Nitride Epitaxial Buffer Structure for GaN-on-Si Stress Relief
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Solution Overview
Problem
The lattice mismatch and thermal expansion coefficient mismatch between GaN and silicon substrates result in stress and warpage during epitaxy, affecting the uniformity and reliability of GaN epitaxial wafers, with conventional stress adjustment methods failing to balance crystal quality and voltage withstand performance effectively.
Innovation Solution
A nitride epitaxial structure with a buffer layer composed of K stacked group-III nitride double-layer structures, where the band gap differences gradually change, alleviating stress and improving crystal quality and voltage withstand performance by filtering dislocations and reducing electric leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a gradient AlGaN structure is used to adjust stress, then stress adjustment capability is improved, but dynamic performance and crystal quality deteriorate
Solution Approach 1:
The buffer layer is segmented into multiple discrete AlGaN/n-GaN superlattice buffer layer pairs with different Al component contents arranged in sequence. Each pair acts as an independent stress adjustment unit, allowing precise control of stress distribution while maintaining crystal quality and dynamic performance through the stepwise gradient structure.
2Stress or pressure
If a superlattice structure is used to control stress, then stress control capability and crystal quality are improved, but voltage withstand performance deteriorates
Solution Approach 1:
Different AlGaN/n-GaN superlattice buffer layer pairs have different Al component contents (x1, x2, ..., xn) that vary locally across the buffer layer thickness. This local quality variation allows each layer pair to provide different stress control characteristics, achieving overall stress control while maintaining voltage withstand performance through optimized local composition.
3Area of stationary object
If the substrate size is increased, then device scale is improved, but warpage impact deteriorates
Solution Approach 1:
The AlGaN/n-GaN superlattice buffer layer acts as an intermediary layer between the silicon substrate and the GaN epitaxial layer. This intermediary structure gradually transitions the lattice and thermal expansion mismatch between Si and GaN, effectively reducing warpage even when the substrate size is increased to larger dimensions.
4Ease of manufacture
If epitaxial growth is performed on silicon substrate, then material availability is improved, but lattice mismatch and thermal mismatch worsen
Solution Approach 1:
The buffer layer uses a composite AlGaN/n-GaN superlattice structure where AlGaN and n-GaN layers are alternately stacked. This composite material approach allows tuning of the average lattice constant and thermal expansion coefficient to match the silicon substrate, reducing mismatch stress while maintaining the ability to grow high-quality GaN epitaxial layers.
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 structure effectively reduces warpage and enhances the uniformity and reliability of GaN epitaxial wafers, allowing for large-size thick nitride epitaxial layers, thereby improving the performance of semiconductor devices.
Implementation Method 1
The structure can effectively and sufficiently release the lattice stress due to lattice mismatch between the sapphire substrate and GaN at the bottom layer growth section, thereby greatly reducing wrapping of the epitaxial wafer throughout high-temperature growth process, improving wavelength concentration and yield of the epitaxial wafer, improving GaN lattice quality, reducing lattice dislocation density
Implementation Method 2
The nucleation layer may provide a nucleation center for subsequent growth of the nitride epitaxial layer, to alleviate a lattice mismatch between the substrate and the epitaxial layer
Implementation Method 3
The structure can effectively and sufficiently release the lattice stress due to lattice mismatch between the sapphire substrate and GaN at the bottom layer growth section, thereby greatly reducing wrapping of the epitaxial wafer throughout high-temperature growth process
Data Source
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AI summary
An embodiment of this application provides a nitride epitaxial structure, including: a substrate; a nucleation layer, formed on the substrate, where the nucleation layer is an aluminum nitride layer or a gallium nitride layer; a buffer layer, formed on the nucleation layer, including K stacked group-III nitride double-layer structures, K ≥ 3, each double-layer structure includes an upper layer and a lower layer that are stacked, a band gap difference of each double-layer structure is a difference between a band gap of a material of the upper layer and a band gap of a material of the lower layer, and band gap differences of the K double-layer structures generally present a gradient trend along a thickness direction of the buffer layer; and an epitaxial layer, formed on the buffer layer, where a material of the epitaxial layer includes group-III nitride. The buffer layer having a plurality of double-layer structures with gradient band gap differences is disposed, so that a lattice mismatch between the substrate and the epitaxial layer can be effectively alleviated, and crystal quality and voltage withstand performance can be well balanced, thereby effectively improving performance of a semiconductor device. An embodiment of this application further provides a semiconductor device including the nitride epitaxial structure.