Detection of process endpoint through monitoring fluctuation of output data

• US 6,745,095 B1
• Filed: 10/04/2000
• Issued: 06/01/2004
• Est. Priority Date: 10/04/2000
• Status: Expired due to Fees

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Ben-Dov, Yuval, Sarfaty, Moshe, Garachtchenko, Alexander Viktorovich
• Primary Examiner(s): Picard, Leo
• Assistant Examiner(s): Bahta, Kidest
• Application Number:
  US09/686,656
• Time in Patent Office: 1,336 Days
• Field of Search: 700/30, 700/31, 700/220, 700/33, 700/121, 438/710, 703/2
• US Class Current: 700/121
• CPC Class Codes: H01L 22/26 Acting in response to an ongoing measurement without interruption of processing, e.g. endpoint detection, in-situ thickness measurement endpoint detection arrangements in CMP apparatus B24B37/013, in discharge apparatus H01J37/32

Abstract

Progress of a semiconductor fabrication process is monitored by detecting data output by the process, and then correlating a specific process event to fluctuations in the output data over a time period of 10 milliseconds or less. In one embodiment, endpoint of a plasma chamber cleaning process may be identified by calculating standard deviation of intensity of optical chamber emissions based upon a local time period. The time at which standard deviation of optical emissions attains a steady state indicates endpoint of the cleaning process. Another approach to characterizing fluctuation is to perform a Fast Fourier Transform (FFT) on the output emissions data, and then to plot over time the total power of the emissions over a relevant frequency range. The time at which total power attains a steady state also reveals endpoint of the process. Other techniques for characterizing fluctuation for process monitoring include calculation of the root-mean-square or entropy of an output signal.

Claims

1. A method for monitoring a semiconductor fabrication process comprising:

measuring a value of an output from the semiconductor fabrication process;

characterizing a fluctuation in the value of the output over a time period of 10 milliseconds or less; and

correlating the fluctuation to an event of the semiconductor fabrication process.

2. The method of claim 1 wherein measuring a value of an output comprises detecting an analog value of the output.

3. The method of claim 2 wherein characterizing fluctuation in the output comprises determining a standard deviation of the output from a local average.

4. The method of claim 3 wherein determining a standard deviation comprises:

passing the analog signal through a band pass filter to produce a filtered analog signal;

multiplying the filtered analog signal by itself to produce a squared filtered analog signal; and

passing the squared filtered analog signal through a low pass filter.

5. The method of claim 2 wherein characterizing a fluctuation comprises calculating a root-mean-square of the value.

6. The method of claim 1 wherein measuring a value of an output comprises:

detecting an analog value of the output; and

sampling the analog value of the detected process output at a sampling rate of 1 kHz or greater; and

converting the sampled analog value to a digital value.

7. The method of claim 6 wherein characterizing a fluctuation comprises calculating a standard deviation of the sampled value over the second time period.

8. The method of claim 6 wherein characterizing a fluctuation comprises:

performing a Fast Fourier Transformation (FFT) to resolve the sampled value into an amplitude of a frequency component; and

plotting a fluctuation of the amplitude.

9. The method of claim 6 wherein characterizing a fluctuation in the value of the output comprises calculating a root-mean-square of the sampled value.

10. The method of claim 1 wherein correlating fluctuation in value of the output to a process event comprises correlating a steady state of the output value to a process endpoint.

11. The method of claim 1 wherein measuring a value of the output comprises measuring an intensity of light emitted from a plasma.

12. The method of claim 11 wherein the light intensity is measured in a chamber in which the plasma is generated.

13. The method of claim 11 wherein the light intensity is measured in a cell downstream from a chamber in which the plasma is generated.

14. The method of claim 11 wherein measuring an intensity of light comprises measuring a current output by a photodiode receiving the emitted light.

15. The method of claim 11 wherein measuring an intensity of light comprises measuring a current output by a monochrometer receiving the emitted light and coupled to a photomultiplier tube.

16. The method of claim 1 wherein measuring a value of the output comprises measuring an RF power supplied during generation of a plasma.

17. The method of claim 16 wherein the RF power is measured in a chamber in which the plasma is generated.

18. The method of claim 16 wherein the RF power is measured in a cell downstream from a chamber in which the plasma is generated.

19. The method of claim 1 wherein measuring a value of the output comprises measuring a temperature.

20. The method of claim 1 wherein measuring a value of the output comprises measuring a mass of a product material by mass spectrometry.

21. An apparatus for processing a substrate, said apparatus comprising:

a substrate processing chamber;

a sensor operatively coupled to said substrate processing chamber to detect a value of an output from the chamber;

a computer processor operatively coupled to said sensor; and

a memory coupled to said computer processor, said memory storing a computer program in computer readable format including computer instructions to permit said processor to;

measure a value of an output from the process, and

characterize a fluctuation in the value of the output over a time period of 10 milliseconds or less.

22. The apparatus of claim 21 wherein:

the substrate processing chamber comprises a plasma chamber;

the sensor comprises a photodiode in optical communication with the plasma chamber through a window; and

the memory stores a computer program including computer instructions to permit said processor to measure an intensity of plasma emission.

23. The apparatus of claim 21 wherein:

the substrate processing chamber comprises a plasma chamber;

the sensor comprises a monochrometer in optical communication with the plasma chamber through a window and coupled to a photomultiplier tube; and

the memory stores a computer program including computer instructions to permit said processor to measure an intensity of plasma emission.

24. The apparatus of claim 21 wherein:

the substrate processing chamber comprises a plasma chamber;

the sensor is in electrical communication with an RF wafer bias generator; and

the memory stores a computer program including computer instructions to permit said processor to measure an RF power.

25. The apparatus of claim 21 wherein the memory stores a computer program including computer instructions enabling the processor to characterize a fluctuation by calculating a standard deviation of the value of the output.

26. The apparatus of claim 21 wherein the memory stores a computer program including computer instructions enabling the processor to characterize a fluctuation by performing a Fast Fourier Transformation of the value of the output.

27. The apparatus of claim 21 wherein the memory stores a computer program including computer instructions enabling the processor to characterize a fluctuation by calculating an entropy of the value of the output.

28. The apparatus of claim 21 wherein the processor comprises:

a band pass filter in electrical communication with the sensor and receiving an analog electrical signal from the sensor;

a multiplier in electrical communication with the band pass filter and receiving a filtered electrical signal from the band pass filter; and

a low pass filter in electrical communication with the multiplier and receiving a multiplied signal from the multiplier.

29. The apparatus of claim 21 wherein the processor comprises:

an analog to digital converter in electrical communication with the sensor and receiving an analog electrical signal from the sensor; and

a logic structure in electrical communication with the analog to digital converter and receiving a sampled digital signal from the analog to digital converter and performing a calculation on the sampled digital signal.

30. The apparatus of claim 29 wherein the logic structure is configured to calculate a standard deviation of the sampled digital signal.

31. The apparatus of claim 29 wherein the logic structure is configured to perform a Fast Fourier Transformation on the sampled digital signal.

32. The apparatus of claim 21 wherein:

the substrate processing chamber comprises a plasma chamber;

the sensor comprises a photodiode in optical communication with a plasma cell remote from the plasma chamber and receiving exhaust from the plasma chamber; and

the memory stores a computer program including computer instructions to permit said processor to measure an intensity of plasma emission.

33. The apparatus of claim 21 wherein:

the substrate processing chamber comprises a plasma chamber;

the sensor comprises a monochrometer in optical communication with a plasma cell remote from the plasma chamber and coupled to a photomultiplier tube, the plasma cell receiving exhaust from the plasma chamber; and

the memory stores a computer program including computer instructions to permit said processor to measure an intensity of plasma emission.

34. The apparatus of claim 21 wherein:

the substrate processing chamber comprises a plasma chamber;

the sensor is in electrical communication with an RF wafer bias generator positioned in the plasma chamber; and

the memory stores a computer program including computer instructions to permit said processor to measure an RF power.

35. The apparatus of claim 21 wherein:

the substrate processing chamber comprises a plasma chamber;

the sensor is in electrical communication with an RF wafer bias generator positioned in a plasma cell remote from the plasma chamber and receiving the exhaust of the plasma chamber; and

the memory stores a computer program including computer instructions to permit said processor to measure an RF power.