INTERDIFFUSION, PHASE-TRANSFORMATION, AND EPITAXIAL COSI2 FORMATION IN MULTILAYER CO/TI-SI(100) SYSTEM

Interdiffusion, phase transformation, and epitaxial CoSi2 formation in a Co/Ti multilayer-Si(100) system have been investigated. Evaporated and sputtered Co/Ti multilayers were deposited on RCA-cleaned and dilute I-IF-dipped Si(100) substrate. The multilayer system was then subsequently heat-treated by a two-step annealing process. An initial Ti(O) amorphous layer formed due to oxygen/carbon incorporation during the deposition, or a TiSi, amorphous layer formed by solid-state amorphization reaction. These interfacial layers evolved into a Co-Ti(O)-Si amorphous alloy which functioned as a diffusion membrane which controlled the phase formed during subsequent annealing. The Co-silicide phase sequence was CoSi2 --> Co2Si --> CoSi, and finally CoSi2 from 550 degrees C to higher temperature. Preferentially oriented (311) CoSi formed as the dominant phase in the temperature range from 650 to 800 degrees C. Epitaxial CoSi2 nucleated from the CoSi template layer and grew substantially during the high temperature second annealing. The resulting epitaxial CoSi2 layer exhibited superior thermal stability and a resistivity as low as 15 mu Omega-cm, even for nanoscale thicknesses. Interface impurity cleansing by Ti, uniform and slow Co supply through the interfacial amorphous membrane, and a positive effect of the capping layers throughout the process promoted preferential (311) CoSi formation and subsequent epitaxial CoSi2 growth.