Experimental investigation of powder formation in SiF4-H2 and SiH4-H2 r.f. discharges

Powder formation in SiF4-H2 and SiH4-H2 glow discharges, by using laser light scattering and absorption diagnostic techniques, has been investigated. The pressure dependence of absorbed and scattered light indicates that the predominant mechanism involved in the solid particle formation is gas-phase nucleation. The number density of particles, as evaluated by the Mie scattering formalism, shows a particle concentration of 1010 cm-3 in the electronegative SiF4 system and of 109 cm-3 in the SiH4 system. For the same pressure increase the particle density doubles in SiF4-H2 and increases one order of magnitude in SiH4-H2 plasmas. Also, in SiF4-H2, differently from SiH4 plasmas, dishomogeneities in the powder development have been observed.