Plasma enhanced selective area microcrystalline silicon deposition on hydrogenated amorphous silicon: Surface modification for controlled nucleation

Selective deposition of $μc-Si$ on hydrogenated amorphous silicon is demonstrated using time-modulated silane reactant flow in a low temperature plasma enhanced process. Alternating cycles of thin silicon layer deposition and atomic hydrogen exposure result in silicon layers on receptive surfaces, with no net deposition on nonreceptive areas of the substrate. Selective deposition could be useful to form self-aligned contacts in hydrogenated amorphous silicon (⁠$a-Si:H$ transistor applications. However, a problem commonly observed in low temperature selective deposition is that the selective process tends to etch amorphous silicon, harming the devices. We describe a technique involving Mo metallization that stabilizes the $a-Si:H$ surface with respect to hydrogen plasma exposure and allows selective $μc-Si$ deposition on $a-Si:H$ in device structures, while avoiding deposition on the top $SiNx$ insulator material. Surfaces and subsequent selective nucleation and growth were characterized using atomic force microscopy, x-ray photoelectron spectroscopy, and Auger electron spectroscopy, which revealed the presence of Mo incorporation in the $a-Si:H$ surface remaining after complete removal of the metal layer. A direct comparison of selective deposition experiments on films prepared with and without Mo treatment demonstrate that the metallization stabilizes nucleation of microcrystalline silicon on amorphous silicon surfaces.