Buffer Layer Structure for Nitride Semiconductor Devices
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Solution Overview
Problem
The existing buffer layers in nitride semiconductor devices on silicon or sapphire substrates face issues such as crack formation, warpage, increased leakage current, and impaired flatness due to lattice mismatch and thermal expansion differences, leading to reduced crystal quality and electrical characteristics.
Innovation Solution
A semiconductor device with a buffer layer structure comprising alternately stacked layers with varying Al composition, where the central layer contains more Al than the upper and lower layers, facilitating lattice relaxation and reducing stress, while maintaining a multi-layer structure to minimize leakage current and enhance flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the GaN layer in the buffer layer is made thicker, then the flatness of the active layer is improved, but a crack appears in the buffer layer or the active layer and warpage cannot be adjusted
Solution Approach 1:
The buffer layer is divided into three regions with different Al composition distributions: a first buffer layer region with Al composition decreasing from bottom to top, a second buffer layer region with Al composition increasing from bottom to top, and a third buffer layer region with Al composition decreasing from bottom to top. This local variation in material composition allows different regions to serve different functions: stress management in the first and third regions, and leakage current suppression in the second region, thereby resolving the contradiction between achieving flatness and preventing cracks.
Solution Approach 2:
The invention changes the parameter of Al composition distribution within the buffer layer. By creating regions with different Al composition gradients (decreasing, increasing, and decreasing from bottom to top), the patent optimizes both the mechanical properties (stress distribution, flatness) and electrical properties (leakage current) of the buffer layer, preventing crack formation while achieving the desired flatness.
2Device complexity
If the GaN layer in the buffer layer is made thinner, then the manufacturing complexity is reduced, but the leakage current in the buffer layer increases
Solution Approach 1:
The second buffer layer region is specifically designed with an Al composition that increases from bottom to top, creating a gradient that effectively suppresses leakage current. This localized optimization in the central region of the buffer layer addresses the leakage current issue without requiring the entire buffer layer to be excessively thick, thereby balancing complexity and performance.
Solution Approach 2:
The buffer layer is constructed as a composite structure with three distinct regions having different Al composition distributions. This composite approach combines the advantages of different material configurations: the first and third regions manage stress and flatness, while the second region specifically addresses leakage current, achieving multiple objectives simultaneously without excessive complexity.
3Shape
If a single thick GaN buffer layer is used, then the flatness is improved, but warpage occurs in the film forming apparatus due to thermal expansion difference
Solution Approach 1:
The first and third buffer layer regions are designed with Al composition that decreases from bottom to top, creating specific stress distributions in these regions. This local stress management, combined with the central second region, enables the overall buffer layer to maintain flatness while compensating for thermal expansion differences, thereby preventing warpage in the film forming apparatus.
Solution Approach 2:
By varying the Al composition parameter across different regions and in different directions (decreasing, increasing, decreasing from bottom to top), the invention optimizes the stress distribution within the buffer layer. This parameter variation allows the buffer layer to accommodate thermal expansion differences without warping while still achieving the desired flatness for the active layer.
4Reliability
If AlN/GaN superlattice structure is formed with large total film thickness, then the leakage current is suppressed, but warpage becomes a problem
Solution Approach 1:
The invention concentrates the leakage current suppression function in the second buffer layer region, which has a specific Al composition gradient (increasing from bottom to top). This localized approach allows effective leakage suppression without requiring the entire buffer layer to be excessively thick, thereby reducing the overall warpage stress while maintaining electrical performance.
Solution Approach 2:
The patent optimizes the Al composition parameter in the second buffer layer region to effectively suppress leakage current. By carefully controlling the Al composition gradient in this specific region rather than uniformly increasing thickness throughout, the invention achieves leakage suppression with minimized warpage stress.
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 proposed buffer layer structure effectively reduces stress, suppresses leakage current, and improves the flatness of the active layer, thereby enhancing the overall performance and reliability of the semiconductor device.
Implementation Method 1
the central layer contains more Al than the upper and lower layers, facilitating lattice relaxation and reducing stress
Implementation Method 2
they also have different coefficients of thermal expansion. Therefore, a high amount of distortion energy is generated in the nitride semiconductor layer formed on the substrate by epitaxial growth
Implementation Method 3
a high amount of distortion energy is generated in the nitride semiconductor layer formed on the substrate by epitaxial growth
Data Source
AI summary
Semiconductor device including: silicon-based substrate; first buffer layer on silicon-based substrate and is formed of first layer containing Al composition and second layer containing less Al than the first layer, the first and second layers being alternately stacked; second buffer layer on the first buffer layer and is formed of third layer containing Al composition and fourth layer containing less Al than the third layer, the third and fourth layers being alternately stacked; and third buffer layer on the second buffer layer and is formed of fifth layer containing Al composition and sixth layer containing less Al than the fifth layer, the fifth and sixth layers being alternately stacked, wherein the second buffer layer contains more Al than the first and third buffer layers. Thus, the semiconductor device leakage can be suppressed while reducing stress which is applied to buffer layer and can improve flatness of active layer upper face.