COMBINED OPTICAL METHOD FOR MONITORING OF THE PHYSICAL PARAMETERS OF THIN DIELECTRIC FILMS ON THE SURFACE OF SINGLE-CRYSTAL SILICON

Abstract

A combined optical method for monitoring the physical parameters of thin dielectric films on the surface of single-crystal silicon is proposed. The method consists of two stages. At the first stage, the answer is given to the question of the applicability of the model “transparent optically isotropic film – absorbing optically isotropic substrate” to the “film – substrate” systems obtained in the technological process, and determine the film thickness. To do this, it is necessary to perform ellipsometric measurements at different points on the surface of the “film-substrate” system and at different angles of incidence of the laser beam of the ellipsometer. As a result of such measurements, the values of the refractive index (n₁ ± Δn₁) and film thickness (d ± Δd) and the corresponding spreads of these quantities (Δn₁, Δd) are obtained. From the magnitude of these variations (Δn₁, Δd), we can draw the first conclusion about the applicability of this model to the object of study. The main goal of the first stage of the combined optical method is to determine the thickness of the dielectric film as precisely as possible. At the second stage, measurements of the reflection spectra of films on the surface of silicon wafers are performed in order to obtain a clear interference pattern. From the obtained spectra determine the exact spectral position of the interference minima (λ_min) and maxima (λ_max). On the basis of these values and the film thickness d determined at the first stage, the dispersion of the refractive index of the dielectric film [n₁ = f(λ)] is calculated. According to the results of research at two stages, a final conclusion is made about the suitability of the object under study for further operations of the manufacturing process of manufacturing integrated circuits. The applicability of the proposed method has been tested on Si₃N₄ – Si systems. The results of testing the combined optical method on Si₃N₄ – Si systems convincingly prove its effectiveness for monitoring the physical parameters of thin dielectric films on the surface of single-crystal silicon. In our article, the main emphasis is placed on the applied value of this method for integrated circuit technology. That is why silicon, the main material of modern microelectronics, appears in the title of the article and in the examples given. However, from the description of this optical method it is quite obvious that it is quite applicable to the study of any systems “dielectric film – semiconductor substrate”. A prerequisite is the fulfillment of two basic requirements. First, the quality of the surface treatment of the semiconductor substrate on which the film is deposited must be high. Secondly, the film thickness should be sufficient to obtain a clear interference pattern at least in the visible and near ultraviolet spectral regions.

Key words: thin dielectric films, ellipsometry, interference, dispersion of the refractive index.