The barrier effect of a W_xTa_((1-x)) nanolayer on formation of single-texture CoSi_2 on Si(100)

摘要

We have studied the phase formation of a CoSi_2 layer by solid-state reaction of ternary Co/W_xTa_((1-x))/Si(100) systems. The effect of cosputtered W_xTa_((1-x)) nanometric interlayers, with different values of x (0, 0.25, 0.5, 0.75 and 1), on the degree of texturing of a CoSi_2 layer and disilicide formation of the refractory metals has been investigated. The annealed samples, in a temperature range of 400-1000℃, were analysed by x-ray diffraction, sheet resistance measurement, scanning electron microscopy, and energy-dispersive x-ray techniques. Using W_(0.25)Ta_(0.75) and W interlayers, the best (100) texture of the CoSi_2 layer with a thermal stability in the range of 900-1000℃ was produced. In the Co/W/Si system, a considerable amount of WSi_2 is formed as a cap layer, while a nearly negligible amount of refractory metal disilicide is formed in the Co/W_(0.25)Ta_(0.75)/Si system. Study of the growth kinetics shows that the activation energies of CoSi_2 formation in these two systems are greater than those of other thermally stable systems. The mechanism of single-texture formation of a nanothickness CoSi_2 layer has been explained on the basis of controlling Co-Si interdiffusion via the intermediate layers.