Atomic Layer Etching of GaN via Segmented Plasma
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Solution Overview
Problem
Current etching techniques for III-V semiconductor materials, such as gallium nitride (GaN), face challenges in achieving precise and selective removal of thin layers while maintaining surface smoothness and conformality, which is crucial for high-electron-mobility transistors (HEMTs) and other applications.
Innovation Solution
The method involves exposing the III-V material to a chlorine-containing plasma without initial biasing, followed by applying a bias voltage to remove the modified surface layer, with the option to repeat these operations. This process is controlled to maintain a self-limiting regime, ensuring selective etching and minimizing damage to underlying layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional etching techniques are used to remove III-V material layers, then etching speed is improved, but manufacturing precision and surface smoothness deteriorate
Solution Approach 1:
The etching process is divided into two distinct sequential steps: (1) a chlorine-containing plasma treatment step that modifies the III-V material surface without significant removal, and (2) a physical sputtering step using argon plasma with bias voltage that removes the modified layer. This segmentation allows each step to be optimized independently - the chlorine step provides chemical modification for precision control, while the argon step provides physical removal with smooth surfaces, resolving the contradiction between speed and precision.
Solution Approach 2:
The chlorine-containing plasma acts as an intermediary that chemically modifies the III-V material surface by forming volatile chlorides or surface complexes. This intermediate chemical state makes the material more susceptible to subsequent physical sputtering while maintaining atomic-layer precision. The intermediary chemical modification enables the physical removal step to proceed with higher precision and surface quality than direct physical sputtering alone.
2Productivity
If high bias voltage is applied during etching, then etching productivity is improved, but manufacturing precision and selectivity deteriorate
Solution Approach 1:
The process separates the chemical modification function (performed without bias voltage or with low bias) from the physical removal function (performed with controlled bias voltage). This segmentation prevents the loss of selectivity that would occur if high bias voltage were applied throughout the entire etching process, while still achieving high productivity through the synergistic combination of chemical enhancement and controlled physical sputtering.
Solution Approach 2:
The bias voltage parameter is dynamically changed between process steps: no bias or low bias during chlorine plasma exposure to maintain selectivity, and controlled bias (e.g., 50-150 V) during argon plasma sputtering to achieve desired etch rates. This parameter change allows the process to achieve both high productivity and high precision by optimizing bias voltage for each specific function.
3Productivity
If continuous etching is performed to increase productivity, then manufacturing precision and surface conformality deteriorate
Solution Approach 1:
The etching process uses periodic alternation between chlorine plasma exposure (chemical modification) and argon plasma sputtering (physical removal). This periodic action prevents the continuous bombardment that would cause surface roughening and loss of conformality, while maintaining high productivity through the cumulative effect of repeated cycles. Each cycle removes a controlled amount of material with smooth surfaces, and multiple cycles achieve high total removal rates.
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 precise and selective etching of GaN and other III-V materials, improving surface smoothness and conformality, and achieving high etch selectivity, which is essential for maintaining the electronic properties of semiconductor devices.
Implementation Method 1
exposing the III-V material to a chlorine-containing plasma
Implementation Method 2
exposing the III-V material to a chlorine-containing plasma without biasing the substrate to form a modified III-V surface layer
Implementation Method 3
applying a bias voltage to the substrate while exposing the modified III-V surface layer to a plasma to thereby remove the modified III-V surface layer
Implementation Method 4
applying a bias voltage to the substrate while exposing the modified III-V surface layer to a plasma to thereby remove the modified III-V surface layer
Data Source
AI summary
Provided herein are ALE methods of removing III-V materials such as gallium nitride (GaN) and related apparatus. In some embodiments, the methods involve exposing the III-V material to a chlorine-containing plasma without biasing the substrate to form a modified III-V surface layer; and applying a bias voltage to the substrate while exposing the modified III-V surface layer to a plasma to thereby remove the modified III-V surface layer. The disclosed methods are suitable for a wide range of applications, including etching processes for trenches and holes, fabrication of HEMTs, fabrication of LEDs, and improved selectivity in etching processes.