GaN HEMT Recess Etching with an AlN Stop Layer
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Solution Overview
Problem
Conventional semiconductor devices face variations in etching depth and access resistance due to insufficient selectivity between GaN channel layers and AlGaN barrier layers during recess formation in high electron mobility transistors (HEMTs), leading to inconsistent performance.
Innovation Solution
Incorporating an AlN layer as an etching stop layer in the semiconductor stack, which provides higher etching resistance than the GaN channel layer, allowing for precise control of recess depth and reducing variations in access resistance by using a hydrogen and ammonia mixed atmosphere during dry etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an AlGaN barrier layer is used without an AlN stopper layer, then the device structure is simpler, but the etching depth varies and access resistance becomes inconsistent
Solution Approach 1:
An AlN layer is introduced as an intermediary etching stop layer between the AlGaN barrier layer and the substrate. This AlN layer has higher etching resistance than AlGaN, serving as a mediator that allows precise control of recess depth by stopping the etching process at a defined interface, thereby eliminating etching depth variations without significantly complicating the overall device structure.
2Ease of manufacture
If the etching selectivity between GaN channel layer and AlGaN barrier layer is insufficient, then the manufacturing process is simpler, but the access resistance varies
Solution Approach 1:
The AlN layer acts as an intermediary with distinct etching characteristics, providing a clear etching stop interface between the GaN channel layer and AlGaN barrier layer. This intermediary layer enables reliable control of recess depth and consistent access resistance while maintaining a straightforward dry etching process using hydrogen and ammonia mixed atmosphere.
Solution Approach 2:
The etching process parameters are optimized by using a hydrogen and ammonia mixed atmosphere, which enhances the etching selectivity at the AlN/AlGaN interface. This parameter change allows the etching process to automatically stop at the AlN layer, ensuring consistent recess depth and access resistance without requiring complex process control.
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 AlN layer stabilizes etching depth and reduces variations in access resistance between ohmic electrodes and channel regions, enhancing the reliability and performance of HEMTs by ensuring consistent etching selectivity and maintaining the crystallinity of the GaN regions.
Implementation Method 1
Incorporating an AlN layer as an etching stop layer in the semiconductor stack, which provides higher etching resistance than the GaN channel layer
Implementation Method 2
allowing for precise control of recess depth and reducing variations in access resistance by using a hydrogen and ammonia mixed atmosphere during dry etching
Data Source
AI summary
A method of manufacturing a semiconductor device comprises steps of: forming a semiconductor stack by growing an AlGaN layer or an InAlN layer, an AlN layer, and a GaN layer on a substrate in this order; forming a recess in the semiconductor stack by a dry etching from a surface of the semiconductor stack, the surface being opposite to the substrate; growing a GaN region in the recess; and forming an ohmic electrode on the GaN region; wherein in the forming of the recess, the dry etching is stopped in response to the recess reaching the AlN layer.