A Test Structure to Characterize Nano-Scale Ohmic Contacts in III-V MOSFETs

We propose and demonstrate a novel test structure to characterize the electrical properties of nano-scale metal-semiconductor contacts. The structure is in essence a two-port transmission line model (TLM) with contacts in the nanometer regime. Unlike the conventional TLM, two types of Kelvin measurements are possible. When performed on devices with different contact spacing, this allows the extraction of the contact resistance, the semiconductor sheet resistance, and the metal sheet resistance. For this, a 2-D distributed resistive network model has been developed. We demonstrate this technique in Mo/n(+)-InGaAs contacts with contact lengths from 19 to 450 nm where we have measured an average contact resistivity of 0.69 +/- 0.3 Omega.mu m(2). For relatively long contacts (> 110 nm), this corresponds to an extremely small contact resistance of 6.6 +/- 1.6 Omega.mu m.