Dynamic Polarization Manipulator for Microlithography Stress Birefringence
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Solution Overview
Problem
Existing optical systems in microlithographic projection exposure apparatuses face challenges in compensating for time-variable disturbances in polarization distribution due to stress birefringence effects and changes in illumination settings, leading to polarization-induced birefringence that increases over time.
Innovation Solution
An optical system with a polarization manipulator comprising a first subelement with a non-planar, optically effective surface and a second subelement with mutually complementary surfaces, where the relative position of these subelements can be manipulated to control the polarization state, allowing for compensation of time-variable disturbances. The position manipulator adjusts the subelements' position along the optical axis, including rotation and displacement, to manage the amplitude of retardation, thereby stabilizing the polarization distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical elements are used in the illumination system, then polarization distribution can be controlled, but time-dependent polarization disturbances occur due to stress birefringence effects and material degradation
Solution Approach 1:
The patent applies the dynamics principle by making the optical element movable along the optical axis. The position manipulator enables dynamic adjustment of the optical element's position, allowing the system to adapt to time-dependent polarization disturbances. This transforms a static optical system into a dynamic one that can compensate for stress birefringence effects and material degradation by adjusting the element's position to maintain optimal polarization distribution.
2Manufacturing precision
If fixed polarization manipulators are used, then initial polarization distribution is optimized, but the system cannot compensate for changes in illumination settings or material degradation
Solution Approach 1:
The patent implements dynamics by enabling the optical element to move along the optical axis in response to changing conditions. This dynamic capability allows the system to maintain optimal imaging contrast not only at the initial state but also when illumination settings change or when material degradation occurs over time, thus combining manufacturing precision with adaptability.
Solution Approach 2:
The patent applies feedback by using a position manipulator that can adjust the optical element's position based on detected polarization distribution changes. This feedback mechanism enables the system to sense deviations from optimal polarization distribution and automatically correct them by repositioning the optical element, thereby maintaining imaging contrast under varying conditions.
3Reliability
If multiple polarization manipulators are added to compensate for time-dependent disturbances, then polarization stability improves, but device complexity increases
Solution Approach 1:
The patent resolves this contradiction by making a single optical element dynamic rather than adding multiple static elements. By enabling movement along the optical axis, one optical element can perform the function of multiple fixed elements, as its position can be adjusted to compensate for different types and magnitudes of polarization disturbances, thereby maintaining stability without increasing the number of components.
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 solution effectively compensates for time-variable disturbances in polarization distribution, ensuring consistent imaging quality by dynamically adjusting the relative position of the subelements to manage both the mean and difference values of wave fronts for p- and s-polarized light, thus addressing the issues of material degradation and changing operational conditions.
Implementation Method 1
changes in the desired polarization distribution in the optical system as a consequence of a change in the illumination setting... Polarization-induced birefringence ('PBR') which increases in its amplitude in the course of time with illumination with the same illumination setting
Implementation Method 2
a maximum effective retardation introduced by the first subelement along the optical axis is less than a quarter of the working wavelength of the optical system
Data Source
AI summary
The invention concerns an optical system having an optical axis (OA) and comprising a polariser (100, 200) having a first subelement (110, 210) which has a non-planar, optically effective surface wherein the maximum effective retardation introduced by the first subelement along the optical axis (OA) is less than a quarter of the working wavelength of the optical system, and a second subelement (120, 220), wherein said first subelement and said second subelement have mutually facing surfaces (110a, 120a, 210a, 220a) which are mutually complementary, and an actuator (150, 250) for changing the relative position of said first subelement (110, 210) with respect to said second subelement (120, 220).