HREM Study of Al-Si Interfaces
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HREM STUDY OF Al-Si INTERFACES MOHAMMAD SHAMSUZZOHA,* PIERRE A. DEYMIER,* AND DAVID J. SMITH** *Department of Materials Science and Engineering, University of Arizona, Tucson, AZ 85721 **Center for Solid State Science, Arizona State University, Tempe, AZ 85287
ABSTRACT Interfaces between aluminum and silicon in samples prepared by solidification of an Al-Si eutectic liquid have been studied by high-resolution electron microscopy. The Al and Si grains have a common [110] axis with a misorientation between grains of 70.5', thus aligning the (lll)si plane with the ("14)I plane. In general, the interfaces have a complex structure with numerous interfacial dislocations and considerable facetting. The core structures can be characterized in terms of structural unit models. The nature of the facetting has also been investigated, in particular one facet which lies approximately along the ("'i)A, and (li5)si planes and another which lies approximately along the (ClO)A4 and (li4)si planes.
INTRODUCTION Heterophase boundaries between elemental metals and semiconductors are an important part of next generation integration of microelectronic devices, and yet relatively few studies have been directed towards a knowledge of the atomic structure of such interfaces [1,2]. Theoretical work concerning interface structures has largely centered around the geometrical modelling of interfaces between the same species of materials [3-5] and therefore lacks predictive power regarding interface structure between dissimilar materials. It is thus obvious that experimental observations are the key to an understanding of the nature and character of these heterophase boundaries. Unidirectionally solidified Sr-modified Al-Si eutectic alloys are known to exhibit a strong texture for the aluminum phase along their transverse section [6]. The silicon phase is fibrous in morphology and exhibits a fiber axis anywhere between and . Such alloys may possess adjacent aluminum and silicon grains with zone axes closely parallel to and therefore they may provide an opportunity to study the atomic stucture of boundaries between metal and semiconductor. Accordingly, we have initiated a program to achieve such interfaces using directionally solidified eutectic of the binary aluminum-silicon system. This paper describes the high resolution imaging of atomic structures observed at Al-Si interfaces.
EXPERIMENTAL Alloys of eutectic composition (12.7 wt% Si) were vacuum cast from silicon of 99.999% purity and aluminum of 99.90% purity. The chief impurity in the aluminum was found to be 0.09% Sr. The cast billets were swaged to 5 mm or less diameter rods and then remelted and unidirectionally solidified at a rate of 50 pms"1. The thermal gradient at the solid-liquid interface was determined by prior calibration of the furnace apparatus. Transverse section specimens taken from near the center of the solidified samples were used for thin foil preparation. The thin foil specimens were prepared by a method described elsewhere [6], using electropolishing followed by io
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