Control of plasma process by use of harmonic frequency components of voltage and current

• US 5,325,019 A
• Filed: 08/21/1992
• Issued: 06/28/1994
• Est. Priority Date: 08/21/1992
• Status: Expired due to Fees

• Current Assignee: Sematech, Inc.
• Original Assignee: Sematech, Inc.
• Inventors: Kamon, Mattan, Miller, Paul A.
• Primary Examiner(s): Pascal, Robert J.
• Assistant Examiner(s): Ratliff, Reginald A.
• Application Number:
  US07/934,091
• Time in Patent Office: 676 Days
• Field of Search: 315/111.21, 315/111.31, 315/111.91, 315/111.71, 156/345, 156/627, 204/192.13
• US Class Current: 315/111.21
• CPC Class Codes: H01J 2237/334 Etching
• CPC Class Codes: H01J 37/32082 Radio frequency generated discharge H01J37/32357, H01J37/32366, H01J37/32394 and H01J37/32403 take precedence
• CPC Class Codes: H01J 37/32174 Circuits specially adapted for controlling the RF discharge
• CPC Class Codes: H01J 37/32183 Matching circuits
• CPC Class Codes: H01J 37/3299 Feedback systems

Abstract

The present invention provides for a technique for taking advantage of the intrinsic electrical non-linearity of processing plasmas to add additional control variables that affect process performance. The technique provides for the adjustment of the electrical coupling circuitry, as well as the electrical excitation level, in response to measurements of the reactor voltage and current and to use that capability to modify the plasma characteristics to obtain the desired performance.

Claims

1. In a plasma processing apparatus, having a reactor for processing a plasma gas and wherein said reactor is coupled to an electrical energy source for generating an electrical signal at a fundamental frequency f in order to provide an electrical energy field for generation of plasma and wherein a non-linear response of said plasma introduces harmonic frequency components of voltage and current of said electrical signal, such that an operating characteristic of said plasma is measurable by observing voltage and current values of said electrical signal at its fundamental frequency and said harmonic frequency components, a combination of said reactor and a variable impedance device coupled between said reactor and said electrical energy source for selecting an operating point of said plasma by adjusting an impedance of said variable impedance device until a desirable electrical operating point of said plasma is selected based on one or more of said fundamental and harmonic frequency components of voltage and current.

2. The apparatus of claim 1 wherein a dc bias voltage from said electrical energy source is observed and utilized to obtain said desirable electrical operating point.

3. The apparatus of claim 1 wherein said variable impedance device adjusts an effective electrical length of a conductor coupled between said variable impedance device and said reactor in order to vary said impedance to select said desirable electrical operating point.

4. The apparatus of claim 1 wherein said variable impedance device includes a variable capacitor in order to vary said impedance to select said desirable electrical operating point.

5. A plasma processing apparatus for processing a plasma gas and in which said apparatus is coupled to an electrical energy source for generating an electrical signal at a fundamental frequency f in order to provide an electrical energy field for generation of plasma and wherein a non-linear response of said plasma introduces harmonic frequency components of voltage and current of said electrical signal, such that an operating characteristic of said plasma is measurable by observing voltage and current values of said electrical signal at its fundamental frequency and said harmonic frequency components comprising:

a reactor for processing said plasma gas therein;

a variable impedance device coupled between said reactor and said electrical energy source for selecting an operating point of said plasma by adjusting an impedance of said variable impedance device until a desirable electrical operating point of said plasma is selected based on one or more of said fundamental and harmonic frequency components of voltage and current.

6. The apparatus of claim 5 wherein a dc bias voltage from said electrical energy source is observed and utilized to obtain said desirable electrical operating point.

7. The apparatus of claim 5 wherein said variable impedance device adjusts an effective electrical length of a conductor coupled between said variable impedance device and said reactor in order to vary said impedance to select said desirable electrical operating point.

8. The apparatus of claim 5 wherein said variable impedance device includes a variable capacitor in order to vary said impedance to select said desirable electrical operating point.

9. A method for processing a semiconductor material by utilizing a plasma process of exposing said semiconductor material to a plasma gas in a reactor wherein said reactor is coupled to an electrical energy source for generating an electrical signal at a fundamental frequency f in order to provide an electrical energy field for generation of plasma and wherein a non-linear response of said plasma introduces harmonic frequency components of voltage and current of said electrical signal, such that an operating characteristic of said plasma is measurable by observing voltage and current values of said electrical signal at its fundamental frequency and said harmonic frequency components comprising:

inserting a variable impedance device between said reactor and said electrical energy source to select an operating point of said plasma by adjusting an impedance of said variable impedance device until a desirable electrical operating point of said plasma is selected based on one or more of said fundamental and harmonic frequency components of voltage and current.

10. The method of claim 9 wherein a dc bias voltage from said electrical energy source is observed and utilized to obtain said desirable electrical operating point.

11. The method of claim 9 wherein said variable impedance device adjusts an effective electrical length of a conductor coupled between said variable impedance device and said reactor in order to vary said impedance to select said desirable electrical operating point.

12. The method of claim 9 wherein said variable impedance device includes a variable capacitor in order to vary said impedance to select said desirable electrical operating point.