STATISTICAL MODELING OF TRANSMISSION-LINE MODEL TEST STRUCTURES .2. TLM TEST STRUCTURE WITH 4 OR MORE TERMINALS - A NOVEL METHOD TO CHARACTERIZE NONIDEAL PLANAR CONTACTS IN PRESENCE OF INHOMOGENEITIES

Extraction of electrical contact parameters by conventional transmission line model (TLM) test structure leads to large errors or yields no results at all, if the three contacts of the structure are not identical (i.e., inhomogeneities within the test structure are present). In this paper, a modified transmission line model (redundant TLM or RTLM) test structure (with four or more terminals) and a novel data extraction method are suggested to improve the accuracy of the method. Statistical modeling by both statistical simulation and the method of error propagation shows that with four terminals and independently known sheet resistances between the contacts, the errors of the extracted parameters can be reduced considerably. With the use of five or more terminals, the accuracy of the parameter extraction can also be determined by a single structure, allowing the separation of inhomogeneities within a test structure from the inhomogeneities over the wafer. Experimental data gathered by Kelvin cross-bridge resistors and by traditional and modified transmission line model structures on Al-Si-Cu/TiW/p-n Si contacts clearly show the advantage of the RTLM method over the traditional TLM method. On a wafer with small inhomogeneities, both methods gave consistent results. On an inhomogeneous wafer, while the TLM method yielded results on only 4, the RTLM method yielded results on 18 out of a total of 20 sites. © 1990 IEEE