| In conventional Cu interconnect fabrication, a sputtered copper seed layer is deposited before the electrochemically deposited (ECD) copper plating step. However, as interconnect dimensions scale down, non-conformal seed layer growth and subsequent voiding of metallized structures is becoming a critical issue. With its established excellent thickness controllability and film conformality, atomic layer deposition (ALD) is becoming an attractive deposition approach for the sub-24nm fabrication regime. However, in order to achieve a smooth and continuous seed layer deposition, a low process temperature (below 100°C) is needed, given the tendency of Cu agglomeration at elevated temperature. In this research, plasma enhanced ALD (PEALD) Cu processes at low process temperature are developed using two novel precursors: Cuprum and AbaCus. The volatility and thermal stability of these two precursors are presented. Self-limiting nature of the PEALD processes are demonstrated. Key film properties including purity, resistivity, conformality, adhesion and platability are evaluated using multiple characterization techniques. In addition, film nucleation and growth of PEALD Cu at room temperature on different liner materials are studied. Via structures are employed for the investigation of film continuity on side walls. It is also shown that film conformality and platability can be improved by over saturating the plasma reactions. |
