Applying the Automatic Virtual Metrology system to obtain tube-to-tube control in a PECVD tool

A joint development project to deploy a Tube-to-Tube (T2T) control scheme for Plasma-Enhanced Chemical Vapor Deposition (PECVD) utilizing the Automatic Virtual Metrology (AVM) system is in progress. In the PECVD process utilized in solar cell manufacturing, the sampling rate is less than 10%. However, T2T control requires 100% total inspection. To accomplish this requirement, a large number of measurements are needed and therefore production cycle time and cost increase. Virtual Metrology (VM) is proposed to resolve this problem. However, a key problem prohibiting effective utilization of VM in T2T control is its inability to take the reliance level in the VM feedback loop of T2T control into consideration. In addition, adopting an unreliable VM value may lead to worse results than not utilizing VM. In this article, the proposed T2T controller utilizes the VM value and its accompanying reliance index and global similarity index of the current run as well as information about a batch obtained in the first run to calculate a suggestion value of the deposition time for the following run to improve the process capability index and resolve unreliability issues.