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

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.