ILT for double exposure lithography with conventional and novel materials

Multiple paths exists to provide lithography solutions pursuant to Moore's Law for next 3-5 generations of technology, yet each of those paths inevitably leads to solutions eventually requiring patterning at k1 < 0.30 and below. In this article, we explore double exposure single development lithography for k1 ≥ 0.25 (using conventional resist) and k1 < 0.25 (using new out-of-sight out-of-mind materials). For the case of k1 ≥ 0.25, we propose a novel double exposure inverse lithography technique (ILT) to split the pattern. Our algorithm is based on our earlier proposed single exposure ILT framework, and works by decomposing the aerial image (instead of the target pattern) into two parts. It also resolves the phase conflicts automatically as part of the decomposition, and the combined aerial image obtained using the estimated masks has a superior contrast. For the case of k1 < 0.25, we focus on analyzing the use of various dual patterning techniques enabled by the use of hypothetic materials with properties that allow for the violation of the linear superposition of intensities from the two exposures. We investigate the possible use of two materials: contrast enhancement layer (CEL) and two-photon absorption resists. We propose a mathematical model for CEL, define its characteristic properties, and derive fundamental bounds on the improvement in image log-slope. Simulation results demonstrate that double exposure single development lithography using CEL enables printing 80nm gratings using dry lithography. We also combine ILT, CEL, and DEL to synthesize 2-D patterns with k1 = 0.185. Finally, we discuss the viability of two-photon absorption resists for double exposure lithography.