Large Area Subgrain-Boundary-Free SOI Induced by Thermal Gradient Control of Transitional Seeded-Growth
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LARGE AREA SUBGRAIN-BOUNDARY-FREE TRANSITIONAL SEEDED-GROWTH
SOT INDUCED BY THERMAL GRADIENT CONTROL OF
El-Hang Lee, Monsanto Electronic Materials Company, MO, 63376
P.O. Box 8,
St. Peters,
ABSTRACT The transitional region of subgrain-boundary-free crystal to subgrain-boundary-laced crystal formed during the initial stage of energy-beam induced seeded recrystallization of thin film silicon on an insulator has been examined to study the primary cause of subgrain boundary formation and the conceptual basis of its suppression. Observations include the systematic variation of: facet, cellular, and dendritic features; subgrain boundary directions and spacings; and the stable growth distance as a function of silicon film thickness and energy beam density. A temperature gradient argument based on constitutional supercooling theory has been used to explain these observations. There are indications that an increased thermal gradient at the solidification front can suppress the onset of growth instability for large area, defect free growth of SOT.
INTRODUCTION One of the most popular techniques to produce large area, oriented single crystal thin film silicon on insulating substrates in recent years has been the energy-beam induced seeded-growth method [1]. In this technique a graphite strip heater, arc lamp, laser beam, or electron beam creates a silicon molten zone which moves from a seed area to the siliconon-insulator area. The seeded growth is normally smooth up to 20Pm-lOOlm from the seed, but the growth abruptly breaks down into a set of defects, called low angle subgrain boundaries which occur extensively throughout the recrystallized film. There have been valuable efforts to understand [2] and control [3] the subgrain boundaries. However, the subject still requires a more complete and fundamental understanding for their ultimate prevention. As a part of this effort, Lee [4,5] recently pointed out the importance of understanding the transition region between the subgrain-boundary-free growth and the subgrain-boundary-laced growth, particularly from the growth stability point of view. The understanding of this transition may provide two aspects of subgrain-boundary-related information: 1) a clue to the cause of subgrain-boundary-formation, and 2) the conditions to allow its suppression. Morphological and thermodynamic analyses of growth features in this region have provided some conceptual framework for large area, subgrain-boundary-free growth of Silicon on Insulator (SO1). EXPERIMENTAL DESCRIPTION The growth features formed on small size (
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