Characteristics of VHF-excited SiH4/H2 plasmas using a ladder-shaped electrode

A VHF-excited SiH4/H2 plasma was produced using a ladder-shaped electrode. By measuring the plasma parameters with a heated Langmuir probe, the effect of hydrogen dilution on SiH4/H2 VHF plasma characteristics was investigated. The ion density of the SiH4/H2 plasma was higher than that of the H2 plasma. The electron temperature tended to decrease for high H2 dilution rate and became minimum at H2 flow rate/(SiH4 flow rate+H2 flow rate)=91%, corresponding to the H2 dilution rate near the deposition condition of hydrogenated microcrystalline silicon films. Negative ions exist in the SiH4/H2 plasma. The negative ion density increased with increases in the radio frequency power. At the H2 dilution rate where the negative ions exist, the electron temperature was high approximately 1.5 eV compared with that at other dilution rates.