Conductive Liner for Solder Connector via Integrity
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Solution Overview
Problem
Conventional far back end of the line (FBEOL) solder connectors rely on a thick aluminum pad between copper via and ball limiting metallurgy (BLM) layers, which is inefficient due to aluminum's low melting point and poor electro-migration characteristics, and requires unnecessary processing steps, posing environmental concerns and limiting device scaling and cost reduction.
Innovation Solution
A thin conformal conductive liner is integrated into the solder connector structure to optimize contact and adhesion between BLM layers and the conductive via, eliminating the need for aluminum by filling divots and enhancing adhesion, using materials like tantalum, tantalum nitride, titanium, and titanium nitride.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick aluminum pad is used between copper via and BLM layers, then adhesion and contact are achieved, but the structure has low melting point and poor electro-migration characteristics
Solution Approach 1:
The patent removes the aluminum pad entirely from the solder connector structure, extracting the problematic material that causes low melting point and poor electro-migration characteristics. The aluminum layer is completely eliminated and replaced with a copper via directly contacting the BLM layers through a conformal conductive liner.
Solution Approach 2:
The patent changes the material composition parameter by replacing aluminum with copper and introduces a conformal conductive liner made of copper or copper alloy. This material substitution improves electro-migration characteristics while the conformal geometry optimizes adhesion and contact properties.
2Reliability
If a thick aluminum pad is used in the solder connector structure, then adhesion is achieved, but the structure requires unnecessary processing steps including deposition, resist and lithography, and reactive ion etching
Solution Approach 1:
The patent extracts and removes the entire aluminum pad deposition process sequence, including the associated resist and lithography steps and reactive ion etching processes. This eliminates multiple processing steps while maintaining adhesion through the conformal conductive liner that directly contacts the BLM layers.
Solution Approach 2:
The patent merges the functions of the aluminum pad (adhesion and contact) into a single conformal conductive liner made of copper or copper alloy. This consolidation achieves the same adhesion and electrical contact functions with a simpler, more integrated structure that requires fewer processing steps.
3Ease of manufacture
If a thick aluminum pad is used, then environmental concerns are addressed through chromium phosphate cleaning, but the process presents environmental concerns and limits device scaling
Solution Approach 1:
The patent extracts and eliminates the chromium phosphate cleaning process that is required when using aluminum pads. By removing the aluminum pad entirely and using a copper-based conformal conductive liner, the harmful chromium phosphate cleaning step is no longer needed, addressing environmental concerns.
Solution Approach 2:
The patent changes the material parameter from aluminum to copper-based conformal conductive liner, which fundamentally alters the process requirements. This material substitution eliminates the need for chromium phosphate cleaning and enables process simplification and device scaling without environmental harm.
4Reliability
If a thick aluminum pad is used, then the solder connector structure is complete, but the structure prevents device scaling and increases cost
Solution Approach 1:
The patent extracts the thick aluminum pad that physically limits device scaling. By removing this bulky material layer and replacing it with a thin conformal conductive liner, the structure becomes more compact and suitable for scaled-down device geometries while maintaining connector integrity.
Solution Approach 2:
The patent uses a thin conformal conductive liner instead of a thick aluminum pad. This thin film structure maintains the necessary electrical and mechanical properties for connector integrity while enabling device scaling to smaller dimensions that would be impossible with a thick aluminum pad.
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 solution eliminates the use of aluminum, improves the integrity and adhesion of BLM layers, and simplifies the processing steps, leading to enhanced robustness and cost efficiency in FBEOL structures by creating a uniform surface for BLM deposition and preventing solder penetration into the copper via.
Implementation Method 1
The conductive liner can be conformal. That is, the conductive liner conform to the uneven surface at the top of the via. For example, the conductive liner can fill any divots formed in the dielectric columns at the top of the via
Implementation Method 2
The conductive material(s) used in the liner can be pre-selected to optimize adhesion of ball limiting metallurgy layers to the sidewalls of the well
Data Source
AI summary
Disclosed are embodiments of a far back end of the line solder connector and a method of forming the connector that eliminates the use aluminum, protects the integrity of the ball limiting metallurgy (BLM) layers and promotes adhesion of the BLM layers by incorporating a thin conformal conductive liner into the solder connector structure. This conductive liner coats the top of the via filling in any divots in order to create a uniform surface for BLM deposition and to, thereby, protect the integrity of the BLM layers. The liner further coats the dielectric sidewalls of the well in which the BLM layers are formed in order to enhance adhesion of the BLM layers to the well.