Ohmic contacts in semiconductor devices are typically quantified by their contact resistance [R_c (Ω)]. In researching such contacts, the more appropriate parameter for comparing two-layer contacts is the geometry independent interfacial resistance parameter termed specific contact resistivity [ρ_c (Ωcm²)]. Various test structures have been employed to determine ρ_c, and Cross Kelvin Resistor (CKR) test structures are most suitable for estimating low ρ_c values. The value determined by CKRs includes parasitic resistances that have been difficult to account for when ρ_c is small. In this paper, an analytical technique for determining the parasitic resistance for particular CKR designs is presented. Finite element modeling (FEM) and experimental results for metal to silicide contacts will be used to validate the analytical expressions; and silicides have been incorporated in the designs as they are used in CMOS technology and contribute to the low ρ_c values.

This paper describes an analytical model for circular contacts based on Bessel function expressions. Using several contacts of different diameter (d) with d/w < 0.4 (w is the width of the CKR arms), the parasitic resistance can be accurately accounted for by extrapolation of experimental data to d/w → 0. This model assumes that the concentric equipotential contours around the contacts extend to the voltage tap. CKR structures with the same geometry were modeled using FEM and the results for both the analytical and FEM models were in agreement for ρ_c values as low as 1×10^-9 Ωcm². FEM contour plots show that the equipotentials are circular around the contact and the value on the tap closely approximates to that obtained using the Bessel function expressions.

Experimental results for ρ_c will be presented for aluminium to titanium silicide contacts. These demonstrate that the technique is reliable for determining low values of ρ_c; and a value of 8×10^-10 Ωcm² was obtained for these contacts using the proposed method.

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