Bulent M. Basol

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.

Mechanically Induced Growth Rate Differential for Copper Layers Electroplated in Presence of Organic Additives

Electrochemical mechanical deposition (ECMD) planarizes copper films as they are plated on patterned wafer surfaces. The technique involves electrochemical deposition (ECD) and simultaneous sweeping of the cathode surface with a pad. Pad sweeping gives rise to a mechanically induced current suppression (MICS) phenomenon if plating is performed in electrolytes containing accelerator and suppressor additives as well as Cl - ions. In this work we studied the MICS phenomenon by partially sweeping blanket wafer surfaces with a small pad and investigating effects of the bath chemistry and wafer surface derivatization on the copper growth rates at the swept and unswept regions of the surface. It was found that, at a given suppressor concentration, copper growth rate differential between the two regions was reduced with increasing accelerator concentration in the bath. Derivatization of the wafer surface in an accelerator-containing solution followed by ECMD in a suppressor-containing bath gave the largest growth differential between the swept and unswept surface portions, suggesting high planarization efficiency. Adsorption-desorption kinetics of the organic additives used in this work were obtained under ECD conditions and found to support the proposed mechanism of MICS.