Influence of hydrogen on the residual stress in nanocrystalline diamond films

Abstract

Nanocrystalline films were deposited by microwave-plasma CVD at a pressure of 200 mbar from an Ar/H 2/CH 4 plasma where the hydrogen fraction in the process gas was varied between 2 and 7%. Residual stress is a critical parameter in thin film deposition and especially important for technical applications of nanocrystalline diamond because high residual stress can lead to cracking or even to delamination of the film from the substrate. An ex-situ optical device was used to measure the residual stress of the substrate. It is shown that by controlling the process parameters the residual stress in the NCD films can be adjusted in a wide range even from compressive to tensile. The films were characterized by two wavelength scanning micro Raman spectroscopy and SEM. In this work a correlation is made between the intrinsic stress measurements and the Transpolyacetylene peaks (around 1120 cm − 1 and 1450 cm − 1) in the Raman spectra of NCD films. It is shown that the intensity and the FWHM of the peaks correlate with the tensile stress in the films. A model correlating the Raman spectra to the grain size and thus to the intrinsic stress measurements is given in this paper.