INTERNAL-STRESSES IN CVD DIAMOND LAYERS

Chemically vapour deposited diamond layers always contain internal stresses. Two types of layer stresses can be distinguished: tensile intrinsic stresses and compressive thermal stresses. Intrinsic stresses were measured in situ during diamond deposition onto silicon substrates using a bending-plate method in a hot-filament reactor. The intrinsic tensile stresses increased with the total gas pressure and the methane content in the reaction gas. The measured stress curves became steeper with decreasing filament temperature. They also depended strongly on the layer morphology and grain size. The intrinsic stresses within a layer increased with decreasing grain size and the transition from well faceted crystallites to spherolitic ballas-type crystals having an extremely fine-grain radial polycrystalline structure. The thermal stresses, determined after cooling to room temperature, increase with higher deposition temperature and show acceptable agreement with calculated values using a simple model.