Strain induced by Ti salicidation in sub-quarter-micron CMOS devices, as measured by TEM/CBED

The use of TiSi2 layers as ohmic contacts in complementary MOS (CMOS) devices is expected to introduce large distortions in the underlying silicon which may degrade the device performances. In this work, the TEM technique known as convergent beam electron diffraction (CBED) has been employed to map the strain distributions across 110 cross-sectional specimens of sub-quarter-micron CMOS structures. Different experimental set-ups in terms of energy filtering, liquid nitrogen cooling and zone axis have been explored and compared to each other by using three differently equipped microscopes. The strain induced on silicon by TiSi2 layers has then been investigated, quantified and compared with that due to the presence of an oxide isolation trench. Also, the effects of depositing a TiN capping layer on TiSi2 have been analysed. Our results show that its presence results in a more tensile strain without altering the strain distribution trend.