Residual stress in silicon substrate with shallow trenches on surface after local thermal oxidation

Residual stress was investigated experimentally and analytically in silicon substrates after local thermal oxidation. Shallow trenches about 0.3 μm deep were formed before 1 000°C oxidation. Residual stress in the substrate after oxidation was measured using microscopic Raman spectroscopy. Tensile stress of about 50 MPa initially occurred at the substrate surface. However, the residual stress decreased to zero as the thermal oxide film thickness increased, and then compressive stress increased. The stress development process was analyzed using the finite-element method, and the results showed that three processes were mainly involved: oxidation-induced stress at the curved surface, deflection of the nitride film, which was used as an oxidation protection mask, and constraint of volume expansion of the newly oxidized film. The predicted and measured results were in good agreement for stress changes caused by increasing oxide film thickness.