The fabrication of Silicon-On-Insulator (SOI) materials has progressed to such an extent over the past decade that the material specifications are approaching those of bulk silicon and many viable manufacturable processes are now in operation. Silicon wafer bonding is one such commercially-employed approach to SOI synthesis in which two (oxide-terminated) Si wafers are directly bonded under ambient conditions and then annealed to elevated temperatures (1100 C) to form a permanent chemical bond. In the conventional process, the device wafer is subsequently thinned to the required dimensions by extensive grinding/polishing. The limitations imposed by this latter step have recently been removed with the advent of a remarkable new process wherein H+ is pre-implanted into the device wafer at a critical concentration and depth, prior to bonding. Upon subsequent joining to the companion 'handle' wafer and annealing to ~400 C, complete lift-off (exfoliation) of the overlying Si occurs, so that the final SOI structure can now be formed in one elegant annealing step, with thickness uniformities of ~50 Å over the entire wafer. Research has played an important role in the advancement of this field, despite the inherent difficulties in obtaining spectroscopic information about the physics and chemistry of interfaces that typically lie ~500 microns below the surface. In this talk, I will describe how we have obtained@footnote 1@ unprecedented insight into the thermal evolution of the buried interfaces that comprise both the bonded and the exfoliation interfaces, using a wide variety of different experimental probes in combination. In particular, I will highlight the pivotal role of infrared spectroscopy in delineating the microscopic mechanisms that permit the intimate chemical bonding of two wafers and the transformation of isolated hydrogenated defects into extended internal cracks that ultimately lead to exfoliation of macroscopically large areas of Si.
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@footnote 1@M.K. Weldon, V.E. Marsico, Y.J. Chabal, A. Agarwal, D.J. Eaglesham, J. Sapjeta, W.L. Brown, D.C. Jacobson, Y. Caudano, S.B. Christman and E.E. Chaban, J. Vac. Sci. Technol. B 15, 1065 (1997).