Fluorocarbon-based plasma etching of SiO2: Comparison of C4F6/Ar and C4F8/Ar discharges

Abstract

A gas phase and surface chemistry study of inductively coupled plasmas fed with C4F6/Ar and C4F8/Ar intended for SiO2 etching processes was performed. Adding Ar to those fluorocarbon gases results in a strong increase of the ion current, by up to a factor of 5 at 90% Ar relative to the pure fluorocarbon gases. The fluorocarbon deposition rate is higher for C4F6/Ar than for C4F8/Ar, whereas the fluorocarbon etching rate is lower, and both quantities decrease as the amount of Ar is increased. For both C4F6/Ar and C4F8/Ar, the CF2 density is more than an order of magnitude greater than the CF density. The CF2 partial pressure decreases as more Ar is added to the C4F6/Ar plasmas. A comparison of these data with corresponding results obtained with C4F8/Ar shows that the CF2 partial pressure in C4F6 is higher for Ar-lean gas mixture than for C4F8/Ar. This remains true up to 40% Ar. Above 40% Ar the CF2 partial pressure in C4F8 is higher than for C4F6. The CF and COF2 partial pressures in C4F8 are higher than for C4F6. The SiO2 etch rate is higher for C4F8/Ar than for C4F6/Ar. This may be attributed in part to the higher F/C ratio of the steady-state fluorocarbon film formed on SiO2 surfaces for C4F8/Ar which was determined by x-ray photoemission spectroscopy (XPS). The etching selectivity of SiO2 over resist and silicon is increased by the addition of Ar to the fluorocarbon gases. Overall, the SiO2/resist and SiO2/Si etching selectivity are higher for C4F6/Ar (i.e., 4 and 9, respectively) at 90% Ar than for C4F8/Ar (i.e., 2 and 5, respectively) at 90% Ar and otherwise identical conditions. Both ellipsometry and XPS measurements show that the steady-state fluorocarbon layer thickness is greater for C4F6/Ar (∼4 nm) than for C4F8/Ar (∼2.8 nm). Argon addition leads to a strong decrease of the fluorine content of the steady-state fluorocarbon layers on both Si and SiO2 surfaces relative to films produced in pure fluorocarbon discharges, and this effect is related to the increase of the SiO2/Si and SiO2/resist etching selectivity.

Nanoelectrode Scanning Probes from Fluorocarbon-Coated Single-Walled Carbon Nanotubes

“…The C (1s) peak profile for a specific set of plasma operating conditions was very reproducible regardless of the base substrate used (Au, Si, or HOPG) or the sample position in the plasma reactor during layer deposition. Similar results have been also reported in the literature for plasma deposition on Si substrates from a C 4 F 8 gas source but at different conditions [5][6][7] .…”

Comparison of etching characteristics of SiO2 with ArF photoresist in C4F6 and C4F8 based dual-frequency superimposed capacitively coupled plasmas

“…In the f HF (13.56)/f LF (2) case, the F/C ratio was higher in the C 4 F 8 based plasmas. The higher F/C ratio of the fluorocarbon layers in C 4 F 8 plasmas compared to C 4 F 6 /Ar plasmas was also reported in 13.56 MHz inductively coupled plasmas [39]. However, the F/C ratio was higher in the C 4 F 6 based plasmas when f HF was increased to 27 and 60 MHz.…”

“…The faster oxide etch rate in the C 4 F 8 based plasmas than in the C 4 F 6 based plasmas observed in Figs. 1-3 is attributed to the smaller fluorocarbon film thickness [36,40,39].…”

“…6b. It is reasonable to assume that the steady-state polymer thickness is a critical parameter in determining the oxide etch rate in the ion-assisted etching mechanism, because the thinner polymer layers facilitate the chemical reaction of the F and C atoms with the Si and O atoms on the oxide surface [36,39,40]. The thicker steady-state polymer thickness in the C 4 F 6 based plasmas compared to that in the C 4 F 8 plasmas is probably due to the higher amount of CF x radicals that are generated, and which act as polymerization precursors.…”

Effect of halogen in high‐density oxygen plasmas on photoresist trimming

“…Sometimes the second constituent is also added to the plasma to slow down the spontaneous reaction between the oxygen and the photoresist. Commonly, fluorocarbons are added to form passivation layers on the feature to maintain the vertical profiles (Doemling et al, 1998;Hsu et al, 2000;Li et al, 2002;Sin et al, 2002).…”