RAMO4 Substrate Curvature Control for GaN Cracking
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Solution Overview
Problem
The existing methods for forming group III nitride crystals on RAMO4 substrates often result in warping and cracking due to lattice mismatch and thermal expansion coefficient differences, leading to substrate instability during and after crystal formation.
Innovation Solution
A RAMO4 substrate with a curvature radius of 52 μm or more and a correlation coefficient ρ of 0.81 or more is fabricated using the Czochralski method, controlling the crystal growth parameters such as temperature gradient, pulling rate, and rotational speed to ensure uniform crystal orientation and reduce warping, thereby minimizing cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a RAMO4 substrate is used as a base substrate for forming group III nitride crystals, then the lattice mismatch with GaN is reduced to about 1/10 of that of sapphire, but warping and cracking occur in the base substrate after the formation of GaN monocrystalline thin film due to lattice mismatch and linear expansion coefficient difference
Solution Approach 1:
The invention controls specific parameters of the RAMO4 substrate including curvature radius (52 μm or more) and crystal plane uniformity (correlation coefficient ρ of 0.81 or more). By adjusting these physical parameters during crystal growth, the substrate maintains both high lattice matching precision and structural integrity during GaN crystal formation.
Solution Approach 2:
The invention introduces a curved surface design for the RAMO4 substrate with a curvature radius of 52 μm or more. This curvature compensates for thermal expansion differences and reduces stress concentration, preventing warping and cracking while maintaining the substrate's lattice matching advantages.
2Manufacturing precision
If GaN monocrystalline thin film is formed at high temperature of 1,050° C. using MOCVD, then high-quality GaN crystals are obtained, but the base substrate cracks in areas of concentrated stress because of the lattice mismatch and linear expansion coefficient difference
Solution Approach 1:
The invention pre-compensates for thermal stress by designing the RAMO4 substrate with specific curvature and uniformity characteristics before the high-temperature MOCVD process. This beforehand cushioning prevents stress concentration and cracking during the high-temperature GaN crystal formation process.
Solution Approach 2:
The invention modifies the substrate's physical parameters (curvature radius and crystal plane uniformity) to create a stress-distributing structure that can withstand the high-temperature MOCVD process without cracking, while still enabling high-quality GaN crystal growth.
3Reliability
If the curvature radius of the crystal plane is increased to 52 μm or more, then warping is reduced and cracking is minimized, but the manufacturing complexity increases due to precise control requirements
Solution Approach 1:
The invention implements feedback control during crystal growth by measuring the curvature radius and correlation coefficient of the RAMO4 substrate and adjusting growth parameters accordingly. This ensures the substrate achieves the required curvature (52 μm or more) and uniformity (ρ ≥ 0.81) while maintaining manufacturability.
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 controlled substrate fabrication process significantly reduces the likelihood of cracking during group III nitride crystal formation, enhancing the yield and quality of the semiconductor products.
Implementation Method 1
A RAMO4 substrate with a curvature radius of 52 μm or more and a correlation coefficient ρ of 0.81 or more is fabricated using the Czochralski method
Implementation Method 2
controlling the crystal growth parameters such as temperature gradient, pulling rate, and rotational speed
Implementation Method 3
the curvature radius r is calculated as an absolute value from a regression line obtained from a relationship between X-ray peak position ωi and position Xi after the X-ray peak position ωi is specified in a diffraction spectrum of an X-ray rocking curve measured at each of a plurality of positions Xi
Implementation Method 4
diffraction spectrum of an X-ray rocking curve
Data Source
AI summary
A RAMO4 substrate that does not easily crack during or after the formation of group III nitride crystal includes a single crystal represented by general formula RAMO4 (wherein R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanoid elements, A represents one or more trivalent elements selected from the group consisting of Fe(III), Ga, and Al, and M represents one or more divalent elements selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd). The RAMO4 substrate has a crystal plane with a curvature radius r of 52 m or more, and a square value of correlation coefficient ρ of 0.81 or more. The curvature radius r is calculated as an absolute value from X-ray peak position ωi and measurement position Xi after the measurements of X-ray peak positions ωi at a plurality of positions Xi lying on a straight line passing through the center of the RAMO4 substrate. The correlation coefficient ρ is a measure of correlation between ω and measurement position Xi.