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

Abstract

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 1µm 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.

Analysis of optical lithography capabilities of pixelized photomasks and spatial light modulators

“…Most of the OML work reported so far assumes that the SLMs have pixels that are deformable micro-mirrors with the dimensions ranging from 1 micron to 16 microns [1,[2][3][4][5][6][7][8][9]. At the object plane, the deformable micro-mirror pixel modulate only the phase and thus r(p j, x-x j , y-y j ) for them does not depend on the modulation parameter p j .…”

“…For the case of an SLM, a typical dimension of the pixel is several microns. For such pixel dimensions and the wavelengths used in modern lithography, a description of the object-plane modulation in terms of the reflectivity function (1) is sufficiently accurate and EMF effects can be neglected [5]. In general, SLM pixels may be designed to operate in either transmitted or reflected light.…”

“…Several approaches to solution of the system of constrained non-linear equations (5) have been suggested and tested [3,4] . The results presented in [3,4] demonstrate the ability of SLMs and pixelized photomasks to match the essential portion of the photomask diffraction pattern and the availability of the efficient algorithms to compute the corresponding rasterizations fast.…”

“…Various physical principles can be used to vary the optical properties of the SLM pixel. The SLMs with deformable micro-mirror pixels have attracted the most attention so far [1,[3][4][5][6][7][8][9]. In SLMs of this type, each pixel varies only the distribution of phase across it.…”

“…Optical Maskless Lithography (OML) [1][2][3][4][5][6][7][8][9] has received a considerable attention, at least in part due to the fact that it can be viewed as a natural extension of the capabilities of the available mask-based optical lithography tools.…”