An Optical Profilometer based on a CD-Pickup Head

The demonstrated anamorphic detection system is based on a commercially available CD–pickup head and is used to measure profiles of sufficiently well reflecting structures. We adopted the pickup for a profile measurement principle, which is based on the focus error signal. Through this signal the profile can be determined without servoeing the focus. The theoretical behaviour of the focus error signal is explained. Also a circuit board was developed to drive the laser diode and to acquire both the radio frequency signal (RF–signal) and the focus error signal (FE–signal) in real–time. We obtain measurement results with high spatial resolution and can determine small structures on semiconductor chips. Further optimization in the measurement setup will be done to achieve a universally applicable low–cost profile measurement device.