Diffractive Optical Element With Glass Etch-Stop Control
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Solution Overview
Problem
Existing diffractive optical elements (DOE) face challenges in precisely controlling etching depth during dry etching, particularly with materials like silicon and fused silica, which are limited by fast etching speeds and require thicker coatings to prevent substrate destruction, affecting optical performance.
Innovation Solution
A diffractive optical element with at least two layers having different etching speeds, where a glass substrate with specific compositions serves as an etching stop layer, controlling etching depth with a ratio of 1:2 to 1:20 compared to the microstructure layer, ensuring precise control and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fused silica is used as substrate material for dry etching, then etching speed is fast, but etching depth control precision deteriorates
Solution Approach 1:
The patent introduces a microstructure layer as an intermediary between the glass substrate and the etching process. This layer has different etching characteristics that mediate the interaction between the etching plasma and the substrate, enabling both fast etching speed and precise depth control by stopping the etching at the interface between the microstructure layer and glass substrate.
Solution Approach 2:
The patent employs a composite structure consisting of a glass substrate combined with a microstructure layer made of materials having different etching speeds. This composite material approach allows the system to leverage the fast etching speed of the microstructure layer while using the glass substrate as an etching stop layer to ensure precise depth control.
2Reliability
If thicker coating layers are used to prevent substrate destruction, then substrate protection is improved, but optical performance deteriorates
Solution Approach 1:
The microstructure layer serves as an intermediary that protects the glass substrate from direct exposure to the etching plasma. By positioning this protective layer at the interface, it prevents substrate destruction while maintaining thin overall thickness to preserve optical performance.
Solution Approach 2:
The patent applies different material properties to different layers: the glass substrate provides mechanical strength and optical transparency, while the microstructure layer provides etching resistance and depth control. This local differentiation of material qualities allows simultaneous achievement of substrate protection and optical performance.
3Manufacturing precision
If glass substrate is used as etching stop layer, then etching depth control precision is improved, but material transmission capability worsens
Solution Approach 1:
The glass substrate acts as an intermediary etching stop layer that enables precise depth control by stopping the etching process at a controlled interface. Its position and material properties allow it to function as a stop layer while maintaining optical transmission capabilities through the overall thin structure.
Solution Approach 2:
The patent optimizes the thickness parameter of the microstructure layer and the composition parameters of the glass substrate to achieve the right balance. By carefully controlling these parameters, the glass substrate can serve as an effective etching stop layer while maintaining sufficient light transmission capability for optical applications.
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 enables high-precision etching depth control, reducing etching speed variations, improving diffraction efficiency from 10% to over 40%, and maintaining optical performance by using glass as a stable, transparent, and isotropic material.
Implementation Method 1
The ratio of dry etching speed in thickness direction of the substrate of glass to that of the microstructure layer is no more than 1:2, preferably no more than 1:5, more preferably no more than 1:10 or most preferably no more than 1:20, so that the substrate functions as an etching stop layer
Implementation Method 2
Diffractive optical elements (DOE) are used in various kinds of optical devices, optical components and optical apparatuses, where the diffraction function is needed
Data Source
Figure 1
Figure 2a~2d
Figure 3a~4
AI summary
A diffractive optical element comprising at least two layers with different etching speeds for dry etching process. The diffractive optical element comprises a substrate of glass (12) and a microstructure layer (10) arranged on the substrate of glass (12). The ratio of dry etching speed in thickness direction of the substrate of glass (12) to that of the microstructure layer (10) is no more than 1: 2, preferably no more than 1: 5, more preferably no more than 1: 10 or most preferably no more than 1: 20, so that the substrate functions as an etching stop layer. The ratio of dry etching speed in horizontal direction of the substrate of glass (12) is substantial equal to that of the microstructure layer (10). The composition of glass (12) includes but not limited to Al 2O 3, alkaline material (M 2O) and alkaline earth material (MO). And the weight percentage of Al 2O 3+M 2O+MO>=5%. The height of the microstructure can be controlled with a high precision.