Investigation of spatial distribution of EEPFs and neutral species in nitrogen inductively coupled plasmas by 2D hybrid simulation

Abstract

Neutral species in nitrogen plasmas play a crucial role in many applications related to semiconductor fabrication. In this research, a two-dimensional fluid/electron Monte Carlo hybrid model is employed to simulate nitrogen inductively coupled plasmas, and the spatial distributions of electron energy probability distributions (EEPFs), as well as their influence on the neutral species, are discussed under various pressures. It is found that the EEPF in the bulk region is relatively uniform, and it exhibits a bi-Maxwellian distribution at 3 mTorr. As pressure increases, the high energy tail declines due to the more frequent collisions. Moreover, a hole appears at around 3 eV in the EEPF above the substrate, and it becomes less obvious toward the skin layer below the dielectric window. Moreover, the maxima of metastable species densities, i.e., N2(A3Σu+), N(2D), and N(2P), are located at the center of the chamber at low pressure, and they gradually move to the skin layer under the coils as pressure increases. The behaviors of neutral species can be understood by examining the reactant densities of the main generation and loss mechanisms, as well as the corresponding rate coefficients which are calculated according to EEPFs. In addition, since the ground state N(4S) is mainly produced by the quenching of metastable atoms and neutralization of ions at the walls, the maximum of the N(4S) density appears below the dielectric window and above the substrate at 3 mTorr, and the peak under the dielectric window becomes more obvious at higher pressure due to the stronger locality.