Plasma diagnostic study of silicon nitride film growth in a remote Ar–H2–N2–SiH4 plasma: Role of N and SiHn radicals

Abstract

A remote expanding thermal plasma operated on an Ar–H2–N2–SiH4 mixture has been studied by several plasma diagnostics to obtain insight into the plasma processes and the hydrogenated amorphous silicon nitride (a-SiNx:H) growth mechanism from the N2–SiH4 reactant mixture. From Langmuir probe measurements, ion mass spectrometry, and threshold ionization mass spectrometry, it is revealed that the Ar–H2–N2 operated plasma source leads mainly to N and H radicals in the downstream region. The H radicals react with the SiH4 admixed downstream creating a high SiH3 density as revealed by cavity ringdown spectroscopy. By cavity ringdown measurements, it is also shown that Si and SiH have a much lower density in the downstream plasma and that these radicals are of minor importance for the a-SiNx:H growth process. The ground-state N radicals from the plasma source do not react with the SiH4 injected downstream leading to a high N density under the a-SiNx:H deposition conditions as revealed by threshold ionization mass spectrometry. From these results, it is concluded that N and SiH3 radicals dominate the a-SiNx:H growth process and the earlier proposed growth mechanism of a-SiNx:H from the N2–SiH4 mixture [D. L. Smith et al., J. Vac. Sci. Technol. B 8, 551 (1990)] can be refined: During deposition, an a-Si:H-like surface layer is created by the SiH3 radicals and at the same time this a-Si:H-like surface layer is nitridated by the N radicals leading to a-SiNx:H formation. This growth mechanism is further supported by the correlation between the SiH3 and N plasma density and the incorporation flux of Si and N atoms into the a-SiNx:H films as deposited under various conditions.

Bulk and surface passivation of silicon solar cells accomplished by silicon nitride deposited on industrial scale by microwave PECVD

“…A model for NH 3 /SiH 4 plasmas has been proposed by Smith, 50 and Hanyaloglu and Aydil 51 and Kessels et al 52 have proposed two similar models for N 2 /SiH 4 plasmas.…”

Characterisation and optimisation of PECVD SiNx as an antireflection coating and passivation layer for silicon solar cells

“…Here we adapt the SiN x growth model proposed by Smith et al, 17 Kessels et al 18 and Oever et al 19 to discuss possible chemical reaction schemes for SiN x growth in this work. For the gas mixture of N 2 and SiH 4 , Smith et al 17 and Kessels et al 18 proposed that an a-Si:H-like surface layer is created by SiH a radicals and the a-Si:H-like surface is simultaneously reacted with N radicals, leading to the formation of SiN x .…”

“…For the gas mixture of N 2 and SiH 4 , Smith et al 17 and Kessels et al 18 proposed that an a-Si:H-like surface layer is created by SiH a radicals and the a-Si:H-like surface is simultaneously reacted with N radicals, leading to the formation of SiN x . Oever et al 19 studied the plasma chemistry for the gas mixture of (i) Gas phase dissociation: -NH 3 is introduced into the system through the shower-head which forms part of the ceiling of the deposition chamber above the μW quartz tubes and is dissociated:…”

The growth kinetics of silicon nitride deposited from the SiH4–N2 reactant mixture in a remote plasma

“…The expanding thermal plasma (ETP) for a-SiN x :H deposition from SiH 4 -N 2 has been described in detail in previous work [4,6] and here only the basics will be summarized. In the ETP, plasma creation, growth precursor formation, and deposition are spatially separated.…”

“…This so-called 'expanding thermal plasma' is able to deposit good quality a-SiN x :H films at high deposition rates (so far mainly used for photovoltaics [4,5]) and the remote nature of the technique is also beneficial for fundamental plasma and surface studies [6].…”