Plasma diagnosing apparatus

Details Plasma diagnosing apparatus Plasma diagnosing apparatus

1992-07-15

1994-10-25

Regan, Maura K.

Electricity: measuring and testing

Determining nonelectric properties by measuring electric...

422 53, 324464, G01N 2706

Patent

active

053592824

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates generally to a plasma diagnosing apparatus, and more specifically to a plasma diagnosing apparatus capable of detecting and removing contamination of the probe.
2. Description of Related Art
In recent years, the plasma processing techniques such as plasma CVD, plasma polymerization, etc., have been widely adopted in various fields of technology. Since most of these techniques employ the reactive plasma, a problem will arise as to contamination of a probe at the time of diagnosing the plasma using such probe.
Recently, not only the basic study in the plasma has made its advancement, but also its applications in various industrial fields have been broadened. As the result, it has become necessary to diagnose instantaneously from outside various parameters within the plasma, in particular its electron temperature and electron density. The so-called "triple probe direct viewing method", as the method of diagnosis, is the most effective way, with which these parameters are instantaneously indicated on the gauges.
In general, there are two principal methods of diagnosing the plasma parameters: the one is a probing method, by which electrodes are directly intromitted into the plasma to take out electric current from it, and then the current is analyzed to find out the parameters of the plasma; and the other is an electromagnetic wave method, by which microwaves, lasers, and others are put into the plasma to directly sense out the results of their interaction, or to detect, by spectroscopy, a beam to be emitted from the plasma, to thereby find out these parameters.
While this latter method, i.e., the electromagnetic wave method is excellent in its horological resolution, it has disadvantages such that the device becomes complicated in its structure, hence expensive in its manufacture. In contrast to this, the former method, i.e., the probing method is characteristically excellent in its spatial resolution, simple in the device construction, and can be manufactured at a low cost, although the plasma to be diagnosed is limited to one having a relatively low temperature and low density.
In general, since most of the plasma used in laboratories, etc. is of relatively low temperature and low density, probing method is the fundamental for diagnosing the plasma having its electron density Ne of as low as 10.sup.14 cm.sup.-3 or below and its electron temperature Te of as low as a few tens of electron volts (eV) or below.
In case the parameters of the reactive plasma are to be diagnosed by the probing method, the surface of the probe becomes covered with a contaminant film as the time passes by, with the consequence that the exposed part of the probe is required to be cleaned.
There has heretofore been adopted a method for cleaning the probe with it being installed in the vacuum device, wherein, after a reactive gas is exchanged for an inactive gas as the case may be, a negative voltage is imparted to the probe with respect to a reference electrode to bring it to a red heat condition by the ion bombardment for removal of the contaminant film.
When, however, the ionic energy increases, the heat generation on the surface of the probe also increases, so that, for avoiding destruction of the probe due to heating, the voltage and other parameters should be controlled with care. The manual control of these parameters was fairly difficult and cleaning of the probe was often unsatisfactory, or the probe becomes molten due to excessive voltage application, hence good result could not always be obtained.
In the diagnosis of the reactive plasma by means of the conventional plasma diagnosing apparatus, if the reactive plasma is silane gas plasma, for example, an amorphous silicon film is produced on the surface of the probe with passage of time, and, if the plasma is styrene plasma, a styrene polymer film is produced on the surface of the probe. On account of this, the voltage-current characteristic of the probe changes with growth of the film, its sh

REFERENCES:
patent: 4023931 (1977-05-01), Wolfgram
patent: 4922205 (1990-05-01), Shimizu et al.

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