A semiconductor device has a semiconductor substrate and a conductive layer formed above the semiconductor substrate. The loop serves as a mirror and as an amplification medium. The control system determines a volume of liquid coating material actually dispensed onto the substrate during the coating program, and compares the dispensed volume to a desired dispensed volume of liquid coating material to produce an error signal representing the difference between the calculated and desired volume values. Component parts are minimized and rigidity and locking action are improved.