Nitride Semiconductor Interlayer for Strain Management
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Solution Overview
Problem
Semiconductor devices face challenges due to lattice mismatch and thermal expansion differences between materials, leading to strain issues that can cause cracking, wafer bow, and uneven growth, which complicates manufacturing processes.
Innovation Solution
A semiconductor structure is developed with a relaxed nitride interlayer comprising aluminum and gallium, conductively doped with silicon, that reduces average strain by having a different lattice constant than the nitride semiconductor layers, and includes a discontinuous mask layer to manage strain and dislocation density, thereby minimizing wafer bow and improving growth uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If GaN layers are grown on sapphire or silicon carbide substrates, then device fabrication is enabled, but lattice mismatch causes strain that leads to cracking
Solution Approach 1:
The patent introduces an intermediate buffer layer structure between the substrate and GaN layers. This buffer layer has a graded composition that transitions from high aluminum content (AlN) at the substrate interface to lower aluminum content closer to the GaN layer, serving as a mediator that gradually accommodates the lattice mismatch between the substrate and GaN, thereby preventing cracking while enabling device fabrication
2Adaptability or versatility
If different materials are used for substrate and epitaxial layers, then device functionality is achieved, but different coefficients of thermal expansion cause lattice constant differential changes with temperature
Solution Approach 1:
The patent employs a buffer layer with graded aluminum composition where the lattice constant gradually changes from the substrate interface toward the GaN layer. This parameter gradient allows the structure to accommodate thermal expansion differences by providing a continuous transition zone, maintaining lattice constant stability across temperature variations while preserving device functionality
3Productivity
If compressively strained epitaxial layers are grown at high temperature, then growth is enabled, but the layers become tensile strained at room temperature causing wafer bow
Solution Approach 1:
The patent divides the epitaxial structure into multiple segments including a buffer layer with graded composition and multiple GaN layers separated by intermediate layers. This segmentation allows each layer to be optimized for its specific function, with the buffer layer accommodating thermal strain gradients and preventing overall wafer bow while maintaining high-temperature growth capability
4Ease of manufacture
If strain is present in semiconductor structure, then lattice mismatch is accommodated, but strain causes wafer bow and uneven growth reducing device yields
Solution Approach 1:
The patent implements local quality by creating a buffer layer with spatially varying aluminum composition, where the aluminum content is highest at the substrate interface and gradually decreases toward the GaN layer. This local variation in composition allows strain accommodation exactly where needed at the interface, while maintaining growth uniformity in the upper GaN layers where device fabrication occurs
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 structure achieves reduced average strain and improved growth uniformity, reducing the likelihood of cracking and wafer bow, and enhances the quality of nitride semiconductor layers, making them suitable for substrateless devices and substrate production.
Implementation Method 1
The unstrained lattice constant of GaN is 3.19 whereas the unstrained lattice constant of sapphire is 4.76 and silicon carbide is 3.07. As a result, the GaN layers grown on the substrate may be strained.
Implementation Method 2
The nitride interlayer... is conductively doped with an n-type dopant, such as silicon and/or germanium
Implementation Method 3
different materials may have different coefficients of thermal expansion, which may cause the lattice constant differential between materials to change with temperature
Data Source
Figure 1~1A
Figure 2
Figure 3
AI summary
A semiconductor structure includes a first layer of a nitride semiconductor material, a substantially unstrained nitride interlayer on the first layer of nitride semiconductor material, and a second layer of a nitride semiconductor material on the nitride interlayer. The nitride interlayer has a first lattice constant and may include aluminum and gallium and may be conductively doped with an n-type dopant. The first layer and the second layer together have a thickness of at least about 0.5 ?m. The nitride semiconductor material may have a second lattice constant, such that the first layer may be more tensile strained on one side of the nitride interlayer than the second layer may be on the other side of the nitride interlayer.