Enhancement of Cu nucleation in Cu-MOCVD by Pd sputtering pretreatment

Cu electroplating which emerges as a viable Cu filling technique for damascene processing relies on the presence of a smooth and continuous Cu seed layer. Metal organic chemical vapor deposition (MOCVD) may be the most promising technique to deposit the Cu seed layer. Plasma pretreatment is widely used as a precleaning technique which is essential for the enhancement of Cu nucleation in Cu-MOCVD. New pretreatment techniques which can replace plasma pretreatments are proposed in this paper. Pd sputtering, Pd–HF dipping or Pd-CVD pretreatment will possibly enhance Cu nucleation significantly if it is conducted on barrier metal films prior to Cu-MOCVD. It was found that Pd sputtering is more effective in enhancing Cu nucleation than direct plasma H₂ precleaning. Pd sputtering pretreatment is effective for a variety of barrier metals including Ta, TiN, TaN and TaSiN. The mechanism through which Cu nucleation is enhanced may be as follows: a thin Pd buffer layer formed by sputtering shields the barrier metal substrate surface with adsorbed oxygen atoms making Cu nucleation difficult and provides preferred sites for Cu nucleation.