Carrier Substrate Structure for Spallation-Free Laser Element Transfer
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Solution Overview
Problem
During the laser lift-off process for transferring GaN-based elements, such as LEDs, from a sapphire substrate, elastic waves generated by the laser beam cause tensile stress and spallation of the element's surface, leading to damage and reduced transfer precision and yield.
Innovation Solution
A carrier substrate is designed with a base layer, an antireflection layer to prevent elastic wave reflection, and an energy absorption layer that evaporates upon laser exposure, allowing for precise element transfer without damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a laser beam is used to separate the GaN thin film from the sapphire substrate, then the separation process becomes efficient and controllable, but elastic waves generated by the laser beam cause tensile stress and spallation of the element's surface
Solution Approach 1:
An antireflection layer is introduced as an intermediary between the element and the base layer. This layer has a refractive index intermediate between the element and the base layer, which reduces the reflection of elastic waves at the interface. By using this intermediary layer, the harmful elastic wave reflection is minimized while maintaining the effectiveness of the laser lift-off process.
Solution Approach 2:
The refractive index parameter of the interface layer is specifically optimized to be intermediate between the element and the base layer. This parameter change in the interface layer's optical properties allows for reduced elastic wave reflection, thereby preventing spallation damage while maintaining separation efficiency.
2Ease of operation
If pressing force is applied to the element edge by a carrier film during picking, then the element can be transferred, but bending stress occurs causing displacement and bending-induced damage
Solution Approach 1:
An energy absorption layer is positioned between the carrier substrate and the element to provide beforehand cushioning. This layer absorbs the impact energy and reduces the bending stress generated during the picking process, preventing element damage while still enabling transfer capability.
Solution Approach 2:
The energy absorption layer utilizes phase transition (evaporation) upon energy absorption from the laser beam. This phase change absorbs significant energy, reducing the mechanical stress transmitted to the element during the picking and transfer process, thereby preventing bending-induced damage.
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
The carrier substrate effectively prevents spallation and bending-induced damage to the elements, ensuring high transfer precision and yield by transmitting elastic waves without reflection and reducing adhesion through energy absorption.
Implementation Method 1
allowing an elastic wave generated by a first laser beam transmitted through an element adhesively bonded to the antireflection layer to be transmitted through the base layer without being reflected towards the element
Implementation Method 2
an energy absorption layer formed between the base layer and the antireflection layer, the energy absorption layer evaporating upon energy absorption
Implementation Method 3
a laser beam is allowed to pass through a sapphire substrate to generate local heat at an interface between the sapphire substrate and a GaN-based element
Data Source
AI summary
A carrier substrate includes a base layer, an antireflection layer, and an energy absorption layer, wherein the antireflection layer is formed on one surface of the base layer and allows an elastic wave generated by a first laser beam transmitted through an element adhesively bonded to the antireflection layer to be transmitted through the base layer without being reflected towards the element, the first laser beam being applied to the element through a source substrate of the element, and the energy absorption layer is formed between the base layer and the antireflection layer to be aligned with the element, and evaporates upon energy absorption.