SiC MOSFET Substrate Doping for Lower Reverse Recovery Current
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Solution Overview
Problem
Conventional silicon carbide (SiC) metal oxide semiconductor field effect transistors (MOSFETs) experience increased reverse recovery current and switching loss due to prolonged carrier lifetime in the n-type drift region, leading to higher switching losses during operation from OFF to ON.
Innovation Solution
A silicon carbide semiconductor device with a substrate structure that includes a n+-type drain region with specific impurity concentrations of nitrogen, boron, aluminum, and titanium, which function as lifetime killers to reduce the carrier lifetime and minimize charge accumulation in the drift region, thereby reducing reverse recovery current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the nitrogen concentration is kept the same and the boron concentration is lowered, then the carrier recombination probability decreases and the majority carrier lifetime increases, but the reverse recovery current increases and switching loss increases
Solution Approach 1:
The invention changes the impurity concentration parameters by introducing aluminum and titanium at specific concentrations (1×10^16/cm³ to 5×10^16/cm³ each) in addition to boron (5×10^16/cm³ to 1×10^17/cm³). This multi-parameter adjustment optimizes the balance between carrier lifetime and reverse recovery characteristics, resolving the contradiction between extended lifetime and reduced switching loss.
Solution Approach 2:
The invention creates a composite doping strategy by combining multiple impurities (boron, aluminum, and titanium) in the n+-type SiC substrate. This composite approach allows simultaneous optimization of carrier lifetime (through boron) and reverse recovery characteristics (through aluminum and titanium), achieving both improved lifetime and reduced switching loss.
2Reliability
If the nitrogen concentration is kept the same and the boron concentration is lowered, then the carrier recombination probability decreases, but the reverse recovery current increases
Solution Approach 1:
The invention adjusts multiple impurity parameters simultaneously: maintaining nitrogen concentration while optimizing boron (5×10^16/cm³ to 1×10^17/cm³), aluminum (1×10^16/cm³ to 5×10^16/cm³), and titanium (1×10^16/cm³ to 5×10^16/cm³) concentrations. This multi-parameter optimization resolves the contradiction by finding the optimal balance point where carrier recombination is enhanced but reverse recovery current is controlled.
Solution Approach 2:
Aluminum and titanium act as intermediary impurities that mediate between boron's effect on carrier lifetime and the harmful reverse recovery current. These intermediary elements provide additional recombination centers that control hole injection into the n−-type drift region, thereby suppressing reverse recovery current while maintaining the benefits of extended carrier lifetime.
3Object-generated harmful factors
If additional epitaxial growth or particle beam irradiation is used to reduce majority carrier lifetime, then the reverse recovery current decreases, but the manufacturing process becomes more complex
Solution Approach 1:
The invention performs preliminary action by incorporating aluminum and titanium impurities during the initial crystal growth process of the n+-type SiC substrate. This preliminary doping strategy pre-establishes the recombination centers needed to control reverse recovery current, eliminating the need for subsequent epitaxial growth steps or particle beam irradiation treatments, thereby simplifying the overall manufacturing process.
Solution Approach 2:
The invention extracts and eliminates unnecessary manufacturing steps (additional epitaxial growth or particle beam irradiation) by achieving the reverse recovery current reduction through impurity concentration control alone. This extraction of unnecessary process steps simplifies the manufacturing workflow while maintaining effective control over reverse recovery characteristics.
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 controlled impurity concentrations in the n+-type SiC substrate enhance reverse recovery characteristics by reducing the reverse recovery current and surge voltage, improving the overall performance of SiC-MOSFETs.
Implementation Method 1
when the boron concentration is lowered, the probability of carrier recombination in the SiC substrate decreases and the lifetime of majority carriers (electrons) in the SiC substrate increases
Data Source
AI summary
An n+-type SiC substrate constituting an n+-type drain region contains a concentration of nitrogen, which is a donor, within a predetermined range (predetermined impurity concentration of the n+-type drain region) and, as impurities other than the nitrogen, contains boron, aluminum, and titanium such that a sum of respective concentrations of the boron, aluminum, and titanium is an amount that does not affect the n-type impurity concentration of the n+-type SiC substrate (impurity concentration of the n+-type drain region). The boron, aluminum, and titanium in the n+-type SiC substrate function as a lifetime killer of majority carriers. The boron concentration of the n+-type SiC substrate is in a range of 5×1016/cm3 to 1×1017/cm3. The aluminum concentration and the concentration of the titanium concentration of the n+-type SiC substrate are each within a range of 1×1016/cm3 to 5×1016/cm3.