SiC Seed Unit With Radially Varying Back-Side Layer for Thermal Stress Control
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Solution Overview
Problem
Existing methods for growing SiC bulk single crystals face challenges in controlling the temperature gradients, leading to defects and reduced quality in the resulting substrates, which in turn affect the performance and yield of subsequent epitaxial processes.
Innovation Solution
A seed unit with a radially varying back-side layer component on the SiC seed crystal, allowing separate adjustment of axial and radial temperature gradients, thereby optimizing the temperature field and reducing internal stresses and dislocations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large axial temperature gradient is used to achieve economically viable growth rates, then the growth rate is improved, but thermal stresses increase leading to defects and warping in the SiC substrates
Solution Approach 1:
The patent applies local quality by creating a non-uniform back-side layer component with radially varying thickness on the SiC seed crystal. The layer thickness increases from the center toward the periphery, establishing a radial temperature gradient that compensates for the axial temperature gradient. This local structural variation allows different regions of the crystal to experience optimized temperature conditions, reducing thermal stresses while maintaining overall growth rate.
Solution Approach 2:
The patent transitions from controlling only the axial temperature gradient (one dimension) to introducing a radial temperature gradient (second dimension) through the back-side layer component. This dimensional expansion of temperature control allows independent optimization of growth rate (axial) and stress reduction (radial), resolving the contradiction between productivity and reliability.
2Temperature
If a multi-part thermal insulation with movable adjustment element is used to uniform the temperature within the SiC seed crystal, then temperature uniformity is improved, but the device complexity increases
Solution Approach 1:
The back-side layer component is pre-configured with a specific radially varying thickness profile before the growth process begins. This preliminary structural arrangement automatically establishes the desired radial temperature gradient without requiring movable parts or complex adjustments during operation, thereby achieving temperature uniformity while avoiding increased device complexity.
Solution Approach 2:
The back-side layer component serves multiple functions simultaneously: it provides thermal insulation, establishes the radial temperature gradient, and prevents material evaporation from the seed crystal back side. This self-service approach eliminates the need for separate movable adjustment elements or complex multi-part thermal insulation systems.
3Reliability
If the SiC seed crystal is coated with a protective coating on the backside to prevent material evaporation, then defect formation is reduced, but the temperature field control capability is limited
Solution Approach 1:
The patent changes the physical parameter of the back-side layer from a uniform thin protective coating to a structured layer with radially varying thickness. This parameter change transforms the layer from a simple protective barrier into an active thermal management component that can establish and control the radial temperature gradient, thereby maintaining defect reduction while enabling temperature field control.
Solution Approach 2:
The back-side layer component functions as a composite structure combining protective coating properties with thermal insulation properties. The radially varying thickness profile integrates the protective function (preventing evaporation) with the temperature control function (establishing radial gradient), achieving both defect reduction and temperature field adaptability within a single integrated component.
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 solution enables the growth of high-quality SiC bulk single crystals with reduced defects, improving the yield and quality of subsequent SiC substrates and components.
Implementation Method 1
The source material is sublimated under controlled temperature, pressure, and gas conditions. The gaseous species (= SiC, Si 2 C, SiC 2) are transported to the SiC seed crystal due to an axial temperature gradient
Implementation Method 2
The gaseous species (= SiC, Si 2 C, SiC 2) are transported to the SiC seed crystal due to an axial temperature gradient, where they precipitate from the SiC growth gas phase onto the SiC seed crystal, causing the SiC bulk single crystal to grow
Implementation Method 3
The gaseous species (= SiC, Si 2 C, SiC 2) are transported to the SiC seed crystal due to an axial temperature gradient
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The seed unit (1) is intended for growing a SiC bulk single crystal and has a disk-shaped, single-crystal SiC seed crystal (2) with a growth surface (4a) arranged on a disk front side (4) for growing the SiC bulk single crystal to be grown. The SiC seed crystal (2) has a crystal center longitudinal axis (6) running in an axial direction. A radial direction is oriented perpendicular to the axial direction. The seed unit (1) also has a back-side layer component (3) arranged on a disk rear side (5) of the SiC seed crystal (2), the structure of which changes in the radial direction starting from the crystal center longitudinal axis (6), such that a radial temperature gradient is established within the SiC seed crystal (2) during the growth of the SiC bulk single crystal.