1999 Electronic Materials Conference

WAFER EDGE MISFIT DISLOCATION NUCLEATION IN P/P+ SILICON VAPOR PHASE EPITAXY

P. Feichtinger, H. Fukuto, M.S. Goorsky, Dept of Materials Science and Engineering, University of California, Los Angeles; D. Oster and J. Moreland, Wacker Siltronic Corporation, Portland, OR.


Determining the hierarchy of initial nucleation sources for misfit dislocations is important for both pseudomorphic epitaxial structures and for intentionally relaxed structures. In particular, the role of damage at the wafer periphery has been indicated as a contributor to misfit nucleation, but this factor has not been addressed in depth. We studied the role of edge damage on misfit dislocation formation in p/p+ silicon wafers to determine i) if careful control of the edge treatment could reduce the density of misfit segments and ii) whether other dislocation sources dominated the kinetics of the process. The samples were 150 mm Czochralski grown highly boron doped wafers (2.6.1019 cm-3). Different combinations of edge treatments were used during the processing of the wafers to create differences in both the edge shape and roughness. 2-12 m m thick lightly boron doped epitaxial layers (1015 cm-3; resulting strain » 10-4) were deposited by vapor phase epitaxy at 1080 1150°C in a single wafer reactor using trichlorosilane as a precursor. Double crystal x-ray topography was used to measure the 60° misfit dislocation segments around the wafer periphery. Misfit dislocations were not observed to nucleate at any other locations on the wafer surface, indicating that particulates or defects in the substrate did not play an observable role in the formation of misfit segments. A variation of misfit segment lengths was observed. On a local scale, the differences in lengths are attributed to the stochastic nature of the nucleation process, and longer scale variations stem from the effects of crystallography and of blocking by orthogonal dislocations. Edge treatments which involved polishing steps exhibited great reductions or even the absence of misfit dislocations (<10 cm-1) compared to unpolished edge treatments (~1000 cm-1). In regions where the misfit dislocations were observed, triple axis x-ray diffraction determined that the amount of layer relaxation was consistent with the dislocation density. High temperature (800-1000 °C) post growth annealing was studied to determine the stability of the layers against subsequent high temperature device processing.