Waveguide Grating Imprinting for Sub-45° Tilt Angles

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Solution Overview

Problem

Fabricating waveguide structures with gratings having tilt angles less than about 45 degrees relative to the surface of the waveguide combiner is challenging due to difficulties in releasing a nanoimprint lithography stamp with tilt angles less than 45 degrees without damaging the nanoimprint resist and configuring an angled etch tool to generate an ion beam at such angles.

Innovation Solution

A method involving imprinting a stamp with inverse gratings having angles greater than 45 degrees into a nanoimprint resist, releasing it at a specific angle, and subjecting it to a cure and anneal process to form gratings with angles less than 45 degrees, using techniques like peeling and lifting to manage stamp removal and modify grating angles and dimensions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a stamp with inverse gratings having tilt angles less than 45 degrees is used for nanoimprint lithography, then the desired grating tilt angle is achieved, but the stamp cannot be released from the nanoimprint resist without damaging the resist or the stamp

Engineering Contradiction:

Improvegrating tilt angle precisionVSAvoidstamp release difficulty

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent applies inversion by using a stamp with inverse gratings having tilt angles greater than or equal to 45 degrees (relative to the stamp surface) to create final gratings with tilt angles less than 45 degrees. This inverted approach allows the stamp to be released easily while achieving the desired precise grating angles through the transformation that occurs during the imprinting and annealing process.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent utilizes parameter changes by transforming the grating tilt angle from the stamp domain (>=45 degrees relative to stamp surface) to the final grating domain (<45 degrees relative to waveguide surface). The cure and anneal processes enable this parameter transformation, allowing the stamp to be removed without damage while achieving the precise angular configuration required for optimal light coupling.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If an angled etch tool is configured to generate an ion beam at angles less than 45 degrees, then precise grating formation is achieved, but the tool configuration becomes complex and difficult to implement

Engineering Contradiction:

Improvegrating angle precisionVSAvoidetch tool configuration complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent replaces the complex mechanical configuration of angled ion beam etching tools with a simpler nanoimprint lithography approach. Instead of configuring etch tools to generate ion beams at precise angles, the invention uses a stamp with inverse gratings that are easier to manufacture and release, substituting a mechanical angle-adjustment problem with a pattern-transfer solution that achieves the same precision without the complexity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Ease of manufacture

If the stamp is released at a high angle to facilitate removal, then the release process is easier, but the grating angles and dimensions are altered from the desired values

Engineering Contradiction:

Improvestamp release easeVSAvoidgrating angle and dimension accuracy

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent uses an inverted stamp design where the inverse gratings have tilt angles greater than or equal to 45 degrees. This inversion allows the stamp to be released at high angles without damaging the resist or altering the final grating geometry. The transformation during cure and anneal processes ensures that the final gratings achieve the precise tilt angles <45 degrees relative to the waveguide surface, regardless of the release angle used.

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

Enables the fabrication of waveguide structures with gratings having optimized tilt angles less than 45 degrees, enhancing light control and increasing the viewing angle for virtual images in augmented reality devices.

Implementation Method 1

The nanoimprint resist is subjected to a cure process

Methodology Applied

Scientific EffectCuring: Photopolymerisation

Implementation Method 2

The nanoimprint resist is subjected to an anneal process to form a waveguide structure

Methodology Applied

Scientific EffectAnnealing: Annealing

Data Source

PatentEP3803503B1Method of imprinting tilt angle light gratings

Publication Date: 2025.10.15 APPLIED MATERIALS INC

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AI summary

Embodiments described herein relate to methods of fabricating waveguide structures with gratings having front angles less than about 45° and back angles less than about 45°. The methods include imprinting stamps into nanoimprint resists disposed on substrates. The nanoimprint resists are subjected to a cure process. The stamps are released from the nanoimprint resist at a release angle ϑ using a release method. The nanoimprint resists are subjected to an anneal process to form a waveguide structure comprising a plurality of gratings with a front angle and a back angle β relative to a second plane of the surface of the substrate less than about 45.