Asymmetric Thermal Insulation for SiC Crystal Growth
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Solution Overview
Problem
Conventional semiconductor single crystal growth systems using physical vapor transport (PVT) face challenges in achieving homogeneous temperature fields, leading to edge defects and reduced crystal quality, especially as crystal diameters increase, despite optimizations in insulation and heating systems.
Innovation Solution
A sublimation system with a crucible and asymmetric thermal insulation unit that intentionally introduces inhomogeneities to counteract asymmetries in the heating system, generating a homogeneous temperature field and reducing edge defects in SiC single crystals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional symmetric insulation and heating systems are used in PVT crystal growth, then the system structure is simple and easy to manufacture, but the temperature field becomes inhomogeneous leading to edge defects and reduced crystal quality
Solution Approach 1:
The patent applies asymmetry by designing the thermal insulation unit with non-uniform thickness or composition around the crucible. Specifically, the insulation is made thicker or more insulating in regions where the heating system provides excessive heat, and thinner or less insulating where heat is insufficient. This asymmetric insulation configuration compensates for the asymmetric temperature distribution caused by the heating system, resulting in a more homogeneous temperature field and reduced edge defects in the grown crystal.
Solution Approach 2:
The patent implements local quality by varying the insulation properties at different locations around the crucible. The thermal insulation unit is designed with spatially varying thickness, material composition, or thermal conductivity to provide differential thermal compensation. This allows each region of the insulation to be optimized for its specific location, counteracting local temperature deviations and achieving overall temperature homogeneity in the crystal growth zone.
2Productivity
If the crystal diameter is increased to improve productivity, then more material can be grown per batch, but edge defects increase due to temperature field inhomogeneity
Solution Approach 1:
The asymmetric insulation design enables larger crystal diameters to be grown with improved quality by compensating for the increased temperature gradients that occur with larger crucible sizes. The insulation asymmetry is specifically configured to counteract the radial temperature variations that become more pronounced in larger crystals, allowing high-productivity large-diameter growth without sacrificing quality.
Solution Approach 2:
The patent changes the thermal insulation parameters (thickness, material composition, thermal conductivity) as a function of position around the crucible. By adjusting these insulation parameters, the system maintains optimal temperature distribution even when growing larger diameter crystals, thus decoupling the relationship between crystal size and edge defect formation.
3Manufacturing precision
If symmetric thermal insulation is used around the crucible, then the insulation structure is uniform and easy to manufacture, but it cannot compensate for asymmetric heating, resulting in inhomogeneous temperature distribution
Solution Approach 1:
The patent deliberately introduces asymmetry into the thermal insulation unit to match and compensate for the asymmetry in the heating system. The insulation is designed with varying thickness or material properties in specific angular positions around the crucible, creating an asymmetric structure that counterbalances the asymmetric heat input, thereby achieving homogeneous temperature distribution.
Solution Approach 2:
The asymmetric insulation is designed in advance to preemptively counteract the known asymmetric heating pattern. By pre-configuring the insulation asymmetry to oppose the heating asymmetry, the system proactively prevents temperature field inhomogeneity before it affects crystal growth, rather than attempting to correct it during the growth process.
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 allows for the growth of high-quality, edge defect-free SiC single crystals by balancing inhomogeneities in the insulation with those in the growth system, resulting in uniform growth rates and reduced defect formation.
Implementation Method 1
A sublimation system with a crucible and asymmetric thermal insulation unit that intentionally introduces inhomogeneities to counteract asymmetries in the heating system
Implementation Method 2
Heating is provided either by induction coils placed outside the reactor or by resistance heaters placed inside the reactor
Implementation Method 3
A thermal insulation unit is at least partly surrounding the crucible, and has a radially and/or axially asymmetric form to compensate the irregular temperature field
Implementation Method 4
Inside the crucible, an SiC source material is sublimated and deposited (i. e. desublimated) onto the SiC seed crystal
Implementation Method 5
SiC single crystals are typically grown by a physical vapor deposition (PVT) process
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 (102) and/or along the longitudinal axis of the crucible (102); a thermal insulation unit (117) at least partly surrounding the crucible (102), wherein the thermal insulation unit (117) has a radially and/or axially asymmetric form to compensate the irregular temperature field.