Microlithography Projection Objective Wavefront Correction
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Solution Overview
Problem
Projection objectives in microlithography face challenges in correcting imaging errors, particularly heat-induced errors and those caused by non-rotationally symmetrical beam paths, which are difficult to address with existing complex correction mechanisms like Alvarez manipulators, especially in free-form surface designs.
Innovation Solution
An imaging optical system with non-rotationally symmetrical optical elements that can be displaced to induce wavefront changes with two-fold or higher symmetry, allowing for correction of imaging errors without additional correction elements, by modifying the surface shapes of optical elements to change the wavefront error through displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an Alvarez manipulator with two aspherical correction elements is used to correct heat-induced imaging errors, then imaging errors can be compensated, but the device complexity increases and intensity losses occur
Solution Approach 1:
The invention extracts the correction function from separate additional elements and integrates it into the existing optical elements themselves. The aspherical surface contours are incorporated directly into the optical elements that are already present in the beam path, eliminating the need for separate Alvarez manipulator components while maintaining the correction capability
Solution Approach 2:
The invention merges the correction function with the existing optical elements by providing them with aspherical surface contours. This combines the imaging function and the correction function into a single integrated system, reducing overall device complexity while maintaining both imaging and correction capabilities
2Manufacturing precision
If an Alvarez manipulator with two aspherical correction elements is used to correct heat-induced imaging errors, then imaging errors can be compensated, but intensity losses occur
Solution Approach 1:
The invention merges the correction function with the existing optical elements that are already part of the beam path. By incorporating aspherical surface contours into these existing elements, the correction is achieved without adding separate components that would cause additional intensity losses through absorption or reflection
3Manufacturing precision
If free-form surface designs with non-rotationally symmetrical surfaces are used, then imaging errors can be corrected, but the addition of correction systems becomes impracticable
Solution Approach 1:
The invention utilizes non-rotationally symmetrical aspherical surface contours that match the free-form surface design philosophy. By employing asymmetric surface shapes in the optical elements, the system can correct complex imaging errors including those from non-rotationally symmetrical beam paths without requiring additional correction systems
Solution Approach 2:
The invention merges the correction function into the existing free-form surface optical elements. The aspherical surface contours are integrated directly into these elements, making the correction system practicable and eliminating the need for separate correction mechanisms that would be incompatible with free-form surface designs
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 enables effective correction of imaging errors, such as heat-induced aberrations, without complex mechanisms, increasing surface tolerances and reducing the need for post-processing or deformable mirrors, while allowing for precise manipulation of wavefront errors.
Implementation Method 1
by displacing at least a first of the optical elements, in particular two, three, four or more of the optical elements, relative to the other optical elements, a change to a wavefront W of the optical system can be brought about
Implementation Method 2
optical elements configured to guide electromagnetic radiation with a wavelength λ in an imaging beam path for imaging an object field into an image plane
Implementation Method 3
During operation, the imaging radiation of the optical elements of the projection objective used is partially absorbed, and this leads to heating of the optical elements. By thermal expansion and, if applicable, associated refractive index changes, imaging errors which can take on complicated field characteristics are induced
Data Source
AI summary
An imaging optical system, in particular a projection objective, for microlithography, includes optical elements to guide electromagnetic radiation with a wavelength in a path to image an object field into an image plane. The imaging optical system includes a pupil, having coordinates (p, q), which, together with the image field, having coordinates (x, y) of the optical system, spans an extended 4-dimensional pupil space, having coordinates (x, y, p, q), as a function of which a wavefront W(x, y, p, q) of the radiation passing through the optical system is defined. The wavefront W can therefore be defined in the pupil plane as a function of an extended 4-dimensional pupil space spanned by the image field (x, y) and the pupil (p, q) as W(x, y, p, q)=W(t), with t=(x, y, p, q).