Dual-Layer Resist Lithography for Fragile Nanoemitters

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Solution Overview

Problem

The challenge lies in performing lithography on fragile individual nanoemitters like colloidal CdSe/CdS quantum dots without photobleaching them, as the laser intensity required for lithography is destructive to these sensitive emitters.

Innovation Solution

A lithography process involving multiple layers of resist, where an upper electron-sensitive layer is exposed to an electron beam while a thicker lower layer protects the nanoemitters, and markers are created using optical lithography to guide the electron beam, allowing precise positioning and patterning without direct exposure to destructive electron beams.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If laser lithography is performed on individual nanoemitters, then lithography can be carried out, but the laser intensity photobleaches and destroys the emitter

Engineering Contradiction:

Improvelithography capabilityVSAvoidemitter integrity

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The resist is divided into two distinct layers: a lower protective layer that shields the emitter from laser damage, and an upper patterning layer that receives the electron beam exposure. This segmentation allows each layer to perform its specific function without compromising the emitter

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The lower resist layer acts as an intermediary protective barrier between the emitter and the lithography process. It absorbs the harmful laser energy while allowing the upper layer to be patterned, thus mediating between the conflicting requirements of lithography and emitter protection

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If direct electron beam lithography is used on individual emitters, then nanometric precision can be achieved, but the electron beam damages or destroys the emitter

Engineering Contradiction:

Improvelithography precisionVSAvoidemitter damage

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The resist structure is segmented into two layers with distinct thicknesses and functions. The lower layer provides sufficient thickness to stop and absorb electron beam energy, preventing emitter damage, while the upper layer maintains sufficient thickness for precise electron beam patterning

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The solution moves from a single-layer to a two-layer vertical structure, adding the vertical dimension as a protective barrier. This allows the electron beam to interact with the upper layer for patterning while the lower layer provides protection in the vertical dimension

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If thick resist is used to protect the emitter, then emitter protection is improved, but lithography precision and resolution are reduced

Engineering Contradiction:

Improveemitter protectionVSAvoidlithography resolution

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The total resist thickness is segmented into two portions: a thick lower layer for protection and a thin upper layer for precision patterning. This segmentation allows the system to benefit from both thick and thin resist properties in different vertical zones

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the resist have different thicknesses optimized for different functions. The lower region has greater thickness for protection, while the upper region has lesser thickness for precision, creating local quality variations that satisfy conflicting requirements

Inventive Principle:

Principle #3Local quality

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 lithography on individual nanoemitters with reduced risk of photobleaching, allowing for the deterministic placement of nanoemitters with controlled lateral and vertical precision, preserving their integrity and functionality.

Implementation Method 1

Acquiring an image imaging the markers and a fluorescence radiation from the selected structure

Methodology Applied

Scientific EffectFluorescence: Fluorescence

Implementation Method 2

Exposing to an electron beam the upper layer of resist above the position of the selected structure

Methodology Applied

Scientific EffectElectron beam: Electron Beam

Data Source

PatentUS11127565B2Electron-beam lithography process adapted for a sample comprising at least one fragile nanostructure

Publication Date: 2021.09.21 CENT NAT DE LA RECH SCI (C N R S)

AI summary

Disclosed is a lithography process on a sample including at least one structure and covered by at least a lower layer of resist and a upper layer of resist the process including: using an optical device to image or determine, in reference to the optical device, a position of the selected structure and positions of markers integral with the sample; using an electron-beam device, imaging or determining the position of each marker in reference to the electron-beam device; deducing the position of the selected structure in reference to the electron-beam device; exposing to an electron beam the upper layer of resist above the position of the selected structure to remove all the thickness of the upper layer of resist above the position of the selected structure but none or only part of the thickness of the lower layer of resist above the position of the selected structure.