A Multi-Wavelengths Interferometry Applied In Nanometer Scale Measurement

With the development of nano-technology, nanometrology is an emergent task for the industry and science research. To the present, many measurement methods have been devised, but seldom of them can satisfy the requirement of mass production, high-speed measurement and high ratio of performance and price. On this problem, this study was to make the multi-wavelengths interferometry researches on nanometer scale measurement.When the spacing is nanometer scale between two objects, one of which is transparent, a thin air film with optic characteristics can be formed with the air stuffed between the two articles. In multi-wavelengths interferometry, incident rays combined with several wavelengths direct through the film, and the recombination of the rays reflected by the upper and lower surface of the thin film results in the generation of interference fringes. Intensity reflectivity of the thin film, the ratio of the reflection ray intensities to the incident ray intensities, is determined by the wavelength of incident ray and the height of the thin film,while other parameters keep invariable. Individual reflectivity of a certain thin film according to different wavelengths can be measured with the help of selection by three different color filters. To establish equation set based on the correlation of the film height, wavelengths of the incident rays and corresponding intensity reflectivities of the film. The film height can be calculated out from the equation set.The main factors which influence the results involve SNR of the channel, phase offset on reflection, bandwidth of the filters, vibration and so on. With corresponding error compensation the measurement precise can be improved. The multi-wavelengths interferometry can avoid the error brought on by phase shifter in PSI (phase-shift interferometry) and it also can correct measurement results of different wavelength rays mutually to reduce error.This study presented a measurement system to measure the flying height of hard disk magnetic head. The system includes an optic subsystem, Electro-Optic converter subsystem, Digital-Analog Converter subsystem and software programming. An experiment with this measurement system was carried out, and the results displayed that the accuracy of measurement was lower than 0.2nm ,so it fully demonstrates the correctness of system and theoretical basis.The multi-wavelengths interferometry characterizes real-time and untouched measurement for nanometer scale spacing with the excellence of high precision, simple installation and easy use.