6.1 OVERVIEW

Metal silicides have many desirable properties such as high melting temperature, superb thermal stability and low resistivity [1]. These characteristics have made metal silicides more and more popular in VLSI process applications. For instance, WSi ₂ is commonly used in poly gate to lower the contact resistance and form ohmic contact [2], whereas TiSi ₂ is often used in IC fabrication to reduce the resistance between the source, drain and the metal layer that is, the so-called silicide reaction [3, 4].

Silicon possesses top quality, inexpensive and easy-to-use native oxide. Nevertheless, it is an indirect bandgap material, making it difficult to produce devices high in illumination efficiency. Hence, silicon-based semiconductors have always been outperformed by III V compound semiconductors in the field of opto-electronics. Equipped with a direct bandgap, compound semiconductors can be applied in illuminating devices such as light emitting diodes (LEDs), laser diodes (LDs) and vertical cavity surface emitting laser (VCSEL). Their exceptionally high electron mobility makes them ideal materials for high-speed devices such as high electron mobility transistor (HEMT) and heterojunction bipolar transistor (HBT). The different lattice constants of compound semiconductors and silicon have prevented the integration between illumination devices made of compound semiconductors and silicon wafers. Fortunately, findings over the past decade have offered some hope. In addition to their known qualities of high melting temperature, superb thermal stability, low resistivity and high Schottky barrier height, silicides including Cr _xSi _y,Mn _xSi _y and Fe _x