Growth Mechanisms During Thin Film Crystallization From the Melt

Abstract

AbstractWe develop a model that appears to account for the existence of a new mode of crystallization recently discovered during zone-melt-recrystallization (ZMR) of silicon thin films on SiO 2 using a scanned strip heater or lamp. Transition to the new crystallization regime is induced by reducing the temperature of the scanned upper heater strip, thus reducing dT/dy, the thermal gradient along the direction of scan at the silicon solidification front. If dT/dy ≤:4 K/mm, the single crystal films have long non-branched subboundaries with tilt misalignments of 0.1 or less, a lateral separation in excess of 50 µm, and consist of rows of short dislocations threading through the film thickness and terminating at the two SiO2 layers. This is in marked contrast to material ZMR scanned at higher dT/dy which shows conventionally branched 1 to 3 subboundaries that consist of edge dislocations running in the plane of the film often for several hundred microns.Our model extends the {111} faceted-freezing-front picture we have developed previously to take into account the freezing profile with respect to film thickness, and in particular to such profiles at the intersections of pairs of {111} facets where subboundaries are known to form. We propose that the melt-freezing interface profiles at these interior corner intersections are aligned approximately normal to the scan in the high gradient case, but become tilted towards the plane of the SiO2 cap layer for the low gradient case. This tilting accounts in a natural way for the transition from in-plane to threading dislocations.