Ion beam sputtering of x-ray multilayer mirrors

Abstract

Ion beam sputtering has been applied for polishing, figuring and multilayer coating on silicon and quartz glass Substrates for the fabrication of x-ray mirrors. For high-performance x-ray optics extremely low microroughnesses of the substrates have to be achieved. Particularly for low d-spacing multilayers (d = 1...2 nm) even small improvements of the surface quality result in significant performance gains of the mirrors. By ion beam polishing silicon substrate surfaces could be smoothed from 0.18 nm rms to 0.11 rim rms (AFM scan length = 5 mu m). Furthermore figuring of spherical substrates into elliptical or parabolic surface contours has been developed and applied. Spherical quartz glass substrates with initial rms roughnesses of 0.73 nm and 0.52 nm show reduced roughnesses after figuring and multilayer coating of 0.26 nm and 0.10 nm using AFM scan lengths of 20 pm and 5 pm, respectively. The testing of the ion beam figured mirrors for the application as parallel beam and focussing optics shows very promising results: The comparison of collimating mirrors, produced either by ion beam figuring or bending, shows very similar x-ray intensities. However, the ion beam figured mirrors open the perspective for further reduced figure errors, improved long-term stability and 2-dimensional focusing

DLC/Si multilayer mirrors for EUV radiation

“…We found the deposition of a thin silicon smoothing layer (IR transparent as well) as a very suitable solution of the problem. The smoothing can be done by means of ion beam deposition and ion beam etching as well [11]. Figure 2 shows the principal layout of the proposed stack of an IR transparent EUV multilayer mirror.…”

“…Therefore we decided to introduce a thin silicon smoothing layer. This material is IR transparent (as used in the DLC/Si multilayer) and it is known that certain spatial frequencies of the surface roughness of a silicon layer can be effectively smoothed by ion beam treatment [11].…”

Computer simulation of layer‐by‐layer sputtering at grazing low‐energy ion‐surface interactions

“…Application of grazing angles of incidence of ions on the solid surface opens new perspectives in the investigation of composition, structure and topography of crystal surfaces and their modification and polishing by ion beams. Such surface ion treatment is progressively used in the semiconductor technologies and in the fabrication of X‐ray mirrors wherein particular Si and SiC crystals have a great importance. In, desirable smooth Si(100) surfaces suitable for nanoscale device fabrication were prepared by wet‐chemical etching followed by 0.3–1.5 keV Ar ion sputtering.…”