ANALYTICAL ELECTRON-MICROSCOPY OF SI1-XGEX SI HETEROSTRUCTURES AND LOCAL ISOLATION STRUCTURES/

The convergent beam electron diffraction (CBED) technique has been app lied to determine the lattice strain in Si1-xGex/Si heterostructures a nd in local isolation structures. Both plan and cross-sections have be en investigated by transmission electron microscopy. In the heterostru ctures, the strain value obtained by CBED along the growth direction e psilon(CBED) is affected by ii relaxation induced by the thinning proc ess in a direction normal to the cross-section plane, being generally smaller than the bulk tetragonal value epsilon(T). This effect can be overcome using the large angle CBED technique on plan sections. In add ition, in the heterostructures the Ge concentration has been determine d by energy dispersive X-ray spectrometry: allowing the pseudomorphici ty of the samples to be evaluated. All the values of strain and Ge con centration thus obtained ale in good agreement with those deduced from Rutherford backscattering spectrometry. In isolation structures, the CBED technique has been applied to determine the distribution of the c omponents of the strain tensor along a line parallel to the pad oxide/ substrate interface. The values obtained are in agreement with the pre dictions of a previously reported simple model.