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 dilu te I-IF-dipped Si(100) substrate. The multilayer system was then subse quently 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 amorphiza tion reaction. These interfacial layers evolved into a Co-Ti(O)-Si amo rphous alloy which functioned as a diffusion membrane which controlled the phase formed during subsequent annealing. The Co-silicide phase s equence was CoSi2 --> Co2Si --> CoSi, and finally CoSi2 from 550 degre es 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 su bstantially during the high temperature second annealing. The resultin g epitaxial CoSi2 layer exhibited superior thermal stability and a res istivity as low as 15 mu Omega-cm, even for nanoscale thicknesses. Int erface impurity cleansing by Ti, uniform and slow Co supply through th e interfacial amorphous membrane, and a positive effect of the capping layers throughout the process promoted preferential (311) CoSi format ion and subsequent epitaxial CoSi2 growth.