Low Temperature Epitaxy of n-Doped Silicon Thin Films Using Plasma Enhanced Chemical Vapor Deposition
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0989-A06-19
Low Temperature Epitaxy of n-Doped Silicon Thin Films Using Plasma Enhanced Chemical Vapor Deposition Mahdi Farrokh Baroughi1,2, Hassan G. El-Gohary1, Cherry Y. Cheng1, and Siva Sivoththaman1 1 Electrical and Computer Engineering, University of Waterloo, 200, Univ. Ave. W., Waterloo, Ontario, N2L3G1, Canada 2 Current affiliation: Electrical Engineering and Computer Science Department, Southa Dakota State University, 201 Harding Hall, Brookings, SD, 57007 ABSTRACT Highly conductive epiraxial silicon thin films, with conductivities more than 680 Ω-1cm-1, were obtained using plasma enhanced chemical vapor deposition (PECVD) technique at 300˚C. The effect of hydrogen in growth of low temperature extrinsic Si thin films was studied using conductivity, Hall, and Raman measurements, and it was shown that epitaxial growth was possible at hydrogen dilution (HD) ratios more than 85%. The epitaxial growth of the extrinsic Si thin films at high hydrogen dilution regime was confirmed by high resolution transmission electron microscopy (HRTEM). INTRODUCTION Highly conductive Si thin films are widely used in semiconductor devices such as emitters in solar cells and bipolar transistors, and as source/drains in MOSFETs. For these applications, the highly doped Si material is obtained either by high temperature diffusion process or by ion implantation followed by a high temperature annealing process [1]. At low temperatures ( 99%) on glass substrates. It has been shown that low temperature PECVD of thin intrinsic Si films on c-Si with similar process conditions of microcrystalline Si films, deposited on glass substrate, results in near epitaxial growth of Si films [6]; this causes some major differences in the structural and the electrical properties of the epitaxial Si and microcrystalline Si thin films. Unlike the development of microcrystalline Si thin films on glass substrates, much less work has been reported on epitaxial Si film growth on Si substrate using PECVD technique at low temperatures [7-9]. Further, the studies of the epitaxial Si films on c-Si substrates using PECVD were mainly limited to the structural study of thin intrinsic (undoped) Si films [7,9]. Near epitaxial films with very high doping concentrations add to the challenge of obtaining high crystallinities in the low temperature Si thin films. Conductivity in an (n+) Si film depends on electron mobility and the free electron density, which depends on active doping density. High crystallinity is the key towards obtaining highly conductive films because an improved crystallinity can improve both the carrier mobility and also the active doping density. We have developed highly conductive near epitaxial (n+) Si thin films using PECVD of hydrogen diluted silane and phosphine. We have studied the electrical and structural properties of the films using conductivity, Hall, Raman and HRTEM analyses and confirmed an epitaxial growth of highly
conductive (n+) Si films. Also we have shown that the epitaxial growth highly improves the electron mobility and th
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