No abstract

Perfluorocarbon gas is widely used in the semiconductor industry. However, perfluorocarbon has a negative effect on the global environment owing to its high global warming potential (GWP) value. An alternative solution is essential. Therefore, we evaluated the possibility of replacing conventional perfluorocarbon etching gases such as CHF 3 with C 6 F 12 O, which has a low GWP and is in a liquid state at room temperature. In this study, silicon oxynitride (SiON) films were plasma-etched using inductively coupled CF 4 +C 6 F 12 O+O 2 mixed plasmas. Subsequently, the etching characteristics of the film, such as etching rate, etching profile, selectivity over Si, and photoresist, were investigated. A double Langmuir probe was used and optical emission spectroscopy was performed for plasma diagnostics. In addition, a contact angle goniometer and x-ray photoelectron spectroscope were used to confirm the change in the surface properties of the etched SiON film surface. Consequently, the etching characteristics of the C 6 F 12 O mixed plasma exhibited a lower etching rate, higher SiON/Si selectivity, lower plasma damage, and more vertical etched profiles than the conventional CHF 3 mixed plasma. In addition, the C 6 F 12 O gas can be recovered in the liquid state, thereby decreasing global warming. These results confirmed that the C 6 F 12 O precursor can sufficiently replace the conventional etching gas.

The influences of both HBr/O2 (at constant Cl2 fraction) and Cl2/O2 (at constant HBr fraction) ratios in HBr + Cl 2 + O2 gas mixture on bulk plasma characteristics, active species densities and etching kinetics of silicon were studied. The results indicated that an increase in O2 content in a feed gas at constant Cl2 fraction in a processing gas (1) produces the stronger impact on plasma chemistry by the influence on the kinetics of electron-impact and atom-molecular reaction; and (2) provides the wider adjustments for both halogen atom flux and ion flux with the opposite tendencies with those for variable Cl2/O2 mixing ratio. The experiments demonstrated that the transition toward more oxygenated plasmas in both cases lowers the Si etching rate as well as result is decreasing effective reaction probability and etching yield. These effects may be associated with decreasing amount of adsorption sites for Cl/Br atoms as well as increasing sputtering (ion-stimulated desorption) threshold for reaction products due to the formation of the low-volatile silicon oxy-chlorides and-bromides in heterogeneous SiClx + O/OH and SiBrx + O/OH reactions.

Silicon oxycarbide (SiOC) film was etched using a CF4/C6F12O/O2 mixed gas plasma through an inductively coupled plasma etcher. Changes in the dielectric constant and surface chemical bonding properties were investigated using ellipsometry and Fourier transform infrared spectroscopy. Plasma diagnosis was carried out using a double Langmuir probe, ultraviolet detector, and residual gas analyzer. The physical and chemical plasma properties of CHF3 and C6F12O exhibited similar trends. However, the C6F12O mixed plasma exhibited a smaller change in dielectric constant compared to that of a conventional CHF3 mixed plasma, because of the lower ion density, ion energy flux, and UV intensity and thinner fluorocarbon-based polymer formation. Therefore, the liquefied C6F12O gas can substitute for the existing etching process gas and reduce the change in dielectric constant.

In this work, we carried out the study of CF4 + O2 + X (X = C4F8 or CF2Br2) gas chemistries in respect to the SiOxNy reactive-ion etching process in a low power regime. The interest in the liquid CF2Br2 as an additive component is motivated by its generally unknown plasma etching performance. The combination of various diagnostic tools (double Langmuir probe, quadrupole mass-spectrometry, X-ray photoelectron spectroscopy) allowed us to compare the effects of CF4/X mixing ratio, input power and gas pressure on gas-phase plasma characteristics as well as to analyze the SiOxNy etching kinetics in terms of process-condition-dependent effective reaction probability. It was found that the given gas systems are characterized by: (1) similar changes in plasma parameters (electron temperature, ion current density) and fluxes of active species with variations in processing conditions; (2) identical behaviors of SiOxNy etching rates, as determined by the neutral-flux-limited process regime; and (3) non-constant SiOxNy + F reaction probabilities due to changes in the polymer deposition/removal balance. The features of CF4 + CF2Br2 + O2 plasma are lower polymerization ability (due to the lower flux of CFx radicals) and a bit more vertical etching profile (due to the lower neutral/charged ratio).