Although lens aberrations in EUV imaging systems are very small, aberration impacts on pattern placement error and overlay error need to be carefully investigated to obtain the most robust lithography process for high volume manufacturing. Instead of focusing entirely on pattern placement errors in the context of a single lithographic process, we holistically study the interaction between two sequential lithographic layers affected by evolving aberration wavefronts, calculate aberration induced overlay error, and explore new strategies to improve overlay.
EUV mask repair techniques have primarily focused on absorber biasing to recover the imaging contrast loss originating
from multilayer blank defects, while exploratory efforts have investigated local multilayer modification for
compensating any through-focus Bossung asymmetry. The work here evaluates these repair techniques and attempts to
expand upon them through finite-difference time-domain (FDTD) simulations. In particular, the possibility of local
material deposition as an added repair technique is considered, and the interactions between various compensation
strategies and illumination modes are explored. A multilayer defect repair methodology that is non-disruptive to the
multilayer stack is introduced for the recovery of both the amplitude loss and phase error originating from native blank
defects. The effectiveness of the compensation technique is shown to be independent of the defect type, providing a
repair solution that is impartial to the phase offset induced by the multilayer defect. Significant lithographic process
window improvements are reported, as compared to conventional absorber-based repair, attributed primarily to the
restoration of symmetric printing behavior through defocus. This provides an alternative, viable approach to HVM
multilayer defect repair.
We have investigated the mechanisms responsible for nonlinear optical processes occurring in azobenzene-doped blue phase liquid crystals (BPLC), which exhibit two thermodynamically stable BPs: BPI and BPII. In coherent two wave-mixing experiments, a slow (minutes) and a fast (few milliseconds) side diffractions are observed. The underlying mechanisms were disclosed by monitoring the dynamics of grating formation and relaxation as well as by some supplementary experiments. We found the photothermal indexing and dye/LC intermolecular torque leading to lattice distortion to be the dominant mechanisms for the observed nonlinear response in BPLC. Moreover, the response time of the nonlinear optical process varied with operating phase. The rise time of the thermal indexing process was in good agreement with our findings on the temperature dependence of BP refractive index: τ(ISO) > τ(BPI) > τ(BPII). The relaxation time of the torque-induced lattice distortion was analogue to its electrostriction counterpart: τ'(BPI) > τ'(BPII). In a separate experiment, lattice swelling with selective reflection of <110> direction changed from green to red was also observed. This was attributable to the isomerization-induced change in cholesteric pitch, which directly affects the lattice spacing. The phenomenon was confirmed by measuring the optical rotatory power of the BPLC.
A critical analysis of various nonlinear mechanisms such as laser induced thermal/order parameter changes and flow orientation effects in nematic liquid crystal is presented, along with feasibility demonstrations of all-optical switching and optical image processing and tunable photonics using these mechanisms. The merits and limitation of nematics are discussed together with some preliminary results with Blue Phase liquid crystals that could circumvent some of the limitations.