Effect of dilution gas on the distribution characteristics of capacitively coupled plasma by comparing SiH4/He and SiH4/Ar

Abstract

In this study, we focus on the difference in the spatial distribution of the plasma parameters between SiH4/He capacitively coupled plasma (CCP) and SiH4/Ar CCP. The SiH4/He mixture is modeled using the chemical reactions that were successfully derived in our previous studies. The chemical reaction model of the SiH4/Ar mixture built in this study is based on the detailed set of chemical reactions in Ar. The spatial distribution of the plasma parameters is examined with the aid of a 2D fluid model. The electron and radical densities of SiH4/Ar CCP are higher than those of SiH4/He CCP. In addition, dilution with Ar results in more uniform reaction rates, which leads to a more uniform deposition profile. Because helium requires higher threshold energies for excitation and ionization, dilution with He had little effect on the precursor production. As a result, the concentration of Si2H6 observed in the inter-electrode region when using Ar for dilution was observed to be about ten times higher than the concentration of Si2H6 observed for He. This high concentration played a large role in influencing the formation of important radicals that determine the deposition rate as well as the difference in the deposition rate profile between Ar and He as diluents. The higher concentration of Si2H6 when using Ar means that the production rate of Si2H5 is higher in Ar. An examination of the effect of the dilution gas on the deposition rate profile indicated that the deposition rate profile with Ar is 100% more uniform and the deposition rate nearly 87% higher than for dilution with He.