Hardware optical correlation method for dynamic detection of micrometer gaps with sub-nanometer resolution.

Abstract

Surface plasmon lithography breaks through the diffraction limit with surface plasmon effect and achieves high-resolution imaging below sub-wavelengths. The dynamic detection and control of the working distance between the mask and the substrate is particularly important for the quality of the lithography samples. In this paper, the mask-substrate gap sensing mechanism is analyzed, and a mask-substrate gap absolute distance measurement model is established based on the principle of white light interference. We design a Fizeau interferometer demodulation system based on a hardware optical correlation method, and focus on analyzing the influence of the sub-nanometer surface profile of the optical wedge on the resolution. Finally, we propose a data processing method for extracting the dynamic gap value by SSA (singular spectrum analysis). The experimental results show that the system shows high performance with a gap detection range of 3.0∼6.0 µm, the stability of ±0.12 nm, and the resolution of better than 0.30 nm.