With the general trend of reduced dimensions in microelectronic devices, local mechanical stresses are increasingly considered a very important issue. The local strain field is worth investigating in particular in Shallow Trench Isolation (STI) which is a key step in the production of non-volatile-memories and transistors. We investigate by High Resolution X-ray Diffraction (HRXRD) the periodic strain field induced in silicon by the STI process. HRXRD is shown to be very sensitive (~10^-4) to local strains and has the distinct advantage of being non destructive. Investigated samples are periodic arrays of SiO₂-filled trenches in single crystal (001) Si. The trenches are etched either along [100] or along [110]. The HRXRD experiments have been performed on a 4 circles goniometer with a laboratory source. We have recorded Si 004 and asymmetric Si 224 or Si 404 reciprocal space maps in order to extract axial strains in the 3 directions. The trenches array induces a periodic strain field in silicon, which gives rise to distinct satellites in reciprocal space, shifted from the substrate peak position. The intensity of these satellites is related to the strain field. We also performed elastic calculations with a Finite Element Modelling (FEM) code. Finally structure factor calculations are performed using the displacement field determined from mechanical modelling. The simulated diffraction maps are compared with experimental ones and allow for a complete validation of the stress field. We focus here on the effect of silicon elastic anisotropy on the strain field in 580nm and 200nm period samples. The influence of line crystallographic orientation ([100] or [110]) on the strain field is evaluated by FEM. These results are compared with experimental ones and discussed.

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