GaN HEMT AlN Etch Stop Layer for Leakage Control
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Solution Overview
Problem
Existing enhancement-mode Gallium Nitride HEMT devices face challenges with high channel leakage current and reliability issues due to difficulties in controlling etching accuracy and the risk of devices switching to depletion-mode at high temperatures and voltages, especially with recessed gate and fluorine plasma treatment methods.
Innovation Solution
A Gallium Nitride HEMT device structure featuring a bi-layer AlGaN isolation layer with varying Al composition, a field plate gate structure, and an etch stop layer to control etching precision, along with a dielectric layer for passivation, which optimizes the trench etching process and reduces channel leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If recessed gate structure is used to achieve enhancement-mode operation, then the device can operate in enhancement-mode, but the etching precision must be extremely high (3nm to 5nm) which is difficult to control, causing large fluctuation in pinch-off voltage
Solution Approach 1:
The patent introduces an etch stop layer (AlN layer) as an intermediary between the AlGaN layer and the etching process. This layer mediates the etching depth control by providing a distinct etching rate difference, allowing the trench to be etched to a precise depth without requiring extreme precision in the AlGaN layer thickness. The etch stop layer acts as a buffer that absorbs etching variability and ensures consistent device performance.
2Reliability
If the AlGaN layer thickness is reduced to achieve pinch-off in recessed gate structure, then enhancement-mode operation is achieved, but channel leakage current increases causing device burnout at high voltage
Solution Approach 1:
The patent changes the compositional parameter of the AlGaN layer by introducing an AlN layer (100% Al composition) at the etching interface. This parameter change creates a sharp compositional gradient that enhances the pinch-off effect while maintaining adequate AlGaN thickness (5nm to 20nm) to prevent channel leakage current. The compositional gradient optimizes both pinch-off effectiveness and leakage current suppression.
3Reliability
If fluorine plasma bombardment treatment is applied to the gate metal contact region, then enhancement-mode operation is achieved, but the crystal structure of AlGaN is damaged, reducing device reliability at high temperature and voltage
Solution Approach 1:
The patent replaces the fluorine plasma bombardment treatment (chemical/mechanical process) with an etch stop layer approach (physical/structural approach). Instead of using plasma to damage the crystal structure for enhancement-mode operation, the patent uses a carefully designed AlN layer that provides the same enhancement-mode effect through controlled etching depth, preserving the crystal structure integrity and device reliability at high temperature and voltage.
4Reliability
If thin AlGaN layer (3nm to 5nm) is used in recessed gate structure, then enhancement-mode operation is achieved, but the pinch-off voltage fluctuates significantly due to difficulty in controlling etching process
Solution Approach 1:
The etch stop layer serves as an intermediary reference layer that decouples the pinch-off voltage control from the AlGaN layer thickness. By etching through a defined thickness of AlGaN to reach the AlN layer, the process achieves consistent etching depth regardless of minor variations in AlGaN thickness. This intermediary layer acts as a stop signal for the etching process, ensuring uniform pinch-off voltage across devices.
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 structure achieves improved pinch-off voltage stability and reduced channel leakage current, enhancing the reliability and operational safety of the device by allowing thicker AlGaN layers and precise etching control, thus preventing device burnout and mode switching issues.
Implementation Method 1
the AlGaN/GaN hetero-junction channel formed by piezoelectric and spontaneous polarizations has a very high concentration of two-dimensional electron gas (2DEG)
Implementation Method 2
the AlGaN/GaN hetero-junction channel formed by piezoelectric and spontaneous polarizations has a very high concentration of two-dimensional electron gas (2DEG)
Implementation Method 3
the thickness of the AlGaN layer under the metal gate must be thinned to a range of 3nm to 5nm, or below, by dry etching
Implementation Method 4
the region under the gate is subjected to fluorine plasma bombardment prior to depositing the metal gate 114. The crystal structure of the AlGaN layer 115 subjected to the fluorine plasma bombardment is damaged, leading to depletion of 2DEG in the channel 118 under the AlGaN layer 115
Data Source
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AI summary
A HEMT device and a manufacturing of the HEMT device, the HEMT device includes: a buffer layer (14) on the substrate (12); a semiconductor layer on the buffer layer (14); an isolation layer (16, 17) on the semiconductor layer; a source electrode (22) and a drain electrode (23) contacted with the semiconductor layer; and a gate electrode (24, 104 114) between the source electrode (22) and the drain electrode (23); wherein, a channel , which is located in the semiconductor layer below the gate electrode (24, 104, 114), is pinched off.