Microlithography Illumination System Polarization Compensation
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Solution Overview
Problem
Microlithographic projection exposure apparatuses face challenges in producing unpolarized light due to residual polarization effects from anti-reflecting and highly reflecting layers, leading to non-homogeneous distribution and complications in polarization-optical compensation.
Innovation Solution
The illumination system configures light components with mutually orthogonal polarization states, which are superposed in the object plane to produce effectively unpolarized light, using a polarization-influencing optical arrangement that rotates or reverses polarization states, allowing for incoherent superposition and simplifying the compensation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If anti-reflecting layers and highly reflecting layers are used in the illumination system, then light reflection and transmission are improved, but residual polarization is introduced causing non-homogeneous polarization distribution
Solution Approach 1:
The illumination system is divided into two subsystems with point-symmetrical optical elements. Each element in one subsystem has a corresponding point-symmetrical element in the other subsystem, allowing the polarization effects to be segmented and subsequently compensated by combining them incoherently in the object plane.
Solution Approach 2:
The patent utilizes point-symmetrical (centrosymmetrical) arrangement of optical elements rather than simple symmetry. This asymmetrical arrangement with respect to the optical axis creates complementary polarization states that, when combined, achieve uniform unpolarized light in the object plane.
2Ease of operation
If conventional polarization compensation methods are used (such as Hanle depolarizer and light mixing system), then depolarization is achieved, but the system complexity and alignment requirements increase
Solution Approach 1:
The illumination system's own optical elements (lenses and mirrors arranged in point-symmetry) generate the polarization compensation effect inherently. The system uses its existing structure to compensate for the polarization effects it produces, eliminating the need for separate depolarization devices and simplifying the overall system.
3Ease of operation
If point-symmetrical optical elements with different orientations are used, then residual polarization compensation is achieved, but the manufacturing and alignment precision requirements increase
Solution Approach 1:
The patent employs point-symmetrical arrangement where each optical element has a counterpart rotated by 180 degrees around the optical axis. This specific asymmetrical configuration ensures that polarization effects from one element are exactly compensated by its point-symmetrical counterpart, achieving precise compensation through geometric arrangement rather than complex alignment procedures.
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 effectively generates unpolarized light in the image plane by transforming the imaging equation, reducing residual polarization and avoiding complex compensation mechanisms, while maintaining efficient production of microstructured components.
Implementation Method 1
Light components in point-symmetrical relationship with each other which are produced during use of the illumination system and which are only superposed in the object plane have mutually orthogonal polarization states
Implementation Method 2
light components in point-symmetrical relationship with each other which are produced during use of the illumination system and which are only superposed in the object plane
Data Source
AI summary
A microlithographic projection exposure apparatus includes an illumination system and a projection objective. During use of the microlithographic projection exposure apparatus, the illumination system illuminates an object plane of the projection objective. The illumination system is configured so that light components in point-symmetrical relationship with each other, which are produced during use of the illumination system and which are only superposed in the object plane, have mutually orthogonal polarization states.