Deep-UV antireflective coating: ellipsometry and XPS characterization

Oxynitride deep-ultraviolet antireflective coating (DARC) of Si wafers is u sed to get better lithography at 248 nm, The thickness and the optical para meters of these films have to be optimized to get good and reproducible res ults. In this context, DARC layers with different N2O flows have been proce ssed and characterized by ellipsometry and XPS in order to determine the op tical parameters n (refractive index) and k (absorption index), the stoichi ometry and the nature of the Si bonds. The DARC layers appear to be homogen eous, although short-range variations (1 nm) could hardly be detected by XP S, The correlation between XPS and ellipsometry results is fairly good and confirms that absorption is directly correlated to the amount of Si-Si bond s. A 'three-component mode' assuming that the DARC layer constitutes Si, Si O2 and Si3N4 has been used to calculate the refractive index. The agreement between this calculated index and the one determined by ellipsometry is fa irly good. Copyright (C) 2000 John Wiley & Sons, Ltd.