Aperiodic Dielectric Multilayer UV Reflective Element
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Solution Overview
Problem
Existing reflective optical elements for ultraviolet radiation in microlithography projection exposure apparatuses face challenges in maintaining high reflectance and minimizing the difference in amplitude and phase of polarization components over a wide range of incident angles, leading to degraded imaging performance due to periodic dielectric multilayer systems that absorb radiation differently for high and low refractive index layers.
Innovation Solution
A reflective optical element with a dielectric multilayer system where the optical thicknesses of high and low refractive index layers in each adjacent pair are different, resulting in an aperiodic design that reduces absorption and phase shift between polarization components, with the optical thickness of high refractive index layers decreasing and low refractive index layers increasing with distance from the reflective surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a periodic dielectric multilayer system with alternating high and low refractive index layers of equal optical thickness is used, then high reflectance is achieved at a specific incident angle, but the reflectance degrades significantly over a wide range of incident angles and polarization components show large amplitude and phase differences
Solution Approach 1:
The patent applies asymmetry by making the optical thicknesses of adjacent high and low refractive index layers different from each other, breaking the periodic symmetry of conventional multilayer systems. This asymmetric design creates a gradient structure that maintains high reflectance across wide angular ranges and minimizes polarization-dependent performance variations
Solution Approach 2:
The patent implements local quality by varying the optical thickness of each layer individually rather than using uniform thickness throughout. Each layer pair has specifically optimized different thickness values tailored to local optical requirements, enabling the system to achieve broad angular acceptance and reduced polarization sensitivity
2Illumination intensity
If a dielectric multilayer system with many alternating layers is used to maximize reflectance, then high reflectance is achieved, but the system becomes complex and absorbs radiation differently for high and low refractive index layers, degrading imaging performance
Solution Approach 1:
The patent applies parameter changes by systematically varying the optical thickness parameters of each layer in the multilayer system. Instead of using equal thicknesses, each layer pair has optimized different thickness values that collectively achieve high reflectance with reduced complexity and minimized differential absorption effects
3Ease of manufacture
If a periodic multilayer system with equal optical thickness layers is used, then the structure is simple to manufacture, but the amplitude and phase difference between s-polarized and p-polarized radiation components becomes significant, degrading imaging performance
Solution Approach 1:
The patent resolves this contradiction by introducing asymmetry in layer thickness design. While the manufacturing process remains relatively simple, the asymmetric thickness configuration specifically addresses polarization performance by minimizing amplitude and phase differences between s and p polarized components through optimized local thickness 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 aperiodic design achieves superior optical performance by maintaining high reflectance and minimizing amplitude and phase differences between polarization components, reducing the overall thickness and number of layers required, and improving imaging quality in microlithography systems.
Implementation Method 1
a dielectric multilayer system formed on the reflective surface, said dielectric multilayer system comprising at least two successive pairs of layers, each pair of layers consisting of a high refractive index layer alternating with a low refractive index layer
Implementation Method 2
Reflective optical element for radiation with a wavelength λ in the ultraviolet wavelength range comprising: a reflective surface
Implementation Method 3
absorb radiation differently for high and low refractive index layers
Data Source
AI summary
A reflective optical element (1) for radiation with a wavelength λ in the ultraviolet wavelength range comprises a reflective surface (6), and a dielectric multilayer system (4) formed on the reflective surface (6) which comprises at least two successive pairs of layers (5.i, 5.i+1), each pair of layers (5.1 to 5.N) consisting of a high refractive index layer (H1 to HN) alternating with a low refractive index layer (L1 to LN), wherein the optical thicknesses (Hi, Hi+1) of the high refractive index layers (Hi, Hi+1) and the optical thicknesses (Li, Li+1) of the low refractive index layers (Li, Li+1) of each adjacent pair of layers (5.i, 5.i+1) are different from each other.