Birefringence Compensation in Microlithography Illumination Systems
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Microlithographic projection exposure systems face challenges in effectively compensating for rotationally symmetric birefringence components, which affect the polarization state of light, leading to suboptimal image transfer in microstructured component production.
Innovation Solution
Incorporating an optical element made of optically uniaxial crystal material with a rotationally symmetric refractive index ellipsoid, oriented parallel to the system's optical axis, to compensate for birefringence by adjusting the refractive index differently for components parallel and perpendicular to the optical crystal axis, thereby achieving effective compensation of rotationally symmetric interference components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical elements are used in the illumination system, then the system structure is simple, but rotationally symmetric birefringence components cannot be effectively compensated, leading to degraded polarization state and suboptimal image transfer
Solution Approach 1:
The patent employs a composite optical element consisting of a birefringent material layer (such as quartz or calcite) combined with a compensating optical element. The birefringent material introduces controlled phase differences between orthogonal polarization components, while the compensating element (such as a wave plate or another birefringent layer with opposite characteristics) counteracts the rotationally symmetric birefringence. This composite structure enables effective polarization compensation without requiring complete system redesign.
Solution Approach 2:
The patent adjusts optical parameters such as the thickness, refractive index, and orientation of the birefringent material layers to compensate for rotationally symmetric birefringence. By changing these parameters, the optical path difference between orthogonal polarization components is controlled to achieve the desired compensation effect. The aperture angle constraint (≤35 mrad) is also a parameter optimization to minimize higher-order aberrations while maintaining compensation effectiveness.
2Area of stationary object
If the aperture angle of the entry beam is increased, then the illumination coverage is improved, but the polarization acquisition deteriorates due to increased sensitivity to birefringence effects
Solution Approach 1:
The patent optimizes the aperture angle parameter to be not more than 35 mrad at the location of the optical element. This parameter constraint balances the trade-off between illumination coverage and polarization acquisition. By limiting the aperture angle, the system maintains sufficient illumination area while minimizing the degradation of polarization state caused by birefringence effects, which increase quadratically with the angle relative to the optical crystal axis.
3Reliability
If optically uniaxial crystal material with optical crystal axis parallel to optical axis is used, then rotationally symmetric birefringence compensation is achieved, but the device complexity increases
Solution Approach 1:
The patent uses a composite optical element where an optically uniaxial crystal material (such as quartz, calcite, or lithium niobate) with its optical crystal axis oriented parallel to the optical axis of the illumination system is combined with compensating optical elements. This composite configuration achieves rotationally symmetric birefringence compensation while managing the increased device complexity through integrated design.
Solution Approach 2:
The patent applies local quality by orienting the optical crystal axis of the uniaxial material parallel to the optical axis specifically in the region where rotationally symmetric birefringence compensation is needed. This localized orientation strategy enables effective compensation of rotationally symmetric interference components without requiring complex adjustments throughout the entire optical system.
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 ensures improved polarization acquisition and stability in the illumination system, allowing for precise control of birefringence compensation, enhancing the quality of image transfer onto substrates during microlithographic processes.
Implementation Method 1
A component of a birefringence present in the illumination system can be at least partially compensated by the optical element. The optical element includes optically uniaxial crystal material which is not optically active, with an optical crystal axis, wherein the optical crystal axis is oriented in parallel relationship with the optical axis of the illumination system.
Implementation Method 2
the two components experience a different refractive index in the optical element and the strength of the birefringence caused thereby increases quadratically with the angle relative to the optical crystal axis
Data Source
AI summary
The disclosure provides an illumination system of a microlithographic projection exposure apparatus, as well as related methods and components. In some embodiments, the illumination system includes an optical element configured so that, when a linearly polarized entry beam which has an angle spectrum is incident on the first optical element, a maximum aperture angle of the entry beam at the first optical element is not more than 35 mrad. A component, which is rotationally symmetric about an optical axis of the system, of a birefringence present in the illumination system can be at least partially compensated by the first optical element.