Slanted Surface-Relief Grating Fabrication via Segmented Mask Etching
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Solution Overview
Problem
Fabricating deep slanted surface-relief gratings with large slanted angles and wide ranges of grating duty cycles is challenging due to shadowing effects from thick etch masks, leading to increased duty cycles and reduced fabrication speed and accuracy in waveguide-based displays.
Innovation Solution
The use of intermediate mask layers with high etch rates and selectivity, combined with thin hard masks, allows for the fabrication of slanted surface-relief structures with reduced duty cycles and increased depth, minimizing shadowing effects and improving productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If thick etch masks are used to etch deep slanted structures, then etching depth is improved, but shadowing effects increase causing duty cycle distortion and manufacturing precision degradation
Solution Approach 1:
The etching process is segmented into multiple steps using different mask layers. A thin hard mask layer (5-20 nm) is used in conjunction with a thick intermediate mask layer, allowing the etching to be performed in stages. This segmentation enables deep etching while maintaining duty cycle accuracy by using the thin hard mask to define the final pattern dimensions.
Solution Approach 2:
An intermediate mask layer is introduced as a mediator between the thin hard mask and the substrate. This intermediate layer has high etch selectivity, allowing it to be etched away faster than the substrate while protecting the thin hard mask. The intermediate mask enables deep etching without the shadowing effects that would occur with a single thick mask layer.
2Use of energy by moving object
If slanted angles are increased to improve light coupling efficiency, then optical performance is improved, but shadowing effects from masks are amplified causing fabrication difficulty
Solution Approach 1:
The fabrication process is segmented into multiple etching steps with different mask layers. The thin hard mask defines the final slanted pattern, while the intermediate mask enables the deep slanted structure to be formed without excessive shadowing during the etching process, making high slant angles manufacturable.
Solution Approach 2:
The etch selectivity parameter is optimized by choosing materials with appropriate etch rate ratios. The intermediate mask layer is selected to have an etch rate at least 3 times faster than the substrate, enabling the formation of deep slanted structures with angles greater than 30 degrees while maintaining fabrication feasibility.
3Productivity
If etching speed is increased to improve productivity, then manufacturing efficiency is improved, but control over duty cycle and depth precision is reduced
Solution Approach 1:
The etching process is segmented into multiple steps: first etching the intermediate mask layer quickly (high productivity), then etching the substrate with controlled precision. This allows overall fast fabrication while maintaining precision in the final structure dimensions through the thin hard mask layer.
Solution Approach 2:
The intermediate mask layer acts as a sacrificial mediator that can be etched away rapidly, enabling the substrate etching to proceed at high speed. The thin hard mask then provides the final precision control, decoupling the speed and precision requirements of the overall process.
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 enables the production of slanted surface-relief gratings with low duty cycles and high depths, enhancing the field of view, brightness, and reducing display artifacts in waveguide-based displays, such as those used in augmented reality systems.
Implementation Method 1
etching the intermediate mask layer at a slant angle using the thin hard mask to form a slanted intermediate mask
Implementation Method 2
etching the material layer at the slant angle using the slanted intermediate mask to form the slanted surface-relief structure in the material layer
Implementation Method 3
the light of the projected images may be coupled into or out of the waveguide using a diffractive optical element, such as a slanted surface-relief grating
Implementation Method 4
deep surface-relief gratings with large slanted angles and wide ranges of grating duty cycles may be used
Data Source
AI summary
Techniques for fabricating a slanted structure are disclosed. In one embodiment, a method of fabricating a slanted surface-relief structure in a material layer includes forming a thin hard mask on top of an intermediate mask layer, etching the intermediate mask layer at a slant angle using the thin hard mask to form a slanted intermediate mask, and etching the material layer at the slant angle using the slanted intermediate mask to form the slanted surface-relief structure in the material layer. The intermediate mask layer is characterized by an etch rate greater than an etch rate of the material layer.