Application of laser induced electron impact ionization to the deposition chemistry in the hot-wire chemical vapor deposition process with SiH₄-NH₃ gas mixtures

Abstract

The application of a laser-induced electron impact (LIEI) ionization source in studying the gas-phase chemistry of the SiH(4)/NH(3) hot-wire chemical vapor deposition (HWCVD) system has been investigated. The LIEI source is achieved by directing an unfocused laser beam containing both 118 nm (10.5 eV) vacuum ultraviolet (VUV) and 355 nm UV radiations to the repeller plate in a time-of-flight mass spectrometer. Comparison of the LIEI source with the conventional 118 nm VUV single-photon ionization (SPI) method has demonstrated that the intensities of the chemical species with ionization potentials (IP) above 10.5 eV, e.g., H(2), N(2) and He, have been significantly enhanced with the incorporation of the LIEI source. It is found that the SPI source due to the 118 nm VUV light coexists in the LIEI source. This allows simultaneous observations of parent ions with enhanced intensity from VUV SPI and their "fingerprint" fragmentation ions from LIEI. It is, therefore, an effective tool to diagnose the gas-phase chemical species involved with both NH(3) and SiH(4) in the HWCVD reactor. In using the LIEI source to SiH(4), NH(3) and their mixtures, it has been shown that the NH(3) decomposition is suppressed with the addition of SiH(4) molecules. Examination of the NH(3) decomposition percentage and the time to reach the N(2) and H(2) steady-state intensities for various NH(3)/SiH(4) mixtures suggests that the extent of the suppression is enhanced with more SiH(4) content in the mixture. With increasing filament temperatures, the negative effect of SiH(4) becomes less important.

Formation of aminosilanes in the hot-wire chemical vapor deposition process using SiH4-NH3 gas mixtures

“…These results are consistent with the proposed formation mechanism, whereby production of NH 2 radicals from NH 3 decomposition acts as the limiting factor in aminosilane formation. As shown in our previous work regarding the interplay of the NH 3 and SiH 4 components in the gas-phase reaction chemistry in HWCVD, by raising the amount of NH 3 in the mixtures, the decomposition efficiency of NH 3 increases 14 . This, in turn, results in the production of more NH 2 radicals and consequently more tetraaminosilane will form.…”

“…Recent work by Umemoto et al regarding the deposition chemistry of the NH 3 -SiH 4 mixtures in the Cat-CVD processes has shown that the silyl (SiH 3 ) and amidogen (NH 2 ) radicals are the major deposition species for silicon nitride 11 . The suppression effect of SiH 4 presence in the mixtures on the NH 3 dissociation efficiency has also been demonstrated by several groups [12][13][14] . This is consistent with the fact that a high gas flow rate ratio of NH 3 to SiH 4 is typically needed under practical deposition conditions for silicon nitride films.…”

“…Our previous experiments on detecting the reaction products from using NH 3 -SiH 4 mixtures in a HWCVD reactor employed a time-of-flight mass spectrometer with an ionization source of coexisting laser induced electron impact ionization (LIEI) and a 118 nm vacuum ultraviolet (VUV) laser single-photon ionization (SPI), 14,15 , the pure VUV SPI source coupled with TOF MS is employed in this work for the examination of aminosilane and disilane/trisilane formation.…”

“…Our examination of the reaction chemistry of NH 3 in the HWCVD process has found that the major gas-phase products correspond to hydrogen and nitrogen. 14,15 The deposition chemistry of ammonia in the HWCVD process has been well characterized by Umemoto et al 29 They have identified H and NH 2 radicals as the primary decomposition products of NH 3 on the hot W filaments. Signals from H 2 and N 2 were also detected using mass spectrometry.…”

Low-temperature deposition of crystalline silicon nitride nanoparticles by hot-wire chemical vapor deposition

“…Endler et al [16] reported the deposition of a-Si 3 N 4 by PECVD, using SiCl 4 -N 2 -H 2 at a substrate temperature of 900 1C. Recently, silicon nitride thin films deposited by hot-wire chemical vapor deposition (HWCVD) have attracted an interest owing to a low hydrogen content [4,8,17,18]. However, silicon nitride films deposited by HWCVD were amorphous under deposition conditions of wire temperatures of 1500-2000 1C, substrate temperatures of 200-500 1C and reactor pressures of 0.001-0.5 Torr [4,5,8,[19][20][21].…”