Abstract
In Digital Micromirror Device (DMD) projection lithography, the precise measurement of the focal plane is critical for achieving high-quality submicron patterns. To ensure pattern fidelity within the depth of focus (DoF), we calibrated the focal plane using an astigmatism-based focus detection system, establishing a reliable reference between the wafer surface and the lithographic imaging plane. We then have explored the DoF boundaries of submicron feature patterns through coherent imaging simulations combined with a constant-threshold photoresist model, predicting resist profiles under varying defocus and exposure doses. Experimental results verified the simulated resist patterns and demonstrated the effectiveness of the calibrated focus system. Additionally, by exposing linewidth patterns with a numerical apertures (NA) of 0.35 and 0.5 , we systematically characterized the DoF via Bossung curve analysis. Results indicate that larger linewidths or smaller NA increase the DoF, with target linewidths of 500 nm, 800 nm, and 1000 nm corresponding to DoFs of approximately 1 μm, 2.5 μm, and 4 μm, respectively. The extracted process factors for resolution and DoF were k1 = 0.61 and k2 = 0.59. This work provides a quantitative framework for controlling DoF and optimizing process windows in submicron DMD projection lithography, offering practical guidance for high-resolution maskless patterning.
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