Nitride Semiconductor Transistor Surface Treatment for High Frequency Performance
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Solution Overview
Problem
Nitride semiconductor devices, such as AlGaN/GaN HEMTs, exhibit lower-than-expected high frequency performance due to a significant drop in intrinsic small-signal transconductance at high frequencies, attributed to defects and current leakage at the interface between the transistor gate and the underlying semiconductor.
Innovation Solution
Surface treatment of the nitride semiconductor layer, specifically using oxygen plasma treatment and selective etching of the gate, to remove defects and create gaps between the gate and the semiconductor, thereby increasing high frequency performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fabrication without surface treatment is used, then manufacturing process is simple, but frequency performance drops significantly at high frequencies
Solution Approach 1:
The patent applies preliminary surface treatment to the nitride semiconductor layer before gate formation. Specifically, oxygen plasma treatment is performed on the semiconductor surface prior to depositing the gate electrode, which pre-passivates the interface and prevents defect formation during subsequent processing steps, thereby maintaining high frequency performance without adding complex post-processing steps
Solution Approach 2:
The patent changes the physical and chemical parameters of the semiconductor surface through plasma treatment. The oxygen plasma treatment modifies the surface chemistry by introducing oxygen-containing groups and passivating dangling bonds, which fundamentally alters the interface properties to reduce trap states and improve high-frequency transconductance characteristics
2Reliability
If gate interface defects are present, then manufacturing is easier, but intrinsic small-signal transconductance drops at high frequencies
Solution Approach 1:
The patent employs oxygen plasma, a strong oxidizing environment, to treat the nitride semiconductor surface. This accelerated oxidation process thoroughly passivates the semiconductor surface by forming oxygen-containing bonds that saturate dangling bonds and eliminate interface trap states, thereby preserving high intrinsic small-signal transconductance at high frequencies
Solution Approach 2:
The patent replaces mechanical or chemical etching methods with plasma treatment to achieve interface quality improvement. The plasma process uses reactive species and ion bombardment to clean and passivate the surface without the mechanical stress or chemical contamination associated with traditional etching methods, maintaining ease of manufacture while improving interface quality
3Speed
If no surface treatment is applied, then processing time is short, but electron velocity and frequency performance remain below theoretical predictions
Solution Approach 1:
The patent introduces oxygen plasma as an intermediary treatment between substrate preparation and gate formation. This plasma treatment acts as a mediator that passivates the semiconductor surface and improves interface quality, enabling electrons to achieve velocities closer to theoretical predictions by reducing scattering at the interface, while the relatively short plasma treatment time minimizes the impact on overall processing time
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 techniques result in a record current-gain cut off frequency of 225 GHz, maintaining high intrinsic small-signal transconductance across a wide frequency range without degrading mobility, and significantly improving electron velocity and frequency performance.
Implementation Method 1
plasma-treating a first region of a nitride semiconductor layer using an oxygen plasma
Data Source
AI summary
A method of forming a transistor over a nitride semiconductor layer includes surface-treating a first region of a nitride semiconductor layer and forming a gate over the first region. Surface-treating the first region can cause the transistor to have a higher intrinsic small signal transconductance than a similar transistor formed without the surface treatment. A portion of the bottom of the gate can be selectively etched. A resulting transistor can include a nitride semiconductor layer having a surface-treated region and a gate formed over or adjacent to the surface-treated region.