Computational Lithography Feature Upsizing for Focus Sensitivity
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Solution Overview
Problem
Integrated circuits manufactured using sub-wavelength lithography and conventional computational lithography with optical proximity correction suffer from high parametric variability due to lower process margins, leading to yield loss and sensitivity issues with focus variation, particularly affecting marginal feature types like line ends and corners.
Innovation Solution
The method involves identifying marginal feature types through Bossung curves analysis and upsizing these features by 1.5σ in the computational lithography model to re-center parametric data, reducing failures in resistance, capacitance, and drive current by adjusting the reticle design to improve depth of field and focus sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional computational lithography with OPC is used, then manufacturing precision is improved, but reliability deteriorates due to high parametric variability and focus sensitivity
Solution Approach 1:
The patent applies preliminary action by performing feature upsizing during the reticle design stage before fabrication. By proactively adjusting feature dimensions in the computational lithography model to account for anticipated focus variations and process variability, the method prevents parametric failures before they occur during manufacturing, thereby improving reliability without sacrificing manufacturing precision.
2Reliability
If feature upsizing is applied to marginal feature types, then reliability is improved by reducing parametric failures, but device complexity increases due to additional computational steps
Solution Approach 1:
The patent applies local quality by selectively applying feature upsizing only to marginal feature types (such as line ends and corners) that exhibit high focus sensitivity, rather than uniformly adjusting all features. This targeted approach improves reliability for critical features while minimizing the overall computational complexity by avoiding unnecessary adjustments to robust features.
3Manufacturing precision
If OPC is used to correct edge placement errors, then manufacturing precision is improved, but reliability deteriorates due to low depth of focus for certain feature types
Solution Approach 1:
The patent applies parameter changes by modifying the feature dimension parameters in the computational lithography model through upsizing. This parameter adjustment compensates for focus variations by creating a larger feature footprint that remains within specifications across a wider focus range, thereby improving reliability without compromising the edge placement accuracy achieved through OPC.
Data Source
AI summary
A method of computational lithography includes providing through-focus critical dimension (CD) curves at a range of different focus values (Bossung curves) for a plurality of feature types that include different ratios of line width to space width. Using software run on a computing device, it is determined if there is at least one marginal feature type from the plurality of feature types based an image tool capability and a predetermined process specification affected by at least one of the plurality of feature types. Provided a marginal feature type is determined to be present, at least the marginal feature type(s) is upsized. A degree of upsizing increases as a curvature of the Bossung curves increases. A computational lithography model is compiled including the upsizing.