AlN Single-Crystal Substrate Pretreatment for Center Defect Control
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Solution Overview
Problem
Current methods for producing aluminum nitride single crystal substrates still suffer from crystal defects, particularly in the proximity of the center, which can lead to reduced performance and yield in electronic devices like LEDs due to stress concentration and residual impurities.
Innovation Solution
A method involving thermal treatment of the base substrate at 1000 to 2300°C for at least 60 seconds before growing the aluminum nitride single crystal layer, using a halogen gas, hydrogen halide gas, and/or ammonia gas, to reduce residual stress and suppress the formation of crystal defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If vapor phase growth methods (PVT, MOCVD, HVPE) are used to produce aluminum nitride single crystal substrates, then high growth rates and thick film formation are achieved, but crystal defects (dislocation defects, cracks, hillocks, bright spots) occur due to lattice constant and thermal expansion coefficient differences between substrate and epitaxial layer
Solution Approach 1:
The patent applies parameter changes by precisely controlling growth temperature, pressure, and gas composition during vapor phase epitaxy. By optimizing these parameters, the method achieves high growth rates while minimizing crystal defects such as dislocations and cracks that arise from lattice mismatch and thermal expansion differences.
Solution Approach 2:
The patent employs preliminary action through substrate pretreatment steps including surface cleaning and activation before epitaxial growth. This preliminary preparation ensures optimal surface conditions that promote defect-free crystal growth and reduce nucleation sites for dislocations and hillocks.
2Productivity
If conventional vapor phase growth is used, then production efficiency is maintained, but impurity contamination (carbon, silicon, oxygen) and foreign material deposition occur due to reactor attacks by atmosphere gases and by-product formation
Solution Approach 1:
The patent implements an inert atmosphere approach by using high-purity carrier gases and maintaining controlled atmospheric conditions during growth. This prevents reactor wall attacks by atmosphere gases, minimizing impurity liberation and contamination of the growing crystal with carbon, silicon, and oxygen impurities.
Solution Approach 2:
The patent replaces conventional growth conditions with optimized gas phase reactions and thermal fields that promote clean crystal growth. By substituting mechanical contact and uncontrolled atmospheric exposure with precisely managed vapor phase processes, impurity incorporation is minimized while maintaining high productivity.
3Loss of time
If aluminum nitride single crystal substrates are grown without thermal treatment, then process time is reduced, but residual stress accumulates and crystal defects form in the proximity of the center, reducing device performance and yield
Solution Approach 1:
The patent applies preliminary action by implementing thermal treatment as a mandatory preprocessing step before or during epitaxial growth. This thermal treatment relieves residual stresses in the substrate, preventing the formation of crystal defects such as hillocks and bright spots that would otherwise occur in the central region of the substrate.
Solution Approach 2:
The patent uses parameter changes by controlling temperature profiles and thermal gradients during growth. By carefully managing thermal parameters, the method achieves stress relief and improved crystal uniformity without excessively extending process time, balancing quality improvement with production efficiency.
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 approach results in an aluminum nitride single crystal substrate with reduced crystal defects, improved uniformity, and enhanced mechanical strength, leading to higher quality and yield in semiconductor devices.
Implementation Method 1
thermal treatment of the base substrate at 1000 to 2300°C for at least 60 seconds
Implementation Method 2
reduce residual stress
Implementation Method 3
growing an aluminum nitride single crystal layer over the main surface by means of vapor phase epitaxy
Implementation Method 4
vapor phase growth methods, such as sublimation (PVT: Physical Vapor Transport)
Data Source
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AI summary
A group III nitride single crystal substrate including a main surface, the main surface including: a center; a periphery; an outer region whose distance from the center is greater than 30% of a first distance, the first distance being a distance from the center to the periphery; and an inner region whose distance from the center is no more than 30% of the first distance, wherein a ratio (vA - vB) / vB is within the range of ±0.1%, wherein vA is a minimum value of peak wave numbers of micro-Raman spectra in the inner region; and vB is an average value of peak wave numbers of micro-Raman spectra in the outer region.