| 摘要 |
PURPOSE:To monitor the characteristics of a dielectric thin film in a forming process of the dielectric thin film accurately, by measuring the transmittance or reflectivity in a wavelength on the short-wavelength side of two wavelengths, and obtaining the refractive index of the dielectric thin film during the formation based on the extreme value of the transmittance or reflectivity. CONSTITUTION:One light beam L1 is transmitted through a glass substrate 13, wherein a thin film is being formed, and guided to the outside of a vacuum evaporating container 11. The light beam is reflected by a mirror 43 and the direction is changed. The light beam is divided into the light having the equal intensity by a beam splitter 32 for 1/2 splitting. The two light beams passed a filter 51, which transmits a wavelength lambda1, and a filter 52, which transmits a wavelength lambda2(lambda1<lambda2). The light beams are converted into electric signals by light receiving devices 611 and 621. The transmitting wavelengths lambda1 and lambda2 of the filters 51 and 52 are different in correspondence with the desired optical film thicknesses. The signals are amplified by amplifiers 61 and 62 by the same amount, and the difference is obtained by a differential amplifier 72. The output of the diffeential amplifier 72 is monitored by a voltmeter 9. At a point when the output of the differential amplifier 72 becomes zero, the film formation is stopped and the optical film thickness is controlled. |
