Self-Aligned Double Patterning With Variable Spacer Widths
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Solution Overview
Problem
The increasing down-scaling of integrated circuits poses challenges due to the optical proximity effect, where closely located features in lithography can short to each other, necessitating advanced patterning techniques to maintain feature density and reduce capacitance effects between metal lines.
Innovation Solution
The implementation of self-aligned double patterning (SADP) technology, which uses a mandrel layer and a spacer layer to create customized spacings between metal lines by varying the thickness of the spacer layer, allowing for flexible separation and capacitance control across a die, enabling smaller die areas while maintaining adequate isolation where needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If double patterning is used to reduce optical proximity effect, then feature density is enhanced, but manufacturing process complexity increases
Solution Approach 1:
The patterning process is divided into multiple stages: forming mandrels at a first pitch, depositing spacer material, selectively removing mandrels, and forming final features at a second pitch. This segmentation allows complex high-density patterning to be achieved through simpler sequential steps rather than attempting to pattern all features in a single exposure.
Solution Approach 2:
Mandrels are introduced as intermediary structures that facilitate the formation of final high-density features. The mandrels are formed at a relaxed pitch, serve as templates for spacer deposition, and are subsequently removed. This intermediary approach enables the creation of features at densities that would be unachievable through direct lithography alone.
2Object-generated harmful factors
If spacer layer thickness is increased to separate metal lines, then capacitance effects are reduced, but die area increases
Solution Approach 1:
The spacer layer thickness is varied locally across different regions of the die based on specific design requirements. Regions requiring higher isolation have thicker spacers, while regions prioritizing density have thinner spacers. This local customization allows optimization of capacitance control without uniformly increasing die area across the entire device.
Solution Approach 2:
The spacer thickness is made dynamic and adjustable rather than fixed, allowing the design to adapt spacing requirements to different functional regions. This enables the structure to optimize between capacitance reduction and area utilization based on local circuit requirements, achieving better overall performance than a uniform spacer thickness would provide.
3Ease of manufacture
If uniform spacing is used between metal lines, then manufacturing is simplified, but design flexibility is reduced
Solution Approach 1:
Different spacer thicknesses are implemented in different regions of the die to achieve locally optimized spacing. This allows the manufacturing process to maintain relative simplicity through standardized spacer deposition while achieving design flexibility through regional variations in spacer thickness that meet different functional requirements.
Data Source
AI summary
A method includes patterning a mandrel layer over a target layer to form first mandrels and second mandrels, the first mandrels having a larger width than the second mandrels. A spacer layer is formed over the first mandrels and the second mandrels, and altered so that a thickness of the spacer layer over the first mandrels is greater than a thickness of the spacer layer over the second mandrels. Spacers are formed from the spacer layer which have a greater width adjacent the first mandrels than the spacers which are adjacent the second mandrels. The spacers are used to etch a target layer.