Variations Of Fractal Dimension During the Phase Transformation To The Silucide Nucleation in Thin Film Systems
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VARIATIONS OF FRACTAL DIMENSION DURING THE PHASE TRANSFORMATION TO THE SIlUCIDE NUCLEATION IN THIN FILM SYSTEMS NAM-LHN CHO* AND i. GIN NAM** * Department of Electronic Enginering, Sung Hwa University San 7, Galsan 1-ri, Tangjeong-myun, Asan-goon, Chungnam Republic of Korea 337-840 ** Semiconductor Technology Division, Electronics and Telecommunications
Research Institute, Daedog P.O. Box 8, Daejeon Republic of Korea 305-606
ABSTRACT Detailed relationship between the fractal dimension and the excess noise frequency exponent has been considered for metal-silicon interfacial structures during the phase transformation to the initial compound phase formation in thin film systems. In the estimation of the fractal dimension of the thin film structures, a technique has been used, which basically employs a digital image processing of highly magnified micrographs of the structures. Previously measured frequency exponent data of the excess noise power spectral density for the same thin film systems has been interpreted by introducing a multiplication process which combines the fractal dimension variations and cluster interactions of the interfaces. It has been assumed that the fractal dimension plays a role as a multiplication factor in the multiplication process. BACKGROUND Silicides are formed by a solid state reaction at interfaces between metal
films and silicon substrates. The application areas of the silicides have become significantly expanded in microelectronic technologies as ohmic contacts, diffusion barriers, and gate electrodes, since recent trends in VLSI/LSI devices are toward large circuit packing density and multilevel interconnections. Metal-silicon interfacial reactions have been extensively studied using various experimental techniques [1-2], and rules to redict the first silicide phase and subsequent phases have been suggested 3-4]. The rules are based on an assumption that glass structures are initially formed at the interface when the metal/silicon system is brought to a supercooled state. The glass layers are thought to be kinetically controlled and thus the nucleation of silicide phases would also be determined by kinetics rather than energetics in the interfacial layer [5]. The electrical properties of the first silicide phase in the specific metal/silicon interface could be improved by modifying the interfacial glass structure during the device fabrication process. The possibility of the modification has been achieved with changing the device processing conditions such as adding chemical species during metal deposition or varying metal-silicon coevaporation ratio [6-71. The structural analysis of the different glass structures in the metal/silicon interfaces is of particular importance in order to know effective ways for more reliable VLS/ULSI metallizations on the silicon devices. Excess noise power spectral density of the interfacial glass structures have been previously measured for nickel and cobalt thin films evaporated on silicon substrates along the reaction path to the first compound nucl
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