Birefringent Element Group for Polarization Compensation
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Solution Overview
Problem
Microlithographic exposure systems face challenges in maintaining optimal polarization distribution due to the use of high refractive index materials that exhibit birefringence, leading to disturbances in the polarization state of transmitted light rays.
Innovation Solution
An optical system comprising three birefringent elements with specific orientations and aspheric surfaces is used to compensate for local disturbances in polarization, allowing for the creation of any desired polarization distribution, particularly transforming circular or linear polarization into tangential polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high refractive index materials are used to enhance resolution and optical performance, then the optical performance and resolution are improved, but birefringence effects occur that disturb the polarization distribution of transmitted rays
Solution Approach 1:
The patent uses birefringent elements with controlled retardation to compensate for the harmful birefringence effects. By introducing additional birefringent components with specific orientations and retardation values, the system converts the harmful polarization disturbances into beneficial corrections, achieving desired polarization distributions (e.g., tangential polarization) while maintaining the use of high refractive index materials for optical performance
2Manufacturing precision
If optical components with strong birefringence are used, then the refractive index and optical performance are enhanced, but the polarization distribution is disturbed requiring complex compensation measures
Solution Approach 1:
The patent applies local quality by positioning birefringent elements at specific locations within the optical system where polarization compensation is most needed. Each birefringent element has locally optimized properties (retardation value, crystal axis orientation) tailored to the specific polarization disturbances at that location, rather than using a uniform compensation approach throughout the entire system
3Object-generated harmful factors
If birefringent elements are added to compensate for polarization disturbances, then the polarization distribution is improved, but the device complexity increases
Solution Approach 1:
The patent achieves effective polarization compensation by carefully selecting and optimizing key parameters of the birefringent elements, including retardation values (e.g., λ/4, λ/2), crystal axis orientations, and positions within the optical system. By adjusting these parameters, the patent achieves desired polarization distributions using a limited number of elements, avoiding excessive system complexity
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 configuration effectively compensates for birefringence-induced retardation, improving the optical performance and resolution of microlithographic exposure systems by allowing precise control over polarization distribution, thereby enhancing imaging quality.
Implementation Method 1
an arbitrary desired polarization distribution can be effectively created... local disturbances of the state of polarization, in particular due the presence of one or more optical elements having a relatively high refractive index and relatively strong birefringence
Data Source
AI summary
In some embodiments, the disclosure provides an optical system, in particular an illumination system or a projection lens of a microlithographic exposure system, having an optical system axis and at least one element group including three birefringent elements each of which includes optically uniaxial material and having an aspheric surface, wherein a first birefringent element of the group has a first orientation of its optical crystal axis, a second birefringent element of the group has a second orientation of its optical crystal axis, wherein the second orientation can be described as emerging from a rotation of the first orientation, the rotation not corresponding to a rotation around the optical system axis by an angle of 90° or an integer multiple thereof, and a third birefringent element of the group has a third orientation of its optical crystal axis, wherein the third orientation can be described as emerging from a rotation of the second orientation, the rotation not corresponding to a rotation around the optical system axis by an angle of 90° or an integer multiple thereof.