Sub-Resolution Assist Features for Lithography Corner Control
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Solution Overview
Problem
As semiconductor manufacturing reaches the limits of optical lithography, it becomes challenging to accurately transfer patterns onto substrates due to optical proximity effects, leading to increased complexity and cost in producing reticles with sufficient fine OPC features, such as serifs and sub-resolution assist features (SRAFs), which require laborious computation and result in manufacturing variations.
Innovation Solution
The use of a set of sub-resolution assist features (SRAFs), including both positive and negative SRAFs, is implemented to improve dimensional control of corner shapes on reticles, enhancing corner rounding and reducing corner rounding errors, thereby improving the accuracy of pattern transfer in optical lithography, particularly for laser writers, to match the precision of electron beam writers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional optical lithography with single SRAF is used, then manufacturing process is simpler, but dimensional control of corner shapes deteriorates
Solution Approach 1:
The patent divides the single SRAF into multiple segmented SRAFs (first and second SRAFs) positioned at different locations relative to the corner shape. This segmentation allows each SRAF to contribute differently to the optical proximity correction, improving dimensional control of the corner shape while maintaining manageable complexity through systematic placement
Solution Approach 2:
The patent applies different SRAF configurations to different corners of shapes based on their specific geometric and optical characteristics. Each corner receives tailored SRAF treatment (first SRAF, second SRAF, or both) depending on its local requirements, optimizing dimensional control for each corner while adapting to local pattern density and geometry
2Manufacturing precision
If multiple SRAFs are used to improve corner dimensional control, then manufacturing precision improves, but computation time and complexity increase
Solution Approach 1:
The patent pre-establishes the placement rules and geometric parameters for multiple SRAFs based on the main pattern geometry before the actual lithography process. The SRAF positions, sizes, and orientations are predetermined according to the corner shape characteristics, reducing computation time by avoiding complex real-time optimization during manufacturing
Solution Approach 2:
The patent systematically varies SRAF parameters (position, size, orientation) based on the corner shape parameters to optimize dimensional control. By establishing parameter relationships and design rules, the computation complexity is reduced while maintaining high precision corner rounding accuracy
3Manufacturing precision
If finer OPC features are added to reticles, then pattern transfer accuracy improves, but manufacturing cost and complexity increase
Solution Approach 1:
The patent optimizes SRAF parameters (size, position, orientation) to achieve high pattern transfer accuracy with manufacturable feature dimensions. By establishing parameter ranges and relationships, the solution balances optical performance with manufacturing capabilities, avoiding excessively fine features that would be difficult to manufacture
Solution Approach 2:
The patent applies SRAF features selectively at specific corners and locations where they are most needed for pattern transfer accuracy. This localized approach concentrates manufacturing effort on critical areas while leaving other areas simpler, improving overall pattern transfer accuracy without uniformly increasing reticle manufacturing complexity across the entire device
4Ease of manufacture
If laser writer is used instead of electron beam writer, then manufacturing cost decreases, but pattern accuracy deteriorates
Solution Approach 1:
The patent introduces multiple SRAFs as intermediary features that mediate between the laser writer's optical capabilities and the desired pattern accuracy. These SRAFs act as optical elements that compensate for the laser writer's lower inherent precision, enabling cost-effective manufacturing while achieving electron beam writer-level pattern accuracy through optical proximity correction
Data Source
AI summary
A method for optical proximity correction includes inputting a physical design having a plurality of shapes. Each shape has a plurality of corners, and the physical design is to be exposed on a surface of a substrate. A set of sub-resolution assist features (SRAFs) for the physical design is determined, where a plurality of SRAFs in the set of SRAFs interact. The plurality of SRAFs together provide better dimensional control of one corner of one shape in the plurality of shapes, when exposed on the substrate, compared to using a single SRAF to control a dimension of the one corner. The plurality of SRAFs includes a positive SRAF and a negative SRAF. A modified physical design is output, where the modified physical design comprises the physical design, as modified by the set of SRAFs.