Off-axis illumination for lithography metrology
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Solution Overview
Problem
Semiconductor lithography tools face challenges in accurately monitoring and maintaining tight tolerances for focal position and illumination dose to ensure precise feature printing, particularly in producing narrow linewidths and high-density patterns, where existing metrology systems are not cost-effective and integrated with production processes.
Innovation Solution
A lithography system utilizing an off-axis illumination source and pattern masks with optimized pattern elements to generate diffracted beams that provide indicators of focal position and illumination dose, allowing for precise monitoring and control through a co-optimized illumination and metrology system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If process-sensitive metrology targets are used to monitor focal position and illumination dose, then measurement precision is improved, but device complexity increases due to the need for specialized targets and co-optimized illumination systems
Solution Approach 1:
The pattern mask serves dual functions: it acts as both the production mask for fabricating semiconductor features and as a metrology target for monitoring process parameters. The same mask patterns are used for both device manufacturing and process control, eliminating the need for separate metrology targets and reducing system complexity.
Solution Approach 2:
The metrology monitoring function is merged with the production lithography process by using the same illumination source and pattern mask for both purposes. The process-sensitive metrology targets are integrated into the production workflow, combining measurement and manufacturing functions into a unified system.
2Manufacturing precision
If tight tolerances are maintained for focal position and illumination dose, then manufacturing precision is improved, but loss of energy increases due to stricter process control requirements
Solution Approach 1:
The system uses process-sensitive metrology targets to provide real-time feedback on focal position and illumination dose during the lithography process. This feedback enables dynamic adjustment of process parameters to maintain tight tolerances, ensuring manufacturing precision while optimizing energy usage through intelligent control rather than brute-force parameter tightening.
3Measurement precision
If specialized process-sensitive metrology targets are implemented, then measurement precision is improved, but ease of manufacture deteriorates due to additional process steps and integration requirements
Solution Approach 1:
The pattern mask is designed to serve both production and metrology functions simultaneously. The same mask patterns used for device fabrication also serve as metrology targets, eliminating the need for separate target fabrication processes and simplifying manufacturing integration.
4Manufacturing precision
If off-axis illumination is used with optimized pattern elements, then manufacturing precision is improved for narrow linewidths, but device complexity increases due to co-optimization requirements
Solution Approach 1:
The system employs off-axis illumination with asymmetric illumination poles positioned at specific angles relative to the pattern mask features. This asymmetric illumination configuration, combined with corresponding asymmetric pattern element designs, enables enhanced control over diffraction patterns and improved printing accuracy for narrow linewidths while managing the complexity through deliberate asymmetric design.
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
Enables accurate and cost-effective monitoring of focal position and illumination dose, ensuring precise feature printing and improving the robustness of printed patterns to deviations in process parameters, thereby enhancing the performance of semiconductor fabrication.
Implementation Method 1
the pattern mask includes a set of pattern elements configured to generate a set of diffracted beams including illumination from the illumination pole
Data Source
AI summary
A lithography system includes an illumination source and a set of projection optics. The illumination source directs a beam of illumination from an off-axis illumination pole to a pattern mask. The pattern mask includes a set of pattern elements to generate a set of diffracted beams including illumination from the illumination pole. At least two diffracted beams of the set of diffracted beams received by the set of projection optics are asymmetrically distributed in a pupil plane of the set of projection optics. The at least two diffracted beams of the set of diffracted beams are asymmetrically incident on the sample to form a set of fabricated elements corresponding to an image of the set of pattern elements. The set of fabricated elements on the sample includes one or more indicators of a location of the sample along an optical axis of the set of projection optics.