SiC Substrate with AlN Buffer for GaN Warpage
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Solution Overview
Problem
Conventional compound semiconductor substrates face issues with warpage, cracking, and low withstand voltage when forming GaN layers due to lattice constant and thermal expansion differences, leading to suboptimal crystal quality and limited GaN layer thickness.
Innovation Solution
A compound semiconductor substrate structure comprising an SiC layer, an AlN buffer layer, a nitride semiconductor layer with Al and Ga, a first GaN layer, a first AlN intermediate layer, and a second GaN layer with compressive strain, where the Al compositional ratio in the nitride semiconductor layers decreases from the lower part to the upper part, and an AlN intermediate layer is used to generate compressive strain and alleviate lattice constant differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an Si substrate is used as a foundation substrate for GaN, then the substrate is readily available and cost-effective, but warpage occurs and cracking in the GaN layer is likely due to large lattice constant and thermal expansion differences
Solution Approach 1:
An SiC layer is introduced as an intermediary between the Si substrate and the GaN layer. This SiC layer serves as a buffer that reduces the lattice constant difference and thermal expansion coefficient difference between Si and GaN, thereby preventing warpage and cracking while maintaining the ease of using Si as the foundation substrate.
Solution Approach 2:
The patent employs a composite structure consisting of Si substrate, SiC layer, and GaN layer. This composite material approach allows combining the advantages of each material: the low cost and availability of Si, the lattice-matching properties of SiC, and the desired electrical properties of GaN, thus resolving the contradiction between manufacturing ease and structural reliability.
2Reliability
If conventional layer structures are used to suppress warpage and cracking, then substrate stability improves, but the GaN layer thickness is limited and withstand voltage remains limited
Solution Approach 1:
The SiC layer serves as a stable intermediary foundation that supports thicker GaN layers. Its lattice constant and thermal expansion properties are intermediate between Si and GaN, providing a stable platform that prevents warpage and cracking even when the GaN layer is thickened, thus breaking the limitation on GaN layer thickness and withstand voltage.
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 structure effectively suppresses warpage and cracking, improves crystal quality, and enhances the withstand voltage of the GaN layers, allowing for thicker GaN layers and improved semiconductor device performance.
Implementation Method 1
there are a large difference of the lattice constant and a large difference of the coefficient of thermal expansion, between GaN and Si. Due to these differences, phenomena such as warpage occurring on the substrate and cracking in the GaN layer are likely to occur
Implementation Method 2
a first AlN intermediate layer formed on the first GaN layer, being in contact with the first GaN layer, and a second GaN layer formed on the first AlN intermediate layer, being in contact with the first AlN intermediate layer
Implementation Method 3
a large difference of the coefficient of thermal expansion, between GaN and Si
Data Source
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AI summary
A compound semiconductor substrate having a desired quality is provided. A compound semiconductor substrate has an SiC (silicon carbide) layer, an AlN (aluminum nitride) buffer layer formed on the SiC layer, an Al (aluminum) nitride semiconductor layer formed on the AlN buffer layer, a first GaN (gallium nitride) layer formed on the Al nitride semiconductor layer, a first AlN intermediate layer formed on the first GaN layer in contact with the first GaN layer, and a second GaN layer formed on the first AlN intermediate layer in contact with the first AlN intermediate layer.