Study on initial growth of particles in low-pressure and low-power GeH₄ RF discharges using the high-sensitivity photon-counting laser-light-scattering method

A high-sensitivity photon-counting laser-light-scattering method is applied to obtain information on initial growth of particles formed in low pressure and low power GeH₄ RF discharges. Particles of about 1 nm in size are detected principally around the plasma/sheath boundary near the RF electrode at an early time of 0.2 s after the discharge initiation and the corresponding particle density of 2 × 10¹¹ cm^-3 is about two orders of magnitude higher than ion density. Spatial profiles of particle amount are very similar to those of Ge emission intensity, which indicates a radical production rate. These results suggest that short-lifetime radicals such as GeH₂, having a high production rate, are candidates for key species contributing to the nucleation and initial growth of particles, even for a low pressure (8-13 Pa) and a low power density (0.04 W/cm²). Furthermore, surface reflection probabilities of particles 1-12 nm in size, measured after RF-power-off, are found to be more than 80%.