Slanted Grating Master Fabrication via Inversion

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Solution Overview

Problem

Conventional fabrication techniques face challenges in creating slanted surface gratings for waveguides due to non-orthogonal relationships, leading to sub-optimal angle control, parallelism, lateral etching, and surface roughness issues, which affect diffraction efficiency in augmented and virtual reality applications.

Innovation Solution

A method involving grayscale lithography and plasma etching processes is used to fabricate a working stamp with slanted gratings, utilizing a sequence of photoresist deposition and etching steps on a master workpiece, allowing for well-defined slanted angles and overcoming the challenges of angle control and surface roughness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional fabrication techniques are used to create slanted surface gratings, then the grating structure can be formed, but angle control and surface roughness deteriorate due to non-orthogonal relationship during fabrication

Engineering Contradiction:

Improvegrating angle controlVSAvoidfabrication difficulty

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent inverts the conventional fabrication approach by first creating vertical sidewall gratings and then tilting the entire grating structure after formation. This inversion resolves the technical contradiction by achieving precise slanted angles through a simple post-processing tilt operation rather than attempting to fabricate slanted gratings directly, which suffers from poor angle control and surface roughness issues.

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If slanted gratings are fabricated using conventional techniques, then the grating pattern can be formed, but surface roughness increases leading to reduced diffraction efficiency

Engineering Contradiction:

Improvediffraction efficiencyVSAvoidsurface roughness

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent achieves smooth slanted grating surfaces by first fabricating vertical gratings with conventional techniques (which produce smooth surfaces) and then tilting the completed grating structure. This inversion eliminates surface roughness issues that would otherwise occur during direct slanted grating fabrication, thereby maintaining high diffraction efficiency.

Inventive Principle:

Principle #13The other way round (Inversion)

3Ease of manufacture

If vertical sidewall gratings are used instead of slanted gratings, then fabrication is easier with conventional techniques, but diffraction efficiency decreases

Engineering Contradiction:

Improvefabrication easeVSAvoiddiffraction efficiency

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent combines the advantages of both vertical and slanted gratings by first fabricating vertical sidewall gratings using easy conventional techniques, then tilting the entire structure to achieve the desired slanted configuration. This inversion allows the fabrication process to benefit from the ease of vertical grating formation while the final tilted structure provides the superior diffraction efficiency of slanted gratings.

Inventive Principle:

Principle #13The other way round (Inversion)

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 method enables the precise fabrication of slanted gratings with improved diffraction efficiency, addressing the challenges of angle control and surface roughness, and results in high-quality waveguides suitable for augmented and virtual reality applications.

Implementation Method 1

a photoresist layer is formed overlying the hard-mask layer, a first lithography process is performed to define an initial grating structure pattern

Methodology Applied

Scientific EffectPhotolithography: Photopolymerisation

Implementation Method 2

a vertical plasma etch process is performed to remove material and form the initial grating structure pattern

Methodology Applied

Scientific EffectPlasma etching: Plasma

Data Source

PatentUS20240168207A1Fabrication of slanted grating master and working stamp using grayscale lithography and plasma etching

Publication Date: 2024.05.23 GOOGLE LLC

AI summary

A method for fabricating a working stamp for forming slanted surface gratings in a waveguide workpiece includes providing a master workpiece comprising a substrate and performing a sequence of photoresist deposition processes, grayscale lithography processes, and etching processes on the master workpiece so as to form an imprint replication master having a pattern of slanted gratings in a working surface of its substrate, the slanted gratings having sidewalls that are not substantially orthogonal to a working surface of the substrate. The method also includes conforming a soft stamp material layer to the working surface of the imprint replication master so that the soft stamp material layer has a pattern of slanted protrusions corresponding to the pattern of slanted gratings, and removing the imprint replication master from the soft stamp material and curing the soft stamp material layer surrounding the pattern of slanted protrusions to form the working stamp.