Local strains induced in silicon channel by a periodic array of nitride capped poly lines investigated by high resolution X-ray diffraction

Abstract

In the framework of the development of strained channel materials, the mechanical stress induced in silicon by a silicon nitride stressor layer is studied. The investigated samples are sub-micrometric periodic arrays of polysilicon lines deposited on thermally oxidised single crystal (0 0 1) Si substrate and capped with silicon nitride. We compare the stress induced in the silicon substrate by three layouts: without Si 3N 4, with a tensile Si 3N 4 or with a compressive Si 3N 4 layer on top of the poly lines. The periodic strain field in silicon is investigated by high resolution X-ray diffraction which is very sensitive to local strain (<10 −4) and is non-destructive. The lines array induces a periodic strain field in silicon, which gives rise to distinct satellites in reciprocal space. The intensity of these satellites is related to the strain field in one cell. X-ray reciprocal space maps are measured on a 4 circles goniometer with a laboratory source. First experimental mappings around the symmetrical 0 0 4 Si Bragg peak are presented here. Elastic calculations are performed with a Finite Element Modelling code in order to extract the displacement field that is useful for structure factor calculations within kinematical approximation. The calculations are necessary for explaining the experimental reciprocal space maps intensity envelope and comparing the strain induced by the three investigated layouts.