Growth and properties of Si films on sapphire with predeposited amorphous Si layers

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Abstract
Si (001) films of high quality were grown successfully on sapphire substrates with thin predeposited amorphous Si layers, less than 40 Å thick. In order to investigate the growth features and properties of the films, the dependence of the film quality on the growth temperature, growth rate, and predeposited layer thickness were studied by various physical analyses including reflection high-energy electron diffraction (RHEED), replica electron microscopy, secondary ion mass spectroscopy (SIMS), Auger electron spectroscopy (AES) and electron spectroscopy for chemical analysis (ESCA), and electrical measurements of effective mobilities of metal-oxide-semiconductor field effect transistors (MOSFETs). The most remarkable feature of this method is that films with a smooth surface and a high crystalline quality grow even at a slow growth rate, less than 0.1 μm/min and a high growth temperature of about 1000 °C, which are concerned with surface reactions in the initial stage of chemical vapor deposition (CVD). The interface region between the film and the substrate has an abrupt concentration gradient of constituent atoms. The effective mobilities of MOSFETs fabricated on the films do not depend on the growth rate, unlike the case of the usual method, and were 1.5–1.25 times as large as those without predeposited layers. Experimental results indicate that the optimum thickness of the predeposited layer is about 20 Å and that the heat treatment of the layer (∼3 min, 1000 °C) before CVD is important. A model to understand this growth method is proposed.