Anisotropic etching of SiO2 in low-frequency CF4/O2 and NF3/Ar plasmas

Abstract

Anisotropic etching of SiO2 films is reported in low frequency (∼100 kHz), moderate-pressure (0.35 Torr) CF4/O2 and NF3/Ar plasmas. Rates up to 2000 Å/min were achieved with high selectivity over GaAs and InP substrates. The etching mechanism was studied with optical spectroscopy and downstream chemical titrations. Anisotropy is attributed to ion-enhanced reactivity of fluorine atoms with SiO2 at rates up to two hundred times larger than purely chemical etching by fluorine atoms. Damage and product sputter desorption models of this process were evaluated. These two models are nearly mathematically equivalent at steady state, and show that the effectiveness of ions in etching by enhanced reaction is roughly 15 times that in physical sputtering under these conditions.

Rf discharge dissociative mode in NF3and SiH4

“…The NF 3 and its radicals possess the following bond dissociation energies: NF 2 [53]), N-F, 2.6 eV [54]. However, the probability of direct splitting the NF 3 molecules with the energy, say, 4 eV, is very small because of the shorttime electron-molecule interaction during which heavy atoms (radicals) have no time to get the momentum required for flying off.…”

“…Rf discharge in NF 3 is widely used for cleaning technological chambers [1][2][3][4][5][6], etching silicon-containing materials [7][8][9][10][11][12][13][14][15][16] and plasma treatment of polymeric dielectrics [17]. This gas is of interest due to the following reasons.…”

Slope and amplitude asymmetry effects on low frequency capacitively coupled carbon tetrafluoride plasmas

“…The simulations consider four types of charged species: CF 3 þ , CF 3 À ,F À ions, and electrons. Although more species may be present, it has been shown in previous studies that these are the dominant ones.…”

“…Furthermore, there is an interest in studying the behavior of CF 4 discharges when excited with low fundamental frequencies, as used in etching applications. 3 In the present paper, the results of particle-in-cell (PIC) simulations are compared to experimental results, including phase-resolved optical emission spectroscopy (PROES) measurements. The impacts of both the amplitude and the slope of the waveform are investigated, using up to five harmonics with a fundamental frequency of 5.5 MHz.…”

“…1 In the case of plasma etching, electronegative gases such as carbon tetrafluoride (CF 4 ) are generally used, 2 often driven by a low frequency 3 of a few megahertz. These processes usually require control of the ion flux as well as the ion energy, a feature unachievable in classical single frequency CCRF discharges.…”