Refractive Index Dispersion of Dielectric Films Used in the Semiconductor Industry

Abstract

In order to obtain accurate film thickness measurements using various spectroscopic reflection techniques, it is necessary to have accurate refractive index measurements over the spectral range. A simplified representation of the dispersion of many of the films and materials used in the manufacture of semiconductor devices is compared with more conventional dispersion relations, especially with the Cauchy series. In the visible range, the simplified dispersion relation gives accurate refractive indexes by use of only one material‐dependent parameter and the refractive index of the material at 546 nm. When the dispersion of the material is large, then two parameters are required in addition to the 546 nm refractive index. Under such conditions, the Cauchy relation requires three terms to give an accurate representation of the dispersion. The various parameters and Cauchy coefficients for oxides, nitrides, photoresists, polyimides, and glasses were determined.