Microstructure and Properties of CoSi 2 Thin Films on (100) Silicon By Laser Physical Vapor Deposition
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MICROSTRUCTURE AND PROPERTIES OF CoSi 2 THIN FILMS ON (100) SILICON BY LASER PHYSICAL VAPOR DEPOSITION P. TIWARI, R. CHOWDHURY, AND J. NARAYAN Department of Materials Science and Engineering North Carolina State University, Raleigh NC 27695-7916. ABSTRACT Laser physical vapor deposition (LPVD) has been used to deposit thin CoSi 2 films on (001)silicon at different substrate temperatures ranging from room temperature to 600'C. Particulate-free silicide thin films were characterized by X-ray diffraction, Rutherford backscattering, and high resolution transmission electron microscopy. We have found that films deposited at 200'C and below are amorphous; 400*C deposited films are polycrystalline whereas films deposited at 600'C are of epitaxial nature. The Effect of subsequent annealing on resistivity of room-temperature deposited thin films has been investigated. The resistivity value decreases to less than 15 ýLtfcm after annealing making these films suitable for microelectronics applications. The correlation between microstructure and properties of these films are discussed. INTRODUCTION In the present IC technology, metal-semiconductor contacts are extensively used for fabricating fast-switching Schottky rectifiers, low-resistance interconnects and ohmic contacts, and as gates for advanced semiconductor devices [1]. Due to device scaling, RC delays associated with commonly used poly-Si for interconnections is one of the major limitations to the performance of VLSI circuits. Use of refractory silicides of transition metals instead of conventional metallization schemes allows formation of interconnects with relatively low electrical resistivity [2]. Additionally, they offer advantages of withstanding oxidizing ambients and chemical reagents at higher temperatures [3,4]. Several techniques for film deposition of silicides have been studied including sputtering with silicide targets [5], coevaporation and/or cosputtering of elemental Si and transition metals [6-8]. A number of investigations have been carried out to characterize various silicide thin films fabricated by the above techniques for various VLSI applications. However, most of these techniques require either a high temperature deposition or high temperature annealing in order to obtain desired silicide phase, resistivity and stoichiometry. This poses a problem for shallow junction VLSI applications where a high-temperature post-metallization step leads to dopant redistribution. Recently Tiwari et al. [9] used laser physical vapor deposition (LPVD) to obtain textured and epitaxial films of TiSi 2 and CoSi 2 on p-type Si at lower temperatures. The electrical resistivity of these films was comparable to the values listed in the literature for these silicides formed by other conventional methods [101. The silicide/Si interface was found to be smooth. In this paper, we report deposition of CoSi 2 thin films on Si (100) by LPVD technique at a series of deposition temperatures (25-600°C). The LPVD deposition at roomtemperature resulted in an amorphous phase of CoSi
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