In-situ measuring of stress development in diamond thin films

Chemical vapor deposition of diamond films on various substrate materials usually leads to residual stress in the film/substrate composite at room temperature. Residual stresses are composed of intrinsic tensile film stress induced during film growth and of a thermal component caused by different thermal expansion coefficients of film and substrate. In the case of planar substrates the intrinsic growth stress in the diamond film causes a bending of the film/substrate composite which was measured by the deflection of two parallel laser beams during deposition. For elastic deformation of the substrate the radius of curvature can be related to the actual film stress in the growing diamond film. Growth stresses determined by the in-situ measurement of the radii of curvature depend on deposition temperature as well as the grain size of the deposited films. At substrate temperatures above 800 degree C, an accelerated bending of silicon substrates can be observed after growing diamond films b eyond a critical thickness, even when stopping deposition but maintaining the deposition temperature. This process is caused by creeping of the substrate and results in a residual curvature of the silicon wafer after removing the diamond layer by reactive ion etching. Due to their role in adhesion and shape stability of the film/substrate composite, residual film stresses as well as film stress induced plastic deformations are of critical importance for the application of polycrystalline diamond coatings.