RESIDUAL-STRESS IN SILICON SUBSTRATE WITH SHALLOW TRENCHES ON SURFACEAFTER LOCAL THERMAL-OXIDATION

Residual stress was investigated experimentally and analytically in si licon substrates after local thermal oxidation. Shallow trenches about 0.3 mu m deep were formed before 1000 degrees C oxidation. Residual s tress 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 ze ro as the thermal oxide film thickness increased, and then compressive stress increased. The stress development process was analyzed using t he 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 protect ion mask, and constraint of volume expansion of the newly oxidized fil m. The predicted and measured results were in good agreement for stres s changes caused by increasing oxide film thickness.