US 5,770,922 AGranted

Baseband V-I probe

AssigneeENI Technologies, Inc.

InventorsKevin S. Gerrish, Daniel F. Vona, Jr.

Life of this patent

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Abstract

An RF probe for a plasma chamber picks up current and voltage samples of the RF power applied to an RF plasma chamber, and the RF voltage and current waveforms are supplied to respective mixers. A local oscillator supplies both mixers with a local oscillator signal at the RF frequency plus or minus about 15 KHz, so that the mixers provide respective voltage and current baseband signals that are frequency shifted down to the audio range. The phase relation of the applied current and voltage is preserved in the baseband signals. These baseband signals are then applied to a stereo, two-channel A/D converter, which provides a serial digital signal to a digital signal processor or DSP. A local oscillator interface brings a feedback signal from the DSP to the local oscillator. The DSP can be suitably programmed to obtain complex Fast Fourier Transforms of the voltage and current baseband samples. The frequency-domain spectra are analyzed to obtain, with great accuracy, magnitude of voltage and current and phase angle. Other parameters are derived from these three.

Claims15

Dependent claims

A plasma arrangement in which an RF power generator supplies an RF electrical wave in an RF frequency range to a power input of a plasma chamber within which said RF electrical wave produces a plasma, and in which a plasma probe picks up an RF voltage waveform of said electrical wave and an RF current waveform of said electrical wave;

comprising the improvement wherein said plasma probe comprises a controllable local oscillator providing a local oscillator signal;
a voltage signal mixer having inputs receiving said RF voltage waveform and said local oscillator signal, respectively, and an output providing a baseband voltage signal;
a current signal mixer having inputs receiving said RF current waveform and said local oscillator signal, respectively, and having an output providing a baseband current signal;
an A/D converter having a first channel input to which said baseband voltage signal is applied, a second channel input to which said baseband current signal is applied, and a serial output providing a time-synchronous serial digital signal containing digital representations of said baseband voltage waveform and said baseband current waveform;
a digital signal processor having an input coupled to the serial output of said A/D converter, said digital signal processor being suitably programmed to compute amplitude and relative phase of said voltage baseband signal and said current baseband signal;
external interface means for providing an output determination based on said amplitudes and relative phase;
and local oscillator interface means coupled to said digital signal processor and to said local oscillator permitting said digital signal processor to control the frequency of said local oscillator.

4 more elements

A method of deriving amplitude and relative phase information for current and voltage of an RF power wave that is applied at a radio frequency (RF) to a power input of a plasma chamber within which said RF power wave produces a plasma, and in which a plasma probe picks up an RF voltage waveform and an RF current waveform of said power wave;

comprising the steps of generating a local oscillator signal;
mixing said local oscillator signal and said RF voltage waveform to produce a voltage baseband signal at an audio frequency;
mixing said local oscillator signal and said RF current waveform to produce a current baseband signal at said audio frequency;
supplying a feedback signal from said digital signal processor to control the frequency of said local oscillator signal. converting said voltage baseband signal and said current baseband signal to a serial digital signal;
supplying said serial digital signal to a suitably programmed digital signal processor;
supplying a feedback signal from said digital signal processor to control the frequency of said local oscillator signal;
and computing the amplitudes and relative phase of said voltage and current baseband signals.

4 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/684,833Filed 22 Jul 1996
Granted: 23 Jun 1998
Term ends: Not estimatedThe source records don’t support an estimate.

Classification5 codes

H01J 37/32082
Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources: radio frequency generated…
H01J 37/32935
Plasma diagnostics: monitoring and controlling tubes by information coming from the object and/or discharge
H05H 1/0081
Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature: by electric means
H01J
Electric discharge tubes or discharge lamps