Mandrel Patterning for IC Layout Density and Precision
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Solution Overview
Problem
Conventional optical lithography technologies face challenges in accurately printing device features at smaller technology nodes, leading to issues like rounding, pinching, and bridging of line patterns, which affect device performance and integration, especially when dealing with mixed design rules in integrated circuits (ICs) containing both logic circuits and SRAM cells.
Innovation Solution
The method involves extending device patterns within layout blocks, adding dummy patterns outside blocks, and inserting mandrel bar patterns to connect device and dummy patterns, optimizing pattern density and preventing uncontrolled connections, while using modified mask data preparation and fabrication processes to improve image printing quality and reduce manufacturing defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional optical lithography is used for patterning at smaller technology nodes, then manufacturing process simplicity is maintained, but image printing quality deteriorates due to resolution limits causing rounding, pinching, and bridging of line patterns
Solution Approach 1:
The patterning process is divided into multiple steps: forming mandrels with first line patterns, depositing spacers, and performing selective etching. This segmentation allows each step to be optimized independently, achieving high precision features that cannot be obtained through single-step conventional lithography.
Solution Approach 2:
Mandrels are formed in advance with relaxed design rules, and spacers are deposited beforehand. These preliminary structures serve as templates for the final high-precision pattern, enabling accurate feature formation while simplifying the overall process planning.
2Manufacturing precision
If restrictive design rules are applied to improve image printing quality, then line pattern accuracy is improved, but layout flexibility deteriorates when integrating different design blocks with varying pitch requirements
Solution Approach 1:
Different regions of the layout can have different design rules applied. Layout blocks requiring high precision can use restrictive design rules, while other regions can use relaxed rules. The mandrel and spacer structure allows local optimization without constraining the entire chip layout.
Solution Approach 2:
Mandrels serve as intermediary structures between the lithography process and the final device pattern. They can be designed with relaxed rules and then transformed into high-precision features through spacer deposition and selective etching, mediating between layout flexibility and manufacturing precision.
3Adaptability or versatility
If layout blocks with different design rules are used to accommodate different circuit requirements, then design adaptability is improved, but manufacturing complexity increases due to regions between blocks requiring special handling for printing inaccuracies
Solution Approach 1:
The mandrel and spacer structure serves multiple functions: it defines final pattern dimensions, provides alignment references, and handles spacing requirements between different layout blocks. This universal approach simplifies manufacturing by using the same basic structure for multiple purposes.
Solution Approach 2:
The spacer structures automatically compensate for printing inaccuracies and define precise spacing between different layout blocks. The process is self-correcting, as the spacer width is determined by conformal deposition rather than direct lithography, eliminating the need for manual adjustment of spacing parameters.
Data Source
AI summary
A method includes receiving an integrated circuit (IC) design layout including a layout block, where the layout block including first line patterns disposed along a first direction, extending lengths of the first line patterns, connecting portions of the first line patterns disposed within a distance less than a preset value, forming second line patterns disposed outside the layout block parallel to the first line patterns, forming mandrel bar patterns overlapping edges of the layout block, where the mandrel bar patterns oriented along a second direction perpendicular to the first direction, and outputting a pattern layout for mask fabricating, where the pattern layout includes the layout block, the first and second line patterns, and the mandrel bar patterns.