Development of in-situ method for measurements of size and density of small particles in SiH₄ rf discharges

A threshold photoemission (TPE) method together with microwave interferometry has been developed to measure in-situ size and density of small particles below a few nm over a wide size range. The mass and density of the particles are deduced from their density decay due to diffusion and electron density decay due to attachment to the particles after rf-off, respectively. The TPE method is found to be useful to get information about the initial growth processes of particles. For He+ SiH₄ (3%), 80 Pa, 6.5 MHz and 60 W(1 W/cm²), the size of particles Si_nH_x reaches about 2 nm(n ≈ 1000) and their density increases at least up to 4.3×10¹¹cm^-3, which corresponds to 200 and 350 times as high as densities of positive and negative ions, at 200 ms after rf-on, respectively. The latter result suggests that a large fraction of particles are neutral and they play essentially an important role in the initial growth processes of particles, at least, under the moderately high rf power condition as employed in the present work.