In situ real time studies of the formation of polycrystalline silicon films on glass grown by a layer-by-layer technique

Abstract

The effect of atomic hydrogen on thin deposited layers of amorphous silicon was studied. Amorphous silicon layers less than 10 nm thick were first deposited from fluorinated precursors. These layers were then exposed to an atomic hydrogen flux. The amorphous layers quickly relaxed to a crystalline structure. Thick films of high crystalline content were prepared through sequential repetition of the deposition and hydrogen exposure process (layer-by-layer technique). The relaxation process was studied by real time in situ ellipsometry and infrared measurements. The relationship between substrate temperature, amorphous layer thickness, hydrogen exposure time, and structure was determined. A new model in which hydrogen acts to ‘‘liquify’’ the subsurface region by breaking Si–Si bonds is suggested. From the ‘‘liquidlike’’ state the subsurface relaxes to its most thermodynamically stable constituents; during relaxation, crystalline silicon is formed with effluence of SiH4, SiFxH4−x, and SiF4 vapors.