A Comparative Evaluation of Different Test Structures for the Extraction of Ultralow Specific Contact Resistivity: A Review

Contact resistance (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>c</i></sub><roman xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">)</roman> constitutes a significant portion of the ON-state resistance in advanced complementary metal-oxide-semiconductor (CMOS) transistors. The reduction of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>c</i></sub> presents a critical challenge with the ongoing miniaturization of CMOS devices, making the reduction of specific contact resistivity (ρ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>c</i></sub><roman xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">)</roman> increasingly imperative. As ρ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>c</i></sub> values have been driven down to the sub-10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-<roman>9</roman></sup> Ω-cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>2</roman></sup> range, the accurate and reliable extraction of such ultralow ρ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>c</roman></sub> necessitates the development of advanced test structures. In this review, the conventional transmission line model (TLM) and circular TLM (CTLM) test structures are examined in detail. Furthermore, multiring CTLM (MR-CTLM) test structure based on CTLM is discussed. Then, several modified test structures derived from TLM are explored, including refined TLM (RTLM), ladder TLM (LTLM), and refined LTLM (R-LTLM), with a particular focus on the reduction or elimination of parasitic metal resistance. In addition, an experimental comparison of these various TLM-based test structures is provided. Moreover, many modified test structures that address other parasitic parameters are also demonstrated.