Photolithography Mask Segmentation for Line End Shortening
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Solution Overview
Problem
The challenge in semiconductor fabrication is line end shortening and corner rounding during photolithography, particularly in SRAM transistor gate fabrication, due to optical system limitations and proximity effects, which restricts the packing density of transistors and increases the risk of leakage.
Innovation Solution
The use of two photolithography masks, one for patterning continuous lines and the other for creating gaps between them, along with sub-resolution assist features, to minimize diffraction effects and reduce line end shortening, allowing for tighter packing of transistors without extensive optical proximity correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the mask is designed with longer lines to compensate for line end shortening, then the line length on the substrate is improved, but the tip to tip gap increases and transistor packing density decreases
Solution Approach 1:
The patent divides the single mask patterning process into multiple exposure steps using different masks. The first mask creates initial line patterns, and subsequent masks add features to compensate for line end shortening. This segmentation allows precise control of line lengths without requiring excessive mask line length, thereby maintaining small tip-to-tip gaps and high transistor packing density while achieving accurate final line dimensions.
2Area of moving object
If the tip to tip gap is reduced to increase transistor packing density, then the area utilization is improved, but line end shortening and corner rounding become more severe
Solution Approach 1:
The patent applies preliminary actions by first forming lines with adequate length using the first mask, then subsequently adding compensation features in later exposure steps. Sub-resolution assist features are pre-positioned near line ends to counteract diffraction effects before the final pattern is developed. This preliminary compensation allows small tip-to-tip gaps to be maintained while preventing severe line end shortening and corner rounding in the final pattern.
3Manufacturing precision
If optical proximity correction is extensively applied to reduce line end shortening, then the manufacturing precision is improved, but the device complexity and process steps increase
Solution Approach 1:
The patent segments the optical proximity correction into multiple discrete exposure steps, each handling specific compensation tasks. Rather than applying complex single-mask OPC, the process uses separate masks for different correction functions, making each step simpler and more controllable. This segmented approach achieves high line dimension accuracy while keeping individual process steps manageable and well-defined.
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 approach significantly reduces line end shortening and corner rounding, enabling tighter transistor packing while maintaining tight tolerances and reducing the need for extensive optical corrections, thereby improving the precision and efficiency of semiconductor feature patterning.
Implementation Method 1
the amount of photoresist that is exposed through the mask to light generally will not exactly match that dictated by the mask due to diffraction of light around the edges between the opaque regions and the transparent regions of the mask
Data Source
AI summary
A method for controlling etching during photolithography in the fabrication of an integrated circuit in connection with first and second features that are formed on the integrated circuit having a gap there between comprising depositing a layer of photoresist on the integrated circuit, selectively exposing portions of the photoresist through at least one photolithography mask having a pattern including means for alleviating line end shortening of the first and second lines adjacent the gap, and developing the photoresist after the selective exposing step.