Reduction of outgassing rate by glow discharge cleaning

The experiments were carried out to determine the vacuum-plasma characteristics (mainly erosion and outgassing rate in a vacuum) of the stainless steel 12X18H10T before and after processing the walls of the vacuum chamber with the glow discharge and combined, glow-microwave plasma discharges in argon atmosphere. The current-voltage characteristics, the electron density and electron temperature were measured. It was observed that the discharge voltage in the combined regime is significantly lower than in glow discharges. In some modes, this voltage decrease can be up to 200 V. It was shown that erosion of stainless steel 12X18H10T in the combined discharges is 70 %, less than in the glow discharges. Measurements were made of the outgassing rate of 12X18H10T stainless steel with the thermal desorption probe in situ in the DSM-1 vacuum chamber. It was shown that cleaning the chamber wall by the glow discharge during 5 h leads to a decrease in the outgassing rate from 5.5·10-5 to 1·10-5 (Torr.l)/(s.cm2) . When the chamber wall is treated with GM discharge starting from nearly the same initial conditions the outgassing rate decreased to 3·10-6 (Torr.l)/(s.cm2). Spectral measurements of the plasma radiation of a glow and combined discharges show a decrease in the ratio of the peaks of argon ions and neutrals during the transition from a glow discharge to a combined one.

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Origin and Incorporation Mechanism for Oxygen Contaminants in a-Si:H and μc-Si:H Films Prepared by the Very High Frequency (70 MHz) Glow Discharge Technique

MRS Proceedings ◽

10.1557/proc-377-39 ◽

1995 ◽

Vol 377 ◽

Cited By ~ 21

Author(s):

U. Kroll ◽

J. Meier ◽

H. Keppner ◽

S. D. Littlewood ◽

I. E. Kelly ◽

...

Keyword(s):

Glow Discharge ◽

Oxygen Concentration ◽

High Frequency ◽

Secondary Ion Mass Spectrometry ◽

Microcrystalline Silicon ◽

Very High Frequency ◽

Oxygen Incorporation ◽

Outgassing Rate ◽

Secondary Ion ◽

Very High

ABSTRACTThe effect of plasma power, reactor outgassing rate and feed gas purity on the oxygen content of amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) layers, prepared by the VHF (70 MHz) glow discharge technique has been investigated. The oxygen concentration in the films was measured by Secondary Ion Mass Spectrometry. The gas purity could be optionally enhanced by the application of a getter-based gas purifier mounted in the gas pipe just before the reactor. The purifier reduces the oxygen contaminants in the feed gas to levels in the ppb range. It was found that oxygen incorporation was enhanced at lower deposition rates. The deposition rate dependence of the oxygen incorporation is in excellent agreement with the proposed incorporation mechanism. Furthermore, the reactor outgassing rate and the purity of the feed gas itself were identified as the main contamination sources for the oxygen contaminants in the deposited a-Si:H films as well as in μc-Si:H films : e.g. at outgassing rates in the range of 10−6 mbar 1 s−1, at least around half of the oxygen detected in both a-Si:H and in the μc-Si:H layers originates from the feed gas if the latter is unpurified. By combining reduced outgassing rates and the use of purified feed gas, a-Si:H and μc-Si:H films with an oxygen concentration of 5×1017cm−3 and 2×1018cm−3, respectively, were deposited. These values both represent the lowest concentrations of oxygen contaminants reported to date for these kinds of materials.

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