Two-step copper electroplating technique using seed enhancement step with alkali-metal-free copper pyrophosphate bath

We have developed the two-step Cu electroplating (EP) technique using alkali-metal-free copper pyrophosphate bath for Cu seed enhancement EP step. Alkali-metal-free copper pyrophosphate bath realizes conformal thickening of thin Cu seed layer without dissolution of Cu seed layer due to high resistivity, high polarization, and low Cu dissolubility of the bath. The two-step technique brings excellent yield of the via-chain resistance in comparison with copper sulfate EP technique. Thus, two-step electroplating is a promising technique for future ULSI fabrication beyond the limitation of PVD seed technology.