EFFECT OF INTERELECTRODE SPACE ON PROPERTIES OF SIH4/H2 DEPOSITION DISCHARGES OPERATING AT DIFFERENT RADIO FREQUENCIES

The combined effect of excitation frequency and the variation of the interelectrode space on properties of highly diluted silane in hydrogen discharges used for the deposition of mu c-Si:H, is presented. For constant operation voltage, the increase of the electrode gap leads to a continuous increase of the power consumed in the discharge at 30 MHz, while at 50 MHz changes on the interelectrode space has almost no effect on the total power dissipation. At both frequencies the increase of the interelectrode space leads to an optimum in radical production that as frequency increases is displaced to lower electrode gaps. Film growth rate appears an optimal that coincides to the maximum of radical production at both frequencies, revealing that mu c-Si:H deposition rate strongly depends on radicals (SiH2, Si2H4) that undergo rather fast reactions in the gas phase.