Dry Etching Performance and Gas-Phase Parameters of C6F12O + Ar Plasma in Comparison with CF4 + Ar

Abstract

This research work deals with the comparative study of C6F12O + Ar and CF4 + Ar gas chemistries in respect to Si and SiO2 reactive-ion etching processes in a low power regime. Despite uncertain applicability of C6F12O as the fluorine-containing etchant gas, it is interesting because of the liquid (at room temperature) nature and weaker environmental impact (lower global warming potential). The combination of several experimental techniques (double Langmuir probe, optical emission spectroscopy, X-ray photoelectron spectroscopy) allowed one (a) to compare performances of given gas systems in respect to the reactive-ion etching of Si and SiO2; and (b) to associate the features of corresponding etching kinetics with those for gas-phase plasma parameters. It was found that both gas systems exhibit (a) similar changes in ion energy flux and F atom flux with variations on input RF power and gas pressure; (b) quite close polymerization abilities; and (c) identical behaviors of Si and SiO2 etching rates, as determined by the neutral-flux-limited regime of ion-assisted chemical reaction. Principal features of C6F12O + Ar plasma are only lower absolute etching rates (mainly due to the lower density and flux of F atoms) as well as some limitations in SiO2/Si etching selectivity.

Comparative study of CF4 + O2 and C6F12O + O2 plasmas for reactive‐ion etching applications

“…These dependencies are in agreement with the corresponding data for other fluorocarbon gas plasmas [5,6] (in fact, with general regularities of plasma chemistry) as well as quite similar to those obtained for CF 4 + Ar and C 6 F 12 O + Ar gas systems under the identical set of processing conditions. [24,32] In our case, the common features of CF 4 + O 2 and C 6 F 12 O + O 2 plasmas may briefly be explained as follows:…”

“…Plasma diagnostics and etching experiments were conducted in the inductively coupled plasma (ICP) reactor used in our previous work. [15,23,24] Plasma was excited using a 13.56 MHz power supply, while another 13.56 MHz RF generator powered the bottom electrode to control the negative dc bias voltage, U − dc . The latter was measured using a high-voltage probe (AMN-CTR; Youngsin Eng).…”

“…The chemical compositions of plasma-treated surfaces were examined using X-ray photoelectron spectroscopy (XPS; K-Alpha; Thermo VG) with a monochromatic Al K α source (1486.6 eV). Details on both the equipment and operating regimes can be found in the study Lim et al [24] 2.2 | Zero-dimensional model for CF 4…”

“…As such, one can just roughly suggest that the C 6 F 12 O-based plasma provides lower densities of F atoms and polymerizing radicals compared with those in the CHF 3 . Another study [24] dealt with a comparison of plasma parameters and RIE characteristics for Si and SiO 2 in CF 4 + Ar and C 6 F 12 O + Ar gas systems. The principal finding was that these two gas systems are quite similar in (a) the behaviors of F atom flux and ion bombardment intensity versus input power and gas pressure; (b) polymerization abilities; and (c) changes in Si and SiO 2 etching rates, which points to a neutral-flux-limited etching regime.…”

“…Accordingly, the main goals were (a) to analyze differences in electron-and ion-related plasma parameters in the presence of oxygen; (b) to compare steady-state densities of F and O atoms (as the main etchants for target materials and fluorocarbon polymer film, respectively) as well as to study their interconnections with processing parameters; (c) to demonstrate the similarities and differences in the etching kinetics and mechanisms for Si and SiO 2 ; and (d) to estimate the general perspective of low-GWP C 6 F 12 O to substitute for high-GWP CF 4 in the dry etching technology. Similarly to our previous work, [24] we selected the specific processing regime with about 10 times lower input power density (and thus, plasma density) compared with the "standard" RIE process. As was reported by Ashraf et al [25] and Veselov et al, [26] such conditions allow one to combine weaker surface damage (due to lower ion flux) and more anisotropic etching (due to reduced neutral/charged ratio).…”