Catadioptric Projection Objective Deflection Mirrors
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Solution Overview
Problem
Microlithographic projection exposure methods face challenges in maintaining high imaging quality and correcting time-dependent imaging aberrations, particularly due to heating effects and material changes in optical elements, which lead to variations in critical dimension (CD) and field uniformity, requiring costly active manipulators for compensation.
Innovation Solution
Catadioptric projection objectives with deflection mirrors that allow for synchronous linear displacement and varying reflection properties, enabling active manipulation of imaging properties without additional optical elements, thereby correcting aberrations and ensuring field-dependent precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If purely refractive projection objectives are used, then the structure is simpler, but correction of chromatic aberrations and image field curvature becomes difficult as numerical aperture increases and wavelength decreases
Solution Approach 1:
The patent combines refractive lenses with a reflective concave mirror to form a catadioptric projection objective. This merging of refractive and reflective optical elements enables effective correction of chromatic aberrations and image field curvature while maintaining high numerical aperture, resolving the contradiction between structural simplicity and aberration correction quality.
2Length of stationary object
If conventional projection objectives without deflection mirrors are used, then the optical path is shorter, but time-dependent imaging aberrations cannot be corrected
Solution Approach 1:
The patent introduces deflection mirrors that can be synchronously displaced in the optical path. This dynamic capability allows the system to actively compensate for time-dependent imaging aberrations such as those caused by heating effects and material changes, ensuring stable imaging quality over the lifetime of the projection objective despite the increased optical path length.
3Manufacturing precision
If active manipulators are added to correct aberrations, then imaging quality improves, but device complexity and cost increase
Solution Approach 1:
The deflection mirrors in the patent serve multiple functions: they define the optical path, enable active correction of time-dependent aberrations through synchronous displacement, and contribute to field uniformity control. This multi-functionality reduces the need for separate active manipulator systems, thereby limiting the increase in device complexity and cost while maintaining improved CD uniformity and imaging quality.
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 ensures high imaging quality and rapid, precise correction of aberrations over the lifetime of the projection objective, reducing the need for costly active manipulators and improving CD uniformity and field uniformity.
Implementation Method 1
uses two deflection mirrors in order to separate the partial beam path running from the object field to the concave mirror from the partial beam path running from the concave mirror to the image field
Implementation Method 2
a concave mirror has a positive refractive power just like a positive lens, but an opposite effect on the image field curvature by comparison with a positive lens
Data Source
AI summary
A method for manufacturing an integrated circuit includes scanning a wafer with respect to a catadioptric projection objective and imaging a pattern on a mask onto a wafer while scanning the wafer. The imaging includes illuminating the mask with radiation; imaging, using the radiation, the pattern into a first intermediate image, the first intermediate image to a second intermediate image, and the second intermediate image into an image field arranged in an image surface where the wafer is arranged; and, manipulating one or more of optical elements while scanning the wafer to reduce errors in the image at the image field. A concave mirror arranged in a region of a pupil surface reflects the radiation. The projection objective also includes mirrors to deflect the radiation from the object field towards the concave mirror and to deflect the radiation from the concave mirror towards the image field. The deflection mirrors are mechanically coupled to a displacement device arranged to displace the first and second deflection mirrors.