Current-voltage characteristics of silicon metallic-silicide interfaces

Abstract

The general quantum and electronic theory of the metal-semiconductor contacts, proposed in previous works, is applied to silicon-metallic silicide interfaces in order to calculate their current-voltage characteristics. The analysis takes into account the actual potential profile due both to the semiconductor depletion layer and to the electric dipole created, around the metal-semiconductor interface (MSI), by the quantum mechanical tunneling of the metal free electrons into the semiconductor and by the metal conduction band bending. The current across the MSI, ascribed to the thermionic assisted tunneling, is calculated by taking into account the anisotropy of the effective masses, the many valley-structure of the semiconductor energy bands and the quantum mechanical reflection and tunneling through the energy barrier by means of the generalized transmission probability of Kemble. The results shown by the analysis, which excludes explicity the image-force lowering of the energy barrier height, are the reduction of the height and width of the barrier itself and (hence) the increase of its “transparency” to the thermionic current produced by the increase of the reverse bias voltage and/or of the semiconductor impurity concentration. The effects of such properties of the energy barrier on the current-voltage characteristics of the MSI are the absence of a true reverse saturation current, an ideality factor n greater than 1 and a value of the energy barrier height, deduced from the forward current-voltage characteristics, lower than that true and than that obtained from the measured of the junction capacitance vs the bias voltage. The analysis, applied to interfaces between n-type silicon and the metallic silicides RhSi, ZrSi 2, PtSi and Pd 2Si, yields numerical values which agree well with the experimental ones obtained by several authors on the same contacts which, when it is necessary to eliminate field-enhancement at the electrode periphery and leakage currents, incorporate a guard ring. Effectively such a guard ring and the absence of intervening layers of oxide and of other contaminants in the silicon-metal silicide contacts allow one to acquire experimental data more easy to interpret quantitatively than those relative to other contact types.