Photomask Dummy Patterns for Lithography Resolution
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Solution Overview
Problem
In semiconductor fabrication, the optical proximity effect leads to resolution losses and deviations in pattern transfer due to overexposure or underexposure during lithography, particularly when dealing with high-density mask patterns, where the exposure limit of optical tools restricts the size of mask segments, and existing methods like optical proximity correction have limitations.
Innovation Solution
A method is introduced that forms a sacrificial pattern with dimensions larger than the exposure limit in a photomask, paired with a self-aligned via process, where a second printable dummy pattern is created to increase luminous flux and prevent its printing on the wafer, thereby enhancing the exposure limit and achieving accurate pattern transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the size of mask segments is reduced to increase integration, then the exposure limit becomes a restricting factor, but resolution losses occur due to optical proximity effect
Solution Approach 1:
The patent divides the mask pattern into target patterns and dummy patterns. The dummy patterns are separate sacrificial elements that can be selectively removed, allowing the target patterns to be exposed with sufficient luminous flux while the dummy patterns prevent optical proximity effects between closely spaced target patterns.
Solution Approach 2:
The dummy patterns act as intermediary elements between target patterns. These sacrificial dummy patterns are positioned between target patterns to block optical proximity effects, and can be selectively removed through self-aligned via processes, allowing accurate pattern transfer.
2Manufacturing precision
If optical proximity correction software is used to correct mask patterns, then pattern accuracy improves, but the exposure limit constraint remains unresolved
Solution Approach 1:
The patent applies preliminary action by pre-calculating and pre-positioning dummy patterns in the mask design before exposure. These dummy patterns are strategically placed to compensate for optical proximity effects and ensure adequate luminous flux, eliminating the need for complex post-exposure corrections and simplifying the overall process.
3Illumination intensity
If dummy patterns are added to increase luminous flux, then exposure limit is improved, but unwanted patterns may be printed on the wafer
Solution Approach 1:
The patent applies local quality by making the dummy patterns locally removable through self-aligned via processes. The dummy patterns have different properties than target patterns - they are positioned and dimensioned to be selectively removed, allowing them to provide luminous flux during exposure while being eliminated before final pattern transfer to the wafer.
Solution Approach 2:
The dummy patterns are discarded after serving their purpose of providing luminous flux and preventing optical proximity effects. Through self-aligned via processes, the dummy patterns are selectively removed, and their space is recovered for the final target pattern formation, ensuring no unwanted patterns remain on the wafer.
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 method effectively increases the luminous flux of target patterns, prevents unwanted dummy pattern printing, and shrinks the exposure limit, allowing for precise and accurate pattern formation on the wafer, addressing the limitations of existing technologies in handling high-density layouts.
Implementation Method 1
By way of lithography processes, the pattern on the mask (i.e. the mask pattern) is transferred to a photoresist layer on the surface of a semiconductor wafer
Data Source
AI summary
A method for forming patterns includes the following steps. A first layout including a first target pattern and a first unprintable dummy pattern is provided. A second layout including a second target pattern and a second printable dummy pattern are provided, wherein at least part of the second printable dummy pattern overlaps the first unprintable dummy pattern exposure limit, such that the second printable dummy pattern cannot be formed in a wafer.