SiC Ingot Surface Layer Thermal Expansion Control
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Solution Overview
Problem
Basal plane dislocation (BPD) defects in SiC wafers and ingots are not sufficiently suppressed, leading to degradation of forward characteristics in semiconductor devices due to anisotropy in the bending direction of the atom alignment plane, which is caused by uneven stress during crystal growth.
Innovation Solution
A SiC ingot with a surface layer having a smaller coefficient of linear thermal expansion than the core portion, where the surface layer is formed with a higher dopant concentration and thickness, and doped with nitrogen or aluminum, is manufactured using a method involving three steps: growing a single crystal core, forming a surface layer in an atmosphere with increased dopant gas concentration, and controlled cooling to alleviate stress and isotropize the bending direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional SiC ingot manufacturing method is used, then the crystal growth can be achieved, but basal plane dislocation defects occur due to anisotropic stress in the atom alignment plane
Solution Approach 1:
The patent applies local quality by creating a surface layer with different dopant concentration (higher nitrogen or aluminum concentration) compared to the core portion. This surface layer has different physical properties (smaller coefficient of linear thermal expansion) that specifically address the stress anisotropy problem at the surface where dislocations originate, without altering the bulk crystal structure.
Solution Approach 2:
The patent changes the dopant concentration parameter in the surface layer to achieve a smaller coefficient of linear thermal expansion. This parameter change modifies the thermal stress characteristics of the surface layer, enabling it to counteract the anisotropic stress that causes basal plane dislocations during cooling and operation.
2Manufacturing precision
If the dopant concentration is increased to control polytypes, then the polytype control is improved, but the thermal expansion anisotropy worsens
Solution Approach 1:
The patent applies local quality by concentrating the high dopant content specifically in the surface layer rather than uniformly throughout the ingot. This localized approach achieves polytype control at the surface where it is most needed while limiting the impact on overall thermal expansion uniformity, as the core portion maintains its original properties.
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 method reduces the density of BPD defects by ensuring isotropic bending of the atom alignment plane, thereby improving the structural integrity and performance of SiC semiconductor devices.
Implementation Method 1
a coefficient of linear thermal expansion of the surface layer is smaller than a coefficient of linear thermal expansion of the core portion
Implementation Method 2
The SiC ingot is obtained by performing a method such as sublimation recrystallization to promote crystal growth of a seed crystal
Implementation Method 3
a surface layer that is formed on a plane of the core portion in a growing direction
Data Source
AI summary
A SiC ingot includes a core portion; and a surface layer that is formed on a plane of the core portion in a growing direction, and a coefficient of linear thermal expansion of the surface layer is smaller than a coefficient of linear thermal expansion of the core portion.