AlGaN Buffer Layer Strain Control for Nitride Semiconductor Devices
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Solution Overview
Problem
The formation of thick nitride layers on silicon substrates for high-power nitride semiconductor devices is hindered by lattice constant and thermal expansion differences, leading to increased leakage current and reduced withstand voltage due to substrate bending or cracking.
Innovation Solution
A semiconductor apparatus with a buffer layer and Strained Layer Superlattice (SLS) buffer layer, where the buffer layer consists of AlGaN layers with varying Al composition ratios and the SLS buffer layer is formed by alternately laminating AlN and GaN layers, with specific thickness and composition ratios to control strain and reduce leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick nitride layer is formed on a silicon substrate, then insulation properties are improved, but substrate bending or cracking occurs due to lattice constant and thermal expansion differences
Solution Approach 1:
The buffer layer is segmented into multiple AlGaN sub-layers with different Al composition ratios (first AlGaN layer with higher Al content, second AlGaN layer with lower Al content), allowing strain management while achieving thick nitride layer formation without substrate bending or cracking
Solution Approach 2:
The Al composition ratio in the buffer layer is varied (parameter change) to control strain distribution - the first AlGaN layer has higher Al composition for strain compensation, while the second AlGaN layer has lower Al composition for reduced lattice mismatch, enabling thick nitride layer formation on silicon substrate
2Reliability
If the nitride layer thickness is increased to reduce leakage current, then withstand voltage is improved, but substrate bending or cracking is more likely to occur
Solution Approach 1:
The buffer layer is divided into multiple AlGaN layers with different Al composition ratios, which segment the strain distribution and enable formation of thicker nitride layers (500nm or more) without causing substrate bending or cracking
Solution Approach 2:
The buffer layer uses a composite structure of AlGaN layers with different compositions on a silicon substrate, creating a graded strain distribution that prevents cracking while enabling thick nitride layer formation for reduced leakage current
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 solution effectively reduces leakage current and enhances withstand voltage by forming a thicker nitride layer with improved insulation properties, minimizing substrate bending and cracking, thereby improving the performance of high-power nitride semiconductor devices.
Implementation Method 1
by forming a buffer layer and Strained Layer Superlattice (SLS) buffer layer, where the buffer layer consists of AlGaN layers with varying Al composition ratios and the SLS buffer layer is formed by alternately laminating AlN and GaN layers, with specific thickness and composition ratios to control strain
Implementation Method 2
when the AlGaN/GaN heterostructure is formed, in the AlGa layer, a piezoelectric polarization may be excited due to lattice distortion between AlGaN and GaN
Implementation Method 3
due to differences in a lattice constant and a coefficient of thermal expansion between silicon and nitride, a bend or a crack is likely to be formed in the substrate or the nitride semiconductor layer
Data Source
AI summary
A semiconductor apparatus includes a buffer layer formed on a substrate; an SLS (Strained Layer Supperlattice) buffer layer formed on the buffer layer; an electron transit layer formed on the SLS buffer layer and formed of a semiconductor material; and an electron supply layer formed on the electron transit layer and formed of a semiconductor material. Further, the buffer layer is formed of AlGaN and includes two or more layers with different Al composition ratios, the SLS buffer layer is formed by alternately laminating a first lattice layer including AlN and a second lattice layer including GaN, and the Al composition ratio in one of the layers of the buffer layer being in contact with the SLS buffer layer is greater than or equal to an Al effective composition ratio in the SLS buffer layer.