Self-Supporting GaN Substrate Transfer for Thicker Epitaxial Growth
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Solution Overview
Problem
The existing methods for manufacturing free-standing gallium nitride substrates face challenges due to thickness limitations caused by lattice mismatch and thermal mismatch between the gallium nitride epitaxial layer and sapphire substrates, leading to device performance issues and high manufacturing costs.
Innovation Solution
A method involving a composite substrate with a sapphire substrate and gallium nitride film, where a temporary bonding layer is formed, followed by laser lift-off to detach the sapphire, and then weak bonding using metal grids to separate the gallium nitride film from a receiving substrate, allowing for thicker epitaxial growth and stress-induced separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser lift-off method is used to separate GaN from sapphire substrate, then the free-standing substrate can be obtained, but the GaN substrate is easily damaged by high-pressure gas and suffers from dislocations and microcracks
Solution Approach 1:
The patent introduces an aluminum nitride (AlN) buffer layer as an intermediary between the GaN film and the sapphire substrate. This buffer layer absorbs the mechanical stress and protects the GaN film from damage during the laser lift-off process, preventing dislocations and microcracks while enabling successful separation.
Solution Approach 2:
The AlN buffer layer is prepared in advance before the GaN film growth. This preliminary action creates a protective structure that will later shield the GaN film from harmful effects during substrate removal, ensuring the film's integrity before the actual separation process occurs.
2Ease of manufacture
If heteroepitaxial growth is carried out on sapphire substrate, then the manufacturing process can be implemented, but the thickness of GaN layer is limited by lattice mismatch and thermal mismatch
Solution Approach 1:
The AlN buffer layer serves as a mediator that reduces the lattice mismatch and thermal expansion coefficient difference between the sapphire substrate and the GaN film. This intermediary structure enables thicker GaN layers to be grown without the severe constraints imposed by direct heteroepitaxial growth on sapphire.
Solution Approach 2:
The patent changes the structural parameters of the substrate system by introducing the AlN buffer layer, which has intermediate lattice constant and thermal expansion properties. This parameter change allows for extended growth thickness by reducing the cumulative stress that would otherwise limit layer thickness.
3Reliability
If sapphire substrate is removed by chemical corrosion or mechanical grinding, then the free-standing substrate can be obtained, but the process is difficult and time-consuming
Solution Approach 1:
The patent replaces mechanical grinding and chemical corrosion methods with laser lift-off technology. This substitution uses optical energy to selectively remove the sapphire substrate, dramatically reducing the time required while maintaining or improving the quality of the freed GaN film through the protective AlN buffer layer.
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 the growth of thicker gallium nitride epitaxial layers with improved quality and reduced manufacturing costs by altering the bonding from strong chemical to weak bonding, utilizing lattice and thermal mismatch stresses for separation.
Implementation Method 1
detaching the sapphire substrate by laser lift-off process
Implementation Method 2
high-pressure gas generated by the high temperature decomposition of GaN at the interface
Implementation Method 3
invalidating the weak bonding between the gallium nitride film and the receiving substrate by the lattice mismatch stress and the thermal mismatch stress
Implementation Method 4
invalidating the weak bonding between the gallium nitride film and the receiving substrate by the lattice mismatch stress and the thermal mismatch stress
Data Source
AI summary
The present disclosure provides a method for fabricating a self-supporting gallium nitride substrate, comprising: 1) providing a composite substrate including a sapphire substrate and a gallium nitride film; 2) forming a temporary bonding layer on the gallium nitride film; 3) bonding a transfer substrate to the composite substrate by means of the temporary bonding layer; 4) stripping the sapphire substrate by means of a laser stripping process; 5) performing weak bonding on a receiving substrate and the gallium nitride film, and detaching the transfer substrate from the gallium nitride film by invalidating the temporary bonding layer, and 6) epitaxially growing a gallium nitride epitaxial layer on the gallium nitride film, and invalidating the weak bonding by means of the lattice mismatch stress and/or the thermal mismatch stress between the gallium nitride film and the gallium nitride epitaxial layer and the receiving substrate, so as to realize separation between the gallium nitride film and the receiving substrate. The present application can effectively overcome the defect that the thickness of a heterojunction gallium nitride epitaxial layer is limited due to lattice mismatch and thermal mismatch, improve the quality of the self-supporting gallium nitride substrate, and reduce the manufacturing cost of the self-supporting gallium nitride substrate.