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 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 400°C 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.