Laser Lift-Off Using Optically Absorbent Layer to Prevent Thermal Degradation

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Solution Overview

Problem

Existing methods for dismantling composite structures using laser lift-off techniques often result in thermal degradation of the layer to be separated due to high temperatures, especially when dealing with materials like ferromagnetic, graphene, or phase-change alloys, and can also affect the final carrier, requiring higher thermal budgets or multiple transfer steps.

Innovation Solution

A composite structure with a distinct sacrificial layer that absorbs light flux, minimizing heat transfer to the layer to be separated, and utilizing thermal barrier layers and films to control temperature, allowing for dissociation at lower thermal budgets below 500°C.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a light flux is used to break down the sacrificial layer in laser lift-off, then the useful layer can be separated from the substrate, but the layer to be separated may be heated to high temperature through thermal conduction causing degradation

Engineering Contradiction:

Improveseparation efficiencyVSAvoidthermal degradation of layer to be separated

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an optically absorbent layer as an intermediary between the light flux and the sacrificial layer. This layer absorbs the light energy and converts it to thermal energy, which then conducts heat to the sacrificial layer for decomposition. The intermediary layer controls the thermal budget by managing the conversion and transmission of energy, preventing direct overheating of the layer to be separated while ensuring sufficient heat reaches the sacrificial layer for effective separation.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the thermal budget is increased to ensure complete dissociation of the sacrificial layer, then separation is achieved, but the final carrier may be affected by the high temperature

Engineering Contradiction:

Improvedissociation completenessVSAvoidthermal damage to final carrier

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent optimizes the optical and thermal parameters of the optically absorbent layer to control the thermal budget. By adjusting the optical absorption coefficient, thickness, and thermal conductivity of this layer, the system achieves complete sacrificial layer dissociation while limiting the maximum temperature to below 500°C, preventing damage to temperature-sensitive final carriers such as polymers and electronic circuits.

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If a thermal barrier layer is added between the sacrificial layer and the layer to be separated, then thermal protection is improved, but the structure complexity increases

Engineering Contradiction:

Improvethermal protection of layer to be separatedVSAvoidstructure complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The optically absorbent layer serves multiple functions simultaneously: it acts as an intermediary for energy conversion, a thermal management layer to control the thermal budget, and a protective barrier for the layer to be separated. By combining these functions in a single layer, the patent achieves thermal protection without significantly increasing structural complexity, maintaining process simplicity while improving thermal management.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 separation of sensitive materials and carriers with reduced thermal damage, allowing for efficient transfer and reuse of the substrate while maintaining the integrity of the layer to be separated and the carrier.

Implementation Method 1

an optically absorbent layer (2) made of a material suitable for at least partially absorbing a light flux

Methodology Applied

Scientific EffectLight absorption: Absorption (EM radiation)

Implementation Method 2

heating the sacrificial layer (3) by thermal conduction from the optically absorbent layer (2)

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 3

a sacrificial layer (3) suitable for dissociating under the application of a temperature higher than a dissociation temperature

Methodology Applied

Scientific EffectThermal dissociation: Thermolysis

Data Source

PatentUS11469367B2Method for separating a removable composite structure by means of a light flux

Publication Date: 2022.10.11 SOITEC SA

AI summary

A method for separating a removable composite structure using a light flux includes supplying the removable composite structure, which successively comprises: a substrate that is transparent to the light flux; an optically absorbent layer for at least partially absorbing a light flux; a sacrificial layer adapted to dissociate subject to the application of a temperature higher than a dissociation temperature and made of a material different from that of the optically absorbent layer; and at least one layer to be separated. The method further includes applying a light flux through the substrate, the light flux being at least partly absorbed by the optically absorbent layer, so as to heat the optically absorbent layer; heating the sacrificial layer by thermal conduction from the optically absorbent layer, up to a temperature that is greater than or equal to the dissociation temperature; and dissociating the sacrificial layer under the effect of the heating.