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>Three-dimensional photolithography simulator including rigorous nonplanar exposure simulation for off-axis illumination
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Three-dimensional photolithography simulator including rigorous nonplanar exposure simulation for off-axis illumination
Abstract: Progress in today's semiconductor industry has been mainly achieved by decreasing the minimal feature size and increasing the complexity and thus the nonplanarity of the devices. Therefore lithography tools have to provide high resolution with a reasonably large depth of focus. Well-established methods to achieve both requirements are off-axis illumination techniques. As topography effects such as nonplanar electromagnetic scattering and notching are critical for line- width control, a rigorous three-dimensional exposure simulation considering both nonplanar surfaces as well as off- axis illumination is of utmost interest. We propose a rigorous method that meets the two challenges of nonplanar substrates and off-axis illumination. Our approach is based on a novel extension of the differential method to the third dimension. It is based on a Fourier expansion of the electromagnetic field in the lateral coordinates and thus belongs to the category of frequency-domain solvers. Due to the moderate computational costs nonplanar topography simulations including off-axis illumination can be performed on common engineering workstations. We will give a survey over the numerical algorithm of the differential method, describe the interface to the imaging and development module, and demonstrate the ability of the overall simulator by comparing simulation results for contact-hole printing over a dielectric and reflective substrates for various illumination apertures. !27
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