Developing an Automatic Virtual Metrology System

Virtual Metrology (VM) is a method to conjecture manufacturing quality of a process tool based on data sensed from the process tool and without physical metrology operations. VM has now been designated by the International SEMATECH Manufacturing Initiative and International Technology Roadmap for Semiconductors as one of the focus areas for the next-generation factory realization roadmap of the semiconductor industry. This paper defines the VM automation levels, proposes the concept of automatic virtual metrology (AVM), and develops an AVM system for automatic and fab-wide VM deployment. The example of automatic VM model refreshing for chemical vapor deposition (CVD) tools is also illustrated in this paper. The AVM system has been successfully deployed in a fifth-generation thin-film-transistor-liquid-crystal-display (TFT-LCD) factory in Chi Mei Optoelectronics (CMO), Taiwan. Note to Practitioners-The AVM system consists of a model-creation (MC) server, a VM manager, several VM clients, and many VM servers. The MC server will generate the first set of data quality evaluation models, VM conjecture models, and VM reliability evaluation models of a certain tool type. Under fab-wide VM deployment, the VM manager can fan out the first generated set of models to all the VM servers of the same tool type. Also, the VM server of each individual fan-out-accepter can perform an automatic model refreshing process to promptly refresh its own model set. Consequently, the VM accuracy of each VM server can be maintained and the VM server is then ready to serve various VM applications.