THE FORMATION OF EPITAXIAL COSI2 THIN-FILMS ON (001) SI FROM AMORPHOUS CO-W ALLOYS

A novel way of forming predominantly epitaxial CoSi2 on (001) Si from an amorphous Co-W alloy layer on Si is explained. Auger electron spectroscopy depth profiling, Rutherford backscattering spectrometry and X-ray diffraction have been used to investigate the interaction between the amorphous alloy and Si. An alloy composition of Co60W40 was chosen which has a crystallization temperature of about 850-degrees-C. By employing anneals below 600-degrees-C, Co diffuses out of the alloy into the substrate to form CoSi2. After the anneal, the remaining amorphous alloy could be selectively removed from the underlying CoSi2 film by wet-chemical etching. X-ray diffraction measurements indicated that about 75% of the disilicide film has an epitaxial relationship with the Si substrate while the other 25% has a simple twin relation with the majority of the material. The formation mechanism of CoSi2 from an amorphous alloy on Si is discussed.