Silicon-Sapphire Interface: A High Resolution Electron Microscopy Study
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and Tan,
eds.
285
Defects in Semiconductors
SILICON-SAPPHIRE INTERFACE: A HIGH RESOLUTION ELECTRON MICROSCOPY STUDY
FERNANDO A. PONCE Hewlett-Packard Laboratories,
Palo Alto,
California, USA
ABSTRACT The structure of the silicon-sapphire interface of CVD silicon on a (1i02) sapphire substrate has been studied in cross section by high resolution transmission electron microscopy. Multibeam images of the interface region have been obtained where both the silicon and sapphire lattices are directly resolved. The interface is observed to be planar and abrupt to the instrument resolution limit of 3 A. No interfacial phase is evident. Defects are inhomogeneously distributed at the interface: relatively defect-free regions are observed in the silicon layer in addition to regions with high concentration of defects.
INTRODUCTION The silicon on sapphire technology has several applications in microelectronics owing to the good insulation of the substrate with the consequent High speed field effect devices reduction in overall parasitic capacitances. and complementary circuits can be fabricated with the added advantage of low Some inherent difficulties exist, however, which manifest power consumption. It is themselves as low MOS channel mobilities and large leakage currents. thought that these difficulties stem from the highly defected nature of the silicon layer. It is therefore desirable to understand the origin and nature of these structural defects and the possible effects on the electrical behavior of the material. The nature of the silicon-sapphire interface has been the subject of several studies. Heiman [1] suggested the existence of a thin glassy layer at the Kohl [2] interface in order to explain the appearance of donor surface states. and Schlotterer [3] interpreted optical interference experiments by postulating the existence of an intermediate layer with a 9 omposition similar to aluminum SIMS measuresilicates and a thickness between 200 and 400 A at the interface. ments were used in support of the transition layer model showing a continuous variation in the aluminum composition in the vicinity of the interface Cullen [5] and Trilhe [6] associated this transition layer (u 500 A) [3-6]. with the thickness necessary to achieve complete coverage of the substrate surface. Observations of the defect structure by transmission electron microscopy (TEM) have been reported [7-9] which indicate the presence of large densities Abrahams and Buiocchi [7] of stacking faults and twins in the silicon layer. reported no evidence for the presence of an aluminum-bearing phase in the proximity of the interface but without reference to the resolution of their technique. In this paper, results from a high resolution TEM study of the siliconLattice images have been obtained where the sapphire interface are presented. lattice structure of both silicon and sapphire regions are resolved in crosssection to a best resolution of about 3.0 A.
286 EXPERIMENTAL ASPECTS The material under study is heteroepitaxial [001] silicon grown on a
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