FORMATION OF DENSE SUBMICRONIC CLOUDS IN LOW-PRESSURE AR-SIH4 RF REACTOR - DIAGNOSTICS AND GROWTH-PROCESSES FROM MONOMERS TO LARGE-SIZE PARTICULATES

The formation of solid particles in the gas phase is a general problem for PECVD technology when looking at high deposition rates of good qu ality layers. The present paper report an overview on particle growth and associated plasma phenomena in a specific situation: Argon-Silane RF low pressure discharge. The diagnostics developped for this study i nclude laser multi-angle Mie scattering for particle diameter above 35 nm and excimer induced light emission for nm scale particles. The evo lution of the free electron concentration is obtained by microwave dia gnostics and electron energy is deduced from OES data. In-situ FTIR ab sorption spectroscopy add insigths on the gas phase chemistry. Four su ccessive steps are evidenced in the story of particle formation: clust erring of negative ions, formation of dense clouds of nn size crystall ites, coalescence to few tens nm diameter particulates and a final gro wth by deposition of a-Si:H on the particles negatively charged and tr apped in the discharge. The gas temperature appears as a sensitive par ameter for the initial step of crystallites formation and a drastic tr ansition of plasma properties occurs during the coalescence step of du st formation.