Process trends for DPS metal etch: a case study for Al-1%Cu logic devices

High density plasma sources are becoming an industry standard for plasma etch tools. They provide enhanced etch rates and improved productivity as well as a wider process space compared to reactive ion etch (RIE) or magnetically enhanced RIE (MERIE) technology. As the complexity of metallization for IC interconnects increases, and as the critical dimension (CD) of advanced devices decreases, high density plasma etch systems are best suited to meet metal etch process requirements. The Decoupled Plasma Source (DPS) metal etch chamber was used at Motorola to develop processes for advanced Al-1%Cu logic devices. Through design of experiments (DOEs) and single variable experiments, general process trends were defined. In particular, the influence of the process parameters on residue removal, profile and CD control are detailed, and possible mechanisms are outlined. The kinetics of the process, as reflected by the etch rate in the main etch step and the duration of the over etch step is also examined. The results suggest that robust, manufacturable, and high productivity processes can be developed for the DPS metal etch reactor for a wide range of devices. This is best achieved by thoroughly characterizing the mechanisms underlying the process trends and by applying this knowledge to optimize the traditional metal etch metrics relevant to devices performance and reliability