Feasibility study of embedded binary masks

Abstract

Towards hyper-NA lithography, the mask blank and mask topography have the opportunity to be optimized for imaging performance. At the resolution limit of hyper-NA imaging, depth of focus and MEEF become critical for conventional mask stacks. Although conventional binary masks (BIM) are the simplest and the most cost-effective to manufacture, other mask types can provide better imaging performance.This study explores the feasibility and imaging performance of an embedded binary mask (EBM). The EBM emphasizes the simple binary manufacturing process with the application of an additional transparent layer. Two types of EBM's, topographic and planar, were evaluated. The mask diffraction properties are studied by both measurements using an ellipsometer (Woollam VUV-VASE) and simulations using Solid-E 3.2.0.2 (Sigma-C). In this first phase, the imaging performance is assessed by rigorous simulations for three different illumination conditions (cross-quad, quasar and annular). By comparing metrics such as contrast, NILS, MEEF, and process windows, simulations determined that an optimized topographic EBM has a better overall through-pitch imaging performance than a conventional binary mask. This preliminary investigation suggests that an embedded binary mask may be considered as an RET option for hyper-NA imaging improvement.

The MEEF NILS divergence for low k1 lithography

“…Several recent publications characterize low k1 patterning of various mask stack and materials [1][2][3][4][5] and in at least some cases 6 simultaneously considered the effect of biasing. Those works generally evaluate contrast, NILS or exposure latitude (all three are proportional to each other) for one-dimensional features as the initial metric for comparison between different mask stacks.…”