ToF Depth Resolution Improved to 6.5nm

OSA Optics Letters issue dated by April 1st, 2018 publishes Peking University, China, KAIST and KRISS, Korea paper "Time-of-flight detection of femtosecond laser pulses for precise measurement of large microelectronic step height."

"By using time-of-flight detection with fiber-loop optical-microwave phase detectors, precise measurement of large step height is realized. The proposed method shows uncertainties of 15 nm and 6.5 nm at sampling periods of 40 ms and 800 ms, respectively. This method employs only one free-running femtosecond mode-locked laser and requires no scanning of laser repetition rate, making it easier to operate. Precise measurements of 6 μm and 0.5 mm step heights have been demonstrated, which show good functionality of this method for measurement of step heights."