Acetylene - Argon Plasmas Measured at a Biased Substrate Electrode for Diamond-Like Carbon Deposition. Part 1: Mass Spectroscopy

TL;DR

This study uses quadrupole mass spectrometry to analyze neutral and ionic hydrocarbon species in acetylene-argon plasmas at a biased electrode, revealing dominant argon species and efficient acetylene conversion, with implications for diamond-like carbon film deposition.

Contribution

First-time measurement of hydrocarbon species in biased plasma using mass spectrometry, providing insights into plasma chemistry relevant for film growth.

Findings

Argon neutrals and ions dominate plasma composition.

Efficient conversion of acetylene to C2H due to high electron density.

Transient formation of CH4 observed with specific reaction rates.

Abstract

We report, for the first time, quadrupole mass spectrometry of neutral and positive ionic hydrocarbon species measured at the rf biased substrate electrode of an inductively coupled plasma for acetylene rich C2H2:Ar mixtures under various bias, frequency and pressure conditions. It has been observed that, irrespective of initial gas mixture, the resultant plasma is dominated by argon neutrals and ions. This is attributed to highly efficient conversion of acetylene to C2H due to the enhanced electron density compared to a standard capacitive plasma where the acetylene (neutral and ion) species remain dominant. This conversion may be crucial to film formation via inert rather than hydrocarbon ion bombardment. In addition, the transient formation of CH4 from acetylene has been discovered using IR absorption spectroscopy with time constants similar to observed pressure variations. Rate coefficients and rates for many of the reaction mechanisms, calculated using measured EEDFs and species densities, are given. These results have important application in plasma models and growth studies for hydrogenated amorphous or diamond-like carbon film deposition. Film growth under similar plasma conditions is reported in an associated paper along with ion energy distributions for important growth species.