Experimental investigation of particulate formation in He-SiH4 modulated RF discharges

Abstract

Formation processes of particulates in radiofrequency power-modulated SiH4 discharges have been studied using two kinds of laser light scattering, a modified Langmuir probe and absorption methods. The results suggest that particulates are formed by three phases of nucleation, rapid growth and growth saturation. In the nucleation phase, the formation may be caused by short-lifetime radicals such as SiH2, SiH or Si. In the rapid growth phase, SiHn+ (n=0-3) ions and/or SiH3 radicals seem to make an important contribution to particulate growth, if only direct influx of the particles onto a particulate is taken into account. In the growth saturation phase, the saturation may be explained by taking into account the decrease in enhancement factor of the ion-collecting areas of particulates and the increase in their loss due to the reduction of ambipolar field in the periphery of the discharge column. Power modulation in SiH4 radiofrequency discharges is found to be practically very effective for decreasing the sizes of particulates.