Implant process control: Going beyond particles and RS

Ion Implant process control has changed considerably over the past 10 years. In the mid 1990s ion implant process control could easily be characterized as a daily dose monitor and particle check. However, as devices have shrunk and become faster, the sensitivity to process variations has increased, requiring a much more sophisticated process control strategy. Traditional test wafer based measurements now include periodic verification of implant angle accuracy, charge control system effectiveness, metals contamination, cross contamination and even ion gauge accuracy that are all known to contribute to process variations. In addition to more varied wafer based process verification methods, the introduction of networked data collection systems has now facilitated the ability to provide process monitoring of virtually every implant for every process recipe run. Automated systems can now monitor implant runs and flag possible out of control situations for review by process and equipment engineers, or depending on the severity of the fault, prevent further processing of material while the fault is investigated. Proper fault detection software and implant parameter databases provide process engineers with powerful tools to use for process optimization, interruption and fault elimination and correlation of tool operation parameters with device performance measurements. As fault detection systems are improved, the need for wafer based process control will decrease, although it is debatable that wafer based process control will ever be completely eliminated.