OPTICAL CHARACTERIZATION OF THE CATHODE PLASMA SHEATH DURING THE BIASING STEP FOR DIAMOND NUCLEATION ON SILICON

In-situ nucleation by negatively biasing the substrate in the microwav e plasma is of crucial importance for diamond deposition on silicon, e specially for the production of oriented diamond nuclei. We have chara cterized the cathode plasma sheath above the substrate by measuring th e optical emission of the hydrogen Balmer lines during the biasing ste p. From the Stark splitting of the lines we deduce a field strength of about 1.5 kV cm(-1) directly at the silicon surface, increasing to ab out 3.5 kV cm(-1) when the surface is covered with a diamond him. At t he same time the voltage drop moves closer to the cathode and the curr ent increases by an order of magnitude. The superimposed broadening du e to the Doppler effect is decomposed into several components. The bro adest component results from hydrogen atoms with several tens of elect ronvolts of kinetic energy.