Micro-LED Mesa Etching with Offset Trenches for MQW Protection
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Solution Overview
Problem
The etching process for micro-LED displays damages the sidewalls of multi-quantum wells, leading to non-radiative recombination of electron-hole pairs and a loss of optical efficiency due to the inability to avoid etching through these wells for electrical isolation.
Innovation Solution
A method involving the use of masks to etch mesa structures and trenches in a semiconductor wafer, where the trenches are nonadjacent to the mesa sidewalls, effectively moving damaged sidewalls away from the light-emitting area, and incorporating a stop layer to control the etching process, allowing for partial mesa formation and electrical isolation without damaging the emission layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the etch process goes through the multi-quantum wells (MQW) to achieve electrical isolation, then electrical isolation between adjacent mesa structures is improved, but the sidewalls of the MQW are damaged resulting in non-radiative recombination and loss of optical efficiency
Solution Approach 1:
The patent divides the etching process into two separate stages: first etching the mesa sidewalls from the first doped layer to the emission layer, then etching trenches from the second doped layer through the emission layer. This segmentation allows electrical isolation to be achieved through the trench etching stage without requiring the first etching stage to penetrate through the MQW, thus protecting the MQW sidewalls from damage while still achieving electrical isolation between adjacent structures.
Solution Approach 2:
The patent performs the mesa sidewall etching as a preliminary action before the trench etching. By first defining the mesa sidewalls and then subsequently etching the trenches for electrical isolation, the process ensures that the MQW remains intact during the critical sidewall formation step, and the isolation trenches are created in a controlled manner that minimizes damage to the light-emitting regions.
2Loss of energy
If the etch process stops before reaching the emission layer to protect the MQW, then optical efficiency is improved, but electrical isolation between adjacent mesa structures cannot be achieved
Solution Approach 1:
The patent segments the electrical isolation function into two parts: mesa sidewall formation (which protects the MQW) and separate trench etching (which provides the isolation). The trenches are etched from the second doped layer through the emission layer to the first doped layer, creating isolation paths that do not require damaging the MQW sidewalls during the initial mesa formation process.
Solution Approach 2:
The patent introduces trenches as an intermediary structure that provides electrical isolation without requiring direct contact between adjacent mesa structures. These trenches act as isolation channels that separate the electrical domains of adjacent pixels, achieving the isolation function while preserving the integrity of the MQW emission layers.
3Device complexity
If a single etch process is used for both mesa formation and electrical isolation, then device complexity is reduced, but damage to the MQW sidewalls occurs resulting in non-radiative recombination
Solution Approach 1:
The patent divides the single etch process into two distinct etching steps with different masks and parameters. The first etching process uses a first mask to define mesa sidewalls and stops at the emission layer, while the second etching process uses a second mask to create isolation trenches through the emission layer. This segmentation allows each process to be optimized for its specific function, reducing overall damage to the MQW.
Solution Approach 2:
The patent applies different etching conditions and mask patterns to different regions of the wafer. The first mask defines the mesa boundaries with etching parameters optimized for sidewall quality, while the second mask defines the isolation trenches with parameters optimized for deep isolation. This local quality approach ensures that each region receives the appropriate processing to achieve its specific function without compromising the overall device performance.
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3B
AI summary
A method (100) is provided for making light emitting mesa structures on a semiconductor wafer, each mesa structure comprising a first doped layer, a second doped layer, and an emission layer in-between. The method comprises the steps of providing (101) a first mask for assigning a shape of a sidewall of the mesa structures, etching (102) from the first doped layer according to the first mask up to the emission layer, providing (103) a second mask for assigning a shape of a trench between two adjacent mesa structures, and etching (104) the trench through the emission layer according to the second mask. In this regard, the trench is nonadjacent to the sidewall of the mesa structures.