Cr75Si25 thin films-Temperature dependence of electrical properties and microstructure
Abstract
Electrical and microstructural changes of Cr75Si25 thin co-evaporated alloy films have been studied as a function of temperature from room temperature to 950°C. In situ resistivity measurements, hot stage transmission electron microscopy, Rutherford backscattering spectroscopy, Seeman-Bohlin and Bragg-Brentano X-ray diffraction methods were applied. The observed two-stage decrease in resistivity, abrupt and then gradual, is associated with "primary" and "secondary" crystallization processes. In the "primary" stage the major portion of the amorphous film crystallizes. In the "secondary" stage the amorphous residue crystallizes. After the crystallization process is completed, a nonlinear, irreversible increase in resistivity, above 670°C, resulting from thermal grooving at grain boundaries, has been observed. Heating to high temperatures also generates mixed preferred orientation. The mechanism of crystallization is random nucleation and quasi-isotropic growth, but the process is primarily nucleation controlled. In the isothermal transformations near 300°C the "secondary" crystallization was not observed, nor was the preferred orientation. A good linear fit between the resistivity and the isothermally transformed volume fraction was found only up to 0.35. For higher values deviation from linearity was noted, which results from the formation of continuous conducting paths along crystallized particles. The isothermal transformations follows a sigmoidal curve. The apparent activation energy of crystallization was found to be 2.71 eV. The mode parameter, n, was found to change from ~2 for films between 500 and 1650 Å thick to ~3 for films of 3000 Å in thickness indicating a change from the two dimensional to the three-dimensional mode of transformation. © 1986.