Sacrificial adhesion promotion layers for copper metallization of device structures

Area of Science:

• Materials Science
• Surface Science
• Chemical Engineering

Background:

• Copper film adhesion to diffusion barriers (TiN, Ta, TaN) is critical for integrated circuit reliability.
• Interfacial oxides and poor adhesion limit device performance and lifespan.

Purpose of the Study:

• To investigate the use of poly(acrylic acid) (PAA) as an adhesion promoter for copper films on diffusion barriers.
• To understand the mechanism by which PAA improves interfacial adhesion and reduces oxides.

Main Methods:

• Deposition of ultrathin PAA layers on TiN, Ta, TaN, and Si wafer substrates.
• Copper film deposition using H2-assisted reduction of a copper precursor in supercritical CO2.
• Surface analysis using X-ray photoelectron spectroscopy (XPS), electron microscopy, atomic force microscopy (AFM), and ellipsometry.

Main Results:

• PAA treatment dramatically increased interfacial adhesion of Cu films.
• PAA acted as a sacrificial layer, decomposing during deposition.
• PAA reduced or eliminated metal oxides (e.g., Ta2O5) at the substrate interface.
• Elemental copper (Cu0) and silicon (Si0) were observed at the interface on PAA-treated Si wafers.
• Elemental tantalum (Ta0) was observed at the interface on PAA-treated Ta substrates.

Conclusions:

• Ultrathin PAA layers are effective adhesion promoters for copper films on diffusion barriers.
• The sacrificial nature of PAA and its ability to reduce oxides are key to improved adhesion.
• This technique offers a viable method for enhancing the reliability of integrated circuits.