Detecting free radicals during the hot wire chemical vapor deposition of amorphous silicon carbide films using single-source precursors

Abstract

A vacuum ultraviolet single photon ionization technique has been used to probe gas-phase species important in the hot wire chemical vapor deposition (HW-CVD) of amorphous silicon carbide(a-SiC:H) films using different single-source precursors. This study focuses on monomethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, and 1,1-dimethyl-1-silacyclobutane, and the reactions of these precursors on tungsten and rhenium filaments between 1000 and 1950°C. Silane is also considered for comparison. Si radicals are found to be major products of hot wire decomposition for all the organosilicon precursors; CH3 is also observed. C and H radicals are expected to be produced as well but are not detected at the ionization energy used in these experiments. Within the series of methylsilanes, the reaction rate on the filament is found to decrease with increasing number of methyl groups on the precursor. We propose a model in which Si–H bonds are cleaved with lower activation barriers than Si–CH3 bonds as the molecule adsorbs onto the hot metal surface. 1,1-dimethyl-1-silacyclobutane produces Si with a lower apparent activation energy than the other molecules. Coverage-dependent reaction pathways are proposed to play a role in the temperature profile of CH3 generation. Infrared spectra of films deposited by HW-CVD show that the film composition and growth rate for the different precursors correlate with the hot wire chemistry studied by single photon ionization.

Mass spectrometric study of gas-phase chemistry in a hot-wire chemical vapor deposition reactor with tetramethylsilane

“…The analysis of gas-phase chemical species generated from the thermal decomposition of TMS in the reactor during the growth process of SiC films by RTCVD [5] indicated that TMS dissociated into hydrogen, silicon atoms, and hydrocarbons such as CH 4 , C 2 H 2 , and C 2 H 4 at the growth temperatures of 1000-1100 • C and a growth pressure of 1 × 10 −4 Torr. In their work on studying the gas-phase species from reactions of methylsilanes, including mono-, di-, tri-and tetra-methylsilane, on tungsten and rhenium filaments in the HWCVD process of silicon carbide films [13], Zaharias et al detected methyl and Si atoms as the products from tetramethylsilane decomposition when the chamber pressure was 5 × 10 −6 Torr. Typical deposition pressures for SiC films using HWCVD or PECVD with either gaseous mixtures of silane and hydrocarbons or single source precursors such as methylsilane range from 0.1 Torr to several Torr [2,3,14,15].…”

Gas-phase diagnoses in catalytic chemical vapor deposition (hot-wire CVD) processes

“…In the decomposition of H 2 O, the production of OH and H is major at low catalyst temperatures, but H and O production becomes more dominant at high temperatures [37]. As for organosilicon compounds, selective and efficient decomposition is possible [51][52][53][54][55][56][57]. The decomposition paths are different from those in thermal decomposition.…”

On the geometric structure, puckering potential and electronic transitions of monosilacyclobutanes and disilacyclobutanes – A theoretical study

“…The reactivity of silacyclobutanes in thermal and photochemical reactions is related to the ring strain in these molecules [10]. The high ring strain energies also lead to reduced decomposition temperatures in the process of chemical vapor deposition, making these molecules excellent choices as single-source precursors for producing silicon carbide thin films [11][12][13][14][15][16]. The strain energy in a four-membered ring structure is closely related to the planarity of the small ring or the extent to which the ring is puckered.…”