Evidence of direct SiO2 etching by fluorocarbon molecules under ion bombardment

Abstract

In a beam apparatus, influence of fluorocarbon gas (C5F8, C4F8, and CF4 molecules) flux onto SiO2 etching reaction is investigated in comparison to a case of CF2 radical flux. Fluorocarbon molecules or CF2 radicals are incident onto SiO2 surface with Ar+ beam of energy 100–900eV. Atomic composition of SiO2 surface under the ion and molecule incidence is measured by in situ x-ray photoelectron spectroscopy. Fluorocarbon∕Ar+ co-incidence enhances the SiO2 etching compared with pure Ar+ incidence, suggesting the etching effect of fluorocarbon molecules under Ar+ bombardment. In the case of C5F8∕Ar+ co-incidence, formation of fluorocarbon layer is observed as the case of CF2∕Ar+ co-incidence. Etching yields of SiO2 by C5F8∕Ar+ and CF2∕Ar+ co-incidences are measured for different Ar+ incident energies and fluorocarbon∕Ar+ flux ratios. The etching yield increases monotonically with the Ar+ incident energy, and reaches the value of 2.4 at 900eV in case of C5F8, which is about 1.5 times as high as in the CF2 case. In the case of C5F8 and CF2, a phenomenon like etch stop, with formation of a thick fluorocarbon layer, is observed for larger fluorocarbon flux, with the threshold of the fluorocarbon∕Ar+ flux, ratio between 2.5 and 25. These results suggest a significant contribution of direct SiO2 etching by fluorocarbon molecules in practical etching reactors, especially in case of the C5F8 molecule.

Role of CF2in the etching of SiO2, Si3N4and Si in fluorocarbon plasma

“…In this case, CF 2 is considered as reactant, which is also proposed by Barela et al [12] . This result is consistent with the observation made by Takada et al [13] , who found that a significant contribution of direct SiO 2 etching by fluorocarbon molecules under ion bombardment.…”

Dependence of photoresist surface modifications during plasma-based pattern transfer on choice of feedgas composition: Comparison of C4F8- and CF4-based discharges

“…[22][23][24] A C 4 F 8 / 90% Ar plasma etching process achieves a low photoresist etch rate because of FC film deposition and low gas phase fluorine radical density. 9,10,[25][26][27] In comparison, a CF 4 plasma etching process is characterized by little FC film deposition and a high gas phase fluorine radical density and results in high PR etching rates.…”

Chemical Reaction Dynamics of SiO2 Etching by CF2 Radicals: Tight-Binding Quantum Chemical Molecular Dynamics Simulations

“…In particular, the CF 2 þ ion is one of the main species generated from CF 4 ; therefore, CF 2 þ ion beam etching has been actively investigated. [12][13][14] In etching processes, the etchant ions are accelerated by a bias voltage in a radio frequency (RF) system; 8,[14][15][16][17] therefore, bias voltage affects the velocity of etchant ions, and thus significantly influences etching efficiency. 17) At low voltages, SiO 2 etching is slow and CF x polymerization occurs on the surface.…”