Formation Processes of Particulates in Helium-Diluted Silane RF Plasmas

Particulate formation processes in SiH4RF plasmas are studied using two laser light scattering (LLS) methods and a newly developed Langmuir probe method together with a discharge-modulation method. From the experiments, the following results are obtained: Particulates tend to appear around the plasma/sheath boundary of the RF electrode in their early growing phase and, in the subsequent rapid growing phase, grow there at a rate of a few tens nm/s high compared to the film deposition rate; after the rapid growing phase, the growth rate decreases considerably; size and density of particulates amount to 60 ~ 180 nm and 108~ 109cm-3; spatial distributions of subnanometer-size particles detected by the probe method are similar to those of particulates of above a few tens nm in size observed by the LLS methods. These results suggest that short lifetime neutral radicals primarily contribute to particulate nucleation and subsequent early growth; the particulate growth rate during the rapid growing phase can be explained by taking into account the contribution of positive-ion and/or neutral radical fluxes to the particulate surface. Furthermore, the considerable decrease in the growth rate after the rapid growing phase may suggest that the positive ions mainly contribute to the rapid growth.