8. Simulation Examples

To demonstrate the capability of the overall lithography simulator we present two simulation examples. The first application is the aerial image simulation of an entire layout of a 4:16 multiplexer realized in 0.25 $\mu$m technology (cf. Section 8.1). The aerial images of four mask layers that are critical with respect to lithography are calculated. Additionally, problematic layout parts are analyzed in detail. Various illumination apertures as well as phase-shifting masks are compared whether they can improve the imaging performance. The second application is a rigorous study of the impact of topography and defocus effects on the printing of a single contact hole (cf. Section 8.2). Three differently shaped topographies are investigated, namely a planar silicon substrate, a dielectric oxide step, and a reflective a-silicon step, i.e., the step material is amorphous silicon with optical properties similar to polysilicon. The nonplanarity seriously reduces the quality of the printed contact hole, whereby the impact of the reflective a-silicon is stronger than that of the dielectric oxide. Off-axis illumination forms are a common approach to achieve a larger depth of focus. We compare the performance of three different apertures, namely ideally coherent, partially coherent, and quadrupole. The tradeoff between high resolution and large depth of focus is demonstrated.