Throughput optimization of electron-beam lithography in photomask fabrication regarding acceptable accuracy of critical dimensions

摘要

The cost of creating a photomask with an electron-beam lithography is determined mainly by the writing time. The writing speed is limited by the resist heating distortions. The local temperature in the area of an e-beam may rise up to a few hundred degrees C, leading to critical dimensions (CD) distortion. It is possible to decrease the temperature by decreasing the beam current density, or flash size, or by applying multipass exposure; however, this increases the writing time. This paper presents an approach on how to optimize exposure parameters to keep the temperature rise within an acceptable range, and at the same time increase writing speed as much as possible. Beam current density, number of passes, and pattern coverage were examined. A commercially available TEMPTATION (Temperature Simulation) software tool was used for simulations. A writing strategy and parameters of a 50 kV variably shaped beam system were considered. This allowed us to maximize the throughput of photomask fabrication while keeping CD distortion within error budget.