LOW-TEMPERATURE INSITU CLEANING OF SILICON-WAFERS WITH AN ULTRA HIGH-VACUUM COMPATIBLE PLASMA SOURCE

A single-step cleaning procedure with the newly developed ultra-high vacuum (UHV) compatible plasma source (Balzers) is described. Utilizing this source, an argon/hydrogen discharge between the heated filament (cathode) and the chamber walls (anode) of the grounded UHV system is established. The discharge is characterized by high currents (up to 100 A) and low voltages (20-35 V). Without additional wet chemical cleaning steps, the silicon wafer as obtained from the manufacturer is placed in the grounded substrate holder and immersed in the plasma. The cleaning procedure results in the removal of the wafer-surface contaminants (native oxide and hydrocarbons) at substrate temperatures well below 500-degrees-C. To investigate the usefulness of the cleaning procedure for low temperature epitaxial growth, silicon was deposited under UHV conditions. Homoepitaxial growth on (100) and (111) silicon was obtained at substrate temperatures of 500-degrees-C and above. For lower temperatures, a short substrate annealing step at 500-degrees-C allowed homoepitaxial layers to be obtained at temperatures as low as 300-degrees-C on (100) silicon and 400-degrees-C on (111) silicon. To characterize the cleaning procedure, the etch rates for thermally grown silicon dioxide, diamond-like carbon and preliminary results for boron and amorphous silicon were investigated using Rutherford backscattering and X-ray rocking curves.