Sub-resolution Rods in Photomask Transition Regions
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Solution Overview
Problem
In semiconductor manufacturing, pattern density variations lead to critical dimension (CD) variations and uniformity issues, particularly in advanced technologies like 45 nm, 32 nm, or 28 nm, causing distortion such as necking or bridge issues, where existing scattering bars are ineffective due to limited side space and re-targeting width limitations.
Innovation Solution
A photomask design incorporating sub-resolution rods (SRRs) in transition regions between dense and isolated patterns, with SRRs connected to IC features, adjusting pattern density and preventing necking issues without amending design rules or shifting features, and optionally using additional assist features like scattering bars for optical proximity correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If scattering bars are used to reduce necking or bridge issues, then CD uniformity is improved, but the method becomes ineffective due to limited side space availability
Solution Approach 1:
The patent transitions from using scattering bars (which require lateral side space) to using sub-resolution rods that extend in the vertical dimension (along the feature length). This dimensional change allows the rods to provide optical proximity correction without requiring additional lateral space, thereby resolving the contradiction between improving CD uniformity and maintaining side space availability.
Solution Approach 2:
The patent changes the geometric parameters of the correction features by using sub-resolution rods with specific dimensions (width less than printable width, length greater than or equal to 0.8 times the IC feature width). These parameter changes enable the rods to function as optical proximity correction elements while occupying minimal space, thus improving CD uniformity without consuming lateral design space.
2Manufacturing precision
If re-targeting the width of IC feature is performed to address necking or bridge issues, then feature distortion is reduced, but the method is limited by side space availability
Solution Approach 1:
Instead of modifying IC feature width (lateral dimension) to compensate for distortion, the patent introduces sub-resolution rods that extend in the longitudinal dimension (along the feature length). This dimensional shift allows distortion correction without requiring lateral space, resolving the contradiction between reducing feature distortion and preserving side space availability.
Solution Approach 2:
The sub-resolution rods act as intermediary elements that mediate the optical interaction between dense and isolated patterns. Rather than directly modifying the IC feature dimensions, these rods serve as intermediate structures that control light diffraction and interference, thereby preventing necking or bridge issues without requiring lateral space reallocation.
3Manufacturing precision
If sub-resolution rods are added in transition regions, then pattern density is adjusted and necking issues are prevented, but device complexity increases
Solution Approach 1:
The sub-resolution rods are placed only in specific transition regions where dense patterns meet isolated patterns, rather than uniformly across the entire photomask. This localized application adjusts pattern density precisely where needed (at transition boundaries) without unnecessarily increasing complexity in other regions, thereby resolving the contradiction between improving pattern density uniformity and minimizing device complexity.
Solution Approach 2:
The photomask design segments the transition regions and applies sub-resolution rods only at these specific locations. By dividing the photomask into distinct regions (dense patterns, isolated patterns, and transition regions) and applying corrections only where needed, the patent achieves pattern density uniformity while minimizing overall structural complexity.
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
The SRRs effectively adjust pattern density, prevent necking issues, and increase the depth of focus, improving the processing window without the need to re-target or shift IC features, thus addressing CD uniformity challenges.
Implementation Method 1
The photomask includes a sub-resolution rod (SRR) formed on the substrate, disposed in the transition region, and connected with the first IC feature. The SRR adjusts pattern density by modifying light diffraction patterns in the transition zone between dense and isolated features.
Implementation Method 2
The SRR in the transition region modifies optical interference patterns during lithography exposure, controlling the intensity distribution to prevent necking between adjacent IC features with different pattern densities.
Data Source
AI summary
The present disclosure provides a photomask. The photomask includes a first integrated circuit (IC) feature formed on a substrate; and a second IC feature formed on the substrate and configured proximate to the first IC feature. The first and second IC features define a dense pattern having a first pattern density. The second IC feature is further extended from the dense pattern, forming an isolated pattern having a second pattern density less than the first pattern density. A transition region is defined from the dense pattern to the isolated pattern. The photomask further includes a sub-resolution rod (SRR) formed on the substrate, disposed in the transition region, and connected with the first IC feature.