Residual Stress in Diamond and Amorphous Carbon Films

Abstract

ABSTRACTBoth diamond and amorphous carbon films can contain substantial residual stresses (up to 10 GPa and higher) due to a combination of thermal and intrinsic effects. Residual stresses in the films limit the maximum thickness to which films can be grown and can lead to weakening and/or failure of the film/substrate interface. In addition, a quantitative measurement of the residual stress in the film is required for an accurate determination of the film/substrate interface fracture toughness. Spectroscopic measurements of residual stresses in diamond and amorphous carbon films based on frequency shifts of Raman-active phonon modes are presented. The spatial resolution of the technique is 1 μm in the lateral direction. In transparent materials such as single crystal diamond, stress profiles with 10 μm resolution in the axial direction can be measured. Examples of such stress profiles are presented for natural and CVD-grown single crystals. Raman measurements of thermal stress in thin polycrystalline diamond films on metal substrates are presented. Initial, spatially resolved measurements of large, compressive intrinsic growth stresses in high-hardness amorphous carbon films grown by ion beam techniques are presented. The accuracy of the Raman residual stress measurement depends on the film structure and is ±60 MPa for single crystal diamond, ±120 MPa for polycrystalline diamond, and ±500 MPa for hard amorphous carbon.