SiC Crystal Growth via Asymmetric Heating and Rotation
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Solution Overview
Problem
Conventional physical vapor transport (PVT) systems for growing bulk semiconductor single crystals, such as silicon carbide, face challenges in achieving high-quality crystals free from screw and step dislocations due to inhomogeneous heat distribution, despite efforts to create a homogeneous and symmetrical temperature field.
Innovation Solution
Introducing a time-variable, asymmetric temperature field during crystal growth by using a heating system with a deformed coil and a rotary drive to cause rotational movement of the seed crystal within the crucible, allowing screw and step dislocations to mobilize and annihilate each other.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a homogeneous and symmetrical temperature field is used during crystal growth, then the heat distribution is uniform, but screw and step dislocations cannot mobilize and annihilate, resulting in higher dislocation density
Solution Approach 1:
The patent applies asymmetry by deliberately introducing an asymmetric temperature field during crystal growth. The temperature field is designed to have different temperature distributions in different regions, which creates thermal gradients that mobilize dislocations. This asymmetric heating allows screw and step dislocations to move and encounter each other, enabling their annihilation and resulting in higher quality crystals with reduced dislocation density.
Solution Approach 2:
The patent employs dynamics by making the temperature field time-variable rather than static. The temperature distribution changes over time during the crystal growth process, creating dynamic thermal conditions that promote dislocation mobility. This temporal variation in the temperature field enables dislocations to be continuously mobilized and annihilated, improving crystal quality.
2Ease of manufacture
If conventional inductive or resistive heating systems are used, then the heating process is simple and stable, but inhomogeneous heat distribution occurs, leading to dislocation formation
Solution Approach 1:
The patent applies parameter changes by modifying the temperature field parameters (distribution and time-variation) rather than changing the fundamental heating method. The heating system maintains its simplicity while the temperature parameters are dynamically adjusted to create asymmetric and time-variable conditions. This allows conventional heating systems to achieve improved heat distribution uniformity and reduce dislocation formation through intelligent parameter control.
3Ease of operation
If a static temperature field is maintained during growth, then the growth process is stable and easy to control, but dislocations remain stationary and cannot annihilate each other
Solution Approach 1:
The patent applies periodic action by implementing time-variable temperature fields that periodically change during crystal growth. The temperature parameters are modulated in a periodic manner, creating oscillating thermal conditions that continuously mobilize dislocations. This periodic variation in temperature enables dislocations to move back and forth, increasing their probability of encountering and annihilating each other, thereby reducing dislocation density while maintaining controllable growth conditions.
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 significantly reduces dislocation density, improving the quality of the grown single crystals by enabling dislocations to encounter and cancel out, resulting in higher-quality semiconductor materials.
Implementation Method 1
PVT is a crystal growing method that essentially involves sublimation of a suitable source material followed by re-condensation at a seed crystal
Implementation Method 2
The sublimed vapor then diffuses in a controlled manner due to a temperature field having a gradient established between source material and seed crystal
Implementation Method 3
a rotary drive that is operable to cause a rotational movement of the fixing means around the longitudinal axis relative to the heating system
Implementation Method 4
Physical vapor transport (PVT) is generally used for growing bulk SiC single crystals
Implementation Method 5
sublimation of a suitable source material followed by re-condensation at a seed crystal, where the formation of the single crystal takes place
Data Source
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AI summary
The present invention relates to systems and methods for growing bulk semiconductor single crystals, and more specifically, for growing a bulk semiconductor single crystals, such as silicon carbide, based on physical vapor transport. A sublimation system for growing at least one single crystal of a semiconductor material by means of a sublimation growing process comprises a crucible (102) having a longitudinal axis (120) and comprising a fixing means for at least one seed crystal (110) and at least one source material compartment (104) for containing a source material (108); a heating system being formed to generate an irregular temperature field around a circumference of the crucible at one or more defined heights along the longitudinal axis of the crucible; a rotary drive that is operable to cause a rotational movement of the fixing means around the longitudinal axis relative to the heating system.