SiC Substrate Screw Dislocation Reduction via PVT Pressure Control
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Solution Overview
Problem
Current methods for growing silicon carbide (SiC) single crystals using the Physical Vapor Transport (PVT) method struggle to reduce screw dislocations effectively, which are detrimental to the performance of SiC devices, and existing solutions like metastable solvent epitaxy and chemical vapor deposition methods have limitations in industrial scalability due to lower growth rates.
Innovation Solution
A method involving specific growth conditions during the PVT process to structurally convert screw dislocations into more stable states like stacking faults and basal plane dislocations, resulting in a SiC single crystal substrate with reduced screw dislocations in one semicircular region compared to the other, achieved by varying growth pressure and temperature in distinct steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the PVT method is used to grow SiC single crystals, then the growth rate is high and industrial scalability is maintained, but screw dislocation density remains high (10³ to 10⁴ /cm²)
Solution Approach 1:
The patent applies parameter changes by systematically varying growth pressure and temperature during different stages of crystal growth. Specifically, the method uses a two-stage pressure control strategy: initially growing at a first pressure (0.13-2.6 kPa) to promote high growth rate, then switching to a second pressure (2.6-65 kPa) to promote dislocation conversion. Temperature is also adjusted in coordination with pressure changes. This dynamic parameter adjustment resolves the contradiction by allowing high productivity during the first stage while achieving low dislocation density during the second stage.
Solution Approach 2:
The patent applies preliminary action by first growing an initial layer of SiC single crystal under controlled pressure and temperature conditions before proceeding to the main growth stage. This initial layer formation at specific parameters (first pressure 0.13-2.6 kPa and first temperature 2100-2400°C) prepares the crystal structure in advance, creating conditions that facilitate subsequent dislocation conversion while maintaining high overall growth efficiency.
2Manufacturing precision
If metastable solvent epitaxy or CVD method is used to reduce screw dislocations, then screw dislocation density decreases (to 67 /cm²), but growth rate becomes very slow (several μm/hr, 1/10 or less of PVT method)
Solution Approach 1:
The patent merges the advantages of different methods by combining the high growth rate capability of the PVT method with the dislocation reduction effect of controlled pressure variation. Instead of using slow-growing epitaxial methods, the patent integrates pressure control (switching between 0.13-2.6 kPa and 2.6-65 kPa) into the PVT process, thereby achieving both high productivity and low dislocation density in a single unified process.
Solution Approach 2:
The patent applies dynamics by making the growth pressure and temperature adjustable and time-dependent rather than static. The method dynamically transitions from a first pressure regime (0.13-2.6 kPa) during initial growth to a second pressure regime (2.6-65 kPa) during the conversion stage, with corresponding temperature adjustments. This dynamic control enables the system to optimize for growth rate at different times, resolving the contradiction between speed and quality.
3Ease of manufacture
If conventional PVT growth is used with uniform conditions, then growth is simple and fast, but screw dislocations are distributed uniformly throughout the crystal
Solution Approach 1:
The patent applies segmentation by dividing the crystal growth process into distinct stages with different pressure and temperature parameters. The growth is segmented into: (1) initial layer growth at first pressure (0.13-2.6 kPa) and first temperature (2100-2400°C), and (2) conversion stage growth at second pressure (2.6-65 kPa) and second temperature. This segmentation creates non-uniform dislocation distribution, concentrating converted dislocations in specific regions while maintaining overall process simplicity through standardized equipment.
Solution Approach 2:
The patent applies local quality by creating different growth conditions in different spatial and temporal regions of the crystal formation process. The method establishes a first growth region with specific pressure (0.13-2.6 kPa) and temperature (2100-2400°C) parameters, then transitions to a second growth region with different pressure (2.6-65 kPa) and temperature parameters. This results in localized dislocation conversion in specific crystal regions, improving overall crystal quality while maintaining manufacturing simplicity.
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 results in a SiC single crystal substrate with significantly reduced screw dislocations in one semicircular region, enhancing the performance and yield of SiC devices, while maintaining industrial scalability by utilizing standard PVT method equipment.
Implementation Method 1
a SiC sublimation raw material is contained in a crucible, then, a seed crystal composed of a SiC single crystal is attached to the lid of the crucible, and the raw material is sublimated, whereby recrystallization causes the SiC single crystal to grow on the seed crystal
Implementation Method 2
growing a bulk SiC single crystal by the Physical Vapor Transport (PVT) method
Data Source
AI summary
Provided are: a silicon carbide single crystal substrate which is cut out from a silicon carbide bulk single crystal grown by the Physical Vapor Transport method; and a process for producing the same. The number of screw dislocations in one of the semicircle areas of the substrate is smaller than that in the other thereof, namely, the number of screw dislocations in a given area of the substrate is reduced. The semicircle areas of the substrate correspond respectively to the halves of the substrate. The present invention pertains to: a silicon carbide single crystal substrate which is cut out from a silicon carbide bulk single crystal grown by the Physical Vapor Transport method and which is characterized in that the average value of the screw-dislocation densities observed at multiple measurement points in one of the semicircle areas, which correspond respectively to the halves of the substrate, is 80% or less of the average value of screw-dislocation densities observed at multiple measurement points in the other of the semicircle areas; and a process for producing the same.