Characterization of inhomogeneous transparent thin films on transparent substrates by spectroscopic ellipsometry.

摘要

Inhomogeneities in dielectric thin films are known to be responsible for the observed irreproducibilities in the film properties. Therefore any reliable method for determining the true optical properties of the film material must take into account the serious perturbing effects of the film inhomogeneity. Spectroscopic ellipsometry (SE) has been used as a nondestructive technique for determining the optical properties of metallic and semiconducting thin films and materials. Unfortunately, when similar measurements on a dielectric material or film are made, SE suffers a serious drawback due to the lack of sensitivity inherent in the basic design of the instrument. To solve this problem, in this thesis, a novel method of incorporating an achromatic compensator into a rotating-analyzer type SE is proposed and tested. For the first time, the refractive index (n) of vitreous silica measured by SE matches the reference data to within 0.001 over a wide spectral range (300-700 nm). More importantly, the sensitivity of SE to the extinction coefficient (k) can also be estimated to the third decimal place.; Using this new measurement method and linear regression analyses procedures for interpreting the SE data, a number of optical thin films deposited on vitreous silica substrates were characterized successfully. All the films studied show inhomogeneities such as surface microroughness, incorporated voids and nonuniform distribution of voids. Quantitative results simultaneously obtained include the refractive index as a function of wavelength, the thickness as well as the void fraction of each optical sublayer. As a result, the true refractive index of the film material, unperturbed by the effect of the film structural inhomogeneity, is reported for several optical coating materials (AlF{dollar}sb3{dollar}, CeF{dollar}sb3{dollar}, HfF{dollar}sb4{dollar}, LaF{dollar}sb3{dollar}, ScF{dollar}sb3{dollar}, Al{dollar}sb2{dollar}O{dollar}sb3{dollar}, ThO{dollar}sb2{dollar}, HfO{dollar}sb2{dollar}, Sc{dollar}sb2{dollar}O{dollar}sb3{dollar}, Y{dollar}sb2{dollar}O{dollar}sb3{dollar} and ZrO{dollar}sb2{dollar}) in the near UV and visible region. Additionally, the power of SE with an achromatic compensator has been demonstrated by successful depth profiling the inhomogeneities in BaTiO{dollar}sb3{dollar} thin films on single crystal SrTiO{dollar}sb3{dollar} substrates.