DUAL MICROWAVE RF PLASMA DEPOSITION OF FUNCTIONAL COATINGS

Plasma silicon nitride (P-SiN) and amorphous hydrogenated silicon (a-Si:H) films were deposited in a dual-frequency plasma, consisting of a microwave discharge with r.f. power simultaneously superimposed on the substrate holder. It is shown that the r.f.-induced negative substrate bias voltage V(b) substantially affects the deposition rate (between 15 and 30 angstrom A s-1), the film composition and electrical properties. Ion fluxes bombarding the growing layers have been measured and found to be several times greater in the dual-frequency mode than in the "pure" r.f. mode. It is estimated that ionic species contribute about 30%-40% to the film growth rate. The increasing ion flux and energy with increasing V(b) enhance the formation of densely packed coatings which, in turn, reduces the dielectric loss of tan-delta of P-SiN, and the resistivity of a-Si:H by several orders of magnitude, when [V(b)[ is raised from 0 to -800V.