Acetylene - Argon Plasmas Measured at a Biased Substrate Electrode for Diamond-Like Carbon Deposition. Part 2: Ion Energy Distributions

TL;DR

This study measures ion energy distributions in acetylene-argon plasmas at a biased electrode, revealing how pressure and bias conditions influence ion energies and film properties for diamond-like carbon deposition.

Contribution

It provides detailed ion energy distribution data at a biased electrode in acetylene-argon plasmas, highlighting effects of pressure and bias frequency on ion energies and film hardness.

Findings

Ion energy distributions are bimodal at pressures up to 25 mTorr.

Dominant ions are Ar+ or ArH+ despite C2H2 presence.

Peak hardness of films occurs at around 90 eV ion energy.

Abstract

Ion energy distributions have been determined at the rf-bias electrode in an inductively-coupled acetylene-argon plasma for various substrate bias voltages and frequencies under conditions suitable for film deposition. These are compared with those obtained at the grounded wall of a capacitively coupled plasma. In the former, for pressures up to 25 mTorr, the IEDs exhibit bimodal structures with peak separation values that follow the expected dependence on voltage and frequency. At higher pressures, 120 mTorr, the bimodal structure is replaced by a single peak. For all conditions, the dominant ion is Ar+ or ArH+ despite a set C2H2:Ar flow ratio of 2:1, and this can be attributed to the high electron dissociation of the parent molecule. Diamond-like carbon films indicate a peak hardness at an ion energy of around 90 eV and a very sharp fall in hardness is noted beyond this value. This is similar to the observed bombardment energy relationship for sp3 bond formation in hydrogen-free tetragonal amorphous carbon or bias-sputtered films. However, due to the lack of carbon-based ions, an alternative film growth mechanism must be considered, possibly based on argon knock-on implantation of surface adsorbed carbon species. The results have shown that the use of high frequency bias or bias harmonics may lead to much narrower ion energy distributions.