Seed Selection for Crack-Free Group III Nitride Crystals
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Solution Overview
Problem
Current methods for growing bulk group III nitride crystals, such as ammonothermal growth, face challenges in achieving crack-free crystals thicker than 1 mm, which is essential for high-quality semiconductor wafers due to stress accumulation from thermal expansion coefficient mismatches between seed and grown crystals.
Innovation Solution
Selecting seed crystals by measuring x-ray rocking curves at multiple points, quantifying peak widths, and evaluating their distribution to ensure low standard deviation, which correlates with reduced crack density in the bulk crystal, thereby minimizing stress and cracking during growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If bulk group III nitride crystals are grown thicker than 1 mm, then the crystal size and quality improve, but stress accumulation from thermal expansion coefficient mismatches causes crack formation
Solution Approach 1:
The patent applies preliminary action by carefully selecting seed crystals with specific orientation relationships (c-plane, a-plane, or m-plane) before the bulk crystal growth process. This pre-selection of seeds with appropriate crystallographic orientations prevents stress accumulation during subsequent growth, enabling the production of thick crack-free crystals greater than 1 mm in size
2Ease of manufacture
If conventional seed selection methods are used, then the growth process is simple, but crack density increases due to thermal expansion mismatches
Solution Approach 1:
The patent changes the selection parameters for seed crystals by specifying precise crystallographic orientation relationships between the seed and the bulk crystal. Instead of using conventional simple selection criteria, the method requires seeds to have specific orientations (c-plane, a-plane, or m-plane) that match the growing crystal, thereby reducing thermal expansion mismatches and crack formation while maintaining manufacturing feasibility
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 method results in crack-free bulk group III nitride crystals, improving the reliability and performance of semiconductor devices like LEDs and transistors by reducing dislocation density and crack formation, enabling the production of high-quality wafers with dislocation density less than 1 cm^-2.
Implementation Method 1
measuring x-ray rocking curves of the seed crystal at more than one point
Implementation Method 2
measuring x-ray rocking curves... quantifying peak widths
Data Source
AI summary
In one instance, the invention provides a method of growing bulk crystal of group III nitride using a seed crystal selected by (a) measuring x-ray rocking curves of a seed crystal at more than one point, (b) quantifying the peak widths of the measured x-ray rocking curves, and (c) evaluating the distribution of the quantified peak widths. The invention also includes the method of selecting a seed crystal for growing bulk crystal of group III nitride.The bulk crystal of group III nitride can be grown in supercritical ammonia or a melt of group III metal using at least one seed selected by the method above.