On the assessment of local stress distribution in integrated circuits

The possibilities and limitations of micro Raman spectroscopy (muRS), convergent beam electron diffraction (CBED) and electron diffraction contrast imaging (EDCI) for the study of localised stress fields in semiconductor substrates are discussed and illustrated with results obtained on local isolation structures in silicon. MuRS has the advantage of being non-destructive but has a spatial resolution which is limited by the wavelength of the laser and which is typically of the order of 1 mum. Other drawbacks are that stresses in the silicon substrate can only be measured through transparent layers and that the recorded Raman shift is a convolution of shifts due to different stress components. The two transmission electron microscopy techniques have a much higher spatial resolution (nm scale) but suffer from the drawback that they are destructive and require elaborated specimen preparation. Furthermore, the preparation of the thin foils suitable for TEM inspection leads to relaxation of the strains in the direction perpendicular to the image plane which has to be taken into account for the interpretation of the results. Nevertheless, useful, complementary information on the strain distributions can be deduced from the combined use of these three techniques. This opens interesting perspectives in the correlation between local stress and electrical properties of microelectronic devices.