Transmission line model test structure with four or more terminals: a novel method to characterize non-ideal planar ohmic contacts in presence of inhomogeneities

The most widely used test procedures for electrical contact characterization are the Kelvin cross bridge resistor method, the transmission line model (TLM) test structure and their combination, which produces a six-terminal Kelvin structure. These structures measure the specific contact resistance (contact resistivity) and the semiconductor sheet resistance beneath the contact. A modified TLM structure combined with a particular evaluation method makes it possible to use the TLM method on wafers with high levels of inhomogeneities. The two independent procedures used to derive the modified method are statistical simulation and propagation of error. Statistical modeling and experimental data show that if inhomogeneities are present, electrical contact parameter extraction by conventional TLM test structures results in large errors or does not yield results at all. However, the errors in the extracted parameters can be reduced considerably using the modified TLM test method with four terminals and a data extraction method. When five terminals are used, the accuracy of the parameter extraction can also be determined by a single structure allowing separation of the die-level and wafer-level inhomogeneities.<
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