GaN Etching Using UV-Illuminated TMAH Solution
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Solution Overview
Problem
Conventional wet etching methods for GaN-based compound semiconductor devices face challenges such as damage to layers, non-uniform etching rates, corrosion of electrodes, and contamination issues due to the use of potassium hydroxide and potassium peroxodisulfate solutions, leading to variations and reduced yield in high electron mobility transistors.
Innovation Solution
A manufacturing method involving the use of a mixed etching solution containing an organic alkali agent, such as tetramethylammonium hydroxide, and an oxidizer, like ammonium peroxodisulfate, under ultraviolet illumination, which allows for uniform wet etching of the n-type GaN layer without applying a bias, preventing damage to underlying layers and simplifying the process by using a resist pattern as an etching mask.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional wet etching using KOH and K2S2O8 solutions is used, then etching of the n-type GaN layer can be achieved, but the etching rate becomes non-uniform and varies across the wafer
Solution Approach 1:
The patent changes the chemical parameters of the etching solution by replacing conventional KOH and K2S2O8 with a mixed solution of TMAH and ammonium peroxodisulfate. This parameter change achieves uniform etching across the wafer surface while maintaining appropriate etching rate, resolving the contradiction between productivity and manufacturing precision.
2Manufacturing precision
If high concentration oxidizer is used to achieve uniform etching, then etching uniformity improves, but electrode corrosion increases
Solution Approach 1:
The patent uses ammonium peroxodisulfate at controlled concentrations (0.01-10 wt%, preferably 0.1-5 wt%) in the etching solution, which provides sufficient oxidizing power for uniform etching while being less corrosive to aluminum electrodes compared to conventional high-concentration oxidizers. This parameter optimization resolves the contradiction between etching uniformity and electrode corrosion.
3Productivity
If bias is applied during wet etching to control electron movement, then etching can proceed, but variation in etching depth occurs across the wafer
Solution Approach 1:
The patent removes the bias application step from the etching process. By using TMAH and ammonium peroxodisulfate together, the etching proceeds uniformly without requiring external bias, thereby eliminating the source of etching depth variation across the wafer and resolving the contradiction between productivity and manufacturing precision.
4Speed
If dry etching is used to form recess structures, then high-speed characteristics can be achieved, but damage occurs to the GaN layers
Solution Approach 1:
The patent replaces dry etching (mechanical/physical process) with wet etching using TMAH and ammonium peroxodisulfate (chemical process). This substitution achieves the desired recess structure formation without causing damage to the GaN channel layer and AlGaN barrier layer, while still enabling high-speed device characteristics.
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 enables uniform etching with improved in-plane uniformity, reduces electrode corrosion, and simplifies the etching process, enhancing the yield and quality of GaN-based electronic devices by maintaining the integrity of the n-type AlGaN barrier layer and achieving desired recess structures without the need for high oxidizer concentrations.
Implementation Method 1
the n-type GaN layer 104 is irradiated with an ultraviolet illumination (UV). As a result, electron-hole pairs are generated on a surface of the n-type GaN layer 104
Implementation Method 2
wet-etching the second compound semiconductor layer with using an etching solution containing an organic alkali agent and an oxidizer
Data Source
AI summary
After an n-type AlGaN barrier layer (3) is formed over a substrate (1), an n-type GaN contact layer (4) is formed over the n-type AlGaN barrier layer (3). Next, the n-type GaN contact layer (4) is wet-etched with using an etching solution containing an organic alkali agent and an oxidizer while the n-type GaN contact layer (4) is irradiated with an ultraviolet illumination.