Bulk SiC Crystal Growth Using Seed Stress Classification
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Solution Overview
Problem
Existing methods for producing bulk SiC single crystals suffer from stress-induced defects and deformations due to initial seed stresses, leading to reduced quality and yield of SiC substrates, which are difficult to address using conventional stress measurement and apparatus design.
Innovation Solution
A method involving stress measurement and classification of SiC seed crystals to identify and counteract initial mechanical stresses by applying stress-reducing measures during sublimation growth, such as using elements with varying heat conductivity and adjusting growth apparatus design to mitigate seed stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sublimation growth methods are used without stress measurement, then the production process is simple and fast, but stress-induced defects and deformations occur in the bulk SiC single crystal
Solution Approach 1:
The patent applies preliminary action by measuring and classifying seed crystals before using them for bulk crystal growth. Seed crystals are measured for stress distribution, classified into groups, and only suitable seeds are selected for growth, preventing stress-induced defects before they can occur during the growth process.
Solution Approach 2:
The patent implements feedback by using stress measurement results to guide the selection and processing of seed crystals. The measured stress distribution information feeds back into the classification system, which then determines the growth conditions and apparatus design to compensate for specific stress patterns in each seed crystal type.
2Manufacturing precision
If stress measurement and classification are performed on seed crystals, then initial seed stresses can be identified and counteracted, but the production time and cost increase
Solution Approach 1:
Stress measurement and classification are performed as preliminary actions before the bulk crystal growth process. By completing these measurements and classifications in advance, the actual growth process can proceed efficiently without interruptions for stress management during growth.
Solution Approach 2:
The patent applies parameter changes by adjusting growth conditions (temperature distribution, pressure, gas flow) based on the classified stress characteristics of each seed crystal. This allows the growth process to be optimized for each seed crystal's specific stress state, reducing overall production time while maintaining high precision.
3Productivity
If seed crystals with high initial stresses are used, then the growth process can proceed without additional measures, but stress-induced defects and deformations occur
Solution Approach 1:
The patent performs stress measurement and classification as preliminary actions to identify suitable seed crystals before growth. This ensures that only seed crystals with acceptable stress levels are used, preventing stress-induced defects while maintaining continuous growth capability.
Solution Approach 2:
The classification system acts as an intermediary between the stress measurement process and the growth process. It mediates by selecting and matching seed crystals with appropriate growth conditions, filtering out problematic seed crystals before they can cause defects during growth.
4Reliability
If conventional growth apparatus design is used, then the equipment is simple and cost-effective, but wall effects and thermal effects cause stresses in the grown crystal
Solution Approach 1:
The patent applies local quality by customizing the growth apparatus design to match the specific stress characteristics of each seed crystal type. Different regions of the apparatus (heating zones, cooling zones, support structures) are optimized locally for the specific requirements of each seed crystal classification, reducing wall effects and thermal stresses.
Solution Approach 2:
The patent implements dynamics by making the apparatus design adaptable to different seed crystal types. The apparatus can be adjusted or configured differently for each seed crystal classification, allowing dynamic optimization of thermal and mechanical conditions to minimize stresses during growth.
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
Significantly reduces internal stresses in the growing bulk SiC single crystals, improving substrate quality and yield by precisely adapting growth conditions to seed stress conditions, resulting in high-quality SiC substrates.
Implementation Method 1
Under controlled temperature, pressure and gas conditions, the source material is sublimated
Implementation Method 2
The gaseous species (=SiC, Si2C, SiC2) are transported to the SiC seed crystal by reason of an axial temperature gradient
Implementation Method 3
thereby the bulk SiC single crystal grows
Implementation Method 4
Measurement methods suitable for this purpose are based on the detection and evaluation of Raman scattering or Raman shift on the SiC crystal lattice
Implementation Method 5
Measurement methods suitable for this purpose are based on the detection and evaluation of Raman scattering or Raman shift on the SiC crystal lattice or of X-ray diffraction on the SiC crystal lattice
Implementation Method 6
using elements with varying heat conductivity and adjusting growth apparatus design to mitigate seed stresses
Data Source
AI summary
A bulk SiC single crystal is produced by sublimation growth. A stress measurement to detect initial internal mechanical seed stresses is carried out on a wafer-shaped single crystalline SiC seed crystal. The seed crystal is classified, according to the stress measurement, into a first class when the initial seed stresses are below a first stress boundary value, into a second class when the initial seed stresses lie between the first stress boundary value and a second stress boundary value, and into a third class when the initial seed stresses exceed the second stress boundary value. The actual sublimation growth for growing the bulk SiC single crystal is carried out with the SiC seed crystal only when it has been classified into the first or second class, and when it is classified into the second class, at least one stress-reducing measure is carried out.