Control of scanning beam interference lithography by real-time compensation of scan angle error through acousto-optic modulation and phase-shift grating interferometry for large area nanostructuring

In scanning beam interference lithography (SBIL), increasing the size of overlapped beams can save time and costs during manufacturing and provides a more uniform distribution of light energy during the exposure step, leading to higher process stability. However, when the scan angle errors become significant, problems arise, such as reduced contrast due to smearing and decreased pattern accuracy as the beam size increases. In this study, we propose a design methodology for scan angle error correction control for true parallel scanning. The direction of the interference pattern is determined using a reference grating and a high-resolution rotary stage. An acousto-optic modulator is used to measure the phase shift of the reference grating through the movements in the scan direction to quantify the scan angle errors. We derive equations that describe the relationship between the scan angle error and the control input of piezo mirrors, resulting in the development of a beam rotation system capable of rotating the interference pattern by a minimum of 0.83 µrad. To validate the scan angle error-compensating SBIL system, we fabricated photoresist nanopatterns on a 4-inch wafer using an expanded beam. By expanding the beam, we successfully achieved a significantly smaller error tolerance of only 3.57 µrad, surpassing the performance of conventional SBIL systems and improving the throughput by more than two-fold, thus demonstrating a remarkable enhancement in efficiency.