Abstract's Details

X-ray Studies of Strained Si on Insulator
Abstract ID	MAT-08
Presenter	Matthew Bibee
Presentation Type	Poster
Full Author List	M. Bibee (1), A. Mehta (1), S. Brennan (1), P. Pianetta (1)
Affiliations	(1) Stanford Synchrotron Radiation Laboratory
Category	Materials Science
Abstract	Inducing tensile stress on a Si layer improves carrier mobility, rendering it an attractive substrate for modern high-speed CMOS devices. Using epitaxy and wafer bonding technology, strained Si on insulator (sSOI) wafers can be reliably fabricated with large diameters (up to 12 inches). However, standard silicon device fabrication processes involve several moderate to high temperature (400-900°C) annealing sequences, which create opportunities for the strain in the thin top Si layer to redistribute or worse relax through formation of threading dislocations and other defects. These defects tend to lower the carrier mobility through scattering processes. We present a study of the strain and defect pattern in sSOI wafers. We used X-ray reflectivity (XRR) measurements on BL 2-1 to characterize layer thickness, density, and roughness, and high resolution x-ray diffraction (SRXRD), on the six circle diffractometer on BL 7-2, to determine average strain and misalignment (due to wafer bonding) of the strained Si layer. XRR indicates that the overall sSOI structure is composed of several layers with a very high degree of flatness. SRXRD indicates that the strained Si layer is aligned within a fraction of a degree to the crystal lattice of the bulk wafer substrate and has compressive strain normal to the sample surface and tensile strain in-plane. Further, it appears that the strained layer is composed of columns of material with uniform strain; understanding the mosaicity of this layer and its alteration on annealing will provide insight into the distribution of defects. Correlating these findings with nanoscopic and electrochemical tools along with DFT calculations promises to improve our understanding of strain relaxation and defect formation in sSOI.
Footnotes
Funding Acknowledgement	Funding for this research was provided by SiWEDS, a National Science Foundation Industry/University Cooperative Research Center. Sample materials were provided by Soitec. Portions of this research were carried out at the Stanford Synchrotron Radiation Laboratory, a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences.