Transition of Particle Growth Region in SiH4 RF Discharges

Abstract

The growth region of particles in SiH4 RF discharges is investigated with the parameters of pressure, SiH4 concentration and RF power. When the diffusion time τD of SiH2 radicals (key species for fast particle nucleation) through their production region is longer than their reaction time τR with SiH4 and sufficient SiH2 radicals are supplied, particles grow at a high growth rate of \\gtrsim10's nm/s localized only around the plasma/sheath (P/S) boundary near the RF electrode where the radicals are produced. Under this condition, neutral clusters (resulting from the polymerization reactions) react with each other many times before they diffuse out of the radical production region. Since the diffusion time of clusters through the radical production region increases with cluster size, large clusters tend to be localized there and grow further to sizes on the order of nm. With τR>τD and/or insufficient supply of SiH2 radicals, particles grow at a low rate of 1 nm/s and exist in the plasma bulk as well as around the P/S boundary. Such low growth rates suggest that negatively charged clusters are indispensable in order for particles to grow to above several nm in size.