Characterization of nucleation and growth of MW-CVD diamond films by spectroscopic ellipsometry and ion beam analysis methods

Abstract

The time evolution of diamond film nucleation and growth have been investigated by spectroscopic ellipsometry (SE). Rutherford backscattering spectrometry (RBS) combined with elastic recoil detection (ERD) techniques. Diamond films were prepared using the microwave plasma CVD (MW-CVD) method on Si. In the plasma chamber, bias voltage of −200 V DC was applied to the Si substrate for 4–12 min in H2-CH4 (10%) to nucleate diamond. The substrate modification by H2 plasma cleaning and the DC bias nucleation of carbon layer followed by diamond film growth in H2-CH4 (0.5%) gas were studied. After H2 plasma cleaning the native 2.7 nm thick SiO2 is partly removed and the bias nucleation resulted in a mixture of SiO2 and SiC. With longer time, a very slow increase in film thickness up to 4.6 nm and a fast enrichment of the SiC contents have been observed. Thicker diamond films were found to consist of a 2–40 nm thick porous SiC-H layer, a bulk microcrystalline diamond layer and an amorphous capping layer 2–6 nm thick. The refractive index and the density of the bulk layers were identical to those of the single crystal diamond mixed with about 2% graphite and hydrogen. Porous layered structures were found in films reaching up to 2–40% porosities.