Image fidelity improvement through optical proximity correction and its limits

Lack of image fidelity, such as corner rounding and line end foreshortening, can have adverse effects on semiconductor devices and circuits, and its magnitude is of interest to lithography integration into the device flow. Yet corner rounding is rarely quantified. The question arises which fraction of the problem can be corrected by optical proximity correction, and which fraction cannot be corrected because of the spatial frequency limitation of the image transfer process. Image fidelity problems typically get worse with highly coherent illumination settings that are used for alternating phase shifting masks, so it is important to investigate corner rounding in connection with such masks. Equally, it is important to understand the impact of numerical aperture on corner rounding. Because of its simple shape, a corner lends itself to simulated and experimental evaluation. We propose a metrology algorithm for corner rounding and investigate it with simulation and experiment. We study the impact of optical settings, mask parameters, and serifs on corner rounding and discuss the impact on optical proximity correction.