GaN Transistor Etch Stop Layer for Spacer Uniformity
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Solution Overview
Problem
Conventional GaN transistor structures face issues with non-uniformity and damage to the barrier layer during gate etching, leading to inconsistent device performance and increased risk of depletion-mode operation.
Innovation Solution
Incorporating a p-type Al-containing etch stop layer (pAlGaN or pAlInGaN) with pGaN layers above and below it, along with a GaN spacer layer above the barrier layer, to minimize damage and improve uniformity during gate etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single photo mask is used to pattern and etch the gate metal and p-type GaN gate layer, then the manufacturing process is simple, but the barrier layer is damaged due to non-uniform etching across the wafer
Solution Approach 1:
The patent divides the gate structure into multiple segments: gate metal layer, p-type GaN gate layer, and a p-type AlGaN etch stop layer. This segmentation allows selective etching where the etch stop layer protects the barrier layer from damage while enabling complete removal of the gate layer in targeted regions, resolving the contradiction between manufacturing simplicity and barrier layer uniformity.
Solution Approach 2:
The p-type AlGaN etch stop layer is deposited in advance before the gate metal and p-type GaN gate layer. This preliminary action creates a protective barrier that prevents etching damage to the underlying AlGaN barrier layer during subsequent gate etching processes, while still allowing precise control over gate pattern formation.
2Reliability
If the gate layer is over-etched to remove residual material, then the barrier layer is protected, but the barrier layer is damaged by removing 0 to 3 nm of material
Solution Approach 1:
The p-type AlGaN etch stop layer is deposited beforehand to serve as a protective barrier during etching. This preliminary protective layer prevents the etching process from damaging the underlying AlGaN barrier layer, eliminating the need for risky over-etching while ensuring complete removal of the gate layer.
Solution Approach 2:
The p-type AlGaN etch stop layer acts as an intermediary between the gate layer and the barrier layer. It mediates the etching process by being selectively removed to expose the gate pattern while protecting the barrier layer from direct etching damage, thus maintaining barrier layer thickness precision.
3Manufacturing precision
If the gate layer is under-etched to preserve the barrier layer, then the barrier layer is protected from damage, but residual gate material remains causing non-uniform device performance
Solution Approach 1:
The gate structure is segmented into p-type GaN gate layer and p-type AlGaN etch stop layer with different etch selectivities. This segmentation enables the etching process to completely remove the gate layer material while the etch stop layer protects the barrier layer, achieving both complete gate removal and barrier layer preservation.
Solution Approach 2:
The patent utilizes parameter changes in etch selectivity between different materials. The p-type AlGaN etch stop layer has different etching characteristics compared to p-type GaN and AlGaN barrier layer, allowing selective removal of gate material while protecting the barrier layer, thus resolving the contradiction between complete gate removal and barrier layer protection.
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 configuration minimizes barrier layer damage and enhances the uniformity of the GaN spacer layer thickness, ensuring consistent enhancement-mode operation and improved manufacturing reliability.
Implementation Method 1
an etch stop layer of p-type Al-containing column III-V material, for example, pAlGaN or pAlInGaN, disposed above the pGaN layer... the etch stop layer minimizes or eliminates damage to the barrier layer during gate etching steps
Implementation Method 2
improves the uniformity of the GaN spacer layer thickness... a GaN spacer layer disposed directly above the barrier layer
Data Source
AI summary
An enhancement-mode transistor gate structure which includes a spacer layer of GaN disposed above a barrier layer, a first layer of pGaN above the spacer layer, an etch stop layer of p-type Al-containing column III-V material, for example, pAlGaN or pAlInGaN, disposed above the first p-GaN layer, and a second p-GaN layer, having a greater thickness than the first p-GaN layer, disposed over the etch stop layer. The etch stop layer minimizes damage to the underlying barrier layer during gate etching steps, and improves GaN spacer thickness uniformity.