Neutral pH Copper Plating on Zinc Seed Layers to Reduce Undercut
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Solution Overview
Problem
Conductor structures in microelectronic devices experience undesirable narrowing and increased design widths due to seed layer removal, which also causes undercuts, restricting conductor structure overlap over underlying conductive elements.
Innovation Solution
A method involving a seed layer with primarily zinc, a neutral pH copper plating bath, and a brass layer formation process to minimize seed layer removal and undercut issues, using a zinc etchant to consume excess seed layer and control brass layer lateral growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the seed layer is removed after electroplating copper, then the plated copper can be exposed and the plating mask can be removed, but the seed layer removal causes undercut of the plated copper and narrowing of conductor structures
Solution Approach 1:
The patent forms a protective layer of copper over the seed layer before removing the seed layer. This preliminary copper deposition creates a protective cap that prevents the etchant from attacking the plated copper during seed layer removal, thereby eliminating the undercut problem while still allowing complete seed layer removal
Solution Approach 2:
The patent introduces a selective etchant that selectively removes zinc from the seed layer without attacking the copper plated structures. This intermediary chemical agent enables differentiation between the seed layer and the plated copper, allowing seed layer removal without damaging the conductor structures
2Object-generated harmful factors
If sufficient overlap of conductor structures over underlying conductive elements is used to compensate for undercut, then the undercut issue is addressed, but the design width of conductor structures increases
Solution Approach 1:
By forming the protective copper layer over the seed layer before removal, the patent eliminates the need for overlap compensation. The preliminary protective layer ensures that the plated copper edges remain intact during seed layer removal, allowing conductor structures to be designed with minimal overlap while maintaining structural integrity
3Quantity of substance
If conventional electroplating baths are used, then copper can be deposited on the seed layer, but the plating process causes undesirable narrowing of conductor structures
Solution Approach 1:
The patent performs preliminary copper deposition to form a protective layer that caps the seed layer. This preliminary action ensures that when the seed layer is subsequently removed, the plated copper maintains its full width without narrowing, as the protective layer prevents etchant access to the copper edges
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 method reduces conductor structure undercuts and design overlap, enabling precise conductor structure formation with improved alignment and reduced fabrication complications.
Implementation Method 1
a copper strike layer is formed on the seed layer where exposed by the plating mask by a strike electroplating process using a neutral pH copper plating bath
Implementation Method 2
The main copper layer, the copper strike layer, and the seed layer are heated to diffuse copper from the copper strike layer and the main copper layer, and zinc from the seed layer, to form a brass layer under the main copper layer
Implementation Method 3
The seed layer between the main copper layer and the substrate is consumed by formation of the brass layer. Remaining portions of the seed layer, which are not part of the brass layer, are removed by a wet etch process
Data Source
AI summary
A microelectronic device is formed by forming a seed layer that contains primarily zinc. A plating mask is formed over the seed layer, and a copper strike layer is formed on the seed layer using a neutral pH copper plating bath. A main copper layer is formed on the copper strike layer by plating copper on the copper strike layer. The plating mask is subsequently removed. The main copper layer, the copper strike layer, and the seed layer are heated to diffuse copper and zinc, and form a brass layer under the main copper layer, consuming the seed layer between the main copper layer and the substrate. Remaining portions of the seed layer are removed by a wet etch process. The main copper layer and the underlying brass layer provide a conductor structure.