Alloy Seed Layer Interface to Prevent Metal Undercut
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Solution Overview
Problem
The formation of metal undercuts during the wet etching process of seed layers in semiconductor dies leads to electrical connectivity failures, causing rejection of dies or wafers due to exposed vias and potential leakage failures.
Innovation Solution
Forming an alloy layer between the seed layer and metal pillar that is resistant to wet etching, preventing undercut formation by converting a portion of the seed layer into an alloy with a different metal that withstands the etching process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a wet etching process is used to remove the exposed portion of the seed layer, then the exposed seed layer is removed, but the seed layer under the metal pillars is also removed causing undercuts
Solution Approach 1:
An alloy layer is introduced as an intermediary between the metal pillar and the seed layer. This alloy layer acts as a protective mediator during the wet etching process, preventing the etchant from attacking and removing the seed layer underneath the metal pillar, thereby eliminating undercut formation while allowing complete removal of exposed seed layer
Solution Approach 2:
The structure transitions from simple metal-seed layer composition to a composite structure involving metal-alloy-seed layer. The alloy layer, formed by converting portions of the metal pillar through thermal treatment or chemical reactions, creates a composite material system where the alloy serves as a protective interface with different etching resistance properties than the original metal
2Ease of manufacture
If the seed layer is completely removed from exposed areas, then clean surfaces are achieved, but undercuts expose vias causing electrical connectivity failures
Solution Approach 1:
The alloy layer serves as a protective intermediary that extends beyond the metal pillar edges during etching, acting as a sacrificial barrier that prevents the etchant from reaching and removing the seed layer at the critical via regions, thus protecting vias while still allowing exposed seed layer removal
3Device complexity
If no alloy layer is used, then the process is simpler, but undercuts form during etching exposing vias
Solution Approach 1:
The alloy layer is formed in advance before the wet etching process through thermal treatment or in-situ chemical reactions. This preliminary action creates a protective barrier that prevents undercut formation during subsequent etching, ensuring via protection and electrical connectivity reliability
Solution Approach 2:
The metal pillar material undergoes parameter changes through thermal treatment or chemical exposure, transforming portions of it into an alloy with different properties. This parameter change creates a material with enhanced etching resistance that serves as a protective layer without significantly complicating the overall 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
Reduces or eliminates undercuts, ensuring reliable electrical connectivity by maintaining the integrity of the seed layer under the metal pillars, thereby reducing the risk of leakage failures and enhancing the manufacturing yield.
Implementation Method 1
converting at least a portion of the first metal layer into an alloy of the first metal and the second metal... The alloy has a third surface opposite the second surface... resistant to wet etching
Data Source
AI summary
A method includes forming a seed layer on a substrate. The seed layer includes a first metal. The method also includes forming a first metal layer over the seed layer. The first metal layer includes a second metal. The method further includes forming a second metal layer over the first metal layer. The second metal layer includes the first metal. The method includes converting at least a portion of the first metal layer into an alloy of the first metal and the second metal. The seed layer is then etched.