Gray-tone Lithography for Waveguide Grating Etch Depth Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical see-through waveguide displays in augmented and mixed reality systems face challenges in fabricating non-uniform grating couplers with variable etch depths and refractive indices, leading to optical artifacts and display leakage.
Innovation Solution
The use of gray-tone lithography techniques to form surface-relief gratings with variable depths and refractive indices, including the gray-tone-first and gray-tone-last processes, which involve depositing photoresist layers and etching to create gratings with desired thickness profiles and etch depths, and the application of overcoat layers to control the top surface and reduce optical artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional lithography is used to fabricate grating couplers, then the manufacturing process is simple, but the etch depth uniformity is poor leading to optical artifacts and display leakage
Solution Approach 1:
The patent applies preliminary action by depositing an overcoat layer on the grating coupler structure before performing lithography and etching. This overcoat layer serves as a protective and reference layer that ensures uniform etch depth across the grating structure, preventing the optical artifacts and display leakage that would otherwise result from non-uniform etching in conventional processes.
2Manufacturing precision
If gray-tone lithography is used to achieve variable etch depths, then the control precision over grating parameters improves, but the manufacturing process complexity increases
Solution Approach 1:
The patent implements local quality by using gray-tone lithography to create spatially varying etch depths across different regions of the grating coupler. The lithography process exposes the photoresist to non-uniform light intensity, resulting in different etch depths in different areas, which allows precise control of grating parameters to optimize optical performance while managing fabrication complexity through systematic process design.
3Object-affected harmful factors
If surface-relief gratings with variable depths are fabricated, then optical artifact reduction is achieved, but the manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by depositing the overcoat layer before lithography and etching processes. This overcoat layer acts as a protective barrier and reference plane that enables the fabrication of surface-relief gratings with variable depths while maintaining manufacturing feasibility. The overcoat ensures that the variable depth structure is achieved with controlled precision, reducing optical artifacts without excessively increasing fabrication complexity.
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 improves the efficiency and image quality by reducing optical artifacts and display leakage, enhancing the performance of waveguide displays by allowing for more precise control over grating parameters and reducing unwanted light diffusion.
Implementation Method 1
The gray-tone photoresist layer may be characterized by a non-binary response to exposure dosage such that a depth of an exposed portion of the gray-tone photoresist layer is a function of the exposure dosage
Implementation Method 2
etching the gray-tone photoresist layer and the overcoat layer to form a flat top surface on the overcoat layer
Data Source
AI summary
Gray-tone lithography techniques for controlling the thickness profile of an overcoat layer on a surface-relief grating that has a non-uniform grating parameter (e.g., depth, duty cycle, or period), compensating for the non-uniform etch rate in a large area, defining etch/block regions, and/or controlling the thickness of the grating layer.