Thermal-flow techniques for sub-35 nm contact-hole fabrication using Taguchi method in electron-beam lithography

In this article, we demonstrate that 100 nm contact-hole resist patterns can successfully and reliably be shrunk to 35 nm after a thermal-flow procedure using Taguchi method. Many critical factors such as structure, thermal-flow baking temperature, baking time period and exposure dwell time affecting the critical dimensions (CDs) were optimized and discussed. The experiments were conducted using Taguchi method orthogonal array (OA) and the optimal thermal-flow parameter settings were determined by signal/noise ratio (SNR) and ANOVA analysis. The experimental results show that the most important factor in thermal-flow procedure is the baking temperature. The optimal parameter settings were Si/SiO2 with thick resist, 155°, 180 s and 6 μs. Experiment results found that higher temperature provided larger shrink ratio but it cannot higher than 160°. It is also noted that the proposed approach was reproducible due to the confirmation experiments SNRs within the 95% confidence interval. For pattern-uniformity study, the contact-hole profiles appear significantly indifferent after the thermal-flow process as distributed on five different locations and two spacings.