DEVICE AND METHOD FOR MEASURING THICKNESS

A thickness measuring device includes a laser emitting a laser beam to an object in a semiconductor processing chamber, a quartz glass inside the chamber reflecting part of the laser beam and to transmit a remainder of the laser beam, a first light receiving sensor detecting an intensity of first reflected light reflected from the quartz glass, a second light receiving sensor detecting an intensity of second reflected light transmitted through the quartz glass and reflected from the object, and a controller configured to calculate input intensity of the laser beam based on the intensity of the first reflected light, to calculate reflectivity of the object by comparing the input intensity of the laser beam with the intensity of the second reflected light, and to measure a thickness of the object by comparing the calculated reflectivity with predetermined reflectivity values for a plurality of thicknesses.