Run-to-run control utilizing the AVM system in the solar industry

The AVM system has been installed in all of the plasma enhanced chemical vapor deposition (PECVD) tools of Motech Industries, Inc. Currently, a joint development project to deploy a run-to-run (R2R) control scheme utilizing the AVM system is underway. R2R control is the technique of modifying recipe parameters or the selection of control parameters between runs to improve processing performance. The R2R control is also called the tube-to-tube (T2T) control for the PECVD tools in the solar industry. In the deposition process of the solar-cell manufacturing, the sampling rate is less than 10%. However, the T2T control requires 100% total inspection. To accomplish this requirement, large amount of measurement is needed, and thus leads to the increase of the production cycle time and cost. To resolve the problem mentioned above, Virtual Metrology for the T2T control was proposed. Incorporation of VM into R2R control is one of key APC focus areas of ITRS for 2009. 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 (Rl) of VM to gauge the reliability of the VM results. This paper proposes a novel scheme of R2R control that utilizes VM with RI/GSI in the feedback loop.