Self-Supporting GaN Substrate Growth Without Cracking
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Solution Overview
Problem
Current methods for preparing GaN self-supporting single crystal substrates face challenges due to lattice mismatch and thermal mismatch between GaN and sapphire substrates, leading to cracking and bending issues, which limit the size and yield of large-sized substrates.
Innovation Solution
A method involving the preparation of a thin film base structure with sequentially stacked substrate layers, followed by stripping of the first substrate layer, growth of a thick film layer, and subsequent stripping of the second substrate layer, to create a self-supporting substrate without the constraints of lattice and thermal mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If HVPE technology is used to grow GaN thick film on heterogeneous substrate, then large-sized single crystal substrates can be obtained, but the substrate becomes bowl-shaped bent and cracks when GaN thickness reaches certain degree due to lattice mismatch and thermal mismatch
Solution Approach 1:
The patent divides the substrate system into multiple layers: a first substrate for initial nucleation, a released thin film layer that serves as a new growth substrate, and a second substrate for final thick film growth. This segmentation allows each layer to be optimized independently, preventing the bowl-shaped bending and cracking that occurs in single-substrate approaches.
Solution Approach 2:
The released thin film layer acts as an intermediary between the first substrate and the second substrate. It serves as a stress-free growth substrate for the thick GaN film, mediating the lattice and thermal mismatch issues that would otherwise cause cracking in direct heterogeneous epitaxy.
2Area of stationary object
If GaN thick film is grown directly on sapphire substrate by HVPE, then large-sized substrates can be produced, but mechanical grinding is required to flatten the curved thick film, limiting accessibility of large-sized thick film
Solution Approach 1:
The patent performs preliminary actions by first growing a thin film on the first substrate, releasing it, and then growing the thick film on this pre-prepared released thin film layer that is already bonded to the second substrate. This preliminary preparation ensures the growth substrate is flat and stress-free before thick film deposition, eliminating the need for mechanical grinding.
3Manufacturing precision
If MOCVD and HVPE equipment are used separately for thin film and thick film growth, then crystalline layer can be grown on sapphire substrate, but the process is complex and time-consuming
Solution Approach 1:
The patent makes the HVPE equipment multi-functional by enabling it to perform both thin film nucleation and thick film growth through the released thin film technique. The same HVPE reactor can complete the entire GaN substrate preparation process, eliminating the need for separate MOCVD and HVPE equipment and simplifying the overall manufacturing system.
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 method allows for the growth of thin films on larger diameter substrates without cracking, enabling the production of large-sized self-supporting GaN thick film substrates with improved yield and reduced R&D and production costs.
Implementation Method 1
preparing a thin film base structure, where the thin film base structure includes: a first substrate layer, a thin film layer
Implementation Method 2
preparing a thick film layer by continuing to grow a same material as that of the thin film layer on a side of the thin film layer far away from the second substrate layer
Data Source
AI summary
A method for preparing a self-supporting substrate includes: preparing a thin film base structure including a first substrate layer, a thin film layer and a second substrate layer stacked in sequence; removing the first substrate layer from the thin film layer; continuing to grow a material the same as that of the thin film layer on a side of the thin film layer far away from the second substrate layer to prepare a thick film layer; and removing the second substrate layer from the thick film layer and remaining the thick film layer. In the method, a thin film may be grown on a substrate that has a larger diameter, and a thinness of the thin film will not cause the thin film and/or the substrate to crack. Therefore, a thin film that has a large diameter may be obtained so as to obtain a large-sized self-supporting thick film substrate.