Graded Refractive Index Anti-Reflection Coating for Broadband Reflectance
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Solution Overview
Problem
In the patterning process of semiconductor devices, unwanted radiation due to unintended reflections poses challenges, particularly in lithographic and metrology apparatuses, where existing anti-reflection coatings have limited effectiveness over a broad wavelength range and high angles of incidence.
Innovation Solution
A graded refractive index anti-reflection coating is formed using a two-step process involving mixtures of aluminum tri-sec-butoxide, chelating agents, and water, with the first mixture applied and then treated to remove alcohol, followed by a second mixture, resulting in a crack-free and striation-free coating with low reflectance across a wide wavelength range and high angles of incidence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional anti-reflection coatings are used, then manufacturing simplicity is maintained, but reflectance control over broad wavelength range and high angles of incidence deteriorates
Solution Approach 1:
The patent applies parameter changes by creating a graded refractive index profile through controlled deposition processes. The refractive index transitions gradually from the substrate value to the ambient value, optimizing reflectance reduction across broad wavelength ranges (300-1200 nm) and high angles of incidence (up to 55 degrees). This gradient structure allows the coating to adapt to multiple wavelengths and angles simultaneously, resolving the contradiction between reflectance control and wavelength range coverage.
Solution Approach 2:
The patent employs composite materials by combining multiple dielectric layers with different refractive indices in a graded structure. Each layer contributes specific optical properties, and their combination creates a progressive refractive index transition. This composite approach enables the coating to achieve low reflectance across broad spectral ranges and wide angular ranges, overcoming the limitations of single-material coatings.
2Object-affected harmful factors
If graded refractive index coating is applied, then reflectance reduction over broad wavelength and angle range is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the graded refractive index coating into multiple discrete dielectric layers. Each layer has a specific refractive index and thickness, collectively forming the gradient profile. This segmentation simplifies manufacturing compared to continuous gradient deposition, as each layer can be deposited using standard techniques, while still achieving the desired broad-spectrum, wide-angle anti-reflection performance.
3Object-affected harmful factors
If tilted or wedged surfaces are used, then ghost images are reduced, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent changes the optical parameters of a flat surface by applying a graded refractive index coating, achieving ghost image reduction without altering the physical geometry of the substrate. The refractive index gradient modifies the optical path and reflection characteristics, eliminating the need for tilted or wedged surface fabrication, thereby simplifying manufacturing while maintaining effectiveness against ghost images.
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 coating achieves reflectance of less than 1% over 300-1200 nm and 0°-55° incidence angles, effectively reducing ghost images and unwanted radiation, improving performance in high numerical aperture systems and eliminating the need for tilted/wedged surfaces.
Implementation Method 1
A graded refractive index anti-reflection coating is formed... achieving reflectance of less than 1% over 300-1200 nm and 0°-55° incidence angles
Data Source
AI summary
A method of forming an anti-reflection layer, the method including applying a first mixture to an object, the first mixture made from a combination of aluminum tri-sec-butoxide (ATSB), a first chelating agent, water and an alcohol; removing a majority of the alcohol from the applied first mixture; after the removing, applying a second mixture to the object, the second mixture made from a combination of aluminum tri-sec-butoxide, a second chelating agent different than the first chelating agent, water and an alcohol; and removing a majority of the alcohol from the applied second mixture, wherein the applied first and second mixtures are used to form the anti-reflection layer.