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Analytical and finite element modelling of an ohmic contact test structure for low specific contact resistivity

Anthony S. Holland ,  Geoffrey K. Reeves ,  Madhu Bhaskaran ,  Sharath Sriram 

RMIT University, Sch. of Elec. and Comp. Engg., Microelectronics and Materials Technology Centre (RMIT), GPO Box 2476V, Melbourne, Victoria, Melbourne 3001, Australia


Ohmic contacts in semiconductor devices are typically quantified by their contact resistance [Rc (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 [ρc (Ωcm2)]. Various test structures have been employed to determine ρc, and Cross Kelvin Resistor (CKR) test structures are most suitable for estimating low ρc values. The value determined by CKRs includes parasitic resistances that have been difficult to account for when ρc 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 ρc 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/w0. 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 ρc 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 ρc will be presented for aluminium to titanium silicide contacts. These demonstrate that the technique is reliable for determining low values of ρc; and a value of 8×10-10 Ωcm2 was obtained for these contacts using the proposed method.


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Related papers

Presentation: Poster at E-MRS Fall Meeting 2007, Symposium G, by Madhu Bhaskaran
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-06 00:11
Revised:   2009-06-07 00:44