Optical Grating Sidewall Angle Control via Hardmask Thickness
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Solution Overview
Problem
The existing methods for forming optical gratings in diffracted optical elements, particularly for augmented and virtual reality devices, face challenges in achieving optimal geometries due to processing complexity, leading to unknown optimal parameters for angled gratings.
Innovation Solution
A method involving the formation of an optical grating layer atop a substrate with a hardmask, where the etching process results in angled components with non-zero inclination, causing the width of the patterned hardmask to be reduced faster than the height, forming first and second sidewalls with different angles, optimizing the grating geometry for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If different etches are used to etch gratings in different regions to achieve varied geometries, then the optical component functionality is improved, but the processing complexity increases
Solution Approach 1:
The patent combines multiple etching operations into a single unified etching process. By forming a single hardmask layer with varying thicknesses that corresponds to different desired grating geometries, the patent eliminates the need for multiple separate etching steps with different parameters. This single etching process simultaneously creates multiple grating regions with different geometries (e.g., different pitches, depths, or profiles) by exploiting the thickness variations in the hardmask layer, thereby reducing processing complexity while maintaining geometric versatility.
Solution Approach 2:
The patent performs preliminary shaping of the hardmask layer before the actual grating etching. By forming the hardmask layer with pre-determined thickness variations (through techniques such as variable thickness deposition, selective removal, or patterning), the desired grating geometry information is encoded in advance. This preliminary action allows the subsequent single etching process to directly transfer these thickness variations into the final grating geometries without requiring complex real-time process adjustments or multiple etching steps.
2Ease of manufacture
If optimal parameters for angled gratings are not known due to processing complexity, then the manufacturing precision deteriorates, but the ease of manufacture improves with simpler processes
Solution Approach 1:
The patent incorporates feedback mechanisms to establish correlations between hardmask layer thicknesses and resulting grating geometries. By systematically varying hardmask thicknesses and measuring the resulting grating parameters (such as sidewall angles, depths, and profiles), the patent builds a knowledge base or process model that provides feedback for optimizing subsequent manufacturing runs. This feedback loop enables precise control over grating geometries even with simplified single-step etching processes, as the thickness-geometry relationships can be used to predict and adjust outcomes.
Solution Approach 2:
The patent exploits parameter changes in the hardmask layer thickness as the primary control variable for achieving different grating geometries. Instead of changing etching parameters (such as etch rate, temperature, or chemistry) for different grating regions, the patent maintains consistent etching conditions and achieves geometric variation through thickness modulation of the hardmask. This parameter change strategy simplifies the etching process while maintaining precision, as thickness control is often more straightforward than coordinating multiple dynamic etching parameters.
Data Source
AI summary
Optical grating components and methods of forming are provided. In some embodiments, a method includes providing an optically transparent substrate, and forming an optical grating layer on the substrate. The method includes forming an optical grating in the optical grating layer, wherein the optical grating comprises a plurality of angled components, disposed at a non-zero angle of inclination with respect to a perpendicular to a plane of the substrate. A first sidewall of the optical grating may have a first angle, and a second sidewall of the grating has a second angle different than the first angle. Modifying process parameters, including selectivity and beam angle spread, has an effect of changing a shape or dimension of the plurality of angled components.