[110] Crystal Cut Beam Splitter for Microlithography
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Solution Overview
Problem
In microlithography, optical components like beam splitters in laser light sources experience thermally induced stress birefringence and degradation-related disruptions, leading to undesirable polarization disturbances and performance impairment under high radiation exposure, especially at wavelengths below 200 nm.
Innovation Solution
A beam splitter with a [110] crystal cut and specific rotational orientation is used, positioned at 45° with respect to the incident radiation, minimizing stress birefringence by ensuring favorable beam propagation angles relative to crystal directions, thereby reducing polarization disturbances for both direct and circulated beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If beam splitters are used in laser light sources for microlithography at high radiation exposure, then the imaging performance is improved, but stress birefringence and polarization disturbances occur due to thermal heating
Solution Approach 1:
The patent changes the physical parameter of the beam splitter by selecting a specific crystal cut orientation ([110] instead of conventional cuts) to fundamentally alter how thermal stress affects the material's optical properties. This parameter change transforms the beam splitter's response to thermal heating, minimizing stress birefringence while maintaining the necessary beam splitting function for high-contrast imaging in microlithography
2Productivity
If beam splitters operate at high light output levels, then the productivity of microlithography is improved, but thermal heating causes stress birefringence and permanent material degradation
Solution Approach 1:
The invention changes the crystal orientation parameter to [110] cut, which fundamentally alters the material's thermal stress response. This allows the beam splitter to operate at high light output levels required for productive microlithography while maintaining polarization stability, as the new orientation minimizes the coupling between thermal stress and optical path differences
Solution Approach 2:
The patent converts the harmful effect of thermal heating into a beneficial outcome by selecting a crystal orientation where thermal expansion and stress distribution actually reduce birefringence. The thermal energy that would normally degrade performance is now accommodated by the [110] oriented crystal structure, which distributes stress in a manner that preserves polarization properties even at high operating powers
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 significantly reduces mechanical stress-induced birefringence, maintaining stable polarization properties and enhancing the performance of microlithographic projection exposure apparatuses by minimizing polarization disturbances across varying operational conditions.
Implementation Method 1
the angles of incidence with respect to the surface normal which occur at the light entry surface during operation of the optical system lie in the range of 45°±5°
Implementation Method 2
the relevant radiation is typically deflected via circulation paths
Implementation Method 3
thermally induced mechanical stresses can occur when generating high light outputs as a result of local heating within the respective optical components or beam splitters, which can then lead to stress birefringence (SB)
Implementation Method 4
local heating within the respective optical components or beam splitters
Data Source
AI summary
An optical system, in particular for microlithography, includes a beam splitter, which has at least one light entry surface. The beam splitter is arranged in the optical system so that the angles of incidence with respect to the surface normal which occur at the light entry surface during operation of the optical system lie in the range of 45°±5°. The beam splitter is produced in [110] the crystal cut.