Propagation effects of partially coherent light in optical lithography and inspection.

摘要

This thesis describes a formulation of a computationally efficient method for analyzing topography scattering with vector polarized partially coherent spatial illumination; presents the implementation of this method into TEMPEST-PCD (TEMPEST with Partial Coherence Decomposition); and shows systematic studies and rules of thumb for the effects of partial coherence in mask imaging, wafer patterning, and wafer inspection by using TEMPEST-PCD.; The effects of partial coherent light scattering from topography on a mask or wafer during printing and inspection have been a long-standing concern in optical projection printing. This thesis attacks this problem through generalizing the optimal decomposition to vector electromagnetic scattering. The generalization here decomposes the coherency matrix developed by Mandel and Wolf. This decomposition is both optimal in an energy compaction sense (since the least number of excitations is needed), and has orthogonal eigenvectors such that the partially coherent case is the direct sum of coherent cases.; With the decomposition technique, up to one order of magnitude can be saved in simulation time. The decomposition technique is recommended for all simulation problems except for truly periodic mask structures.; Simulation with experimental verification is used to evaluate effects and develop rules of thumb for the effect of the partial coherence in optical lithography and inspection. A perturbational model is developed that predicts the interaction and impact of a phase defect on the aerial image of a phase mask by considering the previously known behavior of isolated defects and line features. Where large topographies are encountered in phase shift masks, it is demonstrated that the assumption that the diffraction efficiencies must be independent of the illumination angle used in Hopkins' formulation is valid only when the aspect ratio (depth-to-width) of the mask feature is less than 0.2 for a stepper with {dollar}sigma{dollar}NA less than 0.5.; When simulating the patterning of an image inside a resist on a wafer with device features, interference effects at low {dollar}sigma{dollar} (0.3) due to lateral scattering from the topography are more pronounced. It is shown that when Fickian diffusion occurs after exposure in a subsequent post exposure bake (PEB) process, the net effect can be similar to exposing with less coherent light. Lateral scattering effects in resist also play an important role in printing a dark line from a pre-patterned edge of a phase shift resist layer directly on top of the resist. Lateral refraction of energy into the phase shift edge increases the linewidth beyond the anticipated resolution of {dollar}{lcub}gammaover4n{rcub}{dollar} by severalfold.; A sound methodology for improving wafer inspection is demonstrated. The reciprocity theorem is used to create a filter which compensates for both the topography and the thin-film thickness. Such a filter guides light down the hole and increases the amount of light reaching the bottom of the hole by threefold. (Abstract shortened by UMI.)