Conformal and Stoichiometric Chemical Vapor Deposition of Silicon Carbide onto Ultradeep Heterogeneous Micropores by Controlling the Initial Nucleation Stage.

Abstract

Conformal chemical vapor deposition (CVD) of silicon carbide (SiC) from methyltrichlorosilane (MTS) and hydrogen (H2) onto high-aspect-ratio (HAR; typically >100:1) three-dimensional features has been a challenge in the fabrication of ceramic matrix composites. In this study, the impact of heterogeneous underlayers on the initial nucleation of SiC-CVD was studied using HAR (1000:1) microchannels with a tailored wetting underlayer of Si(100) and dewetting underlayers of thermally formed amorphous silicon dioxide (a-SiO2) and turbostratic boron nitride (t-BN). Incubation periods were distributed in the microchannels on a-SiO2 and t-BN underlayers, with the longest period of 70 min found at the feature-bottom due to a decreased concentration (C) of film-forming species. The longer incubation periods with more dewetting underlayers arose due to demoted initial nucleation. Prolonged incubation at the feature bottom led to poor conformality because thick films had already formed at the inlet when film formation began at the feature bottom. The incubation periods were eliminated by increasing the supply of MTS/H2, in accordance with classical heterogeneous nucleation theory. In the meantime, carbon-rich SiC films formed in the vicinity of dewetting a-SiO2 and t-BN underlayers at the feature bottoms, with greater carbon segregation on more dewetting underlayers. This was probably due to the deposition of pyrocarbons (CH4, C2H2, and/or C2H4) generated from MTS/H2 in the gas phase. Decreasing the temperature (T) from 1000 to 900 °C prevented carbon-rich film formation, and the expected deposition rate of pyrocarbon decreased to 0.6% for the case of CH4. A higher C of MTS/H2 combined with a lower T enabled conformal and stoichiometric film formation on the heterogeneous HAR features.