Solid body and liquid superficial structure study by ellipsometry considering mathematical inverse problem incorrectness. 1. On features of the inverse problem in the study of the superthin superficial films on semiconductors

The work analyses features of the inverse problem of ellipsometry arising in determination of the whole set of parameters of a reflecting system with superthin superficial film. The way for the solution of the inverse problem is developed: the approach to the solution, representing consecutive passage of two stages is stated. Criterion for the choice of optimum values of the corresponding parameters is formulated for each stage. Optimum values of substrate parameters and value of the film parameters corresponding to a point of functional absolute minimum of an inverse problem are determined at the first stage. For superthin films these values are significantly different from the true values of the film parameters because of the experimental errors and because of experimental errors and discrepancies in the choice of the model of the object under study. The second stage is an obvious consequence of the first one and represents realization of the approach described in the previous work [1]. At this stage of the solution of the inverse problem the optimum values of substrate parameters defined at the previous stage are set and by means of criteria of selection offered in the work [1] optimum values of parameters of the film are determined. This approach to the solution of the mathematically incorrect inverse problem is successfully tested in the numerical experiment for different variants of experimental errors. Influence of the broken layer on substrate surfaces is also discussed in the work.