S. Christiansen, M. Becker, and G. Andrae, and F. Falk
Large and small grained polycrystalline silicon thin films on glass substrates can be obtained either by melting amorphous silicon layers using e.g. lasers or by solid phase crystallization in a furnace. Both types of materials are further investigated using scanning and transmission electron microscopy techniques and µ-Raman spectroscopy. Laser molten large grained silicon layers are provided by the IPHT, Jena (www.ipht-jena.de) in the group of Gudrun Andrä and Fritz Falk, small grained solid phase crystallized material is provided by CSG Solar AG in a common project.
Fig. 1 shows the orientation analysis of laser crystallized thin film material as carried out in a scanning electron microscope by electron back scattering diffraction (EBSD). Color coded surface normals are indicated. On the same area micro Raman spectroscopy is carried out and strong local stresses are visible (here: 765Mpa within a few µm length).
Fig. 2 shows a cross sectional TEM image of such a large grain area on glass. Grain boundaries and internal stacking faults are visible together with precipitates at the interface.
These precipitates can be identified as Si-N precipitates using electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM) cf. Fig. 3.
Fig. 2: TEM micrograph of a laser crystallized Si layer on glass.
Fig. 3: EELS study across interfaces: glass-silicon layer. The Si-N precipitates at the interface are discernible from the nitrogen present there.