Double Pattern Lithography Power Rail Density Distribution
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Solution Overview
Problem
Conventional photolithography techniques face limitations in scaling down semiconductor device features due to constraints in pitch reduction, leading to issues with exposure dose balance and critical dimension control, particularly in patterning power rails, which results in variability and manufacturability challenges.
Innovation Solution
The method involves decomposing the overall pattern into a first mask pattern with a power rail base pattern and a second mask pattern with a power rail insert pattern, allowing for improved exposure dose balance by aligning and positioning the insert pattern based on distance from interconnects, thereby reducing stitch length overlap and promoting design rule compliance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If power rails are patterned on a single mask, then the layout is simple, but the exposure dose becomes unbalanced causing critical dimension variability
Solution Approach 1:
The power rail pattern is segmented into two separate masks: Mask 1 contains the base power rail pattern, while Mask 2 contains insert patterns that are selectively placed. This segmentation allows the exposure dose to be distributed more evenly across both masks, preventing the dose concentration that occurs when all power rail features are on a single mask. The result is improved critical dimension uniformity while maintaining the overall power rail structure.
2Productivity
If pitch is reduced to increase device density, then more devices fit on chip, but photolithographic performance limits are reached causing manufacturing difficulties
Solution Approach 1:
The overall pattern is decomposed into two masks with distinct feature sets. Mask 1 contains certain conductive features while Mask 2 contains other features including power rail inserts. This segmentation allows each mask to have optimized pitch requirements that are achievable with current photolithography tools, while the combined result achieves the desired high device density that would be impossible with a single mask at the required pitch.
3Ease of manufacture
If exposure dose is unbalanced on photomask, then manufacturing is simpler, but process control deteriorates causing feature width variability
Solution Approach 1:
The pattern transfer process is segmented into two separate photolithography steps, each with its own mask. This allows the exposure dose to be balanced across both masks, as each mask contains a subset of the total features. The process control is improved because no single mask bears the full burden of complex power rail patterns, enabling more consistent wire width and feature dimensions in the final product.
Data Source
AI summary
Methods, a computer readable medium, and an apparatus are provided. A method includes and the computer readable medium is configured for decomposing an overall pattern into a first mask pattern that includes a power rail base pattern and into a second mask pattern, and generating on the second mask pattern a power rail insert pattern that is at least partially aligned with the power rail base pattern of the first mask pattern. The apparatus is produced by photolithography using photolithographic masks generated by the method.