Investigation of the corner rounding effect near the diffraction limit in advanced projection lithography with a rigorous imaging model

The corner rounding effect in lithography refers to the phenomenon where the corners or angles of a pattern created by lithography are rounded off, rather than remaining square and sharp. This occurs mainly due to the diffraction of light. In addition, mask pattern design, numerical aperture, and the limited resolution of the lithographic process also influence it. The rounding of corners can severely degrade the performance and reliability of microelectronic devices due to incomplete pattern transfer. Therefore, minimizing the corner radius in mask correction is crucial for enhancing pattern fidelity. We propose a methodology that relates the corner radius to the diffraction-limited spot width. By employing aerial image simulation, we delve into the factors that significantly impact the corner radius in projection lithography. By combining a rigorous computational imaging model with the optimization of lithography parameters, the limit of the corner radius is determined in immersion lithography. Our comprehensive investigation reveals the nature of the corner rounding effect, analyzes the contributing factors for corner rounding, and ultimately leads to improvements in imaging quality in photolithography.