AlN Substrate Thinning via Phosphoric Acid Etching
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Solution Overview
Problem
Existing methods fail to effectively remove and thin aluminum nitride (AlN) substrates from light emitting devices, limiting the separation of AlN-grown high-bandgap devices from their native substrates, which restricts the fabrication of stand-alone epitaxial templates and optoelectronic devices.
Innovation Solution
A method involving chemical etching using phosphoric acid to selectively etch the nitrogen polar face of bulk AlN substrates, allowing for the substantial removal or thinning of AlN substrates while monitoring and controlling the etching process based on measured thickness, enabling the separation of epitaxial layers from their substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional removal methods are used, then complete substrate removal is achieved, but the process is inefficient and cannot produce thin remnants
Solution Approach 1:
The patent changes the chemical parameters of the etching process by using phosphoric acid with specific concentration ranges (70-98%) and controlling temperature (20-200°C), along with adjusting etching time, to achieve both high etching efficiency and precise thickness control of the AlN substrate remnant
Solution Approach 2:
The patent implements feedback control by monitoring the etching process and adjusting parameters based on measured substrate thickness to achieve the desired remnant thickness between 1-50 μm, ensuring precise thickness control while maintaining productivity
2Reliability
If complete substrate removal is attempted, then separation is achieved, but defect density increases and device performance deteriorates
Solution Approach 1:
Instead of complete substrate removal, the patent applies partial action by leaving a controlled thin remnant (1-50 μm) of the AlN substrate. This partial removal approach maintains the benefits of separation while preserving the structural integrity and low defect density of the epitaxial layers, thereby improving device performance
3Use of energy by moving object
If thick AlN substrates are used, then epitaxial growth is stable, but light extraction efficiency is poor
Solution Approach 1:
The patent removes part of the thick AlN substrate to create a thin remnant that allows light to pass through while maintaining enough material to preserve epitaxial growth stability during the etching process, thus achieving both improved light extraction and growth stability
4Adaptability or versatility
If substrate removal is not performed, then device structure is simple, but vertical injection architectures cannot be implemented
Solution Approach 1:
The patent extracts the AlN substrate from the device structure through controlled chemical etching, leaving only a thin remnant. This extraction enables the implementation of vertical injection architectures and other advanced device configurations while maintaining process simplicity through the use of straightforward chemical etching methods
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
Enables the successful separation of AlN-grown devices from their substrates, reducing defect density, allowing light emission from the backside of devices, and facilitating vertical injection architectures, while producing optically transparent epitaxial templates for further device integration.
Implementation Method 1
chemical etching using phosphoric acid to selectively etch the nitrogen polar face of bulk AlN substrates
Implementation Method 2
a measurement unit configured to generate a signal indicative of a thickness of the bulk AlN substrate
Data Source
AI summary
Approaches for substantially removing bulk aluminum nitride (AlN) from one or more layers epitaxially grown on the bulk AlN are discussed. The bulk AlN is exposed to an etchant during an etching process. During the etching process, the thickness of the bulk AlN can be measured and used to control etching.