Composite AlN Substrate Structure for Warping and Stress Control
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Solution Overview
Problem
GaN-based devices face issues with stress-induced warping and poor thermal conductivity when using sapphire substrates, which limits their performance in high-power and small-sized applications due to the lack of suitable GaN single-crystal substrates like AlN.
Innovation Solution
A composite substrate is developed with single-crystal AlN, a support substrate, and a transition layer containing an oxygen element, such as AlON, to improve mechanical strength, reduce stress, and enhance thermal conductivity, while a protective layer covers the substrate to prevent defects and deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a sapphire substrate is used for GaN-based LED devices, then the device can be manufactured with current technology, but stress is generated during epitaxy leading to severe warping of the epitaxial wafer
Solution Approach 1:
The patent introduces a transition layer between the sapphire substrate and the GaN-based epitaxial layer. This transition layer acts as an intermediary that reduces the lattice mismatch and thermal expansion coefficient difference between sapphire and GaN, thereby reducing stress during epitaxy and minimizing warping of the epitaxial wafer while maintaining manufacturability with current technology
Solution Approach 2:
The patent creates a composite substrate structure consisting of multiple layers: sapphire substrate, transition layer (containing AlN and/or AlGaN), and GaN-based epitaxial layer. This composite structure combines the advantages of sapphire (low cost, mature manufacturing) with the benefits of AlN (low stress, high thermal conductivity) to resolve the warping issue while maintaining ease of manufacture
2Shape
If the substrate thickness is increased to balance warping, then warping is reduced, but the thermal conductivity remains insufficient due to the poor thermal conductivity of sapphire
Solution Approach 1:
The patent creates a composite substrate structure where the transition layer contains AlN and/or AlGaN materials. AlN has high thermal conductivity and low thermal expansion coefficient, which compensates for the poor thermal conductivity of sapphire. This composite structure improves heat dissipation capability while the layered design helps control warping through stress management at the interfaces
Solution Approach 2:
The patent applies the principle of local quality by having different layers serve different functions: the sapphire substrate provides mechanical support and cost-effectiveness, the transition layer provides stress reduction and enhanced thermal conductivity, and the GaN epitaxial layer provides the active device functionality. This localized optimization of properties at different depths resolves both the warping control and thermal conductivity issues
3Ease of manufacture
If a sapphire substrate is used, then manufacturing is feasible with current technology, but the thermal conductivity is poor leading to device failure and decreased lifespan in high-power applications
Solution Approach 1:
The transition layer serves as an intermediary that not only reduces stress and warping but also provides a thermal conduction pathway. The AlN and/or AlGaN in the transition layer have higher thermal conductivity than sapphire, creating a gradient thermal conduction path that improves overall heat dissipation and device reliability while maintaining manufacturability
Solution Approach 2:
The composite substrate structure combines sapphire (manufacturing advantage) with AlN/AlGaN layers (thermal and mechanical advantages). This composite approach maintains the manufacturability benefits of sapphire while adding the thermal management capabilities needed for high-power applications, thereby improving device lifespan and reliability
Data Source
AI summary
Disclosed are a composite substrate, a semiconductor structure, and a manufacturing method for a composite substrate. The composite substrate includes single-crystal AlN; a support substrate disposed below a bottom of the single-crystal AlN; and a transition layer disposed between the single-crystal AlN and the support substrate, where the transition layer includes an oxygen element. In the composite substrate provided by the present disclosure, mechanical strength of the single-crystal AlN may be indirectly improved through a supporting effect performed on the single-crystal AlN by the support substrate located below the bottom of the single-crystal AlN. Meanwhile, the support substrate also plays a role in regulating the stress on the single-crystal AlN, thereby reducing a warping degree of the single-crystal AlN during the subsequent epitaxial process and avoiding the occurrence of cracks or fragments.