Enhanced transmission line model structures for accurate resistance evaluation of small-size contacts and for more reliable fabrication

Abstract

Two new transmission line model (TLM) techniques are presented, The first structure, LT-TLM, provides very accurate determination of the transfer length LT (within 5%) and the contact resistivity /spl rho//sub C/ (within 12%) of lateral contacts, as compared to typical errors of 30% and 50%, respectively, for conventional TLM patterns, accurate determination of these quantities is important for the optimal design of small lateral contacts in high-performance devices, such as heterojunction bipolar transistors (HBTs). The second structure, a modified concentric TLM pattern, provides the same results as conventional TLM patterns; however, they do not require mesa isolation, and they can be fabricated extremely reliably. In contrast, conventional concentric TLM patterns are often shorted together or distorted by lift-off metallization processes. Both theoretical analysis and experimental verification with analysis of the accuracy of the extracted data is presented for each technique, demonstrating the advantages of these approaches.