Waveguide Grating Contamination Reduction via Blocking Layer
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Solution Overview
Problem
Conventional methods for producing optical gratings in waveguides for head-mounted displays (HMDs) introduce contaminants, such as chromium (Cr), which degrade the optical performance by absorbing or redirecting display light.
Innovation Solution
A method involving the use of a blocking layer, typically SiO2 or SiN, between the grating layer and the hardmask layer, prevents diffusion of contaminants from the hardmask layer into the grating layer during the etching process, thereby reducing or eliminating contamination in the final waveguide product.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used to form optical gratings in waveguides, then the manufacturing process is simple and direct, but contaminants from the hardmask layer diffuse into the grating layer during etching, degrading optical performance
Solution Approach 1:
A blocking layer is introduced as an intermediary between the hardmask layer and the grating layer. This blocking layer prevents contaminant diffusion from the hardmask layer into the grating layer during the etching process, thereby protecting the optical grating purity without requiring changes to the fundamental etching methodology
Solution Approach 2:
The fabrication process is segmented into distinct stages with the blocking layer serving as a separate functional component. The blocking layer is formed, patterned, and removed as independent steps, allowing the contamination prevention function to be isolated and optimized without affecting other parts of the manufacturing process
2Reliability
If a blocking layer is introduced between the hardmask layer and grating layer to prevent contamination, then optical grating purity is improved, but the fabrication process complexity increases
Solution Approach 1:
The blocking layer acts as a temporary intermediary structure that ensures reliable optical performance by preventing contaminant diffusion. It is designed to be formed, patterned, and completely removed after serving its protective function, leaving no residual complexity in the final product
Solution Approach 2:
The blocking layer uses materials with specific etch selectivity parameters that enable it to be selectively removed after protecting the grating layer. By controlling the etch rates and chemical properties of the blocking layer relative to other layers, the process achieves contamination prevention with manageable 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
The implementation of this method results in waveguides with optical gratings that are substantially free from contaminants, enhancing the optical performance by increasing the amount of display light directed to the user.
Implementation Method 1
prevents diffusion of contaminants from the hardmask layer into the grating layer during the etching process
Implementation Method 2
an optical grating, which can be formed on a surface, or multiple surfaces, of the substrate or disposed within the substrate. Once the light beams have been coupled into the waveguide
Implementation Method 3
the light beams are 'guided' through the waveguide, typically by multiple instances of total internal reflection (TIR), to then be directed out of the waveguide
Data Source
AI summary
The present disclosure provides techniques to reduce or eliminate contaminants in a waveguide resulting from the waveguide fabrication process. A blocking layer is deposited on a grating layer to protect the grating layer from contamination, e.g., via diffusion, from a hardmask layer that is used to pattern the grating layer. Accordingly, the optical gratings resulting from the patterning of the grating layer have little or no contamination from the hardmask layer, thereby increasing the optical performance of the final waveguide product.