Preliminary study of run-to-run control utilizing virtual metrology with reliance index

Incorporation of virtual metrology (VM) into run-to-run (R2R) control is one of key advanced process control (APC) focus areas of International Technology Roadmap for Semiconductors (ITRS) for 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 at all is utilized. The authors have proposed the so-called reliance index (RI) of VM to gauge the reliability of the VM results. This paper proposes a novel scheme of run-to-run control that utilizes VM with RI in the feedback loop.