System and method for current-based plasma excursion detection

• US 8,587,321 B2
• Filed: 09/24/2010
• Issued: 11/19/2013
• Est. Priority Date: 09/24/2010
• Status: Expired due to Fees

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Chen, Jian J., Ayoub, Mohamad A.
• Primary Examiner(s): Hollington, Jermele M
• Assistant Examiner(s): PRETLOW, DEMETRIUS R
• Application Number:
  US12/890,089
• Publication Number:
  US 20120074951A1
• Time in Patent Office: 1,152 Days
• Field of Search: 324/509, 324/536, 324/464
• US Class Current: 324/509
• CPC Class Codes: H01J 37/32183 Matching circuits
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge

Abstract

A system and method for the detection of plasma excursions, such as arcs, micro-arcs, or other plasma instability, during plasma processing by directly monitoring RF current just prior to reaching an RF power electrode of a plasma processing chamber is provided. The monitored RF current may be converted to an RF voltage and then passed through a succession of analog filters and amplifiers to provide a plasma excursion signal. The plasma excursion signal is compared to a preset value, and at points where the plasma excursion signal exceeds the preset value, an alarm signal is generated. The alarm signal is then fed back into a system controller so that an operator can be alerted and/or the processing system can be shut down. In one embodiment, the RF current amplified and converted to a digital signal for digital filtering and processing. In certain embodiments, multiple processing regions can be monitored by a single detection control unit.

Claims

1. A method for detecting plasma excursions in a plasma chamber, comprising:

directly sensing a radio frequency (RF) current from an RF transmission line using a RF current probe at a position between an RF matching network and an RF powered electrode within the plasma chamber during plasma processing;

generating a time-varying magnetic field around the RF transmission line when the RF current flowing through the RF transmission line;

generating a time-varying electric field from the time-varying magnetic field;

inducing the RF current by the time-varying electric field to flow through the RF current probe;

converting the RF current to a voltage signal using the RF current probe which comprises a current transformer;

filtering the voltage signal using a plurality of filters to obtain an output voltage signal;

comparing the output voltage signal to a preset voltage value that represents a plasma excursion event; and

generating an alarm signal if the output voltage signal exceeds the preset voltage value.

2. The method of claim 1, wherein the filtering the voltage signal comprises passing the voltage signal through a band pass filter.

3. The method of claim 2, wherein the band pass filter is configured to only pass frequencies between about 250 Hz and about 50 kHz.

4. The method of claim 1, further comprising passing the voltage signal through a frequency mixer prior to the filtering the voltage signal.

5. The method of claim 1, further comprising converting the voltage signal to a digital signal prior to the filtering the voltage signal.

6. The method of claim 5, wherein the comparing is performed by a digital signal processor.

7. The method of claim 1, further comprising measuring the absolute magnitude of the RF current sensed prior to the comparing.

8. The method of claim 1, wherein the filtering the voltage signal comprises serially passing the voltage signal through a low frequency pass filter and a high frequency pass filter.

9. The method of claim 8, wherein the low frequency pass filter is configured to pass frequencies below about 50 kHz and the high frequency pass filter is configured to pass frequencies above about 250 Hz.

10. The method of claim 1, further comprising continually collecting the output voltage signal with a data acquisition module.

11. The method of claim 1, further comprising collecting the output voltage signal with a data acquisition module only when an alarm signal is generated.

12. A system for detecting plasma excursions in a plasma chamber, comprising:

one or more radio frequency (RF) current probes, each RF current probe positioned to sense an RF current from a transmission line at a position between an RF matching network and an RF electrode within a plasma chamber during plasma processing, wherein the RF current is configured to flow through the transmission line to generate a time-varying electric field, inducing the RF current to flow through the RF current probe, wherein each RF current probe comprises a current transformer configured to convert the RF current from the transmission line to a voltage signal; and

a plasma excursion detection unit, comprising;

one or more excursion detection modules, wherein each excursion detection module is configured to receive the voltage signal from one of the one or more RF current probes, wherein each excursion detection module comprises a plurality of filters arranged to filter the voltage signal to obtain an output voltage signal, and wherein each excursion module further comprises a comparator configured to compare the output voltage signal to a preset voltage signal and generate an alarm signal if the output voltage signal exceeds the preset voltage signal;

one or more connection ports configured to receive the preset voltage signal from a host controller and configured to send the alarm signal to the host controller; and

a data acquisition module configured to collect and transfer the output voltage signal from each of the one or more excursion detection modules.

13. The system of claim 12, wherein each of the excursion detection modules comprises a band pass filter configured to pass frequencies between about 250 Hz and about 50 kHz.

14. The system of claim 12, wherein the comparator is an analog voltage comparator.

15. The system of claim 12, wherein the comparator is a digital comparator.

16. The system of claim 12, wherein each excursion detection module further comprises a frequency mixer.

17. The system of claim 12, wherein each of the excursion detection modules comprises a low frequency pass filter and a high frequency pass filter.

18. The system of claim 17, wherein the low frequency pass filter is configured to pass frequencies less than about 50 kHz and the high frequency pass filter is configured to pass frequencies greater than about 250 Hz.

19. The system of claim 12, wherein the system comprises at least two RF current probes configured to sense RF current from separate transmission lines.

20. The system of claim 12, wherein the plurality of filters comprises a filter selected from the group consisting of an RF filter, a band pass filter, an analog band pass filter, a high frequency pass filter, a low frequency pass filter, a notch filter, a digital band pass filter, a digital signal processor (DSP), and combinations thereof.

21. The system of claim 12, wherein the data acquisition module is configured to collect and transfer the output voltage signal from each of the one or more excursion detection modules to a data logging and diagnostic system.