Selective Copper Etching Liquid for Cobalt Barrier Preservation
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Solution Overview
Problem
Conventional etching liquids fail to selectively remove copper seed layers in multilayer structures containing cobalt barrier layers, leading to premature dissolution of cobalt and inadequate bonding strength between solder and barrier layers.
Innovation Solution
An etching liquid comprising hydrogen peroxide and acids like citric acid, oxalic acid, or malic acid, with a pH range of 4.3 to 5.5, is used to selectively etch copper layers without affecting cobalt layers, ensuring proper bonding strength and selective removal of copper seed layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching liquid (SPM liquid, ferric chloride) is used to etch copper seed layer, then copper seed layer can be etched away, but cobalt barrier layer dissolves more quickly than copper due to local cell action
Solution Approach 1:
The patent changes the chemical parameters of the etching liquid by replacing conventional SPM liquid or ferric chloride with a specific composition containing hydrogen peroxide (0.1-10% by weight) and citric acid (0.1-10% by weight) in deionized water. This parameter change modifies the etching mechanism to prevent local cell action between dissimilar metals, thereby selectively etching copper while preserving the cobalt barrier layer and maintaining bonding strength.
2Ease of manufacture
If cobalt is used as barrier layer to substitute nickel or palladium, then safety and costs are improved, but cobalt dissolves preferentially in conventional etching liquid
Solution Approach 1:
The patent modifies the chemical composition parameters of the etching liquid to be compatible with cobalt barrier layers. The specific formulation with hydrogen peroxide and citric acid creates a controlled oxidation environment that etches copper at a faster rate than cobalt dissolution, enabling selective copper removal while preserving the cobalt layer for subsequent solder bonding.
Solution Approach 2:
The etching liquid acts as an intermediary medium that mediates the interaction between the copper seed layer and cobalt barrier layer. By introducing hydrogen peroxide and citric acid as controlled reagents, the liquid creates a selective chemical environment that targets copper for removal while leaving cobalt intact, thus enabling the use of cost-effective cobalt barriers without sacrificing etching precision.
3Manufacturing precision
If barrier layer retreats due to preferential dissolution, then copper seed layer can be removed, but sufficient bonding strength between solder layer and barrier layer cannot be obtained
Solution Approach 1:
The patent optimizes the concentration parameters of hydrogen peroxide (0.1-10% by weight) and citric acid (0.1-10% by weight) to control the etching rate differential between copper and cobalt. This parameter optimization ensures that copper is removed completely while cobalt dissolution is suppressed to minimal levels, preserving the barrier layer integrity and ensuring adequate bonding strength for subsequent soldering operations.
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 etching liquid effectively removes copper seed layers while preserving cobalt layers, maintaining bonding strength and preventing cobalt dissolution, thus enabling efficient solder-bump manufacturing.
Implementation Method 1
The etching liquid includes hydrogen peroxide and at least one organic acid, and has a pH in a range of 4.3 to 5.5. The etching liquid can selectively etch a copper layer without etching a cobalt layer.
Implementation Method 2
The etching liquid includes hydrogen peroxide and at least one organic acid selected from a group consisting of citric acid, oxalic acid, malic acid, and malonic acid. These acids form complexes with copper ions, enhancing selective copper removal.
Data Source
AI summary
An etching liquid which can selectively remove only a copper layer in an etching process of a multilayer structure including a cobalt layer and the copper layer is disclosed. The etching liquid is an etching liquid for etching the copper layer in the multilayer structure including the copper layer and the cobalt layer. This etching liquid includes at least one acid selected from a group consisting of citric acid, oxalic acid, malic acid, and malonic acid, and hydrogen peroxide, the etching liquid having pH in a range of 4.3 to 5.5.