LED Die Metal Contact Barrier Layer Contamination Prevention
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Solution Overview
Problem
Contamination of metal contacts in LED dies due to migration of mobile atoms like silver and aluminum during processing, leading to increased forward voltage and reduced light output, is not effectively addressed by existing methods which often result in large via misalignment and reflective layer etching issues.
Innovation Solution
A barrier layer is applied to encapsulate the metal contact, defining a larger mask pattern than the via to prevent contamination, eliminating the reflective film etch process and ensuring precise control over the critical dimension, thereby maximizing the reflective surface area and reducing voids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a barrier layer is provided to prevent contamination, then contamination prevention is improved, but the total surface area of the Ag layer is reduced and reflective area is reduced
Solution Approach 1:
The patent segments the barrier layer into two distinct layers: a first barrier layer (TiW) deposited conformally on the Ag layer, and a second barrier layer (oxide) deposited over the first barrier layer. This segmentation allows the first barrier layer to provide contamination prevention while the second barrier layer provides the necessary offset, thereby maintaining both contamination prevention and reflective area.
Solution Approach 2:
The patent transitions from a single-layer barrier approach to a multi-layer barrier structure, adding vertical dimensionality to the barrier system. The first barrier layer extends vertically from the Ag surface, and the second barrier layer extends further vertically, creating a stepped barrier structure that prevents contamination while preserving horizontal reflective area.
2Reliability
If a large offset between via in barrier material and via in Ag layer is provided, then contamination prevention is improved, but the critical dimension is enlarged due to masking and photolithography margins
Solution Approach 1:
The patent applies the first barrier layer conformally over the entire Ag layer before any via formation or masking steps. This preliminary application of the barrier layer establishes the contamination prevention mechanism early in the process, allowing subsequent via formation to proceed with standard masking margins without compromising the barrier's protective function.
Solution Approach 2:
The first barrier layer acts as an intermediary between the Ag layer and the second barrier layer, providing a conformal protective interface that prevents direct contact between contaminants and the Ag layer. This intermediary layer allows the second barrier layer to be positioned with standard photolithography margins while maintaining contamination prevention.
3Ease of manufacture
If etching is used to form the via, then via formation is achieved, but a large undercut occurs causing enlarged critical dimension
Solution Approach 1:
The patent deposits the first barrier layer conformally over the Ag layer before via formation. This preliminary barrier layer provides a protective foundation that prevents etch undercut from expanding the via opening, as the conformal barrier layer maintains uniform thickness around the via walls, thereby preserving the critical dimension through the etching process.
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 prevents contamination of metal contacts, reduces voltage increase, and enhances light output by maintaining a larger reflective surface area, improving the topography and efficacy of LED dies.
Implementation Method 1
mobile atoms such as silver (Ag) and aluminum (Al) can migrate or otherwise relocate into vias during deposition or in subsequent processing steps
Implementation Method 2
A barrier layer is applied to encapsulate the metal contact, defining a larger mask pattern than the via to prevent contamination
Data Source
AI summary
A method for allowing a reflective layer to abut against an edge of a metal contact while preventing contamination of a metal contact for an LED die is provided. The method includes encapsulating an electrical contact (i.e. metal contact) via with a barrier layer prior to deposition of a reflective film layer. The barrier layer encapsulates the metal contact by defining a mask pattern with a larger size than the metal contact via, which prevents the metal contact from becoming contaminated by the reflective film. This encapsulation reduces contamination of the metal contact and also reduces the voltage drop during operation of the LED die.