GROWTH OF SINGLE-CRYSTALLINE COSI2 ON (111)SI AT LOW ANNEALING TEMPERATURES BY A NONULTRAHIGH VACUUM METHOD

Abstract

By reducing the thickness of the deposited cobalt film, high-quality single-crystalline CoSi2 phase with a sheet resistivity as low as 15-mu-OMEGA cm has been achieved. A deposition of 3 nm thick cobalt film on (111)Si substrate and a subsequent rapid thermal annealing (RTA) at 500-degrees-C were used. From the examinations of transmission electron microscopy (TEM), the single-crystalline CoSi2 structure was identified as type B orientation. As far as the authors are aware of, such an annealing temperature is the lowest for the solid phase growth of single-crystalline CoSi2 on the silicon substrate in the nonultrahigh vacuum (non-UHV) deposition and annealing systems. Hence, the deposition of thinner cobalt film on the silicon substrate would be favorable to the formation of polycrystalline CoSi2 grains and the growth of single-crystalline CoSi2 structure. It is attributed to the promoting ratio of interface energy and the smaller preliminarily-formed CoSi2 grains. No facet was observed for all samples annealed at 500-degrees-C. It indicates that a smooth single-crystalline CoSi2/Si interface is formed. Annealing at 450-degrees-C yielded coexisting polycrystalline and epitaxial CoSi2 phases. The samples annealed at 700-degrees-C would exhibit a highly strained single-ctystalline CoSi2/Si interface. Furthermore, annealing at 900-degrees-C would generate large pinholes in the CoSi2 crystal to relieve the interface free energy. Sheet resistance results and current-voltage characteristics of these specimens were measured and well correlated with the TEM observations.