SiC Single Crystal Substrate Screw Dislocation Reduction
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Solution Overview
Problem
Existing methods for producing silicon carbide (SiC) single crystals using the physical vapor transport (PVT) method result in high screw dislocation densities, which hinder the production of high-quality SiC devices due to defects like threading edge dislocations and basal plane dislocations, and current techniques do not efficiently reduce screw dislocations across a wide range.
Innovation Solution
A method involving the formation of a facet {0001} plane in the crystal peripheral part of the SiC single crystal, with a growth sub-step at high nitrogen concentration and specific pressure and temperature conditions, structurally converts screw dislocations to stacking faults, reducing their density across a wide range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PVT method is used to grow SiC single crystal, then the crystal can be produced with broad forbidden band width and high voltage resistance, but screw dislocation defects are inevitably generated which reduce device performance
Solution Approach 1:
The patent applies preliminary action by performing a first growth step before the main second growth step. In this first step, a bulk SiC single crystal is grown under specific conditions (temperature 2,070°C to less than 2,200°C, pressure 3.9 to 39.9 kPa) to prepare a foundation that reduces screw dislocation generation in subsequent growth, thereby improving device performance while controlling defect density
Solution Approach 2:
The patent employs parameter changes by dividing the growth process into two distinct steps with different temperature and pressure parameters. The first growth step uses lower temperature (2,070-2,200°C) and moderate pressure (3.9-39.9 kPa), while the second step uses higher temperature (less than 2,400°C) and lower pressure (0.13-2.6 kPa). This parameter optimization reduces screw dislocation density while maintaining high-quality crystal growth
2Manufacturing precision
If dislocation-controlled seed crystal with screw dislocation-generatable region is used, then screw dislocation density can be controlled in specific regions, but multiple growth steps (c-plane and a-plane) are required which reduces productivity
Solution Approach 1:
The patent applies segmentation by dividing the crystal growth process into two sequential steps with distinct purposes. The first growth step focuses on preparing a bulk crystal with controlled dislocation characteristics, while the second step optimizes for high-quality substrate formation. This segmentation allows precise screw dislocation density control without requiring complex multi-directional growth approaches
Solution Approach 2:
The patent uses parameter changes to achieve different growth objectives in each step. By adjusting temperature and pressure parameters between steps, the process achieves both screw dislocation control and high productivity, eliminating the need for multiple c-plane and a-plane growth cycles required by conventional methods
3Manufacturing precision
If high temperature exceeding 2,000°C is used for crystal growth, then SiC single crystal can be formed with desired properties, but crystal defects such as dislocation defects and stacking faults are inevitably contained
Solution Approach 1:
The patent applies parameter changes by implementing a two-step growth process with optimized temperature and pressure parameters. The first step uses temperature of 2,070°C to less than 2,200°C and pressure of 3.9 to 39.9 kPa, while the second step uses temperature of less than 2,400°C and pressure of 0.13 to 2.6 kPa. This parameter optimization reduces crystal defects while maintaining desired SiC properties
Solution Approach 2:
The patent uses preliminary action by performing the first growth step to prepare a bulk crystal foundation with reduced defect density before proceeding to the second growth step. This preliminary preparation minimizes the propagation of dislocation defects and stacking faults in the final substrate
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 effectively reduces screw dislocation density across a wide range, ensuring a high-quality SiC single crystal substrate with improved device yield and performance.
Implementation Method 1
a bulk SiC single crystal is grown by sublimation on an SiC single crystal seed
Implementation Method 2
an impurity can be doped into the single crystal under growing and, for example, in the case of an n-type SiC single crystal, a nitrogen (N2) gas can be added to the atmosphere gas during growth
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
The present invention provides a method for producing an SiC single crystal, enabling obtaining an SiC single crystal substrate in which a screw dislocation-reduced region is ensured in a wide range, and an SiC single crystal substrate. The SiC single crystal substrate is produced using a seed crystal having an off angle in the off orientation from a {0001} plane by a production method wherein in advance of a growth main step of performing crystal growth to form a facet {0001} plane in the crystal peripheral part on the crystal end face having grown thereon the bulk silicon carbide single crystal and obtain more than 50% of the thickness of the obtained SiC single crystal, a growth sub-step of growing the crystal at a higher nitrogen concentration than in the growth main step and at a growth atmosphere pressure of 3.9 to 39.9 kPa and a seed crystal temperature of 2,100°C to less than 2,300°C is included.