Method for Removing Dissolved Oxygen and Maintaining Oxygen-Free Electroplating Baths
Publication Date: 2005-Aug-23
The IP.com Prior Art Database
METHOD FOR REMOVING DISSOLVED OXYGEN AND MAINTAINING
OXYGEN-FREE ELECTROPLATING BATHS
The invention involves a method for removing dissolved oxygen (O2) to negligible concentrations (termed “oxygen-free) within electroplating bath solutions and maintains the solution in an oxygen-free state for subsequent electroplating. The advantage of an oxygen-free plating bath solution is that organic additive degradation by oxidation and subsequent additive depletion will be reduced. Specifically, the invention applies to the organic additives in copper plating bath solutions used to deposit copper interconnects on silicon wafers in semiconductor manufacturing.
The invention is related to management of electroplating baths. More particularly, the invention is related to management of dual-damascene copper electroplating baths.
A new technology, called dual-damascene copper electroplating, has emerged in the manufacturing of copper interconnect wiring for sub-micrometer sized integrated circuits. Dual-damascene electroplating requires a phenomenon called “superfilling” or “bottom-up plating” to deposit copper into the extremely small, 0.13 mm size, trenches and vias that form the wiring layout in integrated circuit designs. The plating bath solutions contain copper sulfate and sulfuric acid with the addition of chloride ions, but the key components in the plating process are the organic additives used in the plating bath. These critical components, called accelerators, suppressors, and levelers, promote copper plating from the bottom of the feature and allow high-aspect ratio trenches and vias to be filled correctly.
The accelerators are usually propane sulfonic acid derivatives: either MPSA or SPS. They provide growth sites and accelerate the copper deposition process at the bottom of the feature. The suppressor is a polyalkylene glycol, often PEG (polyethylene glycol), which adsorbs evenly on the wafer surface and decreases the deposition rate. Levelers, such as JGB, an organic dyeing agent, are used to decrease the growth rate at regions with high mass transfer rates. Among the additives used in copper electroplating baths, accelerators are the least stable, but suppressors are also known to decompose by oxidation.
Healy et al. studied the chemical stability of both SPS and MPSA in the presence or absence of copper metal, Cu2+ ions, or dissolved oxygen in solution (J.P. Healy, D. Pletcher, M. Goodenough.. J. Electronal. Chem. 167-177 (1992)). They concluded that the Cu2+ ions and the SPS or MPSA form a CuI-thiolate complex that is a key intermediate in promoting the copper deposition process.
In terms of accelerator degradation, in normal operating conditions of the plating bath in contact with air, dissolved oxygen can react with the CuI-thiolate complex to produce a more oxidized product, which is detrimental to the copper deposition process. In a separate study, Koh et al....