Work

Effective mid-range correction for improving spatial gap uniformity in dense TLM structures on InP substrates

Year: 2026

Type: article

Abstract: Accurate extraction of ultralow contact resistivity has become increasingly challenging for advanced InP-based device technologies, where specific contact resistivity values have already reached the low-10 −8 Ω·cm 2 regime. To improve the reliability of transmission line method (TLM) measurements under these conditions, narrow-gap TLM structures with sub micrometer spacing are required. However, in large-area dense TLM layouts on InP substrates, maintaining spatially uniform gap dimensions using conventional electron-beam lithography proximity effect correction (PEC) remains difficult. In this work, the spatial gap non-uniformity of dense narrow-gap TLM structures fabricated on InP substrates was systematically investigated. Despite PEC calibration, significant center-to-edge gap-width variations were observed in extended dense TLM layouts. Finite-element simulations demonstrated that local gap narrowing induces current crowding and compromise contact-resistivity extraction accuracy. To address this limitation, an effective process-induced mid-range correction term was introduced into the PEC workflow. The correction significantly improved spatial gap uniformity. The extracted effective mid-range length scale was approximately 7 μm. Using the optimized correction parameters, reproducible fabrication of TLM structures with gap sizes down to 0.25 μm was achieved on InP substrates. The proposed approach demonstrates that local critical-dimension control alone is insufficient for reliable dense-layout fabrication and provides a practical correction strategy for improving spatial uniformity in scaled TLM structures on high-Z substrates.

Source: Micro and Nano Engineering

DOI: 10.1016/j.mne.2026.100390