Application of rigorous electromagnetic simulation to SLM-based maskless lithography for 65nm node

Maskless lithography imaging based on SLM tilt mirror architecture requires illumination of light on a non-planar reflective topography. While the actual mirror dimensions can be much larger than the wavelength of light, the spacing between mirrors and the tilt range of interest are on the order of the wavelength. Thus, rigorous electromagnetic solution is required to capture light scattering effects due to the non-planar topography. We combine high NA imaging simulation with rigorous simulation of light scattering from the mirrors to study its effects on 65nm maskless lithography imaging. We vary mirror size, mirror tilt arrangement, feature type and illumination settings and compare the rigorous light scattering imaging results with standard imaging simulations using Kirchoff approximation. While electromagnetic scattering effects are present in the form of lateral standing waves and edge streamers in reflected light near-field intensity, they have negligible effects on SLM imaging for mirror sizes more than 1mum(2). The effects of mirror tilt arrangement on diffraction orders are used to study the through-focus behavior of alternating rows arrangement used in the SIGMA maskwriters as well as alternative arrangements. The good imaging properties of the alternating rows arrangement are confirmed and a multipass overlay scheme giving further image fidelity improvements is suggested.