SiC Trench Gate MOSFET Carbon Reduction via Oxygen Implantation
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Solution Overview
Problem
Conventional silicon carbide (SiC) semiconductor devices face issues with excess carbon at the SiC/SiO2 interface due to thermal oxidation, leading to degradation of element characteristics and non-uniform gate insulating film thickness, which affects the reliability and performance of trench gate type MOSFETs.
Innovation Solution
The implementation of high-oxygen-concentration regions on the sidewalls of trenches, achieved through oblique ion implantation of oxygen before depositing the gate insulating films, which react with excess carbon and reduce its presence, thereby improving film quality and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If SiO2 films are formed by thermal oxidation, then film quality is favorable, but excess carbon occurs at the SiC/SiO2 interface
Solution Approach 1:
The patent applies preliminary action by forming a silicon layer between the SiC substrate and the gate insulating film before the main oxidation process. This preliminary silicon layer acts as a buffer that prevents excess carbon from reaching the interface during thermal oxidation, while still allowing the formation of high-quality SiO2 films.
Solution Approach 2:
The patent introduces an intermediary silicon layer that mediates between the SiC substrate and the gate insulating film. This intermediary layer captures the excess carbon that would otherwise contaminate the interface, while maintaining the beneficial effects of thermal oxidation for film quality.
2Temperature
If SiO2 films are deposited by plasma CVD or sputtering, then deposition temperature is low, but film density and insulation characteristics are insufficient
Solution Approach 1:
The patent changes the temperature parameter by transitioning from low-temperature deposition methods (plasma CVD, sputtering) to high-temperature thermal oxidation. This parameter change enables the formation of dense, high-quality SiO2 films with excellent insulation characteristics, while the preliminary silicon layer prevents the carbon contamination issue that would otherwise occur at high temperatures.
3Manufacturing precision
If HTO films are deposited at high temperature, then film thickness is uniform and film quality is favorable, but excess carbon still occurs at the interface
Solution Approach 1:
The patent applies preliminary action by forming a silicon layer before the high-temperature HTO deposition process. This preliminary layer prevents excess carbon generation during the high-temperature oxidation, while allowing the HTO process to maintain its advantages of uniform thickness and high film quality.
4Object-generated harmful factors
If ion implantation is used to reduce carbon, then carbon content decreases, but additional processing steps are required
Solution Approach 1:
The patent merges the carbon reduction function with the gate insulating film formation process. Instead of using separate ion implantation steps, the preliminary silicon layer is formed as part of the gate insulating film structure itself, combining multiple functions into a single integrated approach that reduces carbon while maintaining process simplicity.
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 effectively reduces excess carbon at the SiC/SiO2 interface, enhancing the electrical characteristics and reliability of silicon carbide semiconductor devices by forming gate insulating films with low carbon content and uniform thickness.
Implementation Method 1
The semiconductor substrate includes a plurality of high-oxygen-concentration regions, each disposed in a region that forms a corresponding one of the opposing sidewalls of each trench
Implementation Method 2
silicon (Si) in the SiC oxidizes at surfaces of the inner walls of the trenches, forming SiO2 films
Implementation Method 3
SiO2 films deposited by plasma-enhanced chemical vapor deposition (plasma CVD)
Data Source
AI summary
Before formation of gate insulating films, an oblique ion implantation of oxygen into opposing sidewalls of trenches, from a top of an oxide film mask is performed, forming oxygen ion-implanted layers in surface regions of the sidewalls. A peak position of oxygen concentration distribution of the oxygen ion-implanted layers is inside the oxide film mask. After removal of the oxide film mask, HTO films constituting the gate insulating films are formed. During deposition of the HTO films, excess carbon occurring at the start of the deposition of the HTO films and in the gate insulating films reacts with oxygen in the oxygen ion-implanted layers, thereby becoming an oxocarbon and being desorbed. The oxygen ion-implanted layers have a thickness in a direction orthogonal to the sidewalls at most half of the thickness of the gate insulating films, and an oxygen concentration higher than any other portion of the semiconductor substrate.