# US 5,703,488 A · Instrument for measuring plasma excited by high-frequency

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- Number: US 5,703,488 A
- Document ID: US5703488A
- Status: Granted
- Kind: A
- Application number: 08/481,285
- Filed: 1995-07-05
- Granted: 1997-12-30
- Earliest claimed: 1993-01-15
- Assignees: Tadahiro Ohmi
- Inventors: Tadahiro Ohmi; Masaki Hirayama
- Web page: https://patentgrep.com/patent/US5703488A

## CPC

- H01J 37/32935: {Monitoring and controlling tubes by information coming from the object and/or discharge}
- H05H 1/0081: {by electric means}
- H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H)
- H05H: PLASMA TECHNIQUE (apparatus or processes specially adapted for producing X-rays H05G2/00); PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS

## Abstract

This instrument can measure parameters of a plasma accurately and easily even though the plasma is exited by a high-frequency. The instrument for measuring parameters of a plasma generated in a vacuum chamber by high-frequency discharge at a given frequency comprises a wire (106) for electrically connecting a first electrode (101) arranged in a space where a plasma is produced and a terminal (110) arranged outside the vacuum chamber for taking out signals, and a first insulator (105) so arranged as to cover at least a part of the surface of the wire therewith. The absolute value of the impedance at the given frequency between the first electrode and the ground when looking into the terminal side from the first electrode is five times or more the absolute value of the impedance at the given frequency between the first electrode and the plasma in a state where no direct current flows through the first electrode.

## Claims

### Claim 1

A measuring instrument for measuring all values of a plasma produced by means of a high frequency discharge at a given frequency within a vacuum chamber, said measuring instrument comprising: a wire for electrically connecting a first electrode disposed within a plasma and a terminal disposed outside said vacuum chamber for providing output signals; and an insulator covering at least a portion of a surface of said wire; wherein the absolute value of the impedance at said given frequency between said first electrode and ground via said wire is at least five times the absolute value of the impedance at said given frequency between said first electrode and said plasma in a state in which no direct current flows through said first electrode.

### Claim 2 (depends on 1)

A measuring instrument for plasma excited by a high frequency in accordance with claim 1, further comprising a second electrode disposed in said plasma wherein said second electrode and said first electrode are connected via a capacitor.

### Claim 3 (depends on 1)

A measuring instrument for plasma excited by a high frequency in accordance with claim 1, further comprising circuitry coupled to said terminal such that the impedance at said given frequency between said terminal and ground via said circuitry is variable.

### Claim 4 (depends on 1)

A measuring instrument for plasma excited by a high frequency in accordance with claim 1, wherein at least a portion of said wire comprises a coaxial cable, a length of an outer conductor of said coaxial cable is approximately equivalent to an odd multiple of one-fourth of a wavelength associated with said given frequency, and a core of said coaxial cable and said outer conductor of said coaxial cable are electrically connected via a capacitor at an end of said coaxial cable coupled to said terminal.

### Claim 5 (depends on 1)

A measuring instrument for plasma excited by a high frequency in accordance with claim 1, wherein at least a portion of said wire comprises a coaxial cable, a resistor is disposed between said first electrode and a core of said coaxial cable, and a measuring device for measuring the high frequency voltage at said terminal is coupled to said terminal.