Group III Nitride LED Reflective Film Patterning
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Solution Overview
Problem
Conventional methods for patterning reflective films and electrodes in group III nitride semiconductor light emitting elements result in non-uniform thickness and decreased reflectivity due to the use of strong detergents for resist removal, leading to adhesion issues with insulating films.
Innovation Solution
A method involving the formation of a barrier metal film resistant to wet etching, followed by wet etching using this film as a mask, and subsequent dry ashing to improve adhesion and maintain reflectivity, with the barrier metal film being preferably made of Ti or Cr and having a thickness between 50 to 1,000 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a lift-off method is used for patterning the reflective film, then the patterning process is simplified, but the reflective film thickness becomes non-uniform and reflectivity decreases
Solution Approach 1:
A barrier metal film is formed on the reflective film before the patterning process. This preliminary action creates a protective layer that prevents the reflective film from direct contact with the resist film and etching solutions, thereby maintaining uniform thickness and reflectivity during subsequent patterning operations.
Solution Approach 2:
The barrier metal film acts as an intermediary layer between the reflective film and the resist film. It mediates the interaction during patterning, preventing harmful effects such as resist residue adhesion and etching damage to the reflective film, while allowing the patterning process to proceed effectively.
2Productivity
If strong detergency liquid remover is used for resist removal, then resist removal efficiency is improved, but the reflective film is etched and reflectivity decreases
Solution Approach 1:
The barrier metal film serves as a protective intermediary that shields the reflective film from strong detergency liquid removers. This allows efficient resist removal while preventing etching damage to the reflective film, as the barrier metal film is resistant to these chemical agents.
Solution Approach 2:
The barrier metal film is a sacrificial layer that can be selectively removed after serving its protective function. It is designed to be removed after resist removal and before final device assembly, having served its purpose of protecting the reflective film during the patterning and resist removal processes.
3Ease of operation
If ashing is used for resist removal, then clean removal is achieved, but Ag flocculates by oxidation and reflectivity decreases
Solution Approach 1:
The barrier metal film acts as a protective intermediary that prevents direct oxidation of the Ag-containing reflective film during ashing. It allows clean resist removal through ashing while preventing Ag flocculation and reflectivity loss, as the barrier metal film is oxidized instead of the Ag layer.
4Reliability
If the barrier metal film thickness is increased, then wet etching resistance is improved, but adhesion to insulating film becomes difficult
Solution Approach 1:
The thickness of the barrier metal film is optimized to a specific range (50-1000 nm) to balance two competing requirements: sufficient thickness to provide wet etching resistance and protect the reflective film, while maintaining thin enough thickness to allow proper adhesion and formation of the insulating film on top.
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 allows for uniform patterning of reflective films without impairing reflectivity and enhances adhesion to insulating films, ensuring improved light extraction efficiency in semiconductor light emitting elements.
Implementation Method 1
patterning a barrier metal film including a material having resistance to wet etching on the reflective film
Implementation Method 2
Dry ashing such as photo-excited ashing or oxygen plasma ashing is desirably conducted before forming an insulating film on a barrier metal film
Implementation Method 3
a film for reflecting light emitted toward an electrode lower part, thereby preventing the light from being absorbed in the electrode
Data Source
AI summary
A reflective film including Ag of an Ag alloy is patterned in a uniform thickness without decreasing reflectivity. The reflective film is formed on the entire surface of a first insulating film by sputtering, vacuum deposition or the like, and a barrier metal film having a given pattern is formed on the reflective film by a lift-off method. The reflective film is wet etched using a silver etching liquid. The barrier metal film is not wet etched by the silver etching liquid, and therefore functions as a mask, and the reflective film in a region on which the barrier metal film has been formed remains not etched. As a result, the reflective film having a desired patter can uniformly be formed on the first insulating film.