Large area PLD of nanometer-multilayers

Abstract

The deposition of nanometer-multilayers on technical relevant substrates, used as X-ray optics, makes extreme demands on the deposition process concerning precision, reproducibility and long-term stability. Across a stack of more than 150 layers with single layer thicknesses in the range between 1 and 10 nm, a variation of single layer thickness considerably lower than σ D=0.1 nm and an interface roughness below σ D=0.25 nm have to be realized. Thickness homogeneity Δd/ d<1% and lateral thickness gradients Δ d/Δ x≈10 −8 have to be guaranteed across macroscopic substrate dimensions. Magnetron sputtering and e-beam evaporation are well-established deposition techniques to fabricate X-ray optical multilayers. For particular material combinations and for tailored thickness profiles, PLD has become an interesting alternative to these predominant technologies. Within the last years the established 4 in. large area PLD technology of X-ray optical metal/carbon and carbon/carbon multilayers has been up-scaled to the deposition of substrates up to 6 in. diameter. An improvement of long-term stability, which is necessary due to the increased substrate dimensions, is achieved by the modified target geometry and an increase in the accuracy of target and substrate positions in the range below 0.1 mm. Metal/carbon, metal/B 4C, carbon/carbon X-ray optics both with homogeneous thickness distribution and with tailored thickness gradients can be deposited on 6 in. substrates by means of a completely automated deposition process. A period thickness homogeneity better than 1% across 6 in. substrate length, a layer by layer reproducibility of σ D≤0.01 nm and a run-to-run stability Δ d<0.05 nm are achieved. As a result of the realized precision, Ni/C gradient multilayers, used as Göbel-Mirrors in X-ray analysis, can be deposited both on flat and on pre-curved substrates.