CaF2 Crystal Orientation for UV Laser Polarization
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Solution Overview
Problem
Current semiconductor exposure apparatuses face challenges in maintaining high resolution due to chromatic aberrations caused by the wide spectral linewidth of KrF and ArF excimer laser apparatuses, leading to decreased polarization and power of the laser beam, which affects the quality of the exposure process.
Innovation Solution
The use of CaF2 crystal optical elements with specific orientations and cutting angles to align the electric field axis of the laser beam with the crystal's axis, reducing thermal stress and birefringence, and optimizing the configuration of windows, beam splitters, and prisms to minimize absorption and reflection losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the spectral linewidth of the laser light is narrowed to avoid chromatic aberrations, then resolution is maintained, but the degree of polarization and power of the laser beam decrease
Solution Approach 1:
The patent changes the parameter of angle of incidence to optimize the balance between spectral linewidth narrowing and power maintenance. By setting the angle of incidence to Brewster's angle, the P-polarized component is transmitted with minimal reflection loss, maintaining high power while achieving sufficient linewidth narrowing to reduce chromatic aberrations and preserve resolution
2Ease of manufacture
If the angle of incidence of the laser beam on the CaF2 crystal window is increased to improve polarization, then the degree of polarization increases, but reflection losses increase and power decreases
Solution Approach 1:
The patent converts the harmful effect of reflection losses into a beneficial outcome by deliberately setting the angle of incidence to Brewster's angle. At this specific angle, P-polarized light experiences zero reflection loss, transforming what would normally be a loss mechanism into a means of achieving both high polarization and high power transmission simultaneously
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 enhances the degree of polarization and power of the laser beam, improving the durability and performance of the optical elements, thereby maintaining high-resolution exposure capabilities.
Implementation Method 1
an optical element that is made of a CaF2 crystal and configured to transmit an ultraviolet laser beam obliquely incident on one surface of the optical element, an electric field axis of a P-polarized component of the laser beam propagating through an interior of the optical element coinciding with one axis contained in <100> of the CaF2 crystal
Implementation Method 2
reducing thermal stress and birefringence
Data Source
AI summary
A laser apparatus including an optical element made of a CaF2 crystal and configured to transmit an ultraviolet laser beam obliquely incident on one surface of the optical element, the electric field axis of the P-polarized component of the laser beam propagating through the optical element coinciding with one axis contained in <111> of the CaF2 crystal, with the P-polarized component defined with respect to the one surface. A method for manufacturing an optical element, the method including causing a seed CaF2 crystal to undergo crystal growth along one axis contained in <111> to form an ingot, setting a cutting axis to be an axis inclining by an angle within 14.18±5° with respect to the crystal growth direction toward the direction of another axis contained in <111>, which differs from the crystal growth direction, and cutting the ingot along a plane perpendicular to the cutting axis.