SiC Substrate Dopant Distribution for Uniform Absorption
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Solution Overview
Problem
The existing methods for producing silicon carbide (SiC) substrates face challenges in achieving uniform absorption characteristics, leading to inhomogeneous thermal coupling and lower quality epitaxial layers due to variations in impurity distribution and absorption coefficients across the substrate surface.
Innovation Solution
The approach involves creating an SiC substrate with distinct regions of controlled dopant concentrations, where the mean concentration of impurity atoms in the inner and peripheral regions differ by no more than 5×10^18 cm^-3, ensuring a uniform absorption coefficient distribution, typically with a ring-shaped peripheral region and an inner region, to enhance epitaxial layer quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional physical vapor transport method is used to grow SiC single crystals, then bulk SiC crystals can be produced, but the surface absorption characteristics become inhomogeneous due to curved isothermal lines causing different impurity incorporation in center versus peripheral regions
Solution Approach 1:
The patent applies local quality by introducing a dopant source positioned to supply dopant atoms preferentially to peripheral regions of the growing crystal. This creates a non-uniform dopant distribution that compensates for the non-uniform impurity distribution caused by the curved isothermal lines, thereby achieving uniform absorption characteristics across the substrate surface while maintaining bulk crystal production
Solution Approach 2:
The patent changes the chemical composition parameter by introducing dopant atoms (such as nitrogen) during the crystal growth process. By controlling the dopant concentration and distribution, the absorption characteristics of the SiC crystal are modified to achieve uniformity across the substrate surface, transforming the harmful effect of curved isotherms into a beneficial uniform absorption profile
2Manufacturing precision
If curvature of isothermal lines is reduced to minimize lateral differences in foreign atoms, then absorption uniformity improves, but low defect crystals can no longer be fabricated
Solution Approach 1:
The patent maintains the necessary curvature of isothermal lines for defect-free crystal growth by applying local quality through dopant introduction. The dopant source is positioned to provide localized dopant atoms to peripheral regions, achieving uniform absorption characteristics without requiring reduction of the isothermal line curvature that would compromise crystal quality
Solution Approach 2:
The patent creates a composite structure at the atomic level by incorporating dopant atoms into the SiC crystal lattice. This composite material approach allows the crystal to maintain the curved isothermal growth conditions while achieving uniform absorption characteristics through the combined effect of the base SiC structure and the dopant distribution
3Stability of the object's composition
If higher substrate thickness is used to ensure low bow and warp values, then mechanical stability improves, but material consumption increases and thermal coupling in radiation-dominated epitaxial systems remains insufficient
Solution Approach 1:
The patent changes the optical parameter of the substrate by achieving uniform absorption characteristics through controlled dopant distribution. This allows thin substrates to maintain their thermal coupling efficiency in radiation-dominated epitaxial systems, eliminating the need for increased thickness while preserving mechanical stability through optimized substrate design
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 results in homogeneous heat coupling during epitaxial processes, leading to higher quality epitaxial layers with reduced defects and improved mechanical properties, while also allowing for more efficient production processes.
Implementation Method 1
Physical vapor transport (PVT) is essentially a sublimation and re-condensation process, in which a source material and a seed crystal are placed inside a growth furnace in such a way that the temperature of the source material is higher than that of the seed, so that the source material sublimes
Implementation Method 2
the vapor species diffuse and deposit onto the seed to form single crystals
Implementation Method 3
Physical vapor transport (PVT) is essentially a sublimation and re-condensation process
Data Source
AI summary
The present invention relates to a silicon carbide (SiC) substrate with improved mechanical and electrical characteristics. Furthermore, the invention relates to a method for producing a bulk SiC crystal in a physical vapor transport growth system. The silicon carbide substrate comprises an inner region (102) which constitutes at least 30% of a total surface area of said substrate (100), a ring shaped peripheral region (104) radially surrounding the inner region (102), wherein a mean concentration of a dopant in the inner region (102) differs by at maximum 5·1018 cm−3, preferably 1·1018 cm−3, from the mean concentration of this dopant in the peripheral region (104).