Improved electrical and thermal properties of nickel silicides by using a NiCo interlayer

We have investigated the effects of a NiCo interlayer on the electrical and thermal properties of nickel silicide as a function of the annealing temperature. For the interlayered samples, 3 nm-thick NiCo(10 at.% Co) films are electron-beam evaporated on Si substrates, on which 27 nm-thick Ni films are deposited without breaking the vacuum. It is shown that all the samples exhibit a distinctive increase in the sheet resistance at temperatures above 900 ^{{ring operator}}C. However, the NiCo interlayer sample produces the lowest sheet resistance at 900 ^\circC. X-ray diffraction results show that the Ni only and NiCo interlayer samples produce NiSi and NiSi₂ phases, while NiCo full samples give NiSi and Ni_1-xCo_xSi₂ phases. Scanning electron microscopy results exhibit that for all the samples, the surfaces become degraded with numerous arbitrarily-shaped spots, corresponding to areas uncovered by the silicides. The areal fractions of the silicides for the Ni only, NiCo full, and NiCo interlayer samples are about 57%, 72%, and 81%, respectively. The temperature dependence of the electrical properties of the silicide samples is explained in terms of the formation of resistive phases and the agglomeration of the silicide.