NITROGEN STABILIZED (100) TEXTURE IN CHEMICAL-VAPOR-DEPOSITED DIAMONDFILMS

We have studied the influence of nitrogen impurities in CH4/H-2 gas mi xtures on the structure and morphology of polycrystalline diamond film s prepared by microwave plasma assisted chemical vapor deposition. The nitrogen concentration in the process gas was varied between 1 and 10 00 ppm. Optical emission spectroscopy was applied to detect the nitrog en in the plasma via emission from CN radicals. The morphology and tex ture of polycrystalline films prepared with various N2 impurity levels and CH4 concentrations in the range 0.5%-2% was investigated using sc anning electron microscopy and x-rav texture analysis. For the films p repared with low methane concentrations (e.g., 0.5%) only a minor infl uence of the nitrogen was observed. However, most interestingly, for h igher methane concentrations (1%-2%) the addition of small amounts of nitrogen turned out to have a tremendously beneficial effect on the fi lm morphology and structure. Films prepared without additional nitroge n are of nanocrystalline structure and of minor quality, whereas films prepared with nitrogen concentrations in the range 10-100 ppm exhibit a pronounced [100] texture and a considerably improved crystalline qu ality as judged by Raman spectroscopy.