Residual Stress in the Silicon Substrate with Shallow Trenches on the Surface after Local Thermal Oxidation

Residual stress in the silicon substrate after local thermal oxidation was investigated experimentally and analytically. Shallow trenches about 0.3 µm deep were formed before 1 000°C oxidation. Residual stress in the substrate after the oxidation was measured using microscopic Raman spectroscopy. Tensile stress of about 50 MPa initially occurred at the substrate surface. However, the residual stress decreased with increasing thermal oxide film thickness, and then compressive stress increased. The stress development mechanism was analyzed using a finite element method. There were three main mechanisms, oxidation-induced stress at the curved surface, deflection of the nitride film which was used as an oxidation protection mask, and constraint of free volume expansion of the newly oxidized film. The predicted stress change with increasing oxide film thickness agreed well with the measured results.