A. Bouchoule et al., FORMATION OF DENSE SUBMICRONIC CLOUDS IN LOW-PRESSURE AR-SIH4 RF REACTOR - DIAGNOSTICS AND GROWTH-PROCESSES FROM MONOMERS TO LARGE-SIZE PARTICULATES, Pure and applied chemistry, 68(5), 1996, pp. 1121-1126
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.