NOVEL CHEMICAL ROUTES TO SILICON-GERMANIUM-CARBON MATERIALS

We report the use of novel molecular precursors and ultrahigh vacuum c hemical vapor deposition techniques to synthesize solid solutions of c ubic SiC-GeC and diamond-structure Si1-x-yGexCy materials. Thin films with composition Si0.37Ge0.13C0.50 were deposited on Si by thermal dec omposition of Ge[Si(CH3)3]4 at 650-700-degrees-C. Electron microscope observations showed a polycrystalline zinc-blende-type structure and i nfrared (IR) analyses revealed carbide-type Si-C and Ge-C vibrations. The Si1-x-yGexCy (y > 2%) alloys were deposited at 550-600-degrees-C o n Si and SiO2 by interactions of (1) C(SiH3)4 and GeH4; (2) CH3GeH3 an d SiH4; and (3) CH3GeH3 with mixtures of GeH4 and SiH4. A homogeneous alloy phase of composition Si56Ge30C14 with diamond cubic structure wa s obtained from reaction 1. Reactions 2 and 3 produced films with carb on compositions ranging from 2 to 27 at.%. The materials containing le ss than 10% carbon appeared to be exclusively diamond cubic, whereas t hose with greater carbon compositions showed mixtures of diamond cubic and carbide phases as indicated by vibrational and structural charact erization. Secondary ion mass spectrometry experiments revealed that a ll materials had excellent chemical purity. (C) 1994 American Institut e of Physics.