Silicon Homoepitaxy at Low Temperature Using Microwave Multipolar Plasma for Cleaning and Deposition
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SILICON HOMOEPITAXY AT LOW TEMPERATURE USING MICROWAVE MULTIPOLAR PLASMA FOR CLEANING AND DEPOSITION
R. BURKE, M. GUILLERMET, L. VALLIER and E. VOISIN PMI, UJFG & URA D0844 of CNRS ; CNS-CNET, BP 98, 38243 Meylan Cedex, FRANCE
ABSTRACT The Microwave Multipolar Plasma (MMP) offers unique features for plasma assisted deposition by combining multipolar magnetic confinement and microwave excitation. Independent control of the plasma-surface interaction parameters (neutral 0 flux, ion flux and ion impact energy) has led to low temperature (400-800 C) silicon epitaxial growth in pure or H2 diluted silane MMPs. Prior to the epitaxial growth of Si, a plasma cleaning is applied to remove 0 and C atoms contaminant from the substrate surface. Ar and H2 were tested on 2 and 4 inch, (100) oriented, silicon wafers loaded "as received" and heated at the deposition temperature. The cleaning is effective in both cases giving a pure Si Auger spectrum. However, a LEED signature is only observed when operating at very low bias of the sample (low energy ions) and the lower the substrate temperature, the lower the energy allowed to obtain a LEED pattern. The cleaning process is also checked and inspected by post-deposition analyses, including TEM, RBS, SIMS and Secco etch. Various layer thicknesses were grown according to the characterization method. Specular epitaxial films are obtained for a large range of plasma and substrate parameters. The temperature may be as low as 4001C but the best results are obtained in the 600-700'C range. Interestingly, epitaxy is lost when the ion energy is increased. These results show a compromise between ion energy and substrate temperature. One needs to work at low ion energy to enhance the surface reaction while avoiding surface damage, but the temperature has to be sufficiently high to restructure the surface. Preliminary results on intentional doping reveal further potentialities of this low energy controlled interaction for low temperature plasma processing.
INTRODUCTION Plasma assisted epitaxy is now widely developing for low temperature (< 800'C) silicon epitaxial growth in order to minimize diffusion and auto-doping effects tl,2]. We present results on a new technique using (silane) Microwave Multipolar Plasma which combines both the surface cleaning prior to deposition and a high epi-growth rate. Due to the independant control of plasma production and the electrical bias of the substrate, the user is in control of the energy of the ion impinging the surface from a few 10's eV down to 0 eV ; we will show the unique nature of this low energy controlled interaction to achieve an efficient surface cleaning step or an abrupt doping profile. Therefore Microwave Multipolar Plasma appears to be an efficient and versatile tool in advanced material research. EXPERIMENT The results presented in this paper are based on an experiment dedicated to silicon homoepitaxy using silane microwave plasma. Special care was given to the design of the apparatus which consists of the parts : a load-lock, the deposit
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