The use of a direct current saddle-field plasma for the deposition of hydrogenated amorphous silicon

Abstract

The electrical characteristics of a saddle-field glow discharge were studied. The saddle-field electrode configuration consisted of a semitransparent anode sandwiched between two outer cathodes of similar diameter. The gases used were a mixture of silane and hydrogen, and pure nitrogen. The anode and cathode currents were correlated with anode voltage, pressure, and electrode separation. The use of a grounded enclosure as opposed to a floating enclosure, to confine the discharge, was shown to enhance the discharge currents for similar pressures and voltages. Data obtained from the variation of the discharge current with anode transparency, where the anode transparency is defined as the ratio of the sum of the area of the apertures in the anode to the area of a solid anode with the same diameter, shows that below 100 mTorr a dc saddle-field discharge gives rise to larger currents than those obtained using a conventional dc diode discharge. Hydrogenated amorphous silicon films were prepared and studied. Films exhibited a smooth surface morphology and good adhesion to the substrate. Growth rates as high as 10 Å/s were obtained for relatively low pressures (50–100 mTorr), flow rates (5–9 SCCM) and anode voltages (600–900 V). Preliminary studies indicated that the deposited films possessed good optoelectronic properties.