Highly reflective Mo/Be/Si multilayer mirrors with zero stress values for 13.5 nm wavelength

This study investigates mechanical stresses in Mo/Be/Si multilayer mirrors. We determined layer thicknesses (for Si-1.0 nm, Mo-2.8 nm and Be-3.2 nm) in the period that simultaneously provided high reflection coefficients (R-66-67%) at a wavelength of 13.5 nm with zero internal stress values. At the wavelength of 13.5 nm, the reflection coefficient of a stressless Mo/Be/Si multilayer mirror deposited on a micro-electro-mechanical system of micromirrors had a value of about 23% with a reflection from the witness of 67%. An interferometric method for determining the stress values in films, which is able to provide a measurement accuracy at the level of Delta s +/- 0.24 MPa, is described in detail.