OPC Photomask Scattering Bar Phase Shift
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Solution Overview
Problem
The existing optical proximity correction (OPC) photomasks face challenges in precisely transferring feature patterns, such as contact holes, due to reduced process windows and adjacent pattern linking, especially as feature size and pitch narrow, leading to difficulties in imprinting patterns onto the photoresist during photolithography.
Innovation Solution
The OPC photomask design features a configuration of opening patterns and scattering bar patterns arranged on a substrate with a 180° phase shift, where scattering bar patterns are positioned adjacent to spacing regions without overlapping the opening patterns, maintaining a non-reduced process window even as feature sizes narrow, and enhancing light intensity contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If scattering bar patterns are made thin to enhance pattern sharpness during lithography, then pattern sharpness is improved, but the process window is reduced and adjacent patterns are easily linked together
Solution Approach 1:
The patent transitions from conventional 2D planar scattering bars to 3D protruding scattering bar structures that extend vertically from the photomask surface. This dimensional change allows the scattering bars to maintain enhanced pattern sharpness while reducing their horizontal footprint, thereby preventing adjacent pattern linking and maintaining a wider process window.
Solution Approach 2:
The scattering bar structures are segmented into multiple vertical levels or stages of protrusion from the photomask surface. This segmentation allows different regions or features to have optimized scattering characteristics, improving pattern sharpness for critical features while maintaining process window for other features, thus resolving the contradiction between sharpness and reliability.
2Productivity
If feature size and pitch are narrowed to increase integration of ICs, then integration is improved, but scattering bar patterns become very close to feature patterns causing pattern linking
Solution Approach 1:
By extending scattering bars vertically from the photomask surface, the patent creates a 3D structure that provides stronger light scattering effect within a smaller horizontal space. This allows feature pitch to be narrowed for higher integration while maintaining adequate separation between adjacent patterns, as the enhanced vertical scattering prevents lateral pattern merging.
3Measurement precision
If scattering bar patterns are positioned close to opening patterns to enhance resolution, then resolution is improved, but process window is reduced
Solution Approach 1:
The patent positions scattering bars in the vertical dimension protruding from the photomask surface, allowing them to be spatially close to opening patterns in the horizontal plane without causing process window reduction. The vertical protrusion creates strong scattering effects that improve resolution while the compact horizontal footprint maintains adequate process window.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration improves the profile and contrast of imprinted patterns on the photoresist, maintaining a wide process window and increasing flexibility in photoresist material selection, even at smaller feature sizes, by reducing light intensity at edges without affecting the center intensity, thus enhancing photolithography precision.
Implementation Method 1
due to diffraction or other causes, the feature patterns on the photomask cannot successfully be imprinted onto the photoresist
Implementation Method 2
A common OPC photomask, which is widely known, has sub-resolution scattering bars
Implementation Method 3
a phase shift of 180° exists between each opening pattern and each scattering bar pattern
Data Source
AI summary
An optical proximity correction (OPC) photomask is provided. The photomask includes two opening patterns and a pair of scattering bar patterns. The two patterns are arranged on a substrate along a first direction and separated from each other by a predetermined distance. The pair of scattering bar patterns is arranged on the substrate along a second direction perpendicular to the first direction and adjacent to two opposing sides of each opening pattern. Each scattering bar pattern does not overlap with the opening patterns on the first and second directions as viewed from a cross sectional perspective. A phase shift of 180° exists between each opening pattern and each scattering bar pattern.