Reflective Electrode Formation Using Sacrificial Layer in Nitride LEDs
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Solution Overview
Problem
Conventional methods for forming reflective electrodes on p-type layers in Group III nitride semiconductor light-emitting devices face challenges such as increased contact resistance due to resist residue and limitations in material and structure selection, particularly when using materials like Ag, Ag alloys, Ru, Rh, and Pt, which are difficult to wet etch or require layered structures.
Innovation Solution
A method involving the formation of a sacrificial layer, a resist layer with specific openings, and subsequent wet etching to remove the sacrificial layer, allowing for the formation of a reflective electrode on a clean p-type surface without resist residue, enabling the use of a wide range of materials and structures, including layered films like Ag alloy/Ti/Au/Al or Pt-based materials, and reducing contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If lift-off method is used to pattern reflective electrode, then material selection is flexible, but contact resistance increases due to resist residue
Solution Approach 1:
The patent divides the process into two independent parts: (1) forming the reflective electrode pattern using lift-off method with resist, and (2) removing resist residue using plasma treatment. This segmentation allows the benefits of lift-off (material flexibility) to be preserved while eliminating its drawback (resist residue causing high contact resistance).
Solution Approach 2:
The patent introduces plasma treatment as an intermediary step between lift-off and electrode formation. The plasma process acts as a mediator that removes resist residue without affecting the reflective electrode materials, thereby reducing contact resistance while preserving the material selection flexibility provided by lift-off.
2Reliability
If wet etching is used to pattern Ag reflective electrode, then contact resistance is reduced, but material selection is restricted
Solution Approach 1:
The patent separates the patterning function from the material constraint by using lift-off for pattern formation and plasma treatment for residue removal. This segmentation eliminates the need for wet etching, thereby removing material restrictions while still achieving low contact resistance through effective resist residue removal.
Solution Approach 2:
The patent changes the process parameter from wet etching to plasma treatment. This parameter change enables the use of materials like Ag, Ag alloys, Ru, Rh, and Pt that are difficult to wet etch, while still achieving effective resist residue removal and low contact resistance through the plasma process.
3Reliability
If insulating film is formed on entire top surface, then device protection is improved, but reflective electrode area is reduced
Solution Approach 1:
The patent performs the reflective electrode patterning and plasma treatment before forming the insulating film. This preliminary action ensures that the full desired area of the reflective electrode is established before the insulating film is applied, preventing any reduction in electrode area while still providing device protection through the subsequent insulating film formation.
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 method effectively reduces contact resistance and enhances light output by allowing the selection of materials with optimal reflectance for the emission wavelength, improving the forward voltage and light extraction efficiency of the light-emitting device.
Implementation Method 1
a sacrificial layer removal step of removing the sacrificial layer entirely by wet etching
Implementation Method 2
an electrode (reflective electrode) also serving as a reflective film is formed on a p-type layer to reflect light toward the rear surface of a substrate, thereby improving the light extraction efficiency
Data Source
AI summary
A sacrificial layer is formed on a region for forming the reflective electrode later on the p-type layer, Subsequently, a part of the p-type layer is dry etched to expose an n-type layer. Then, a resist layer having an opening is formed through photolithography on the p-type layer and the n-type layer exposed in the previous step. The opening has a pattern to enclose the sacrificial layer in a plan view. Next, the sacrificial layer is wet etched using a buffered hydrofluoric acid to remove the entire sacrifice layer. Subsequently, a reflective film is formed by sputtering on the p-type layer and the resist layer. Next, the resist layer is removed using a resist stripper, and only the reflective film on the p-type layer is left to form the reflective electrode.