STRAIN DETERMINATION IN SEMICONDUCTORS BY CONVERGENT BEAM ELECTRON DIFFRACTION. A. Armigliato, R.Balboni, A.Benedetti, S.Frabboni^* and J.Vanhellemont⁺, CNR-Istituto LAMEL, via P.Gobetti 101, I-40129 Bologna, Italy, ^*Dipartimento di Fisica, Universit di Modena, via Campi 213/A, I-41100 Modena, Italy, ⁺IMEC, Kapeldreef 75, B-3001 Leuven, Belgium

The determination of strain in nanoscale structures of semiconductors requires the availability of techniques with a high spatial resolution. Convergent beam electron diffraction, which is performed in a transmission electron microscope (TEM/CBED), is a point-to-point technique, with a resolution of the order of ten nm, which allows the strain tensor to be deduced from the shift of HOLZ lines in the central spot of the pattern. In its large angle version (LACBED) this technique has the advantage of combining both real space and reciprocal space information, with a spatial resolution limited by the probe size; in this case strain information can be obtained from a single pattern in different points of the imaged area through the shift and splitting of the ZOLZ Bragg contours. However, when applied to cross-sectioned specimens, the strain measured by CBED or LACBED is affected by the relaxation, which occurs in a direction parallel to the thinning direction. Methods of quantitative determination of relaxation in both uniform and graded Si_1-xGe_x/Si heterostructures will be discussed; the bulk tetragonal distortion values thus obtained from (LA)CBED are in good agreement with the ones deduced from double crystal X-ray diffraction. Integrated circuits with submicron features are a promising field of application of this technique; the determination of strain profiles in local isolation structures in silicon and their agreement with the corresponding simulated ones will be reported.