Post deposition nitridation of Si in W/Si soft X-ray multilayer systems

•Improved sharpness of the interfaces as a result of nitridation.•Analysis was performed by a reconstruction of refractive index profiles.•Formation of a thick silicon nitride layer was revealed.•Silicon nitride formation reduced reflectivity at 0.84 nm. Partial nitridation of W/Si multilayer systems with a nm period was investigated in an attempt to reduce optically unfavorable tungsten silicide formation in the systems. Nitridation was applied directly after the deposition of every Si layer by exposing the Si surfaces to reactive nitrogen species from an ion source. As a result the formation of substantially sharper interfaces and a reduction in the silicide formation were observed in the systems. However, the passivation treatment caused a pronounced reduction in the X-ray reflectivity at 0.84 nm wavelength because of deep nitrogen penetration in the Si layers. This reduced the optical contrast between the reflector and spacer layer, which compensated the effect of the improved interface profile.