The Random Errors (advanced mode) allows you to perform a simultaneous or combined search for random and systematic errors in layer thickness, optical constants corrections and systematic inhomogeneities. This search is a multiparametric inverse problem which solution may be unstable and non unique.

The option is able to provide excellent results in complicated cases, but application of this option requires experience in solving reverse engineering problems.

Example: reverse engineering of three-layer sandwiches consisting of thin silver-island films surrounded by SiO2 layers. Wavelength dependencies of optical constants of metal-island films are  quite complicated. At the same time thicknesses of Ag-SiO2 and SiO2 layers are to be determined. In this complex case, Random Errors (advanced version) is to be applied. 

Anim Sandwich Psi

Fitting of experimental ellipsometric angles Psi  measured at 45, 55 and 65 degrees by model angles.

Anim Sandwich Delta

Fitting of experimental ellipsometric angles Delta  measured at 45, 55 and 65 degrees by model angles.

Anim Sandwich Depol

Fitting of experimental depolarization measured at 45, 55 and 65 degrees by model depolarization.

Anim Sandwich n

Wavelength dependence of Ag-SiO2 refractive index in the course of the reverse engineering process.

Anim Sandwich k

Wavelength dependence of Ag-SiO2 extinction coefficient in the course of the reverse engineering process.

In order to describe optical constants of Ag-SiO2 films, n(lambda) and k(lambda) models are used. These models assume arbitrary but smooth dependence of refractive index and extinction coefficient on wavelength. They should be used in most complicated cases when other models are not adequate. See the details in Unique n-k option article and in our publications.

You can find detailed descriptions of the application of this option in our papers:

 

  1. T.V. Amotchkina, V. Janicki, J. Sancho-Parramon, A.V. Tikhonravov, M.K. Trubetskov, and H. Zorc. "General approach to reliable characterization of thin metal films." Appl. Opt. 50, 10, 1453-1464 (2011).
  2. T.V. Amotchkina, M.K. Trubetskov, A. V. Tikhonravov, V. Janicki, J. Sancho-Parramon, and H. Zorc. "Comparison of two techniques for reliable characterization of thin metal-dielectric films." Appl. Opt. 50, 6189-6197 (2011).