Composite Silicon Substrate for GaN Epitaxy Stress Management
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Solution Overview
Problem
The challenge is to reduce stress-induced warping and cracking of gallium nitride epitaxial layers on silicon substrates due to lattice and thermal mismatch, which leads to damage and high losses during manufacturing, especially when using thick silicon substrates that are difficult to process.
Innovation Solution
A composite silicon substrate structure is proposed, where two silicon layers with different crystallographic directions are used, with their cleavage planes staggered to reduce stress accumulation and prevent cracking, allowing for the growth of gallium nitride epitaxial layers with improved robustness and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick silicon substrates are used to prevent cracking and damage from stress, then the reliability and robustness of gallium nitride epitaxial layers are improved, but the substrate cannot be processed by lithography apparatus and manufacturing complexity increases
Solution Approach 1:
The silicon substrate is divided into multiple thin layers (first silicon layer, second silicon layer, third silicon layer) with different crystallographic orientations. This segmentation allows each layer to be thinner and processable by lithography apparatus while collectively providing sufficient stress resistance when stacked together.
Solution Approach 2:
The patent uses a composite substrate structure combining multiple silicon layers with different crystal orientations (e.g., <100>, <110>, <111>). This composite structure leverages the complementary mechanical and thermal properties of different crystal orientations to achieve both processability and stress resistance.
2Reliability
If thick silicon substrates are used to avoid breakage during manufacturing, then the reliability of gallium nitride epitaxial layers is improved, but lithography alignment and focusing cannot be performed
Solution Approach 1:
By dividing the thick substrate requirement into multiple thin layers, each layer remains thin enough for lithography apparatus to focus and align precisely, while the stacked combination provides the overall structural integrity needed to prevent breakage during manufacturing processes.
Solution Approach 2:
The solution moves from a single-dimensional thick substrate to a multi-layered vertical structure. Each layer is thin for precision processing, but the stacked arrangement in the vertical dimension provides the necessary mechanical strength and stress distribution.
3Reliability
If single crystal orientation silicon substrate is used for gallium nitride epitaxial growth, then crystal quality and electrical/optical properties are improved, but stress accumulation causes triangle symmetrical damages and cracking
Solution Approach 1:
The patent introduces asymmetry by using silicon layers with different crystallographic orientations rather than a single orientation. This asymmetric stacking pattern disrupts the triangle symmetrical stress distribution, preventing concentrated stress points and reducing cracking risk while maintaining good crystal quality for gallium nitride growth.
Solution Approach 2:
The composite substrate uses multiple silicon layers with different crystal orientations (e.g., combining <100>, <110>, and <111> orientations). This composite structure distributes stress more evenly across different crystal planes, preventing the concentrated stress that leads to cracking in single-orientation substrates.
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 composite substrate structure effectively reduces stress-induced damage to silicon substrates, enhancing the reliability and processing feasibility of gallium nitride semiconductor devices without increasing substrate thickness, thereby improving the robustness and reliability of the semiconductor layers.
Implementation Method 1
the first silicon layer and the second silicon layer have different crystallographic directions, and directions of cleavage planes of the first silicon layer and the second silicon layer which contact each other do not coincide with each other
Data Source
AI summary
A semiconductor substrate, a semiconductor device and a manufacturing method of the semiconductor substrate are provided. The semiconductor substrate comprises a first semiconductor layer and a second semiconductor layer located on the first semiconductor layer. The first semiconductor layer and the second semiconductor layer, as well as semiconductor layers obtained by symmetrically rotating the first semiconductor layer and the second semiconductor layer according to their respective lattice structures, have different cleavage planes in a vertical direction. By providing the semiconductor substrates having composite structures, even if thicknesses of the substrates are not changed, the damages to the semiconductor substrates due to stresses by the semiconductor epitaxial layers can be reduced, thereby decreasing the likelihood of breakage of the semiconductor substrates. Furthermore, the processing difficulty is reduced and the reliability of the semiconductor devices is improved.