Porous Membranes as Sacrificial Layers Enabling Conformal Chemical Vapor Deposition Involving Multiple Film-Forming Species

Abstract

We propose a new, concise method for conformal chemical vapor deposition (CVD) using sacrificial layers (SLs) to fill three-dimensional features with microscopic pores. SLs are porous membranes (e.g., ceramic felts) that filter film-forming species having high sticking-probability (η). CVD processes with multiple film-forming species generally suffer from poor conformality due to preferential film deposition at the inlets of features by the high-η species, such as reactive intermediates. An SL traps such high-η species before they reach the target features and selectively supplies film-forming species with lower η (e.g., source precursors or stable intermediates) that enables conformal film deposition. Here the trapping efficiency of an SL was predicted and a procedure for designing an optimal SL was established. The procedure was demonstrated by CVD of silicon carbide (SiC) with multiple film-forming species of high-η species (η = 8.0 × 10–3) and lower-η species (η = 5.9 × 10–5 and 2.2 × 10–7). The trapping of 99.2% of incident high-η species was achieved with an optimized SL, wherein the deposition rate (m/s) contribution by high-η species declined from 0.546 at the SL inlet to 0.014 at its outlet. Finally, using these optimized SLs, SiC-CVD filling of micron-scale trenches was demonstrated with an aspect-ratio of 16:1.

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

“…Here, as shown in previous work, three film-forming species were present during SiC-CVD. 29,30 In this case, three different η (η low , η mid , and η high ) and three relative contribution ratios, Z, to the total deposition rate at the microchannel inlet (Z low , Z mid , and Z high ; Z low + Z mid + Z high = 1) for low-, middle-, and high-η species, respectively, were the fitting parameters. After η and Z had been determined, three different C (C low , C mid , and C high ) for low-, middle-, and high-η species, respectively, at the microchannel inlet were extracted from the total deposition rate.…”

“…The CVD parameters under the present conditions (T = 900 and 1000 °C) were examined. Figure 2 29,30 Note that, when applying the CVD kinetic data obtained using the Si microchannels to the real fibrous bundles, the difference of geometry should be taken into account. The pores of Si microchannels are perfectly uniform parallel-plate space, while those of fibrous bundles are random pores.…”

“…22,29,30 Furthermore, we have demonstrated conformal SiC-CVD via selective trapping of high-η species by using a sacrificial layer. 30 Although the above experiments were conducted solely on heterogeneous Si surfaces due to the limited availability of test structures, the Si underlayers promoted the initial nucleation of SiC-CVD; thus kinetic studies on SiC-CVD during the continuous filmformation stages were successful. However, the actual SiC-CVD process for fabricating SiC f /SiC-CMCs is conducted on h-BN underlayers 3,4 that may demote the initial nucleation of SiC-CVD because β-SiC (cubic lattice−sp 3 covalent bonds) has a different crystal structure with h-BN (two-dimensional hexagonal lattice−in-plane sp 2 covalent bonds and out-of-plane π bonds).…”

“…19−22 Combined with the time evolution of the gasphase composition starting from an MTS/H 2 mixture, and calculated using elementary reaction simulations, 23−28 precise characterization of the surface reaction of SiC-CVD has been attempted. [20][21][22]29,30 It has been shown that SiC-CVD involves three film-forming species: a high-η species (η ≈ 10 −2 ; probably CH 2 SiCl 3 ), a middle-η species (η ≈10 −4 ), and a lowη species (η ≈ 10 −6 ; MTS). 22,29,30 Furthermore, we have demonstrated conformal SiC-CVD via selective trapping of high-η species by using a sacrificial layer.…”

“…[20][21][22]29,30 It has been shown that SiC-CVD involves three film-forming species: a high-η species (η ≈ 10 −2 ; probably CH 2 SiCl 3 ), a middle-η species (η ≈10 −4 ), and a lowη species (η ≈ 10 −6 ; MTS). 22,29,30 Furthermore, we have demonstrated conformal SiC-CVD via selective trapping of high-η species by using a sacrificial layer. 30 Although the above experiments were conducted solely on heterogeneous Si surfaces due to the limited availability of test structures, the Si underlayers promoted the initial nucleation of SiC-CVD; thus kinetic studies on SiC-CVD during the continuous filmformation stages were successful.…”