Field-Dependent Illumination for Microlithography M3D Compensation
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Solution Overview
Problem
In microlithographic projection exposure apparatuses, three-dimensional mask effects (M3D) lead to wavefront tilt and image offset, resulting in image blur and decreased contrast, particularly under extensive illumination like dipole illumination.
Innovation Solution
The method involves field-dependent illumination, where different field regions of the object plane are illuminated with varying settings, producing a field-dependent image offset that compensates for the aberrations caused by mask structures, thereby reducing the overall image offset and enhancing imaging contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If dipole illumination is used to improve imaging capability, then illumination coverage is improved, but image contrast decreases due to image offset
Solution Approach 1:
The patent applies local quality by varying the illumination settings (NA, illumination angle) according to the local field position. The control unit adjusts illumination parameters dynamically for different field regions to compensate for M3D effects locally, thereby maintaining high image contrast across the entire field while preserving the benefits of extended illumination coverage.
2Manufacturing precision
If split dipole illumination is used to reduce M3D effects, then image offset is reduced, but throughput decreases
Solution Approach 1:
The patent maintains continuous useful action by performing exposure in a single scanning operation rather than dividing it into multiple operations. The dynamic adjustment of illumination settings during the continuous scanning process enables real-time compensation for M3D effects without interrupting the exposure workflow, thereby maintaining high throughput while reducing image offset.
3Manufacturing precision
If new mask materials are used to overcome M3D effects, then image quality is improved, but device complexity increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting illumination parameters (numerical aperture, illumination angle, intensity distribution) rather than changing mask materials. The control unit modifies these parameters in real-time during scanning to compensate for M3D effects, providing a flexible and cost-effective solution that avoids the complexity and cost associated with developing and implementing new mask materials.
Data Source
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AI summary
The invention relates to a method for operating a microlithographic projection exposure apparatus (1), in which for the - at least partial - compensation of an image offset produced due to the extent for example of dipole illumination (300) and which ultimately results in an unwanted loss of imaging contrast (M3D effect), the following are provided: field-dependent illumination, in which different field regions of the object plane (6) are illuminated with differing illumination settings, and the production of a field-dependent image offset during the imaging of the object plane onto the image plane (12). Here, the interaction between the field-dependent illumination and the field-dependent image offset can lead to the loss of imaging contrast as a whole being reduced. The field-dependent illumination can be implemented for example by a MEMS facet mirror (20) in the illumination device (2), and the field-dependent image offset can be implemented for example by a horizontal and/or vertical mask distortion in combination with an adapted feed modification.