Layout small-angle rotation and shift for EUV defect mitigation

Abstract

Blank defect mitigation is crucial for extreme ultraviolet (EUV) lithography. One of the existing options is to relocate patterns to avoid defect impact. However, when the defect number increases, only pattern shift in X-Y directions becomes far from enough, requiring the reticle holder rotate a small angle to provide a third exploring dimension. This non-trivial extension from 2D to 3D exploration requests efficient runtime as well as enough accuracy to handle different defect sizes and locations on the different features. In this paper, we present the first work with a detailed algorithm to find the optimal shift and rotation for layout patterns on blanks. Compared to the straightforward method, which is to check every pair of defect and feature at every possible relocation position, our proposed algorithm can significantly reduce the runtime complexity to scale linearly with the size of the full solution space. The experimental results validate our method and show a largely increased success rate of defect mitigation by shift and rotation.

Comprehensive defect avoidance framework for mitigating EUV mask defects

“…Prohibited region based defect avoidance methods [24,25] allows continuous pattern shift and small angle rotation, but cannot handle mask floorplanning. Simulated annealing based defect avoidance method [16] allows pattern shift and mask floorplanning, but arbitrary angle rotation is not possible.…”

“…Prohibited Region Simulated Annealing [16] Pattern Shift [24] Pattern Shift Pattern Shift Pattern Shift + Rotation [25] + Mask Floorplanning 10 100% 100% 100% 100% 20 81% 100% 100% 100% 30 8% 97% 0% 6% 40 1% 11% 0% 0% 50 0% 0% 0% 0% field pattern and the total field size (W F × H F ). Since the size of one ARM Cortex M0 layout is 162µm × 159µm, the total field size becomes 486µm × 636µm and the usable area of the mask is 511µm × 662µm.…”

“…• Arbitrary Angle Rotation: The work on small-angle rotation in [25] assumes that sin Θ ≈ Θ for all the defect-layout edge interactions, which limits the maximum allowed rotation angle. Our work does not make this assumption, which makes this approach viable even for larger rotation angles.…”

“…• Continuous: Our method explores the continuous solution space, instead of making discrete moves as done in the previous works on defect avoidance floorplanning [16] and small-angle rotation [25].…”

Extreme ultraviolet lithography and three dimensional integrated circuit—A review

“…In the near future, it will be impossible to produce real defect-free photomask, so several compromised approaches were examined, including pattern shift, pattern rotation, and design-aware defect-avoidance floorplanning of EUVL masks. [32][33][34] Production cost control requires that the EUVL mask blanks be inspected and repaired. Amplitude defects can be identified by using optical or electron-beam inspection; however, phase defects have to rely on at-wavelength light (actinic) [35][36][37][38] to carry out inspections.…”