AVS 47th International Symposium
    Thin Films Wednesday Sessions
       Session TF-WeM

Paper TF-WeM8
Models of Electrochemical Deposition of Copper Thin Films:The Effect of Leveling Agents

Wednesday, October 4, 2000, 10:40 am, Room 203

Session: Modeling of Thin Film Growth
Presenter: T.S. Cale, Rensselaer Polytechnic Institute
Authors: S. Soukane, Rensselaer Polytechnic Institute
T.S. Cale, Rensselaer Polytechnic Institute
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As device sizes decrease, the ability of electroplating to create conformal films in deep features make it very attractive. Especially beneficial in interconnect applications is the "leveling" effect of certain organic additives. With the use of these leveling agents, electroplating offers the possibility of a superfilling effect, leading to void-free structures. This effect is often attributed to the inhibition of plating along feature sidewalls. Much feature-scale modeling work has been focused on reproducing the effect of the additive during deposition. The inhibition has been assumed to be due to operation at a mass transport-limited rate that allows the leveling agent to be completely depleted in the region near the surface. This may be a good assumption if the agent is highly reactive and used in quantities on the order of hundreds of ppm. Its inhibiting effect is usually correlated to the expression of the current density by a factor that is a function of the leveling agent flux to the surface. This approach limits the opportunities to look for explanations via chemical mechanisms. We show that the leveling effect can be explained via a more detailed chemical mechanism involving adsorbed species. We present a feature-scale model coupling the potential and concentration fields via the current density at the feature surface, together with a chemical mechanism involving surface species. In this chemical mechanism, copper ions go through two successive irreversible reactions. The first step is a charge transfer reaction, leading to an adsorbed copper species on the surface. The second is much faster, consisting of the adsorbate reduction and insertion into the film. It is assumed that the leveling agent is completely transformed on the surface to new species that play the important roles in the inhibition effect. These proposed surface species can undergo slow desorption reactions or can be incorporated in the solid at a rate much slower than copper insertion.