TEM Study of a RTO Oxide-Interfacial Layer on Epitaxial-Cobalt Silicide (CoSi2) Formation

Abstract

Metal silicides have been used for some time as a contact diffusion barrier. CoSi2 has been attracting a lot of interest due to its low sheet resistance, thermal stability, low stress state and interfacial uniformity with the silicon substrate. Recently, there has been many studies to investigate the growth of epitaxial CoSi2 on Si using a interlayer material such as Ti (TIME) and SiOx (OME).

In this project, transmission electron microscopy (TEM) technique has been used study a Ti-capped oxide mediated epitaxy (OME) process, where the oxide interlayer is grown by rapid thermal oxidation (RTO), and the anneal is done by rapid thermal annealing (RTA).

Void formation in the CoSi2 film has been observed above the RTA temperatures of 660?C. The voids extend into Si, indicating some Si out-diffusion. The CoSi2 / Si interface is also rough and non-uniform. There is some local epitaxy of CoSi2 on Si. The epitaxial orientation is (001)CoSi2

(001)Si and [100]CoSi2

[100]Si. A combination of the interfacial stresses between the oxide and Si interface, bond energies between SiOx-Si, different stoichiometry of the RTO oxide, ramp cycles in the RTA, difference in coefficient of thermal expansion between CoSi2 and Si, local enhancement of the out-diffusion of Si, and lattice mismatch between CoSi2 and Si could be the cause for the voiding.

This TEM study was done in the FA lab of Chartered Semiconductor Manufacturing Ltd.