Photomask Dark Pattern Spacing for Thermal Expansion Control
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Solution Overview
Problem
The alignment accuracy in semiconductor lithography is compromised due to thermal expansion of the photo mask during exposure, which is exacerbated by uneven distribution of dark films, leading to biased absorption heating and reduced dimensional accuracy of transferred patterns.
Innovation Solution
A photo mask design with specific regions and patterns, where dark patterns are arranged with varying spacings and pitches to minimize thermal expansion and prevent optical proximity effects, including a shield region between circuit formation and dark regions to uniformly distribute heat and prevent excessive exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dark film is concentrated in specific regions to define patterns, then pattern definition capability is improved, but thermal expansion becomes biased and alignment accuracy deteriorates
Solution Approach 1:
The patent applies local quality by creating different dark pattern densities in different regions: the first region has sparse dark patterns for minimal heating, the second region has dense dark patterns for thermal balancing, and the third region has medium-density patterns for gradient transition. This spatial variation in dark pattern density allows simultaneous optimization of pattern definition and thermal expansion control.
Solution Approach 2:
The patent uses asymmetric arrangement of dark patterns across different regions of the transparent substrate. Rather than uniform distribution, the dark patterns are strategically placed with varying densities in specific zones (first, second, and third regions) to create intentional asymmetric thermal profiles that compensate for expected thermal expansion biases during exposure.
2Productivity
If dark patterns are arranged closely to increase pattern density, then manufacturing capability is improved, but optical proximity effects increase and dimensional accuracy deteriorates
Solution Approach 1:
The patent segments the transparent substrate into multiple regions (first, second, and third regions) with different dark pattern densities. This segmentation allows high-pattern-density areas to be separated from low-pattern-density areas by shield regions, preventing optical proximity effects from compromising dimensional accuracy while maintaining overall productivity through increased total pattern capacity.
Solution Approach 2:
The patent introduces shield regions filled with dark patterns as intermediaries between high-density pattern regions and low-density pattern regions. These intermediary zones act as optical buffers that prevent direct optical interaction between closely spaced patterns, thereby eliminating optical proximity effects while allowing high pattern density in functional regions.
3Manufacturing precision
If shield region is added between first and second regions, then optical proximity effects are prevented, but device complexity increases
Solution Approach 1:
The shield regions serve multiple functions simultaneously: they act as optical barriers to prevent optical proximity effects, they contribute to thermal balancing by absorbing radiation in proportion to their area, and they maintain structural continuity of the dark pattern layer. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity.
4Temperature
If dark patterns are sparsely arranged to reduce thermal absorption, then thermal expansion is reduced, but pattern definition capability deteriorates
Solution Approach 1:
The patent resolves the contradiction by moving from a single-dimensional consideration (pattern density) to a multi-dimensional solution: spatial distribution across multiple regions (first, second, third regions with different densities), temporal consideration during the exposure process (gradual thermal buildup), and functional differentiation (pattern-defining regions vs. thermal-balancing regions). This allows sparse arrangements for thermal control in non-critical areas while maintaining dense arrangements for pattern definition in critical areas.
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 design effectively suppresses thermal expansion of the photo mask substrate, improving alignment accuracy and preventing detrimental optical proximity effects, thereby enhancing the dimensional accuracy of transferred patterns.
Implementation Method 1
Absorption energy from a radiation beam during exposure heats the photo mask (the reticle) to make the photo mask (the reticle) expand.
Implementation Method 2
the photo mask (the reticle) comprises a mask substrate (a reticle substrate) composed of a transparent substrate, and a dark film (a dark portion) which is provided on the mask substrate (the reticle substrate) and which has either a function for shielding light or a function for passing through the light partially. Absorption energy from a radiation beam during exposure heats the photo mask (the reticle) to make the photo mask (the reticle) expand.
Implementation Method 3
the second patterning region in proximity to the first patterning region become over-exposure locally due to diffraction of the light.
Data Source
AI summary
A photo mask includes a plurality of dark patterns disposed on a transparent substrate, a first region, a shield region, and a second region. The first region includes the dark patterns that are disposed with a wider space than a first distance. The shield region is adjacent to the first region on the transparent substrate and is filled with the dark pattern. The second region is faced to the first region across the shield region and includes the dark patterns that are disposed with a narrower space than a second distance. The second distance is narrower than ninety percent of the first distance.