for producing a set of samples;

means for processing the samples;

means for determining a first parameter associated with an immediately preceding sample set;

means for determining a second paragraph associated with a current sample set;

means for incrementing a delay count when the threshold has been exceeded by a predefined number and the mode is met, otherwise setting the delay count equal to zero, wherein the mode is met when the first parameter is greater than the second parameter;

means for repeating said processing step for each set of samples until the delay count reaches or exceeds the minimum value; and

means for terminating the process when the delay count reaches or exceeds the minimum value.

35. An apparatus for detecting an endpoint for terminating a process, comprising:

means for defining the endpoint in the form of a mode, a minimum value of a delay count, and a threshold;

means for producing a set of samples;

means for processing the samples;

means for determining a first parameter associated with an immediately preceding sample set;

means for determining a second paragraph associated with a current sample set;

means for incrementing the delay count when the threshold has been exceeded by a predefined number and the mode is met, otherwise setting the delay count equal to zero, wherein the mode is met when the first parameter is less than the threshold and less than the second parameter;

means for repeating said processing step for each step of samples until the delay count reaches or exceeds the minimum value; and

means for terminating the process when the delay count reaches or exceeds the minimum value.