N-Type 4H-SiC Substrate Co-Doping for Low Dislocation Density
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Solution Overview
Problem
Existing methods for producing n-type 4H-SiC single crystal substrates face challenges in reducing threading dislocation density and maintaining crystallinity when co-doping donor and acceptor elements, leading to increased stacking faults and resistivity issues in SiC power devices.
Innovation Solution
A method involving pre-sublimation of 0.1 mass % or more of the raw material containing silicon, carbon, and an acceptor element, followed by co-doping with nitrogen and boron, where the concentrations of both elements are maintained at 3.0×10^18/cm^3 or more, and the threading dislocation density is kept below 4,000/cm^2, using a specific crucible configuration and growth conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the concentration of nitrogen as a donor element increases to lower resistivity, then the resistivity of the n-type SiC single crystal substrate decreases, but stacking faults increase and crystallinity deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-sublimating 0.1 mass % or more of the raw material before crystal growth. This pre-sublimation process removes volatile impurities and prepares a cleaner raw material composition, which enables subsequent co-doping with nitrogen and boron to achieve low resistivity without the usual deterioration of crystallinity and increased stacking faults
Solution Approach 2:
The patent changes the chemical composition parameters by co-doping with both nitrogen (donor element at 3.0×10^18/cm³ or more) and boron (acceptor element at 3.0×10^18/cm³ or more). This dual-doping approach with specific concentration ratios modifies the electrical properties while maintaining structural integrity, resolving the contradiction between low resistivity and high crystallinity
2Manufacturing precision
If boron is added to reduce BPD and stacking faults, then the crystallinity improves, but threading dislocation density increases at the initial stage of crystal growth
Solution Approach 1:
The patent applies preliminary action by pre-sublimating the raw material containing boron before crystal growth. This pre-sublimation step ensures uniform distribution and proper incorporation of boron during the growth process, preventing the formation of threading dislocations at the initial stage while still achieving the desired reduction in BPD and stacking faults
Solution Approach 2:
The patent optimizes the boron concentration parameter by maintaining it at 3.0×10^18/cm³ or more through controlled co-doping. This specific concentration range, combined with pre-sublimation, allows boron to effectively reduce basal plane dislocations and stacking faults without causing excessive threading dislocation density
3Ease of manufacture
If an n-type SiC single crystal substrate with low resistance is used as a base substrate, then device production is facilitated, but the threading dislocation density and stacking faults increase
Solution Approach 1:
The patent applies preliminary action through pre-sublimation of the raw material, which creates a purified starting composition that enables the growth of low-resistance substrates without the usual penalty of high threading dislocation density. This makes the substrates suitable for device production while maintaining high crystalline quality
Solution Approach 2:
The patent achieves the desired parameter combination by co-doping with nitrogen and boron at specific concentrations (both 3.0×10^18/cm³ or more). This parameter optimization enables the substrate to have low resistance for ease of device production while simultaneously maintaining low threading dislocation density for high manufacturing precision
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 approach results in an n-type 4H-SiC single crystal substrate with improved crystallinity and reduced threading dislocation density, enhancing the reliability and performance of SiC power devices by maintaining low resistivity and reducing defects.
Implementation Method 1
a process of pre-sublimating 0.1 mass % or more of the raw material in the crucible
Implementation Method 2
a process of supplying a gas containing an element as a donor into the crucible, sublimating the pre-sublimated raw material in the crucible, and allowing a single crystal layer to grow on a surface of the seed crystal
Data Source
AI summary
In an n-type 4H-SiC single crystal substrate of the present disclosure, the concentration of the element N as a donor and the concentration of the element B as an acceptor are both 3×1018/cm3 or more, and a threading dislocation density is less than 4,000/cm2.