AlGaN Multi-Layer Epitaxial Structure for Crack-Free GaN Growth
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Solution Overview
Problem
Gallium nitride (GaN) epitaxial layers face challenges when grown on silicon substrates due to lattice and thermal mismatch, leading to stress-induced cracking and degradation of crystalline quality, particularly with the use of low-temperature AlN interlayers which introduce tensile stress and increase dislocation density.
Innovation Solution
A semiconductor epitaxial structure with a multi-layer structure is developed, where Al composition is adjusted to control stress, and pre-stress layers are introduced to protect the nitride layer, allowing growth at high temperatures to avoid temperature ramping and maintain crystalline quality, incorporating a nitride nucleation layer on silicon, sapphire, or silicon carbide substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a low-temperature AlN interlayer is introduced to compensate tensile stress, then crack generation is avoided, but the crystalline quality is degraded and dislocation density increases
Solution Approach 1:
The patent changes the temperature parameter from low-temperature (conventional AlN interlayer growth) to high-temperature growth for the AlGaN layer. This parameter change allows the layer to serve both as a stress compensation mechanism and as a high-quality crystalline structure, eliminating the need for separate low-temperature interlayer processing that degrades quality
Solution Approach 2:
The patent uses AlGaN (aluminum gallium nitride) as a composite material that combines the stress compensation properties of AlN with the crystalline quality of GaN. By adjusting the aluminum composition in the AlGaN layer, both stress management and high crystalline quality can be achieved simultaneously
2Strength
If low-temperature AlN interlayer growth is performed to control stress, then crack-free layers are obtained, but manufacturing complexity increases due to temperature ramping
Solution Approach 1:
The patent merges the stress compensation function and the protective layer growth into a single high-temperature AlGaN growth step. This eliminates the need for separate low-temperature interlayer growth and temperature ramping cycles, simplifying the manufacturing process while maintaining crack-free growth
Solution Approach 2:
The patent maintains continuous high-temperature growth throughout the epitaxial process, avoiding interruptions for temperature ramping down and back up. This continuous useful action simplifies the process and improves manufacturing efficiency while achieving the same stress compensation effect
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 high-temperature growth of the multi-layer structure minimizes defects, avoids cracking, and enhances crystalline quality, improving manufacturing yield and device performance by maintaining a two-dimensional structure and reducing the complications associated with low-temperature AlN interlayers.
Implementation Method 1
Because of the large thermal mismatch between GaN and Si, a huge tensile stress is generated during cooling down to the room temperature after the GaN layer is grown at a high temperature. If the average value of the compressive stress is equal to that of the tensile stress, the warpage of the silicon substrate can be minimized.
Implementation Method 2
Both the nitride layer and the sandwich-like multilayer are formed at high temperature, which avoids a complicated temperature ramping process during low temperature AlN interlayer growth, thereby saving time and increasing manufacturing yield.
Implementation Method 3
The pre-stress layer may change the growth pattern of the inserted Al-rich layer, to achieve a two-dimensional structure.
Data Source
AI summary
A semiconductor epitaxial structure is provided, which includes: a nitride nucleation layer, formed on a substrate including silicon, sapphire, patterned sapphire substrate (PSS) or silicon carbide, a nitride layer on the nitride nucleation layer and an multi-layer structure in the nitride layer. The multi-layer structure includes a first intermediate layer and a second intermediate layer formed on the first intermediate layer. The first intermediate layer includes AlGaN, the second intermediate layer includes AlGaN or aluminum nitride, and the average composition of Al in the first intermediate layer is less than that in the second intermediate layer. A method for forming a semiconductor epitaxial structure is provided. The semiconductor epitaxial structure according to the present disclosure can not decrease the crystalline quality when a compressive stress is introduced, which may avoid a crack phenomenon or quality degradation caused by the change of temperature.