Surface stress measurement with interference microscopy of thick homoepitaxial single-crystal diamond layers

In this article, we present a study of surface stress measurements of a thick single-crystal diamond (SCD) layer (110 μm) deposited onto a high-temperature high-pressure (HTHP) Ib substrate. The measurement is based on observations of the deformation of the backside of the HTHP substrate due to internal stress that varies as the thickness of the SCD layer is modified by ion-beam etching. The deformation is obtained from the height-distribution analysis of interference microscopy (IM) observation. The results show that the tensile surface stress σ increases linearly with SCD-layer thickness with tf according to σ = 0.065tf MPa/μm. The tensile surface stress may be attributed to the intrinsic stress that originates from the lattice mismatch between the CVD-diamond layer and the HTHP-Ib substrate. The increased internal stress is a principle cause of crack formation of the crystal.

Research Highlights
► Surface stress of a thick CVD diamond can be estimated with interference microscopy.
► The tensile surface stress increases linearly with thickness over a depth scale.
► This measurement is a useful technique to predict crack in the synthesizing process.