Research On Optical Measurement Methods Of Nanometer Film Thickness

Thickness is one of the key parameters associated with the film performance.With the rapid development of coating technology,precise measurement of the film thickness(a few nanometers to hundreds of nanometers)becomes very important.Optical method has the advantages of high precision,fast response and non-destructive testing among the common measurement method and becomes the major measurement technology.This thesis mainly takes two materials as the research object: the semiconductor germanium and the metal gold.The methods of white light interferometry,surface plasmon resonance and heterodyne interferometry to measure the thickness of nanometer film were studied.Due to the different characteristics of different material films,we should use different methods to measure the thickness.The semiconductor germanium film has the characteristics of high refractive index.It is the absorption region in the communication wavelength band(near 1550 nm),then we chose the measurement method of white light interferometry;the refractive index of gold film is complex,and could excite the surface plasmon effect,thus the measurement method based on surface plasmon resonance was chosen.In order to improve the accuracy of measurement,the method of heterodyne interferometry is realized by measuring the phase difference between P and S polarized light.In this thesis,the thickness of the germanium film is about 300 nm,which result in that only one peak exists in the measurable interference spectrum,traditional white light interference demodulation techniques based on two adjacent interference peaks are not a suitable choice.We report an experimental approach to measure the peak wavelength shifts with only a single interference peak in a fiber white light interferometer.The temperature measurement experiments prove a linear relationship between the peak wavelength and the temperature.With this demodulation scheme,we measured the thickness of germanium film is 338.8 nm,the experimental error mainly come from the temperature error and the light source wavelength shifts.The method based on surface plasmon resonance has used to measure the thickness of metal film.The surface plasmon resonance curve has three characteristic parameters: the SPR angles,half width and minimum reflectance.With these parameters,we finally get the thickness by inversion calculation.Thickness and the dielectric constant can be measured with this method at the same time.The Kretschmann surface plasmon resonance experiment system was set up,with a gold film as the measurement object.The resonance curve at 632.8 nm and 652.1 nm were measured.Finally we get the thickness of the gold film with d=55.2 nm.But this method is one of the strength measurement method,the accuracy is restricted by environment.Then we papered an improved scheme based on heterodyne interferometry.The thickness is measured by the phase difference between P and S polarization light.The thesis is focused on the optical measurement method of nanometer film thickness,and measured the thickness of germanium and gold film.The mainly innovation of this thesis is a demodulation scheme with the peak wavelength shifts in a fiber white-light interferometer.This demodulation scheme was applied to measure the short optical path difference.