Growth and characterization of polysilicon films deposited by reactive plasma beam epitaxy

Abstract

<p>Polycrystalline silicon was deposited at low temperatures (400-550°C) by using a new technique, reactive plasma beam epitaxy. The technique consists of using an intense flux of hydrogen radicals, generated by an electron cyclotron resonance (ECR) source to promote nucleation and crystallinity at low temperatures. The film structure could be smoothly changed from polysilicon to amorphous by changing the flux of incoming H radicals on the surface of the sample. The flux of hydrogen radicals can be controlled by changing the deposition pressure, with lower pressures leading to a higher H radical flux and greater degree of crystallinity. The effect of H radicals on the growth of polysilicon films was studied by using two different plasma characterizations techniques, namely Langmuir probe and optical emission spectroscopy. Both n and p type films were deposited by using a phosphine and diborane mixture in hydrogen. The growth rate is found to be independent of the doping or of the deposition temperature. The crystalline nature of the films was verified by using Raman spectroscopy. The crystallographic orientations of the films were examined by x-ray diffraction. The grain size of the polysilicon films was estimated by using the full width at half maximum of x-ray diffraction spectra, and were of the order of 200A. There was no significant change in either the grain size or the orientation of the films as the deposition temperature was increased from 400 to 550°C. Surface morphology of the films was studied by using scanning electron microscope and ultraviolet reflectance measurements. The electronic properties of the polysilicon films were examined by conductivity, activation energy and Hall mobility measurements. The results of these characterization techniques indicate that the as deposited films are slightly n type, and they have high mobilities (40 cm[superscript]2/v.s).</p>