Birefringent Retardation Arrangement for Microlithography
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Solution Overview
Problem
Microlithographic projection exposure apparatuses face challenges in reducing unwanted variation in retardation due to the angle of incidence or propagation direction of electromagnetic radiation, particularly with existing retardation arrangements that are sensitive to component thickness and tilt angles.
Innovation Solution
A birefringent retardation arrangement is implemented, comprising a combination of optically positively and negatively uniaxial crystal materials with specific orientations of their optical crystal axes, either perpendicular or parallel to each other, to minimize the dependency of retardation on the angle of incidence or propagation direction, allowing for thicker components with reduced angle dependency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single uniaxial crystal material is used for retardation, then the component can be simpler in structure, but the retardation varies significantly with angle of incidence and propagation direction
Solution Approach 1:
The patent combines two uniaxial crystal materials with opposite optical signs (positive and negative) to create a composite retardation arrangement. This composite structure compensates for the angle-dependent retardation variation of individual materials, achieving stable retardation across different angles of incidence and propagation directions while maintaining structural simplicity.
2Length of stationary object
If thicker retardation components are used, then higher-order retardation elements can be implemented, but the angle dependency of retardation increases
Solution Approach 1:
By combining thicker components of opposite uniaxial crystal materials, the patent achieves higher-order retardation elements that maintain acceptable angle acceptance. The opposite optical signs of the two materials cause their angle-dependent retardation variations to compensate each other, allowing thicker components without proportionally increasing angle dependency.
Solution Approach 2:
The patent changes the optical parameters by selecting materials with opposite optical signs and specific birefringence values. This parameter selection enables the compensation of angle-dependent effects and allows optimization of thickness while maintaining reliable angle acceptance characteristics.
3Manufacturing precision
If retardation arrangements are made sensitive to component thickness, then manufacturing precision can be controlled, but the retardation becomes highly dependent on tilt angles and incidence angles
Solution Approach 1:
The patent uses composite materials with opposite optical signs to create a retardation arrangement where the total retardation is less sensitive to both thickness variations and angle variations. The compensating effects of the two materials reduce the overall sensitivity, providing both manufacturing precision and angle independence.
Solution Approach 2:
The patent applies different crystal materials with specific optical properties to different regions of the retardation arrangement. By carefully selecting and positioning materials with opposite optical signs, the local optical qualities compensate for each other, reducing overall sensitivity to manufacturing tolerances and angular variations.
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 reduces the variation in retardation with tilt angles and directions, enabling the use of higher-order retardation elements with acceptable angle acceptance, thus addressing manufacturing challenges and improving the stability of microlithographic processes.
Implementation Method 1
The term 'retardation' is used to denote the difference in the optical paths of two orthogonal (mutually perpendicular) polarisation states. The birefringent arrangement includes a retardation element, which, in turn, includes a first subelement and a second subelement. The first subelement includes an optically positively uniaxial crystal material which has a first optical crystal axis. The second subelement includes an optically negatively uniaxial crystal material which has a second optical crystal axis
Data Source
AI summary
Microlithographic projection exposure apparatuses, as well as related components, subsystems and methods are disclosed.