Nitride Semiconductor Gate Insulator with ALD Oxidation
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Solution Overview
Problem
The fabrication of semiconductor devices using nitride semiconductors faces challenges in reducing threshold voltage variation and achieving high uniformity and yield, primarily due to electron traps in aluminum oxide layers formed by Atomic Layer Deposition (ALD), which affect the formation of normally-off devices and lead to poor step coverage.
Innovation Solution
The method involves forming a nitride semiconductor layer with a gate insulator layer using steam oxidation or oxygen plasma oxidation by ALD, followed by the deposition of additional insulator layers to reduce electron traps and improve uniformity, specifically using trimethylaluminum and H2O or Al(CH3)3 and O2 as source gases to form aluminum oxide layers with controlled O/Ga ratios and densities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum oxide layer is formed by ALD using H2O source gas, then gate insulator layer is formed, but electron traps are generated causing threshold voltage variation
Solution Approach 1:
The gate insulator layer is divided into multiple aluminum oxide sub-layers formed by sequential ALD processes. Each sub-layer is formed with controlled thickness and oxidation conditions, allowing the harmful electron traps to be distributed and minimized across multiple interfaces rather than concentrated in a single layer, thereby reducing overall threshold voltage variation
Solution Approach 2:
The oxidation parameters are changed by switching from H2O source gas to O3 source gas for forming subsequent aluminum oxide layers. This parameter change modifies the oxidation mechanism and reduces the formation of electron traps, thereby improving threshold voltage stability while maintaining the gate insulator function
2Reliability
If aluminum oxide layer is formed by ALD, then gate insulator layer is formed, but step coverage becomes poor in gate recess structure
Solution Approach 1:
A gate recess structure is formed in the nitride semiconductor layer before depositing the aluminum oxide gate insulator layer. This preliminary action creates a pre-defined geometry that guides the subsequent ALD process, ensuring that the aluminum oxide material conformally fills the recess region and achieves satisfactory step coverage
Solution Approach 2:
The gate recess structure acts as an intermediary geometric feature between the nitride semiconductor layer and the aluminum oxide gate insulator layer. This intermediary structure enables the ALD process to achieve both good conformal coverage and proper electrical isolation, resolving the contradiction between gate insulator quality and step coverage
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 threshold voltage variation and enhances the uniformity and yield of semiconductor devices by minimizing electron traps and improving the characteristics of the gate insulator layer, leading to better performance and reliability.
Implementation Method 1
GaOx may be formed at an interface between the GaN and the aluminum oxide layer
Implementation Method 2
forming a second insulator layer on the first insulator layer by oxygen plasma oxidation of ALD using O2 source gas
Data Source
AI summary
A method of fabricating a semiconductor device may form a nitride semiconductor layer on a substrate, form a first insulator layer on the nitride semiconductor layer by steam oxidation of ALD, form a second insulator layer on the first insulator layer by oxygen plasma oxidation of ALD, form a gate electrode on the second insulator layer, and form a source and drain electrodes on the nitride semiconductor layer. The nitride semiconductor layer may include a first semiconductor layer on the substrate, and a second semiconductor layer on the first semiconductor layer.