Copper Etching Solution Using Cationic Polymers to Prevent Undercutting
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Solution Overview
Problem
Conventional etching solutions for copper and copper alloys in the electronics industry often result in undesired undercutting, line shape alteration, and line width reduction, which can lead to circuit shorts and impaired electrical conductivity due to differences in grain structure between copper layers and insufficient adhesion to dielectric substrates.
Innovation Solution
An aqueous etching solution comprising a polyamide with a specific polymeric moiety, an oxidizing agent, acid, and halide ions, which maintains the geometrical shape of copper lines and improves adhesion by controlling etching behavior, preventing undercutting and line shape alteration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional etching solutions (sulphuric acid and hydrogen peroxide) are used, then etching of copper layers occurs, but undercutting of the first copper layer is caused which results in insufficient adhesion
Solution Approach 1:
The patent changes the chemical parameters of the etching solution by replacing hydrogen peroxide with ferric ions as the oxidizing agent and adding specific polymers (PVP or cationic polymers with Mn≥10,000). This parameter change modifies the etching mechanism to prevent undercutting while maintaining etching effectiveness, thereby resolving the contradiction between productivity and adhesion strength.
Solution Approach 2:
The patent introduces polymer intermediaries (PVP or cationic polymers) that mediate between the etching solution and the copper surface. These polymers adsorb onto the copper surface and control the etching reaction, preventing the formation of undercuts and ensuring vertical etching profiles that maintain adhesion strength.
2Productivity
If etching solutions with ferric ions and PVP are used, then etching occurs, but undercuts are still caused
Solution Approach 1:
The patent changes the polymer parameter by specifying cationic polymers with number average molecular weight Mn≥10,000, which provides better steric hindrance and surface coverage compared to PVP. This parameter change in polymer molecular weight and charge density effectively prevents undercut formation while maintaining etching productivity.
3Productivity
If etching solutions based on sulphuric acid and ferric ions are used, then etching occurs, but line shape alteration to trapezoidal shape is caused
Solution Approach 1:
The patent introduces cationic polymers as intermediaries that adsorb onto the copper surface and provide steric protection during etching. This intermediary layer ensures uniform etching rates across the copper surface, maintaining vertical sidewalls and rectangular line shapes, thereby preventing trapezoidal distortion while preserving etching efficiency.
4Productivity
If conventional etching solutions are used, then etching of copper tracks occurs, but line width reduction is caused
Solution Approach 1:
The patent employs polymer intermediaries (PVP or cationic polymers with Mn≥10,000) that adsorb onto the copper surface and provide steric hindrance during etching. This intermediary protection limits the etching reaction to the intended depth while preventing lateral etching, thereby maintaining line width and preventing reduction while preserving etching productivity.
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 effectively maintains the rectangular shape of copper lines, reduces line width reduction, and enhances adhesion to organic matrices, ensuring reliable electrical conductivity and improved durability of electronic components.
Implementation Method 1
an aqueous etching solution comprising a polyamide with a specific polymeric moiety, an oxidizing agent, acid, and halide ions
Implementation Method 2
The solution effectively maintains the rectangular shape of copper lines, reduces line width reduction, and enhances adhesion to organic matrices
Data Source
AI summary
An etching solution for copper and copper alloy surfaces comprising at least one acid, at least one oxidising agent suitable to oxidise copper, at least one source of halide ions and further at least one polyamide containing at least one polymeric moiety according to formula (I)wherein each a is independently from each other selected from 1, 2 and 3; each b is an integer independently from each other ranging from 5 to 10000; each R1 is a monovalent residue independently from each other selected from the group consisting of substituted or unsubstituted C1-C8-alkyl groups and a method for its use are provided. Such etching solution is particularly useful for retaining the shape of treated copper and copper alloy lines.