GaN Substrate on Silicon with Rod Buffer for Crack Prevention
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Solution Overview
Problem
The challenge lies in manufacturing large area gallium nitride (GaN) substrates on silicon substrates, where cracks and warpage occur due to differences in thermal expansion coefficients and lattice constants, leading to non-uniform thickness and reduced quality.
Innovation Solution
A method involving the formation of silicon rods on a silicon substrate, followed by the growth of a crystalline silicon layer and a GaN substrate, using a buffer layer and insulation patterns to manage stress and prevent cracks, with a water jet splitting method to remove the silicon rods, allowing for a flexible structure that absorbs tensile stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a GaN layer is grown on a large area silicon substrate, then the area of the GaN substrate is increased, but cracks and warpage occur due to differences in thermal expansion coefficient and lattice constant
Solution Approach 1:
The patent introduces a buffer layer between the GaN layer and silicon substrate, and creates a patterned structure with recesses and protrusions. This segmentation allows the structure to accommodate thermal expansion differences and lattice mismatch, preventing cracks while maintaining large substrate area. The buffer layer acts as an intermediate structure that divides the stress path, reducing the direct stress between dissimilar materials.
Solution Approach 2:
The patent modifies the physical and chemical parameters of the interface structure by creating patterned recesses and protrusions, and by controlling the composition and thickness of the buffer layer. These parameter changes enable the structure to better match the thermal and mechanical properties between silicon and GaN, preventing warpage and cracks while maintaining large area.
2Ease of manufacture
If a GaN layer is grown on a silicon substrate, then manufacturing cost is reduced compared to sapphire substrate, but uniformity of thickness is reduced due to differences in thermal expansion coefficient and lattice constant
Solution Approach 1:
The buffer layer with patterned recesses and protrusions segments the interface between silicon and GaN, creating multiple localized contact points. This segmentation allows for more uniform stress distribution across the large substrate area, improving thickness uniformity while maintaining the cost advantage of using silicon substrates.
Solution Approach 2:
By controlling the depth, width, and spacing of the recesses and protrusions, as well as the buffer layer composition, the patent optimizes the interface parameters to achieve uniform GaN layer growth. This enables manufacturing precision comparable to sapphire substrates while retaining the cost benefits of silicon.
3Reliability
If a buffer layer is introduced between the silicon substrate and GaN layer, then cracks and warpage are prevented, but the device structure becomes more complex
Solution Approach 1:
The buffer layer is patterned with recesses and protrusions rather than being a continuous layer. This segmented structure provides crack prevention functionality while using less material and creating a more manageable structure for fabrication processes, reducing overall device complexity compared to a thick continuous buffer layer.
Solution Approach 2:
Instead of using a uniform thick buffer layer throughout, the patent applies the buffer layer selectively in patterned regions with recesses and protrusions. This local quality approach provides stress management only where needed at the interface, reducing unnecessary material and simplifying the overall device structure while maintaining reliability.
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 enables the production of high-quality, uniformly thick GaN substrates with increased breakdown voltage, preventing cracks and warpage, and allowing for the reuse of silicon wafers.
Implementation Method 1
Each of the plurality of silicon rods may include a silicon core and a silicon oxide shell surrounding the silicon core
Implementation Method 2
changing the amorphous silicon layer to a crystalline silicon layer
Implementation Method 3
growing a GaN substrate on the crystalline silicon layer
Data Source
AI summary
A structure includes a silicon substrate, a plurality of silicon rods on the silicon substrate, a silicon layer on the plurality of silicon rods, and a GaN substrate on the silicon layer.