Graded Buffer Layer for Nitride Semiconductor Stress Management
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Solution Overview
Problem
The production yield of large-sized nitride semiconductor structures on silicon substrates is low due to thermal expansion mismatch and lattice mismatch, leading to stress-related cracks and high fabrication costs, and the use of expensive processes like laser ablation.
Innovation Solution
A nitride semiconductor structure with a silicon substrate, a nucleation layer, and a buffer layer comprising multiple sub-buffer layers with island structures that have specific roughness, height, or distribution density relationships, reducing thermal expansion mismatch stresses and eliminating the need for laser ablation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a silicon substrate is used for growing nitride semiconductor material, then thermal conductivity and electrical conductivity are improved, but thermal expansion mismatch and lattice mismatch cause stress and cracks
Solution Approach 1:
The buffer layer is divided into multiple sub-buffer layers (first, second, third sub-buffer layers) with different aluminum contents, creating a graded structure that segments the stress distribution and reduces thermal expansion mismatch between the nitride semiconductor layer and silicon substrate
Solution Approach 2:
Different regions of the buffer layer have different aluminum contents (first sub-buffer layer has higher aluminum content than the second, which has higher than the third), creating local compositional variations that optimize stress management and lattice matching in different zones
2Area of stationary object
If large-sized nitride semiconductor structures are fabricated on silicon substrates, then production scale is increased, but yield rate decreases due to stress-related cracks
Solution Approach 1:
The graded buffer layer structure is prepared in advance before growing the nitride semiconductor layer, pre-establishing a stress-managed foundation that prevents crack formation during subsequent large-scale fabrication processes
Solution Approach 2:
The intermediate buffer layers with graded aluminum contents act as cushioning zones that absorb and distribute thermal and mechanical stresses before they can propagate into the nitride semiconductor layer, preventing crack formation in large-sized structures
3Ease of manufacture
If laser ablation equipment is used for substrate lifting, then substrate removal is achieved, but equipment cost and process complexity increase
Solution Approach 1:
The silicon substrate is extracted or removed from the final device structure through the buffer layer interface, allowing the nitride semiconductor layer to be separated from the substrate without requiring complex laser ablation equipment
Solution Approach 2:
The buffer layer serves as an intermediary between the silicon substrate and the nitride semiconductor layer, facilitating substrate removal and device separation through its graded composition and structural properties
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 approach effectively reduces stress and defect density, improving the yield rate of large-sized nitride semiconductor structures without cracks, enhancing their quality and reducing fabrication costs.
Implementation Method 1
the stresses resulted from thermal expansion mismatch (i.e. difference between the coefficients of thermal expansion) can be effectively reduced between the nitride semiconductor layer and the silicon substrate
Data Source
AI summary
A nitride semiconductor structure including a silicon substrate, a nucleation layer, a buffer layer and a nitride semiconductor layer is provided. The nucleation layer is disposed on the silicon substrate. The buffer layer is disposed on the nucleation layer, in which the buffer layer includes n sub-buffer layers where n≧2, and each of the sub-buffer layers has island structures. The nitride semiconductor layer is disposed on the buffer layer.