Study of subboundary generation in silicon-on-insulator films recrystallized by a pseudoline electron beam

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Abstract
We investigated subboundary generation in silicon-on-insulator (SOI) structures which have square-shaped SOI regions and surrounding seed stripes. The SOI films were melted using a pseudoline electron beam, which was produced by oscillating a spot beam faster than the thermal response time of the substrate, and recrystallized through laterally seeded epitaxial growth from the seed stripes. It was found that a molten zone with a concave trailing edge was not effective to form a subboundary-free SOI region wider than several tens of micrometers, since the curved liquid-solid (L-S) interface easily generated subboundaries along 〈100〉 directions. It was also found that the temperature fluctuation due to the oscillation of the spot beam was not directly related to subboundary generation, although it produced some crystalline defects in the films. Concerning the size of SOI patterns, a two-dimensional array of small SOI patterns, each of which is surrounded by seed stripes, was found much more effective to increase the total subboundary-free area than that of larger SOI patterns. From these results, an optimum oscillation waveform was synthesized by combining the triangular and sinusoidal waveforms, so that the trailing edge of the molten zone became straight. Then, in order to minimize generation of {111} facets at the L-S interface which is known to be the origin of subboundaries, the pseudoline beam was swept in the 〈110〉 direction as a whole. As a result, a 150-μm-square SOI region or 5×7 array of 50-μm-square SOI regions was recrystallized by a single sweep without generation of subboundaries.