Waferlevel method for direct bumping on copper pads in integrated circuits

A structure for metallurgical connections between solder bumps and contact pads positioned on integrated circuits having copper interconnecting metallization protected by an overcoat, comprising:

• a portion of said copper metallization exposed by a window in said overcoat;
• said exposed copper having a clean surface;
• a patterned copper layer directly positioned on said clean copper metallization, whereby said metal structure has an electrical conductivity about equal to the conductivity of pure copper, said layer overlapping the perimeter of said overcoat window;
• a copper stud positioned on said copper layer;
• and
• one of said solder bumps bonded to said copper stud.

A wafer-level method for cleaning the surface of copper metallization used as integrated circuit interconnection and exposed in contact pads, comprising the steps of:

• exposing said wafer to organic solvents, thereby removing organic contamination and mechanical particles from said copper contact pads, and drying said wafer;
• exposing said wafer to an oxygen and nitrogen/argon/helium plasma, thereby ashing any organic residue on said copper contact pads and oxidizing said copper surface to a controlled thickness of less than 10 nm;
• without breaking the vacuum, exposing said wafer to a first hydrogen and nitrogen/helium/argon plasma, thereby removing said controlled copper oxide from said pad surface and passivating said cleaned surface;
• sputter-etching said passivated pad surface with energetic ions, thereby creating a fresh surface and concurrently activating it;
• sputter-depositing a layer of copper covering said fresh pad surface and pad perimeter, said layer providing minimal electrical resistance and thermo-mechanical stress to said pad;
• exposing said wafer to a second hydrogen and nitrogen/argon plasma, thereby passivating said copper layer;
• and
• without exposing said passivated copper layer to fresh contamination, depositing a copper stud onto said copper layer.