Plasma etching with fast endpoint detector

• US 6,104,487 A
• Filed: 12/12/1997
• Issued: 08/15/2000
• Est. Priority Date: 12/20/1996
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Buck, David Wallace, Barna, Gabriel G.
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): Smith, Zandra V.
• Application Number:
  US08/989,607
• Time in Patent Office: 977 Days
• Field of Search: 216/60, 356/311, 356/316
• US Class Current: 356/316
• CPC Class Codes: G01N 21/68 using high frequency electric fields

Abstract

A system and process for analyzing the plasma discharge for various frequency components that can be correlated to wafer, chamber or equipment conditions. This system and process monitors (step 210), by using optical or electrical signals from the plasma, the low frequency plasma variations (step 220) generated during the wafer manufacturing process. For example, in endpoint detection applications, the amplitude variations of the plasma glow at a selected audio frequency, chosen for sensitivity to the etched material, is used to generate the endpoint signal (step 230). This endpoint signal has a potential response time equal to one cycle of the selected frequency plus minimal filtering due to noise reduction. To extract the vital parameters from the plasma glow, DSPs for frequency analysis or simple frequency filtering methods can be used.

Claims

1. A method for plasma etching, comprising the steps of:

(a.) plasma etching a wafer; and

(b.) monitoring audio-frequency or infrasonic variation in the plasma intensity during said etching step; and

(c.) discontinuing said etching step (a.) at a time which is dependent on said monitoring step (b.).

2. The method of claim 1, wherein said monitoring step uses a photodiode having a peak sensitivity in the infrared to detect variations in broadband optical emission from the plasma.

3. The method of claim 1, wherein said monitoring step uses an electrical connection to detect variations in RF voltage or current.

4. A system for analyzing a plasma discharge, comprising:

a photodetector optically coupled to monitor the intensity of light emission from at least one portion of the plasma discharge, said photodetector providing a corresponding electrical output; and

at least one filter connected to receive said electrical output and monitor therein amplitude variations at at least one audio frequency, and provide an output which is dependent on said amplitude variations.

5. The system of claim 4, wherein said filter is a digital signal processor or bandpass filter.

6. The system of claim 4, wherein said at least one portion of the plasma discharge is directly adjacent to the wafer surface.

7. The system of claim 4, wherein said photodetector is optically coupled to monitor the intensity of light emission over a range of wavelengths which includes at least 400 nm of difference between maximum and minimum wavelengths.

8. The system of claim 4, wherein said photodetector is a photodiode having a peak sensitivity in the infrared.

9. A plasma reactor system, comprising:

a chamber which encloses a wafer support;

at least one electrode positioned to generate a plasma discharge in proximity to said wafer support, when RF power is applied to said electrode;

a photodetector optically coupled to monitor the intensity of light emission from at least one portion of said plasma discharge, said photodetector providing a corresponding electrical output; and

at least one filter connected to receive said electrical output and monitor therein amplitude variations at at least one audio frequency, and provide an output which is dependent on said amplitude variations.

10. The system of claim 9, wherein said filter is a digital signal processor or bandpass filter.

11. The system of claim 9, wherein said at least one portion of the plasma discharge is directly adjacent to the wafer surface.

12. The system of claim 9, wherein said photodetector is optically coupled to monitor the intensity of light emission over a range of wavelengths which includes at least 400 nm of difference between maximum and minimum wavelengths.

13. The system of claim 9, wherein said photodetector is a photodiode having a peak sensitivity in the infrared.