In-situ GISAXS monitoring of ultrashort period W/B4C multilayer x-ray mirror growth

Abstract

Ultrashort period multilayer X-ray mirrors with the layer thickness down to 1 nm or less represent a technological challenge. Here, the layer thickness becomes comparable to the interface roughness and discontinuous layers producing strong diffuse scattering may appear. The grazing-incidence small-angle X-ray scattering (GISAXS) is a unique nondestructive technique to probe the mirror quality in terms of the statistical interface roughness and its correlation properties. We present the first in-situ laboratory GISAXS experiments of monitoring the multilayer mirror growth in order to better understand and optimize the deposition process. A microfocus X-ray source IμS with focusing Montel optics (Incoatec) and 2D X-ray detector Pilatus 200K (Dectris) were mounted on a custom-designed dual-ion beam sputtering apparatus (Bestec). Two W/B 4 C mirrors with 15 periods of 1.8 nm and 2.1 nm were prepared as determined from the post-deposition specular X-ray reflectivity measurements. The in-situ GISAXS tracking was done by a fast repeated collection of the GISAXS frames with the integration time of 8 s at the incidence angle of 0.25 degree. Two distinct features along q z at q y = 0, namely Yoneda and Bragg-like (BL) multilayer peaks evolved in the GISAXS pattern. Oscillatory behavior of the latter in terms of intensity and FWHM was observed after the initial stage. Lateral cuts of the diffuse scattering concentration stripes surrounding BL peaks in particular GISAXS frames provided temporal evolution of the correlation and fractal interface parameters. Their potential for tailoring the multilayer properties is discussed.