Ar addition effect on mechanism of fluorocarbon ion formation in CF4/Ar inductively coupled plasma

Abstract

Using a Langmuir probe and an energy-resolved ion mass spectrometer, gas-phase kinetics of fluorocarbon ions has been investigated as a function of the Ar percentage in a mixed CF4/Ar plasma. Spatially resolved electron energy distribution function, plasma potential, and ion density are measured in an inductively coupled plasma. As the Ar percentage increases, the average electron energy decreases while the electron density remains flat. The ion density also stays constant at low Ar percentages but increases over the Ar percentage larger than 63% mainly due to the increase of the Ar+ density. The plasma potential decreases as a result of the increase of Ar partial pressure, and this is confirmed by measuring the ion energy distributions of argon and fluorocarbon ions using the ion mass spectrometry. With the mass spectrometry, it is found that the most prominent ions, CF3+ and CF+, are formed predominantly by a process of dissociative ionization or radical ionization while CF2+ ions are formed dominantly by a process of charge transfer. As a practical application of this study for SiO2 etching, the densities of the fluorocarbon ions and radicals are correlated with the SiO2 etch rate and its selectivity to photoresist. Microtrench profile is also investigated as a function of Ar percentage and it is observed that the microtrench tends to be suppressed with the increase of the Ar percentage. This tendency is correlated with changes in the plasma chemistry as the Ar percentage increases.

Etching mechanisms of (Ba,Sr)TiO3 thin films in CF4/Ar inductively coupled plasma

“…As for the electron density, the behavior of this parameter may be explained by the changes of total ionization rate as well as electron diffusion coefficient due to the corresponding changes of electron temperature. Choi et al [15] reported similar experimental results for CF 4 /Ar plasma in ICP system.…”

Improved etch characteristics of SiO2 by the enhanced inductively coupled plasma

“…It is reported that the addition of Ar, as a dilution gas, to CF 4 improves selectivity, 9 and the variation of total ion density is measured as in Fig. 6͑a͒ by the Langmuir probe ͑Heiden-ESP4.12͒ measurement.…”

Parallel 2D Axisymmetric Fluid Modeling of CF4 Discharge in an Inductively Coupled Plasma Source During SiO2 Etching

“…The etching products from the quartz such as COF x þ , CO þ , and oxygen radical were detected by a mass spectrometer in CF 4 and CF 4 /Ar ICPs. [24,25] Hebner [26,27] observed the spatially non-uniform concentrations of etching products SiF and SiF 2 by means of a laser-induced fluorescence in the inductively driven C 2 F 6 and C 4 F 8 discharges. Cruden et al [28,29] examined the etching products SiF 4 , CO and COF 2 in CF 4 plasma using the Fourier transform infrared spectroscopy (FTIR).…”

“…Coburn et al found that the escaping oxygen hinders polymerization on the SiO 2 surface through forming volatile CO, CO 2 , and COF 2 , which allows etching process to continue without feeding oxygen. The etching products from the quartz such as COF x + , CO + , and oxygen radical were detected by a mass spectrometer in CF 4 and CF 4 /Ar ICPs . Hebner observed the spatially non‐uniform concentrations of etching products SiF and SiF 2 by means of a laser‐induced fluorescence in the inductively driven C 2 F 6 and C 4 F 8 discharges.…”