ANALYSIS OF THE STRUCTURE OF INTERFERENCE COATINGS FOR THE OPTIMIZATION OF THE PARAMETERS OF NARROWBAND OPTICAL FILTERS

To monitor the parameters of semiconductor layers deposited from solid solutions of A3B5 compounds during the epitaxy, optical control methods are used. The choice of optical monitoring methods is determined by the reactor design, which requires non-contact, fast, and precise measuring of wafer surface parameters. During the growth of epitaxial layers, the deposition of semiconductor compounds causes changes in the optical parameters of the wafer surface. To ensure precise measurements, it is essential to monitor these parameters within a narrow spectral range. In electro-optical monitoring systems, narrowband interference filters are used to select the desired spectrum. However, this type of filters is sensitive to several factors, such as environmental conditions, aging of the coating, and the angle of incidence. As a result, the manufacturing of narrowband optical filters with stable and precisely controlled optical characteristics presents a complex challenge. This article analyzes the impact of various factors on the optical characteristics of interference coatings. Quantitative analysis of these shows that shift of the selected spectral band with central wavelength λmax can approach or even exceed the full width at half maximum (FWHM). These changes in the optical characteristics of narrowband filters lead to a decrease in the accuracy required for optical monitoring during epitaxial processes, which leads to inaccuracies in measurements. The results of this analysis will guide the optimization of thin-film structures used in narrowband optical filters. The study of the shift in the selected band also enables, within certain limits, controlled changes to λmax or the compensation of its shift its shift during regular factor variations. Ultimately, it enables to take these changes into account when designing electro-optical systems for monitoring the epitaxial growth of semiconductor heterostructures, which increases the accuracy and stability of optical measurements in the required accuracy range.