SiC MOSFET Inversion Layer Mobility via Rapid Oxidation and Hydrogen Annealing
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Solution Overview
Problem
SiC MOSFETs fabricated on the Si-face of a SiC substrate exhibit poor inversion layer mobility due to a high density of interface traps, leading to significant power dissipation and efficiency losses, and rapid oxidation methods to reduce these traps result in increased threshold voltage.
Innovation Solution
A method involving the formation of an oxide layer on the Si-face of a SiC substrate at a high oxidation rate, followed by hydrogen annealing to passivate deep traps, thereby reducing the density of near interface traps and deep traps, which improves inversion layer mobility and lowers the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If rapid oxidation is performed to reduce near interface trap density, then inversion layer mobility is improved, but threshold voltage increases
Solution Approach 1:
The invention divides the treatment process into two distinct stages: first performing rapid oxidation to reduce near interface traps and improve mobility, then performing separate hydrogen annealing to passivate deep traps and control threshold voltage. This segmentation allows each process to be optimized independently, resolving the contradiction between mobility improvement and threshold voltage control.
Solution Approach 2:
Hydrogen serves as an intermediary substance that is introduced during the annealing process to passivate deep interface traps. The hydrogen atoms diffuse into the oxide-SiC interface and bond with trap sites, reducing the threshold voltage increase caused by rapid oxidation while preserving the mobility benefits.
2Reliability
If conventional oxidation is used, then threshold voltage remains controlled, but inversion layer mobility remains poor due to high interface trap density
Solution Approach 1:
The invention changes the oxidation rate parameter from conventional slow oxidation to rapid oxidation, achieving a tenfold or greater increase in oxidation rate. This parameter change reduces near interface trap density and dramatically improves inversion layer mobility while the subsequent hydrogen annealing step maintains threshold voltage control.
3Manufacturing precision
If oxidation rate is increased to reduce near interface traps, then trap density decreases, but deep traps are formed requiring additional processing
Solution Approach 1:
The invention combines two beneficial effects into a single rapid oxidation process: reduction of near interface traps and formation of deep traps that can be subsequently passivated. The subsequent hydrogen annealing step serves dual purposes: passivating deep traps and preventing further trap formation, effectively merging multiple functions into one processing step.
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 significantly increases inversion layer mobility by a factor of 10 to 100 and reduces the threshold voltage, achieving improved performance and efficiency in SiC MOSFETs.
Implementation Method 1
forming an oxide layer on a Si-terminated face of the SiC substrate at an oxidation rate sufficiently high to achieve a near interface trap density below 5×1011 cm−2
Implementation Method 2
annealing the oxidized SiC substrate in a hydrogen-containing environment, in order to passivate deep traps formed in the oxide-forming step
Data Source
AI summary
A method of manufacturing a semiconductor device based on a SiC substrate involves forming an oxide layer on a Si-terminated face of the SiC substrate at an oxidation rate sufficiently high to achieve a near interface trap density below 5×1011 cm−2; and annealing the oxidized SiC substrate in a hydrogen-containing environment, to passivate deep traps formed in the oxide-forming step, thereby enabling manufacturing of a SiC-based MOSFET having improved inversion layer mobility and reduced threshold voltage. It has been found that the density of DTs increases while the density of NITs decreases when the Si-face of the SiC substrate is subject to rapid oxidation. The deep traps formed during the rapid oxidation can be passivated by hydrogen annealing, thus leading to a significantly decreased threshold voltage for a semiconductor device formed on the oxide.