In semiconductor manufacturing processes, electrochemical plating (ECP) of metal layers is a key step in constructing the complex interconnects within a chip. Following the ECP process, an indispensable subsequent operation is edge cleaning. While this operation may appear simple, it has a profound impact on the overall quality, performance, and production efficiency of chip manufacturing.
01
Removing Edge Burrs: Eliminating Potential “Time Bombs” in Subsequent Processes
During the ECP process, when the wafer is removed from the plating solution, the edge region, though largely shielded by the plating ring and thus not fully plated with copper, is highly prone to burr formation. These burrs result from the irregular flow and drying of the plating solution at the wafer’s edge. Under surface tension, the plating solution forms droplets at the edge, which leave behind fine protrusions upon drying.
02
Preventing Copper Seed Contamination: Safeguarding a Clean Manufacturing Environment
After copper plating, residual copper seeds often remain on the wafer edge. This occurs because copper ion adsorption and deposition at the edge are more complex due to uneven electric field distribution and fluid dynamics effects, leading to irregular copper particle formation.
These copper seeds are highly threatening contaminants in subsequent processes. During steps such as deposition, etching, or polishing, external forces from mechanical arm gripping or equipment vibrations can cause copper seeds to detach from the wafer edge. These detached particles may spread through airflow or vacuum systems inside the equipment, contaminating other chambers or wafer carriers.
Once contamination spreads, copper seeds adhering to other wafer surfaces can cause severe failures. As an excellent conductor, copper may short-circuit signal lines if it lands on circuit nodes. If it deposits on insulating layers, it can degrade the dielectric’s insulating properties, increasing leakage current. These issues not only lead to chip malfunctions but may also cause widespread quality incidents during mass production.
03
Optimizing Edge Morphology: Building a Solid Foundation for the Bonding Process
Wafer substrates usually feature beveled edges designed to reduce stress concentration and prevent chipping during transport and processing. However, during copper chemical mechanical polishing (CMP), it is difficult to fully remove copper layers from the beveled edge. Due to the unique contact angle between the edge and the polishing pad, the flow of slurry is restricted, reducing polishing efficiency and resulting in copper residues.
In wafer-level direct bonding interconnect processes, residual copper on the edge can critically affect bonding quality. The bonding requires tight surface contact between two wafers; copper particles on the edge disrupt local pressure distribution. This can cause minor edge cracks or, more severely, create bubble defects at the bonding interface, leading to wafer warpage, delamination, and failure. These defects compromise the 3D interconnect structure of the chip, affecting signal transmission stability and potentially resulting in chip failure post-packaging.
Therefore, performing ECP edge cleaning before CMP, using chemical solutions to selectively remove copper residues on the bevel, ensures the flatness and cleanliness of the bonding interface. This provides reliable support for high-precision wafer bonding and significantly improves product yield.
Generally, the edge cleaning width is determined by the process. In advanced packaging HB processes, the cleaning width is around 3 to 5 millimeters. For standard processes, it is usually less than 3 millimeters.
04
Conclusion: Edge Cleaning – The “Guardian of Details” in Semiconductor Manufacturing
From microscopic burr removal to macroscopic bonding quality assurance, the edge cleaning step after metal layer ECP in semiconductor processes connects full-process quality control through what seems like a simple operation. It is not merely a remedy for process defects, but a practical implementation of precision manufacturing logic in advanced processes—where, in a nanoscale world, every detail at the edge may determine a chip’s performance and reliability.
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