INTERFACE EVOLUTION AND EPITAXIAL REALIGNMENT IN POLYCRYSTAL SINGLE-CRYSTAL SI STRUCTURES

Our recent work on the poly/single crystal Si interface evolution and on the expitaxial realignment under high temperature (approximately 10 00-degrees-C) rapid thermal annealing is reviewed. The roles of the mi crocrystalline morphology, of the interfacial native oxide film, of th e doping level and of the processing temperature on the realignment ki netics are addressed. Two different realignment modes are observed. Fo r undoped layers a quasi planar interface motion occurs, while in high ly doped polycrystalline layers the realignment proceeds via the forma tion of epitaxial columns and their lateral growth. These two differen t modes arise from the doping enhancement of the interface kinetics. I t is shown that these processes can be interpreted within an Avrami-Me hl-Johnson nucleation and growth scheme. In the early stages of interf ace realignment the process is controlled by oxide clustering, arising from the evolution of the native oxide layer, and by the density of g rain boundaries intersecting the interface with the single crystal. On ce nucleated at specific sites the epitaxial front can then proceed, t he kinetics and mode of realignment depending on the density of nuclea tion sites and on the growth velocity. It is also demonstrated that wh en narrow (approximately 0.25 mum) polycrystalline strips defined by o xide layers (as in real devices) are used in place of infinite planar layers the realignment mode and kinetics change due to the presence of size effects. These data are presented and their implications for app lications to bipolar devices are discussed.