Simulation of the gas-phase processes in remote-plasma-activated chemical-vapor deposition of silicon dielectrics using rare gas–silane-ammonia mixtures

Remote-plasma-activated chemical-vapor deposition (RPACVD) is a method whereby thin films are deposited with the substrate located out of the plasma zone. The lower rate of energetic ion and photon bombardment in RPACVD compared to conventional direct-plasma-enhanced chemical-vapor deposition (DPECVD) reduces damage to the substrate. The use of RPACVD also enables one to more carefully tailor the flux of radicals to the substrate compared to DPECVD. This selectivity results from both physically isolating the substrate from undesirable radicals and limiting the variety of chemical pathways that produce radicals. A model for RPACVD is described and results from the model are discussed in the context of comparing gas mixtures and geometries in which this selectivity may be achieved. The chemistries investigated are Rg/SiH4 (Rg=Ar, He) for deposition of Si and Rg/NH3/SiH4 (Rg=Ar, He) for deposition of Si3N4. It is found that the selectivity in producing radicals that can be obtained by excitation transfer from excited states of rare gases is easily compromised by reactor configurations that allow injected gases to penetrate into the plasma zone.