Mechanical stress at the (111) Si surface covered by SiO 2 and AlSiO 2 layers

Abstract

The mechanical stress σ Si at the (111) Si surface was studied on SiO 2Si and AlSiO 2Si sandwich structures as a function of temperature and layer thickness. The surface warp was measured with a Michelson interferometer in the temperature range between 4.2 and 370 K. For the SiO 2Si structure an isotropic tension was observed at the Si surface. The tension is a function of oxide thickness and is of the order of 1 N mm 2 for a 120 nm thick SiO 2 layer at room temperature. It remains unchanged while varying the temperature from 4.2 to 370 K. In contrast AlSiO 2Si structures show an isotropic compression at the Si surface. For a sandwich with a thin oxide (3 nm) interface film and a 300 nm thick Al layer it amounts to (5.8 ± 0.6) N mm 2 at room temperature. This compression increases with decreasing temperature and saturates after a stress variation of 28 N mm 2 at about 100 K. By heating the structure the stress decreases and becomes zero at 90°C.