Plasma Deposition of Diamond at Low Pressures: A Review

Plasma deposition techniques of nanocrystalline and microcrystalline diamond and related mechanisms at pressures below 0.1 torr are reviewed. The mechanism of nucleation and growth of diamond in low-pressure conditions is discussed theoretically and experimentally along with the role of radicals and ions in two different ion-energy ranges. For ion impact energies below 20-30 eV, diamond deposition occurs on a surface. The growth process is limited by the substrate temperature and the flux of hydrogen radicals when the ion energy is reduced enough to several eV as shown by a kinetic rate analysis for radical species. The nucleation process is limited mainly by the degree of carbon saturation and, hence, the flux of carbon-containing species. For ion impact energies above 20-30 eV, diamond deposition occurs beneath a surface. Renucleation hinders the growth and diamond nanocrystals are embedded in an amorphous carbon matrix. The nucleation process depends strongly upon the ion energy, ion-to-depositing flux ratio, and substrate temperature as shown by the film density increment based on the subplantation model.