On nitrogen incorporation during PE-CVD of diamond films

Abstract

Nitrogen is one of the most widely studied impurities in diamond films. The reason is that nitrogen takes part in a number of defects and therefore has a deep influence on the optical and electrical properties of diamond films. The mechanism of nitrogen incorporation in diamond is still an open question. This is mainly due to the complexity of the N-incorporation processes, depending not only on experimental parameters (e.g. type and concentration of the N-containing gas, substrate temperature etc.) but also on the surface termination and on the orientation of the chemical vapor deposition (CVD) diamond film. The aim of this paper is to compare nitrogen incorporation in CVD diamond films by addition of small amounts (ppm range) of two different N-containing precursors--nitrogen and vaporised nitromethane--to a conventional CH4/H-2 gas mixture during microwave PE-CVD. Optical emission spectroscopy (OES) was used to survey the plasma chemistry during deposition. The relative intensities of the H-beta atomic hydrogen emission line and of the CN and C-2 emitting radicals were recorded as a function of the nitrogen fraction added to the plasma. The influence of nitrogen incorporation on the diamond film properties was investigated by a number of complementary techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), photothermal deflection spectroscopy (PDS-optical absorption) and Raman spectroscopy. (C) 1998 Elsevier Science S.A.