SiC MOSFET Interface Nitrogen Profile for Stable Threshold Voltage
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Solution Overview
Problem
Silicon carbide (SiC) MOSFETs face challenges with reduced carrier mobility and threshold voltage fluctuations due to carbon vacancies and defects at the SiC-gate insulating layer interface, leading to increased leakage current and reduced reliability.
Innovation Solution
A semiconductor device structure with a silicon carbide layer, a silicon oxide gate insulating layer, and an interface termination region with a high concentration of tricoordinate nitrogen atoms to terminate dangling bonds and reduce carbon vacancies, along with a manufacturing method that includes ion implantation of aluminum and carbon, followed by heat treatments to form a high-density silicon oxide film and optimize nitrogen distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a silicon carbide MOSFET is formed using conventional methods, then the device can operate at high temperatures, but carrier mobility drops and threshold voltage fluctuations arise
Solution Approach 1:
The patent applies local quality by creating an interface termination region with a specific nitrogen concentration profile (peak concentration of 1×10^21 to 1×10^22 atoms/cm³) localized at the SiC-gate insulating layer interface. This localized nitrogen enrichment terminates dangling bonds and reduces carbon vacancies specifically at the interface, improving carrier mobility and threshold voltage stability without affecting the bulk SiC material properties that enable high-temperature operation.
Solution Approach 2:
The patent changes the nitrogen concentration parameter at the SiC-gate insulating layer interface from conventional low levels to a high peak concentration of 1×10^21 to 1×10^22 atoms/cm³. This parameter change is achieved through ion implantation and heat treatment processes, transforming the interface region to have superior electrical characteristics while maintaining the high-temperature operational capability of the SiC MOSFET.
2Device complexity
If the silicon carbide layer is used directly with gate insulating layer, then the structure is simple, but carbon vacancies and defects at the interface increase leakage current
Solution Approach 1:
The patent applies preliminary action by forming an interface termination region with high nitrogen concentration before final device operation. The nitrogen ions are implanted and the structure is heat-treated to establish this protective region in advance, which then prevents carbon vacancy formation and reduces leakage current during subsequent device operation without requiring complex structural modifications.
3Reliability
If nitrogen concentration is increased at the SiC-gate insulating layer interface, then carrier mobility is suppressed, but threshold voltage fluctuations are reduced
Solution Approach 1:
The patent resolves this contradiction by applying local quality - the high nitrogen concentration (1×10^21 to 1×10^22 atoms/cm³) is confined specifically to the interface termination region, while the bulk SiC material maintains its intrinsic properties. This localized approach allows threshold voltage stability improvement at the interface without significantly degrading carrier mobility in the channel region.
Solution Approach 2:
The patent optimizes the nitrogen concentration parameter by establishing a peak concentration of 1×10^21 to 1×10^22 atoms/cm³ at the interface, which is sufficient to terminate dangling bonds and stabilize threshold voltage, while the concentration gradient ensures that carrier mobility in the bulk material is not excessively suppressed.
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 solution effectively suppresses carrier mobility reduction and threshold voltage fluctuations, enhancing the reliability and performance of SiC MOSFETs by reducing carbon vacancies and defects, resulting in improved Hall mobility and reduced leakage current.
Implementation Method 1
a region disposed between the silicon carbide layer and the silicon oxide layer and having a nitrogen concentration equal to or more than 1×10^21 cm−3
Implementation Method 2
a region disposed between the silicon carbide layer and the silicon oxide layer and having a nitrogen concentration equal to or more than 1×10^21 cm−3
Data Source
AI summary
This semiconductor device according to an embodiment includes: a silicon carbide layer; a gate electrode; a silicon oxide layer between the silicon carbide layer and the gate electrode; and a region between the silicon carbide layer and the silicon oxide layer and having a nitrogen concentration not less than 1×1021 cm−3.A nitrogen concentration distribution in the silicon carbide layer, the silicon oxide layer, and the region has its peak in the region, and a state density Z1/2 in a portion is not more than 1×1011 cm−3. The portion is within 100 nm from the silicon oxide layer toward the silicon carbide layer. A nitrogen concentration and a carbon concentration in a position 1 nm from the peak toward the silicon oxide layer is not more than 1×1018 cm−3, and a nitrogen concentration in a position 1 nm from the peak toward the silicon carbide layer is not more than 1×1018 cm−3.