Electroplating Apparatus with Resistive Element and Auxiliary Cathode
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Solution Overview
Problem
The challenge in achieving uniform electroplating on thin-metal seeded wafers, particularly those with large diameters, due to significant voltage drops across resistive seed layers, leading to non-uniform plating thickness distribution.
Innovation Solution
An electroplating apparatus and method utilizing an ionically resistive element with electrolyte-permeable pores or holes, positioned close to the wafer substrate, in combination with an auxiliary cathode to divert current and create a uniform current density, effectively acting as a high-resistance virtual anode to compensate for voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If electrical contact is made only at the edge region of the wafer, then the plating tooling structure is simplified, but the voltage drop across the resistive seed layer causes non-uniform current distribution and non-uniform plating thickness
Solution Approach 1:
A conductive electrolyte medium is introduced as an intermediary between the edge contact point and the central region of the wafer. This electrolyte layer enables ionic conduction paths that bypass the high-resistance seed layer, allowing current to reach the central region without traversing the resistive metal film, thus eliminating the voltage drop and achieving uniform current distribution
Solution Approach 2:
The invention utilizes ionic conduction through the electrolyte solution to replace electronic conduction through the resistive seed layer. By establishing ionic current paths through the electrolyte medium, the system achieves uniform current distribution across the wafer surface without requiring direct electrical contact at multiple points
2Reliability
If thin seed layers are used to minimize diffusion barrier thickness, then copper diffusion blocking is improved, but the seed layer resistance increases causing extreme terminal effects and non-uniform plating
Solution Approach 1:
The conductive electrolyte acts as an intermediary that bypasses the high-resistance thin seed layer. By providing alternative ionic conduction paths through the electrolyte medium, the system eliminates the terminal effects caused by the resistive seed layer while maintaining the benefits of thin barrier layers for copper diffusion blocking
Solution Approach 2:
The invention changes the conduction mechanism parameter from electronic conduction through the seed layer to ionic conduction through the electrolyte. This parameter change eliminates the resistance issue inherent in thin seed layers while maintaining their diffusion barrier function
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 approach significantly improves plating uniformity by reducing edge-to-center voltage drops, ensuring consistent metal deposition across the wafer surface, even on high-resistance seed layers, thereby enhancing the electroplating process efficiency.
Implementation Method 1
an ionically resistive element with electrolyte-permeable pores or holes, where the element resides in close proximity of the wafer substrate
Implementation Method 2
The ionically resistive ionically permeable element described herein presents a uniform current density in the proximity of the wafer cathode
Implementation Method 3
an auxiliary cathode configured to divert or remove a portion of current from the anode that would otherwise pass to the edge region of the wafer
Implementation Method 4
Method and apparatus for electroplating... electroplating metal onto the substrate
Implementation Method 5
The seed layer carries the electrical plating current from the edge region of the wafer... to all trench and via structures located across the wafer surface
Data Source
AI summary
An apparatus for electroplating a layer of metal onto the surface of a wafer includes an ionically resistive ionically permeable element located in close proximity of the wafer and an auxiliary cathode located between the anode and the ionically resistive ionically permeable element. The ionically resistive ionically permeable element serves to modulate ionic current at the wafer surface. The auxiliary cathode is configured to shape the current distribution from the anode. The provided configuration effectively redistributes ionic current in the plating system allowing plating of uniform metal layers and mitigating the terminal effect.