Mechanisms of Surface Reaction in Fluorocarbon Dry Etching of Silicon Dioxide-An Effect of Thermal Excitation

Abstract

Ion bombardment-induced thermal reaction between a fluorocarbon adlayer and a SiO2 surface in a reactive-ion-etching (RIE) environment which was simulated in an ultrahigh-vacuum thermal desorption mass spectroscopy (TDS) apparatus has been studied. The RIE-induced fluorocarbon chemisorbed layer, covering the SiO2 surface, was observed to be thermally stimulated to react chemically with the SiO2 in the TDS apparatus with an activation energy of approximately 1.9 eV. A terminal group, chemisorbed at the adlayer/SiO2 interface, could be an active participant in the thermal reaction. This observation indicates the possibility that chemical sputtering could occur in the actual RIE through a thermal excitation step, induced by ion bombardment. A significant difference in the RIE-induced mixing of fluorine atoms between SiO2 and Si also appeared in their TDS spectra.

Surface Reactivity of CF2 Radicals Measured Using Laser-Induced Fluorescence and C2F6 Plasma Molecular Beams

“…This suggested that physical sputtering was not responsible for the production of CF 2 in this system. Additional experiments demonstrated that chemical sputtering was indeed producing CF 2 at the surface, agreeing with radical/ion beam experiments that indicate the number of radicals chemically sputtered by ions in the presence of fluorine radicals can be much greater than unity. ,, Thus, chemical sputtering is a likely source of CF 2 generation in our system.…”

“…This is important because it provides insight into the interactions of gas-phase radicals with a surface under different plasma surface modification processes. Although fluorocarbon film deposits from FCPs continually, under etching conditions the polymer film is ablated during plasma processing of a substrate . In our IRIS experiments, we do not observe net film deposition from the 100% C 2 F 6 plasma molecular beam .…”

“…Another probable source of CF 2 is either physical or chemical sputtering of the fluorocarbon adlayer that is deposited on the surface during plasma processing . Haverlag et al found that the net CF 2 flux from the rf electrode in a CHF 3 plasma was nearly 2 orders of magnitude higher than the positive ion flux to the electrode .…”

Comparison of Pulsed and Continuous-Wave Deposition of Thin Films from Saturated Fluorocarbon/H2 Inductively Coupled rf Plasmas

“…Deposition of etch products has been seen previously in saturated fluorocarbon plasmas containing little or no H 2 . Furthermore, etching studies have shown a fluorocarbon adlayer is formed during fluorocarbon etching of SiO 2 …”

Experimental verification of SO2and S desorption contributing to defect formation in MoS2by thermal desorption spectroscopy

“…Here, thermal desorption mass spectrometry (TDS) is used to study the surface reaction and desorption kinetics in Si 28,29 Ge, 30 and HOPG 31 by detecting a small amount of desorption species using a quadrupole mass spectrometer (QMS). By using this TDS system, it may be possible to detect SO 2 and/or S desorption from MoS 2 flakes transferred onto SiO 2 /Si substrates in ambient air.…”