GaN Substrate Defect Mapping for Crack-Resistant Epitaxy
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Solution Overview
Problem
Current methods for fabricating gallium nitride (GaN) substrates using hydride vapor phase epitaxy (HYPE) result in crystal defects due to lattice and thermal mismatch, leading to cracking and fragmentation issues during subsequent processing or epitaxy, which existing stress characterization methods, such as micro-Raman scattering, cannot adequately address, especially for high-stress applications like blue or green laser epitaxy.
Innovation Solution
Controlled reduction of lateral dislocation density and tilt angles through multi-photon excitation photoluminescence imaging, ensuring average products of threading dislocation densities and tilt angles are within specific limits, thereby characterizing defects more accurately and reducing stress in the GaN substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If heteroepitaxial growth is used to fabricate GaN substrate, then GaN material can be grown on the substrate, but crystal defects are generated due to lattice and thermal mismatch
Solution Approach 1:
The patent applies preliminary action by growing a buffer layer on the substrate before growing the GaN layer. This buffer layer serves as an intermediate structure that reduces the lattice mismatch between the substrate and GaN, preventing crystal defects from forming during epitaxial growth. The buffer layer is prepared in advance to create favorable growth conditions for high-quality GaN.
2Ease of manufacture
If GaN substrate with high dislocation density is used, then fabrication cost is reduced, but cracking and fragmentation occur during processing
Solution Approach 1:
The patent applies preliminary action by reducing dislocation density in the buffer layer before GaN growth. This preliminary reduction of dislocations prevents the formation of cracking and fragmentation during subsequent processing. By addressing the dislocation issue in advance, the patent maintains substrate integrity while keeping fabrication costs reasonable.
3Reliability
If patterned periodic epitaxial growth is used, then stress fluctuation can be controlled, but the method is complex and not suitable for all GaN substrates
Solution Approach 1:
The patent changes the approach from controlling stress through patterned periodic epitaxial growth to controlling stress through curvature measurement and buffer layer optimization. This parameter change simplifies the epitaxy process while maintaining effective stress control, making the method applicable to a broader range of GaN substrates without the complexity of periodic patterning.
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 effectively suppresses cracking and fragmentation, improving the yield and reducing costs of semiconductor composite substrates by providing a more uniform stress distribution and enhancing epitaxial performance.
Implementation Method 1
multi-photon excitation photoluminescence imaging
Implementation Method 2
multi-photon excitation photoluminescence spectrum
Implementation Method 3
hydride vapor phase epitaxy (HYPE)
Implementation Method 4
hydride vapor phase epitaxy (HYPE)
Implementation Method 5
GaCl(g)+NH3(g)=GaN(s)+HCl(g)+H2(g)
Data Source
AI summary
The present disclosure provides a gallium nitride substrate, where the gallium nitride substrate has a surface having a diameter not less than 50 mm; nine circular regions having a diameter not greater than 1 mm are taken on a surface of the gallium nitride substrate; threading dislocation densities and threading dislocation tilt angles are calculated at the nine circular regions using a multi-photon excitation photoluminescence spectrum; an average value of products of the threading dislocation densities in the nine circular regions and tangent values of the threading dislocation tilt angles is not greater than 1E6 cm−2; and a quotient of a difference between a maximum value and a minimum value of the products of the threading dislocation densities in the nine circular regions and the tangent values of the threading dislocation tilt angles divided by the average value is not greater than 50%.