A system for tool monitoring is provided. The system comprises a first cassette, a second cassette, a processing tool, a first metrology tool, and a second metrology tool. The first cassette contains a first control wafer used for a first metrology process. The second cassette contains a second control wafer used for a second metrology process. The processing tool receives the first cassette and processes the first control wafer, and receives the second cassette and processes the second control wafer. The first metrology tool receives the first cassette from the processing tool, and performs the first metrology process on the first control wafer processed by the processing tool. The second metrology tool receives the second cassette from the processing tool, and performs the second metrology process on the second control wafer processed by the processing tool.