Cyprian Uzoh

PLANAR COPPER PLATING AND ELECTROPOLISHING TECHNIQUES

ABSTRACT Electrochemical mechanical deposition (ECMD) is a novel technique that has the ability to deposit planar conductive films on non planar substrate surfaces. This technique involves electrochemical deposition (ECD) while simultaneously polishing the substrate surface. Preferential deposition of the conductor into the cavities on the substrate surface may be achieved through two different mechanisms. The first mechanism is more mechanical in nature and it involves material removal from the top surface. The second mechanism is more chemical in nature, and it involves enhancing the deposition into the cavities where mechanical sweeping does not reach and reducing deposition onto surfaces that are swept. In this study we demonstrate that in an ECMD process, low-pressure mechanical sweeping of the wafer surface during copper plating can establish a differential in the activity of the organic accelerator species between the surface and the cavity regions of the substrate and thus give rise to bottom-up filling in even the lowest aspect-ratio cavities. Planar layers obtained by the ECMD technique have been successfully employed in an electrochemical polishing technique for stress-free removal of Cu.

Planarization Efficiency of Electrochemical Mechanical Deposition and Its Dependence on Process Parameters

Electrochemical mechanical deposition (ECMD) is a technique that has the ability to deposit planar metal films on nonplanar substrate surfaces with cavities. The method involves electrochemical deposition and simultaneous sweeping of the substrate surface with a planarization pad. Mechanical action of the pad increases suppression at the swept surface and therefore, mechanically induced superfilling of the cavities takes place. In this study we show that the planarization efficiency of the ECMD process for copper deposition is a strong function of the plating chemistry. Electrolytes containing no organic additives or only accelerators do not yield any planarization. Plating baths with only suppressors show low planarization capability, whereas those containing both suppressors and accelerators yield the highest planarization efficiency. Soaking the wafer surface in an accelerator-containing solution before the ECMD process step increases the planarization efficiency significantly. The presence of levelers in the plating electrolyte is detrimental to planarization efficiency of ECMD. High-acid copper plating solutions display higher planarization capability than low-acid electrolytes.