LED Mesa Sidewall Passivation Against Etchant Undercutting
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Solution Overview
Problem
Conventional LED chip passivation structures are vulnerable to etchant damage during mesa formation, leading to unwanted undercutting and erosion, which compromises reliability and increases moisture ingress, limiting the flexibility for additional chip structures like light extraction features.
Innovation Solution
A passivation layer, typically made of silicon nitride, is applied to bound the mesa sidewalls, providing a robust seal that protects against etchant damage and allows for improved reliability and the integration of additional structural features such as light extraction elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional passivation structures are used during mesa formation, then the LED chip can be manufactured, but the passivation layer is vulnerable to etchant damage causing undercutting and erosion
Solution Approach 1:
A robust passivation layer is applied to the mesa sidewalls before the mesa etching process begins. This preliminary protection prevents etchant from attacking the underlying semiconductor layers, eliminating undercutting and erosion that would otherwise compromise the passivation structure's integrity during manufacturing.
Solution Approach 2:
The passivation layer serves as an intermediary protective barrier between the etchant and the underlying LED chip structures. This intermediate layer is specifically designed to be resistant to the etching chemicals, allowing the mesa to be formed while protecting vulnerable areas from harmful etchant exposure.
2Reliability
If the passivation layer is extended to bound mesa sidewalls, then reliability and moisture protection are improved, but device complexity increases
Solution Approach 1:
The passivation layer is extended from a conventional planar configuration into the third dimension by coating the vertical mesa sidewalls. This dimensional extension creates a comprehensive seal that prevents moisture ingress along the mesa perimeter, transforming the passivation from a simple top-surface layer to a multi-dimensional protective barrier.
Solution Approach 2:
A thin film passivation layer is applied conformally to the mesa sidewalls, creating a flexible yet protective seal. This thin film approach provides effective moisture barrier protection without adding significant structural complexity or bulk to the device, maintaining manufacturing feasibility while enhancing reliability.
3Manufacturing precision
If a robust passivation layer is used to protect against etchants, then manufacturing precision is improved, but the ability to add additional chip structures is limited
Solution Approach 1:
The robust passivation layer is applied as a preliminary protective measure before mesa etching, enabling precise mesa formation by preventing etchant-induced damage. This preliminary protection ensures that the mesa sidewalls are formed with high precision and clean edges, free from undercutting or erosion that would compromise manufacturing accuracy.
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
The passivation layer effectively reduces undercutting and erosion, enhancing the reliability and performance of LED chips by creating a hermetic seal and enabling more robust processing and structural optimizations, including texturing and the addition of dielectric reflective structures.
Implementation Method 1
The passivation layer includes a material that is robust to etchants of active LED structures when forming the mesas to reduce damage in underlying portions of the LED chip
Implementation Method 2
The passivation layer effectively forms a seal along the mesa sidewalls that reduces unwanted undercutting or erosion during etching, thereby providing improved reliability, reduced moisture ingress
Data Source
AI summary
Solid-state lighting devices including light-emitting diodes (LEDs) and more particularly passivation structures for LED chips are disclosed. LED chips include active LED structures, typically formed of epitaxial semiconductor layers, that include mesas with mesa sidewalls. Passivation structures include a passivation layer that bounds the mesa sidewalls. The passivation layer includes a material that is robust to etchants of active LED structures when forming the mesas to reduce damage in underlying portions of the LED chip. The passivation layer effectively forms a seal along the mesa sidewalls that reduces unwanted undercutting or erosion during etching, thereby providing improved reliability, reduced moisture ingress, and the flexibility to enable additional chip structures, such as light extraction features.