Composite Substrate Structure for Low-Stress GaN Epitaxial Wafers
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Solution Overview
Problem
Current GaN epitaxial wafers face challenges due to lattice mismatch and thermal expansion coefficient mismatch with heterogeneous substrates like sapphire and silicon, leading to poor optical performance and high tensile stress.
Innovation Solution
A composite substrate is introduced, comprising a support substrate layer, a first amorphous alumina layer, and a sapphire substrate layer, with an optional second amorphous alumina layer, which reduces stress and improves bonding, allowing for high-quality GaN epitaxial growth by minimizing lattice and thermal mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a heterogeneous substrate (sapphire or silicon) is used for GaN epitaxial growth, then the substrate can be obtained with large area and reasonable cost, but large lattice mismatch and thermal expansion coefficient mismatch occur, resulting in poor material quality and high tensile stress
Solution Approach 1:
The substrate is divided into multiple layers: a support substrate layer (silicon or ceramic), a first alumina layer, and a sapphire substrate layer. This segmentation allows each layer to serve specific functions - the support substrate provides mechanical strength and large area, while the sapphire layer provides good lattice match for GaN growth, and the alumina layers manage stress and thermal expansion differences between layers
Solution Approach 2:
The patent uses a composite substrate structure combining different materials (silicon/ceramic support substrate, alumina intermediate layer, sapphire epitaxial layer) to achieve properties that single materials cannot provide. The composite structure balances mechanical strength, thermal expansion characteristics, and lattice matching requirements
2Area of stationary object
If a heterogeneous substrate (sapphire) is used for GaN epitaxial growth, then the substrate can be obtained with large area and reasonable cost, but large tensile stress occurs in the GaN epitaxial layer
Solution Approach 1:
The alumina layers serve as intermediary layers between the support substrate and the sapphire layer. These intermediate layers gradually transition the thermal expansion coefficient from the silicon/ceramic support substrate to the sapphire layer, reducing the sudden stress that would otherwise occur at the interface and preventing high tensile stress in the GaN epitaxial layer
Solution Approach 2:
The patent changes the thermal expansion parameter gradient by introducing alumina layers with intermediate thermal expansion coefficients between the silicon/ceramic support substrate and the sapphire layer. This gradual parameter transition reduces thermal stress and prevents cracking in the GaN layer
3Manufacturing precision
If a GaN-based substrate is used for epitaxial growth, then lattice mismatch is minimized and thermal expansion coefficient is low, but the extremely high melting point and high nitrogen saturation vapor pressure make it difficult to obtain large-area high-quality substrates
Solution Approach 1:
The alumina layers act as intermediary buffer layers that protect the GaN epitaxial layer from the harsh thermal and chemical environment during growth on the silicon or ceramic support substrate. This intermediary structure enables the use of lower-cost, easier-to-manufacture support substrates while maintaining high material quality
Solution Approach 2:
The composite substrate structure combines the manufacturing advantages of silicon or ceramic substrates (easy fabrication, large area availability, low cost) with the superior lattice matching and thermal properties of sapphire, creating a substrate that is both easy to manufacture and produces 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 composite substrate reduces internal stress and warping in GaN epitaxial wafers, enhancing material quality and optical performance while being compatible with existing large-scale processes.
Implementation Method 1
both sides of which are respectively covered with a first alumina layer and a second alumina layer... the first alumina layer and the second alumina layer reduce internal stress and warping in the GaN epitaxial wafer
Implementation Method 2
a preparation of commercial large-scale gallium nitride epitaxial wafers. A substrate material used for epitaxial growth of GaN through the MOCVD method
Data Source
AI summary
Disclosed are a composite substrate, an epitaxial wafer, and a semiconductor device. The composite substrate includes: a support substrate layer; a first alumina layer disposed on the support substrate layer; and a sapphire substrate layer disposed on the first alumina layer. The first alumina layer may increase a bonding force between the sapphire substrate layer and the support substrate layer and release a stress between the sapphire substrate layer and the support substrate layer. Meanwhile, the existence of the first alumina layer may improve a breakdown voltage of a material without increasing a thickness of the sapphire substrate layer.