N-Polar III-Nitride HEMT Gate Structure Without AlGaN Etch Stop
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Solution Overview
Problem
The thin AlGaN etch stop layer in N-polar HEMTs leads to secondary parasitic channels, increased oxygen incorporation, alloy scattering, and channel charge depletion, limiting the performance and manufacturability of these devices.
Innovation Solution
The solution involves removing the thin AlGaN etch stop layer and instead using additive regrowth to insulate the channel from surface effects, maintaining a high aspect ratio and suppressing detrimental effects under the access regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a thin AlGaN etch stop layer is used to enable gate recess formation, then the gate foot can be formed by accurately terminating deep dry etch, but secondary parasitic channels are formed at the AlGaN layer/GaN cap layer interface in the access regions
Solution Approach 1:
The patent removes the thin AlGaN etch stop layer from the device structure. By eliminating this layer, the source of parasitic channel formation at the AlGaN/GaN interface is completely removed, while alternative methods are used to achieve gate recess formation without requiring this problematic intermediate layer.
Solution Approach 2:
The patent converts the etching process into a beneficial tool by using it to create the gate recess directly in the GaN cap layer without the AlGaN intermediate layer. The etch process that would have created harmful interfaces is instead used to form the desired gate structure in a cleaner manner.
2Ease of manufacture
If a thin AlGaN etch stop layer is incorporated in the device structure, then gate recess can be formed, but oxygen incorporation and alloy scattering increase
Solution Approach 1:
The patent eliminates the thin AlGaN etch stop layer from the structure, thereby removing the source of oxygen incorporation and alloy scattering that this layer introduces. The device structure is simplified to avoid these harmful effects while maintaining the necessary gate recess formation capability.
3Ease of manufacture
If a thin AlGaN etch stop layer is used to form the gate foot, then the gate structure can be completed, but channel charge depletion occurs due to increased band bending
Solution Approach 1:
The patent removes the thin AlGaN etch stop layer that causes increased band bending and subsequent channel charge depletion. By eliminating this layer, the electrical characteristics of the channel are improved and charge depletion is prevented.
4Ease of manufacture
If a thin AlGaN etch stop layer is incorporated, then gate recess can be formed, but the etch selectivity between etch material and etch stop is insufficient for manufacturing
Solution Approach 1:
The patent eliminates the thin AlGaN etch stop layer that suffers from insufficient etch selectivity. By removing this layer, the manufacturing process avoids the precision problems associated with selective etching, while gate recess formation is achieved through alternative means with better process control.
Data Source
AI summary
A HEMT comprising a channel layer of a first III-Nitride semiconductor material, grown on a N-polar surface of a back barrier layer of a second III-Nitride semiconductor material; the second III-Nitride semiconductor material having a larger band gap than the first III-Nitride semiconductor material, such that a positively charged polarization interface and two-dimensional electron gas is obtained in the channel layer; a passivation, capping layer, of said first III-Nitride semiconductor material, formed on top of and in contact with a first portion of a N-polar surface of said channel layer; a gate trench traversing the passivation, capping layer, and ending at said N-polar surface of said channel layer; and a gate conductor filling said gate trench.