Run-to-run control utilizing virtual metrology with reliance index

The incorporation of virtual metrology (VM) into run-to-run (R2R) control was one of the key advanced process control focus areas of the International Technology Roadmap for Semiconductors in 2009. However, a key problem preventing effective utilization of VM in R2R control is the inability to take the reliance level in the VM feedback loop of R2R control into consideration. The reason is that the result of adopting an unreliable VM value may be worse than if no VM is utilized at all. The authors have proposed the so-called reliance index (RI) and global similarity index (GSI) of VM to gauge the reliability of the VM results. This paper proposes a novel scheme of R2R control that utilizes VM with RI and GSI in the feedback loop. Simulation results of five random-generated rounds are performed. These random-generated rounds simulate the situation as if five modifications are performed on the process or the equipment due to predictive maintenances. As such, the issue of the R2R controller-gain management in real-production environment may be addressed whenever a modification is performed on the process or the equipment.