Chloride-Free Copper Plating Solution for Solar Cell Seed Layers
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Solution Overview
Problem
Conventional copper plating solutions containing chloride ions and acids are unsuitable for plating over metal seed layers on silicon solar cell wafers, as they cause delamination of the seed layer and adverse effects on aluminum paste, leading to inefficiencies and increased costs in solar cell manufacturing.
Innovation Solution
A copper plating solution comprising copper ions and lithium sulfate as a conductivity salt, with a pH between 1.7 and 3.5 and free of chloride ions, which enhances plating distribution and avoids adverse effects on metal seed layers, using additives like 2 mercaptoimidazole to achieve smooth and bright copper deposits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional copper plating solutions containing chloride ions and acids are used, then copper plating can be achieved, but delamination of metal seed layers and adverse effects on aluminum paste occur
Solution Approach 1:
The patent removes chloride ions and strong acids from the copper plating solution, extracting the harmful components that cause delamination and dissolution while retaining the essential copper plating functionality through alternative chemistry
Solution Approach 2:
The patent changes the chemical parameters of the plating solution by using a controlled pH range (1.7-3.5) with lithium sulfate instead of conventional strong acids and chloride ions, fundamentally altering the solution chemistry to eliminate harmful effects while maintaining plating effectiveness
2Reliability
If copper plating is performed on solar cell wafers with metal seed layers, then conductivity is improved, but the metal seed layer adhesion is compromised by conventional plating solutions
Solution Approach 1:
The patent modifies the chemical environment by controlling pH within 1.7-3.5 and using lithium sulfate instead of conventional acids and chlorides, creating conditions that enable copper deposition while preserving seed layer adhesion through gentler chemistry
Solution Approach 2:
Lithium sulfate acts as an intermediary conductivity salt that provides ionic conductivity for copper plating without the harmful effects of strong acids and chloride ions, mediating between the need for conductivity and the need to protect the seed layer
3Ease of manufacture
If conventional copper plating solutions are used, then plating process is simple, but aluminum paste dissolves and adhesion is lost
Solution Approach 1:
The patent extracts chloride ions and strong acids from the plating solution, removing the components that cause aluminum paste dissolution while maintaining the essential copper plating function through alternative chemistry
Solution Approach 2:
The patent changes the solution chemistry parameters by using lithium sulfate and controlling pH to a moderate range, eliminating the aggressive conditions that dissolve aluminum paste while preserving plating effectiveness
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 solution enables efficient and cost-effective copper plating on solar cell wafers without compromising the adhesion of metal seed layers, improving solar cell efficiency and reducing material costs by preventing delamination and dissolution issues.
Implementation Method 1
contacting the substrate with a copper plating solution comprising a source of copper ions and a conductivity salt provided as lithium sulfate
Data Source
AI summary
The present technology generally relates to copper plating solutions. Specifically, the present technology includes a copper plating solution comprising a source of copper ions and a conductivity salt wherein the copper plating solution has a pH between 1.7 and 3.5 as is essentially free of chloride ions. The present technology also relates to a method of using such copper plating solutions.