High-speed Nanometric-precision Profilometry using Vertical Scanning Interferometry and Two high-power LED

• Published in: Journal of the Japan Society for Precision Engineering, Contributed Papers Vol. 71; no. 11; pp. 1404 - 1409
• Main Authors: ADACHI, Masaaki, ENOMOTO, Fumihiko, UEDA, Kakuji
• Format: Journal Article
• Language: English
• Published: Tokyo The Japan Society for Precision Engineering 2005; Japan Science and Technology Agency
• Subjects: LED; nanometer; phase shift; profilometry; two wavelengths; vertical scanning; white light interferometry
• ISSN: 1348-8724; 1881-8722
• DOI: 10.2493/jspe.71.1404

We propose a high-speed vertical scanning profilometry which has nanometric height precision. The proposed profilometry is equipped with two short-coherent-light sources, which are made of extremely-high-power light emitting diodes (LED). In 3-D profile measurements, the profilometry acquires many interferograms while vertically scanning a Mirau-type objective with 0.407-μm movement/interferogram and alternately-flashing LED. Odd-numbered interferograms are acquired with 503-nm LED and even-numbered interferograms are with 591-nm LED. Regarding the acquired interferograms, a computer calculates phase and modulation contrast using a phase-shifting technique. As two movements are repeated between acquirements of the same-color interferograms, phase step corresponds to approximately 6π + π/2 with 503 nm and approximately 6π - π/2 with 591 nm, respectively. After searching the interferogram having a contrast peak, the computer extracts optical path difference of the searched interferogram with nanometric resolution from the phase information. From the vertical movement length of 0.407 μm and a frame rate of 111 Hz, a vertical scanning speed is given as 45.2 μm/s. Nanometric height precision of the profilometry is checked using the measured data of a step height standard.