Current Thief Electrode Isolation in Wafer Electroplating
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Solution Overview
Problem
Existing electroplating processors for RDL and WLP wafers face challenges with excessive metal plating on current thief electrodes, leading to frequent deplating needs and contamination in the electrolyte bath, which is inefficient and costly.
Innovation Solution
The electroplating processor incorporates a two-membrane stack using cationic membranes and high conductivity electrolytes to separate the copper-containing catholyte from a low-copper isolyte, and further from a copper-free thiefolyte, preventing copper ions from migrating to the thief electrode and allowing for recirculation of the thiefolyte.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a current thief electrode is used to control plating thickness at the wafer edge, then plating uniformity is improved, but excessive metal plates onto the thief electrode requiring frequent deplating
Solution Approach 1:
The system segments the electrolyte environment into three separate compartments (catholyte chamber, isolyte chamber, and thiefolyte chamber) using ion-exchange membranes. This segmentation prevents copper ions from reaching the thief electrode while maintaining the current thieving function for plating control.
Solution Approach 2:
The patent introduces an intermediate isolyte chamber between the copper-containing catholyte and the copper-free thiefolyte. This intermediary layer, separated by ion-exchange membranes, acts as a barrier that blocks copper ion migration to the thief electrode while allowing the system to maintain its current distribution control function.
2Manufacturing precision
If a current thief electrode is used with high conductivity electrolyte baths, then terminal effect control on thin seed layers is improved, but metal plating on the thief electrode increases requiring frequent maintenance
Solution Approach 1:
The electrolyte system is segmented into three distinct chambers separated by ion-exchange membranes, isolating the thief electrode from copper ions while maintaining the benefits of high conductivity electrolyte baths for terminal effect control on thin seed layers.
Solution Approach 2:
The isolyte chamber serves as an intermediary barrier that prevents copper ion migration to the thief electrode, eliminating the need for frequent deplating maintenance while preserving the ability to use high conductivity electrolytes for precise terminal effect control.
3Reliability
If frequent deplating operations are performed on the thief electrode, then metal build-up is removed, but the processor must be removed from use and contamination particles are introduced into the electrolyte bath
Solution Approach 1:
The ion-exchange membranes and intermediate isolyte chamber act as barriers that prevent copper ions from reaching the thief electrode, eliminating metal build-up and the need for deplating operations, thereby preventing contamination particles from being introduced into the electrolyte bath.
Solution Approach 2:
The system extracts copper ions from the path to the thief electrode using ion-exchange membranes that selectively block copper ion migration, allowing the thief electrode to remain clean without requiring removal from service for deplating operations.
4Device complexity
If a single membrane is used to separate catholyte from thiefolyte, then device complexity is reduced, but copper ions can still pass through and plate onto the thief electrode
Solution Approach 1:
The separation system is segmented into multiple stages with two ion-exchange membranes creating three distinct chambers, ensuring effective copper ion blocking while maintaining manageable device complexity through modular construction.
Solution Approach 2:
The intermediate isolyte chamber with its bounding membranes acts as a dual-barrier intermediary system that provides effective copper ion blocking, with the first membrane preventing copper ion entry into the isolyte chamber and the second membrane preventing any copper ions from reaching the thiefolyte chamber.
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 design effectively reduces copper build-up on the thief electrode, allows for the recirculation of the thiefolyte, and minimizes contamination, thereby enhancing processing efficiency and reducing maintenance costs.
Implementation Method 1
A first electrolyte or thiefolyte in a first compartment separated from a second electrolyte or isolyte by a first membrane. A third electrolyte or catholyte in a second compartment is separated from the isolyte by a second membrane. Build-up of metal on the current thief electrode is reduced or avoided via the membranes preventing metal ions from passing from the catholyte into the thiefolyte.
Data Source
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AI summary
An electroplating processor has a head including a wafer holder, with the head movable to position a wafer in the wafer holder into a vessel holding a first electrolyte and having one or more anodes. A thief electrode assembly may be positioned adjacent to a lower end of the vessel, or below the anode. A thief current channel extends from the thief electrode assembly to a virtual thief position adjacent to the wafer holder. A thief electrode in the thief electrode assembly is positioned within a second electrolyte which is separated from the first electrolyte by a membrane. Alternatively, two membranes may be used with an isolation solution between them. The processor avoids plating metal onto the thief electrode, even when processing redistribution layer and wafer level packaging wafers having high amp-minute electroplating characteristics.