Silicon Carbide Ingots via Sublimation Control
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Solution Overview
Problem
The growth of bulk crystalline silicon carbide is challenging due to the need for extremely high temperatures and the difficulty in controlling reaction variables in sublimation methods, which affects the repeatability and purity of the crystal, especially in commercial applications where impurity incorporation is a concern.
Innovation Solution
A method involving a mixture of polysilicon metal chips and carbon powder is introduced into a cylindrical reaction cell, sealed and heated in a vacuum furnace with inert gas, allowing sublimation and condensation to occur, which helps control the growth process and reduce impurity incorporation, enabling the production of high-purity silicon carbide ingots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sublimation method is used for bulk crystalline SiC growth, then crystal growth can be achieved, but control of reaction variables is difficult and purity is compromised
Solution Approach 1:
The patent changes the physical state parameters of the source material from solid powder to liquid molten state, enabling better control of composition and purity. By melting the SiC source material before sublimation, the process achieves more reliable control over vapor composition and reduces impurity incorporation, directly resolving the contradiction between achieving high purity crystals and controlling reaction variables.
Solution Approach 2:
The patent introduces a liquid molten state as an intermediary between the solid source material and vapor phase. This liquid intermediate allows for homogeneous mixing of source materials and controlled composition of vapor, serving as a mediator that improves both the controllability of reaction variables and the purity of the resulting crystal.
2Reliability
If powder form SiC is used as source material, then sublimation can proceed, but particle size distribution affects repeatability
Solution Approach 1:
The patent changes the physical state from solid powder to liquid molten, eliminating particle size distribution issues. In the liquid state, the source material forms a homogeneous mixture that vaporizes uniformly, ensuring repeatable growth processes without the complexity of controlling powder particle size distributions.
3Reliability
If high purity SiC powder is used, then crystal purity improves, but cost increases
Solution Approach 1:
The patent changes the physical state to liquid molten, allowing the use of lower purity source materials that are more cost-effective. The liquid state enables better control over the vapor composition through homogeneous mixing, maintaining high crystal purity while reducing dependence on expensive high-purity powder sources.
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 method achieves repeatable and high-purity silicon carbide crystal growth, suitable for semiconductor devices, by controlling the size distribution of polysilicon and carbon powder, and managing the reaction environment, resulting in ingots that can be machined into wafers for device fabrication.
Implementation Method 1
allowing for substantial sublimation and condensation of the vapors on the inside of the lid of the cylindrical reaction cell
Implementation Method 2
allowing for substantial sublimation and condensation of the vapors on the inside of the lid of the cylindrical reaction cell
Data Source
AI summary
This invention relates to a method for the manufacture of monolithic ingot of silicon carbide comprising: i) introducing a mixture comprising polysilicon metal chips and carbon powder into a cylindrical reaction cell having a lid; ii) sealing the cylindrical reaction cell of i); iii) introducing the cylindrical reaction cell of ii) into a vacuum furnace; iv) evacuating the furnace of iii); v) filling the furnace of iv) with a gas mixture which is substantially inert gas to near atmospheric pressure; vi) heating the cylindrical reaction cell in the furnace of v) to a temperature of from 1600 to 2500° C.; vii) reducing the pressure in the cylindrical reaction cell of vi) to less than 50 torr but not less than 0.05 torr; and viii) allowing for substantial sublimation and condensation of the vapors on the inside of the lid of the cylindrical reaction cell of vii).