Virtual metrology system and method

A virtual metrology system and a method therefor are provided herein. In the system, data of equipment tool conditions is gathered and clustered according to a plurality of predetermined patterns. The clustered data is calculated according to the corresponding pattern and a comparing result is obtained therefrom. If the result obtained meets a desired output, a corresponding process will be performed based on the result. In one case, the corresponding process is performing a normal sampling process if the clustered data meets the corresponding pattern. If the clustered data does not meet the corresponding pattern, an alarm will be generated thereby and the corresponding equipment may be shut down. In another case, the corresponding process is performing an equipment maintaining process if the clustered data meets the corresponding pattern.