Micromirror Coating Segmentation for Stray Light and Stability
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Solution Overview
Problem
Micromirror arrangements face issues with coatings degrading under intensive irradiation, leading to increased stray light and inadequate performance at different wavelengths, particularly in microlithography applications where calibration requires varying wavelengths.
Innovation Solution
A micromirror arrangement with a reflective coating on the mirror substrate within the reflective surface and an antireflection coating composed of nonmetallic materials outside the reflective surface, featuring a periodic sequence of high and low refractive index layers optimized for specific wavelengths, along with an absorbent layer to minimize extraneous light reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a reflective coating is applied to increase reflectivity, then the reflectivity at the used wavelength is improved, but the coating degrades under intensive irradiation and produces stray light
Solution Approach 1:
The coating is divided into multiple functional layers: a reflective layer (e.g., aluminum or silver) for high reflectivity, and a protective overlay layer (e.g., silicon oxide, silicon nitride, or diamond-like carbon) that is radiation-resistant. This segmentation allows each layer to perform its specific function without compromising the other.
Solution Approach 2:
The patent employs composite coating structures combining different materials with complementary properties. The reflective metal layer provides high reflectivity, while the overlay layer made of radiation-resistant materials protects against degradation and hillock formation, creating a composite structure that achieves both high reflectivity and long-term stability.
2Ease of manufacture
If a single-layer coating is used, then the manufacturing process is simplified, but the coating cannot simultaneously optimize reflectivity at different wavelengths
Solution Approach 1:
The coating is segmented into multiple functional layers: a reflective layer (e.g., aluminum or silver) for high reflectivity, and a protective overlay layer (e.g., silicon oxide, silicon nitride, or diamond-like carbon) that is radiation-resistant. This segmentation allows each layer to perform its specific function without compromising the other.
Solution Approach 2:
The patent employs composite coating structures combining different materials with complementary properties. The reflective metal layer provides high reflectivity, while the overlay layer made of radiation-resistant materials protects against degradation and hillock formation, creating a composite structure that achieves both high reflectivity and long-term stability.
3Area of stationary object
If the reflective surface areas are placed directly adjacent to one another, then the device area is minimized, but stray light from adjacent micromirrors increases
Solution Approach 1:
The patent applies different coating properties to different regions: the reflective surfaces have high-reflectivity coatings, while the non-reflective regions between micromirrors have absorptive or blackening coatings. This local differentiation ensures that light falling on non-reflective areas is absorbed rather than scattered, eliminating stray light without requiring larger spacing between micromirrors.
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
The solution provides stable reflectivity at the intended wavelength while suppressing stray light, enabling effective use in microlithography systems by optimizing reflectivity for both the used and measurement wavelengths, thus enhancing the micromirror's performance and reducing extraneous light issues.
Implementation Method 1
an antireflection coating formed at the mirror substrate outside the reflective surface has at least one absorbent layer composed of a preferably nonmetallic material having an absorption coefficient of 0.1 or more, preferably of 0.2 or more, in particular of 0.4 or more, at a wavelength in the UV range, in particular at 193 nm
Implementation Method 2
a reflective coating formed at the mirror substrate within the reflective surface, wherein the reflective coating has at least two layer subsystems, wherein the first layer subsystem has layers composed of a periodic sequence of alternate high and low refractive index layers composed of a nonmetallic material and is optimized with regard to the reflectivity in respect of a used wavelength
Data Source
AI summary
A micromirror arrangement (1) having: at least one micromirror (3) having a reflective surface (11) formed at a mirror substrate (2), and an antireflective coating (7) formed at the mirror substrate (2) outside the reflective surface (11). A reflective coating (8) is formed within the reflective surface (11) and has at least two layer subsystems, wherein the first layer subsystem has layers (8e, 8f) composed of a periodic sequence of alternate high and low refractive index layers composed of a nonmetallic material and is optimized with regard to the reflectivity in respect of a used wavelength of the micromirror arrangement, and wherein the second layer subsystem is optimized with regard to the reflectivity in respect of a measurement wavelength of the micromirror arrangement, said measurement wavelength deviating from the used wavelength.