Characterization of stress induced by Si_1-xGe_x in the active epitaxial film on a SOI substrate via Scanning Surface PhotoVoltage Microscopy.

The mobility and breakdown voltage of field-effect transistors fabricated on a Silicon-on-Insulator substrate can be improved by embedding a Si_1-xGe_x layer in the active epitaxial silicon layer¹. The choice of the Ge fraction, x, dictates the mobility improvement due to band-bending proportionate to misfit strain. The thickness of the embedded Si_1-xGe_x layer, modulates associated stress relaxation, the density of extended defects, and degree of amorphozation of the epitaxy. Techniques such as TEM and Raman spectrosopy are traditionally used to characterize the film stress state in such heterostructures. We present here a systematic study of the evolution of the stress state and relaxation as a function of the Si_1-xGe_x layer thickness in the active epitaxy on production SOI wafers using a novel technique, Scanning Surface PhotoVoltage Microscopy (SSPVM). These results are correlated with those obtained by Raman spectroscopy. Some advantages of the use of SSPVM are noted, as well other uses of it for semiconductor characterization.

^1"A novel SiGe-inserted SOI structure for high performance PDSOI CMOSFETs”, G.J. Bae et al. International Electron Devices Meeting 2000, https://doi.org/10.1109/IEDM.2000.904407