Nitride Semiconductor Gate Insulator Stack for Threshold Voltage
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Solution Overview
Problem
Nitride semiconductor devices struggle to achieve high threshold voltage for normally-off characteristics, as existing gate insulating film stacks do not effectively increase the threshold voltage, leading to low normally-off performance.
Innovation Solution
A semiconductor device with a gate insulating film stack comprising alternately stacked crystalline Al2O3 and SiO2 films, where the Al2O3 films are crystallized, is used to increase the threshold voltage by forming dipoles at the interface, enhancing the normally-off characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional gate insulating film stack is used in nitride semiconductor devices, then the device structure is simple, but the threshold voltage is low and normally-off characteristics are not achieved
Solution Approach 1:
The patent uses a composite gate insulating film stack consisting of alternating crystalline Al2O3 and SiO2 layers. This composite structure creates interfacial dipoles that increase the threshold voltage to achieve normally-off characteristics, while the alternating layer structure optimizes both electrical performance and structural integrity
Solution Approach 2:
The patent applies different materials (crystalline Al2O3 and SiO2) with distinct local properties at different positions within the gate insulating film. The crystalline Al2O3 layers provide dipole formation for threshold voltage control, while the SiO2 layers provide structural stability and interface quality, creating local functional differentiation within the stack
2Reliability
If the Al2O3 film is made crystalline to increase threshold voltage, then the normally-off characteristics are achieved, but the manufacturing process becomes more complex
Solution Approach 1:
The patent performs preliminary crystallization treatment of the Al2O3 film before forming the complete gate insulating film stack. This preliminary action ensures the Al2O3 is crystalline when interfacing with SiO2 layers, maximizing dipole formation effectiveness for threshold voltage control while managing the complexity of the overall manufacturing process
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 proposed solution effectively increases the threshold voltage, achieving good normally-off characteristics while maintaining the integrity of the nitride semiconductor device's performance.
Implementation Method 1
the effect of increasing the threshold voltage is explained by a dipole model
Data Source
AI summary
Characteristics of a semiconductor device are improved. A method of manufacturing a semiconductor device of the invention includes a step of forming a gate insulating film over a nitride semiconductor layer. The step includes steps of forming a crystalline Al2O3 film on the nitride semiconductor layer, forming a SiO2 film on the Al2O3 film, and forming an amorphous Al2O3 film on the SiO2 film. The step further includes steps of performing heat treatment on the amorphous Al2O3 to crystallize the amorphous Al2O3, thereby forming a crystalline Al2O3 film, and forming a SiO2 film on the crystalline Al2O3 film. In this way, since a film stack, which is formed by alternately stacking the crystalline Al2O3 films and the SiO2 films from a bottom side, is used as the gate insulating film, threshold voltage can be cumulatively increased.