SiC Seed Unit With Radially Varying Rear Layer for Thermal Stress Control
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Solution Overview
Problem
Existing methods for growing bulk SiC single crystals face challenges in separately controlling axial and radial temperature gradients, leading to thermal stresses and defects in the crystal, which affect the quality and yield of subsequent components.
Innovation Solution
A seed unit with a rear side layer component having a radially varying structure is used to independently adjust the radial and axial temperature gradients, optimizing the temperature field and reducing thermal stresses in the growing bulk SiC single crystal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high axial temperature gradient is used to achieve economically beneficial growth speeds, then productivity is improved, but thermal stresses increase leading to defects in the crystal
Solution Approach 1:
The patent applies local quality by introducing a rear side layer component with radially varying structure that creates a localized radial temperature gradient on the wafer rear side. This allows the axial temperature gradient to remain high for fast growth while a compensating radial gradient reduces thermal stresses locally, preventing defects without sacrificing productivity
Solution Approach 2:
The patent changes the temperature field parameters by introducing a radial temperature gradient component through the rear side layer component. This modifies the overall temperature distribution parameters, allowing simultaneous optimization of growth speed (axial gradient) and crystal quality (radial gradient compensation)
2Reliability
If a rear side protective layer is applied to prevent material vaporization, then reliability is improved, but device complexity increases due to additional layers and fastening mechanisms
Solution Approach 1:
The patent merges the protective function and the temperature control function into a single rear side layer component. This component simultaneously prevents material vaporization from the wafer rear side and generates the beneficial radial temperature gradient, eliminating the need for separate protective layers and fastening mechanisms
Solution Approach 2:
The rear side layer component serves multiple functions: it acts as a protective barrier against material vaporization, generates a radial temperature gradient to reduce thermal stresses, and integrates directly with the wafer structure. This multi-functionality reduces overall device complexity while maintaining reliability
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 results in reduced internal mechanical stresses and dislocations, improving the quality and yield of SiC substrates, allowing for high-quality component production with minimal defects.
Implementation Method 1
a structure of said rear side layer component varying from the crystal longitudinal mid-axis outward in the radial direction, thus adjusting a radial temperature gradient within said SiC seed crystal during a growth of the bulk SiC single crystal
Implementation Method 2
a single crystalline SiC wafer as an SiC seed crystal is introduced into a growth crucible together with a suitable source material. Under controlled temperature, pressure and gas conditions, the source material is sublimated. The gaseous species (═SiC, Si2C, SiC2) are transported to the SiC seed crystal by reason of an axial temperature gradient
Implementation Method 3
the source material is sublimated
Implementation Method 4
at this location they are deposited on the SiC seed crystal from the SiC growth gas phase, whereby the bulk SiC single crystal grows
Data Source
AI summary
A seed unit for growing a bulk SiC single crystal has a wafer-like single crystalline SiC seed crystal with a growth surface arranged on a wafer front side for growing the bulk SiC single crystal to be grown. The SiC seed crystal has a crystal longitudinal mid-axis extending in an axial direction. A radial direction is oriented perpendicular to the axial direction. The seed unit also has a rear side layer component arranged on a wafer rear side of the SiC seed crystal, the structure of which changes starting from the crystal longitudinal mid-axis in the radial direction, and so a radial temperature gradient is adjusted during the growth of the bulk SiC single crystal within the SiC seed crystal.