Thin Waveguide Metal Grating Fabrication for Precise Light Diffraction

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Solution Overview

Problem

Existing methods for creating metal gratings in waveguides face challenges in achieving precise control over critical dimensions and high reflectivity, particularly in reducing the thickness of waveguide materials while maintaining efficient light propagation across a wide spectrum of wavelengths.

Innovation Solution

A method involving the formation of a waveguide material with a thickness less than or equal to 100 nanometers over a substrate, using chemical vapor deposition or other processes, followed by the creation of photoresist patterns and metal fillings in the waveguide material to form gratings with controlled pitch and width, enabling efficient light diffraction and combination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the waveguide material thickness is reduced to improve critical dimension control and reduce thermal expansion, then manufacturing precision and stability are improved, but the ability to maintain efficient light propagation across a wide spectrum may deteriorate

Engineering Contradiction:

Improvecritical dimension controlVSAvoidlight propagation efficiency

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent employs composite material structures by combining the waveguide material with metal gratings and dielectric layers. The waveguide material is formed over a substrate with specific thickness (less than or equal to 100 nm), and metal gratings are integrated into the structure to provide wavelength-selective reflection. This composite approach allows the thin waveguide material to maintain both precise dimensional control and effective light propagation by leveraging the complementary properties of different materials.

Inventive Principle:

Principle #40Composite materials

2Stability of the object's composition

If the waveguide material thickness is reduced to reduce thermal expansion, then stability is improved, but the reflectivity and thermal management capabilities may worsen

Engineering Contradiction:

Improvethermal expansionVSAvoidreflectivity

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent introduces dielectric layers as intermediary components between the substrate and the waveguide material, and between the waveguide material and the metal gratings. These dielectric layers serve as thermal management intermediaries, helping to regulate heat flow while maintaining the stability benefits of thin waveguide material. The dielectric layers also provide optical interference effects that enhance the overall reflectivity of the grating structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Manufacturing precision

If metal gratings are formed with controlled pitch and width to improve diffraction efficiency, then manufacturing precision is improved, but the process complexity increases

Engineering Contradiction:

Improvegrating pitch and width controlVSAvoidprocess complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent employs preliminary patterning steps where photoresist is formed over the waveguide material before the metal grating formation. The photoresist pattern is created using photolithography, which allows precise definition of the grating pitch and width before the metal deposition step. This preliminary action enables accurate metal grating formation without requiring complex post-processing, as the metal is deposited conformally over the pre-defined photoresist pattern.

Inventive Principle:

Principle #10Preliminary action

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 allows for highly reflective gratings with improved critical dimension control and reduced thermal expansion, enhancing the ability to split or combine light wavelengths effectively across a wide spectrum, including visible, UV, and IR light.

Implementation Method 1

Waveguides are used to control a propagation of light from one element to another

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 2

A transmission grating separates an incoming light beam into component wavelengths by refracting the incident light beam

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 3

A reflecting grating separates the incoming light beam into component wavelengths by reflecting the incident light beam

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 4

Diffraction gratings are used in waveguides to separate different wavelengths of a light beam or to combine different wavelengths into a single light beam

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS10866361B2Method of making a metal grating in a waveguide and device formed

Publication Date: 2020.12.15 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A method of making a grating in a waveguide includes forming a waveguide material over a substrate, the waveguide material having a thickness less than or equal to about 100 nanometers (nm). The method further includes forming a photoresist over the waveguide material and patterning the photoresist. The method further includes forming a first set of openings in the waveguide material through the patterned substrate and filling the first set of openings with a metal material.