Abstract
Modeling of dry etching processes requires a detailed understanding of the relevant reaction mechanisms. This study aims to elucidate the gas-phase mechanism of reactions in the chemical dry etching process of SiO2 layers which is initiated by mixing NF3 gas with the discharged flow of an NH3/N2 mixture in an etching chamber. A kinetic model describing the gas-phase reactions has been constructed based on the predictions of reaction channels and rate constants by quantum chemical and statistical reaction-rate calculations. The primary reaction pathway includes the reaction of NF3 with H atoms, NF3 + H → NF2 + HF, and subsequent reactions involving NF2 and other radicals. The reaction pathways were analyzed by kinetic simulation, and a simplified kinetic model composed of 12 reactions was developed. The surface process was also investigated based on preliminary quantum chemical calculations for ammonium fluoride clusters, which are considered to contribute to etching. The results indicate the presence of negatively charged fluorine atoms in the clusters, which are suggested to serve as etchants to remove SiO2 from the surface.
Highlights
Dry etching of materials is one of the key components in the fabrication of sophisticated semiconductor devices
The present study focuses on chemical dry etching using NF3 gas and remotely discharged mixture of NH3 and N2.2–4 Fig. 1 shows a schematic diagram of an equipment used in this process
Pure NF3 gas supplied via the other inlet port reacts with the radicals in the chamber to generate etchant species
Summary
Dry etching of materials is one of the key components in the fabrication of sophisticated semiconductor devices. The continuous scaling down of circuit dimensions requires narrower and deeper contact patterns, which are difficult to create with the conventional wet process. In this regard, dry processes are suitable for high-aspect ratio etching and have many other advantages, such as uniformity and selectivity, over wet cleaning processes. The present study focuses on chemical dry etching using NF3 gas and remotely discharged mixture of NH3 and N2.2–4 Fig. 1 shows a schematic diagram of an equipment used in this process. A mixture of NH3 and N2 gases is introduced into the chamber via an inlet port a er passing through the microwave cavity where radical species are generated by the microwave discharge at 2.45 GHz. Pure NF3 gas supplied via the other inlet port reacts with the radicals in the chamber to generate etchant species. A er etching, the wafer surface is covered by some deposited compounds, which are considered to be (NH4)2SiF6 and possibly contain ammonium uorides.[1,5] These residues are removed by heating the substrates in a post processing procedure
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