Electron Density and Optical Emission Measurements of SF₆/O₂Plasmas for Silicon Etch Processes

Abstract

This work investigates internal plasma process parameters using a hairpin resonance probe and optical emission spectroscopy. The dependence of electron density and atomic fluorine on the percentage of oxygen in an SF6/O2 discharge was measured using these methods. An RIE Oxford Instruments 80 plus chamber was used for the experiments. Two different process powers (100 W and 300 W) at a constant pressure (100 mTorr) were used, and it was found that the optical emission intensity of the 703.7 nm and 685.6 nm lines of atomic fluorine increased rapidly as oxygen was added to the SF6 discharge, reached their maximum at an O2 fraction of 20% and then decreased with further addition of oxygen. The plasma electron density was also strongly influenced by the addition of O2.

Etching of GeSe2 chalcogenide glass and its pulsed laser deposited thin films in SF6, SF6/Ar and SF6/O2 plasmas

“…Such variation of the F/Ar ratio is a direct consequence of the conversion of the SF 6 into other gases (SO x F y , F 2 , etc.). Similar curves of the F/Ar intensity ratio have been obtained, or can be retrieved in extensive amount of studies related to fluorine-based plasmas [45,74,78]. Simultaneously, for an O 2 percentage lower than 10%, the oxygen atom density is believed to be negligible because of recombination processes leading to SO x F y molecules.…”

Reliable Nanofabrication of Single-Crystal Diamond Photonic Nanostructures for Nanoscale Sensing

“…For our process, this means that, during removal of the 25 nm thick silicon adhesion layer, less than 2 nm of the HSQ mask, which in our case is several hundreds of nanometer thick, will be lost. This result corresponds well to similar plasmas obtained in different systems showing highly selective silicon etching while conserving SiO2 (in our case HSQ) [28]. We furthermore observed no or minor etching of SCD during the SF 6 pulse and no roughening of the exposed SCD surface.…”

Experimental investigation of SF6–O2 plasma for advancement of the anisotropic Si etch process

“…Another reason for the reduction of F could be due to the resonance enhanced quenching of the Argon transition 750 nm which is correlated to the electron density. Morshed et al [53] found that the electron density decreases with increased O2 dissociation rate (above O2=30%) in the plasma. Argon provides stability and enhances anisotropic etching and it decreases with decrease in the electron density in the plasma.…”

“…Morshed et al experimentally investigated that electron density increases with applied power and is correlated to the concentration of fluorine [53], [63]. The increase in power increases the electron density and hence increases the F density due to the electron collision with the SF6 gas.…”

“…In 2008, Lim et al[26] studied the roles of F and O radicals in the formation of via structures and its effect on the vertical etching rates. In 2012, Morshed et al[27] studied the electron density and fluorine density as a function of percentage of oxygen in an SF6-O2 plasma. However, the detailed study on etch process and how it changes with the plasma parameters has not been investigate in this research.…”