Lithographic Illumination Profile Matching via CD Sensitivity Maps
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Solution Overview
Problem
Lithographic apparatus from different manufacturers or models struggle to produce consistent results due to difficulties in matching critical dimension (CD) as a function of pitch, requiring numerous trial exposures and inadequate coherence of illumination adjustments.
Innovation Solution
A method is developed to determine a suitable illumination profile by obtaining reference and target CD vs. pitch functions, generating a CD sensitivity map, and calculating a matching illumination profile to ensure consistent imaging across different lithographic apparatus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional illumination coherence adjustment is used to match CD vs. pitch functions for two different apparatus, then some matching is achieved, but the match is not sufficiently close and requires many trial exposures
Solution Approach 1:
The patent performs preliminary characterization of each lithographic apparatus to obtain its specific optical parameters (pupil radius, illumination sigma values, optical transfer function characteristics) before attempting to match CD vs. pitch functions. This preliminary action enables the subsequent calculation of an optimized illumination profile that achieves accurate matching in a single attempt rather than through multiple trial exposures.
Solution Approach 2:
The patent systematically varies illumination profile parameters (illumination sigma inner and outer values, pupil radius, coherence factor) to optimize the match between reference and target apparatus CD vs. pitch functions. By changing these optical parameters and recalculating the illumination profile, the method achieves precise CD matching across different pitch values without requiring numerous trial exposures.
2Adaptability or versatility
If different models or manufacturers of lithographic apparatus are used, then versatility is improved, but matching difficulty increases significantly
Solution Approach 1:
The patent obtains specific optical parameters for each apparatus model and manufacturer (pupil radius, illumination sigma, optical transfer function characteristics) and uses these parameters to calculate a customized illumination profile. This approach accommodates differences between various apparatus models and manufacturers while maintaining consistent CD vs. pitch performance through parameter-based optimization.
Solution Approach 2:
The patent uses the measured CD vs. pitch data from both reference and target apparatus as feedback to iteratively optimize the illumination profile parameters. By comparing the actual CD measurements with the target values and adjusting the illumination profile accordingly, the method achieves accurate matching across different apparatus types through a systematic feedback-driven process.
3Manufacturing precision
If straightforward calibration to a common reference is used for same or similar models, then consistent results are achieved, but this approach does not work for different models or manufacturers
Solution Approach 1:
The patent extends the calibration approach by obtaining apparatus-specific optical parameters (pupil radius, illumination sigma values, optical transfer function) and using these parameters to calculate customized illumination profiles for each apparatus type. This parameter-based approach maintains consistent results across different apparatus models and manufacturers, not just for similar models.
Solution Approach 2:
The patent performs preliminary characterization of each apparatus's optical system to determine its specific parameters before calibration. This preliminary action enables the method to adapt to different apparatus types by understanding their unique optical characteristics, thereby extending the applicability of calibration beyond just similar models to include different models and manufacturers.
Data Source
AI summary
An illumination profile useable in a lithographic apparatus to match the output of a target lithographic apparatus is obtained by obtaining a reference CD vs. pitch function for the lithographic projection apparatus at at least a plurality of pitch values using a reference illumination profile; obtaining a target CD vs. pitch function at at least the plurality of pitch values; generating a CD sensitivity map for the lithographic projection apparatus for a given pattern; calculating from the reference CD vs. pitch function, the target CD vs. pitch function and the CD sensitivity map, a suitable illumination profile to be used in said lithographic apparatus to expose said given pattern.