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The thickness dependence of interface layers in FeCo–Si multilayers on sputtering voltage, argon pressure and substrate bias potential was examined. The multilayers were characterised by in situ kinetic ellipsometry, X-ray reflection, X-ray diffraction, polarized neutron reflection and atomic force microscopy. A minimum thickness for the sum of both interface layers per period between 23 A and 24 A was found for different combinations of production parameter values. For an argon pressure of 1.3×10 −3 mbar the minimum interface thickness was found at a sputtering voltage of 708 V, and for an argon pressure of 2.3×10 −3 mbar at 880 V. These values were determined for a floating substrate potential of approximately +60 V relative to ground. Applying a substrate bias potential of −70 V the minimum interface thickness occurred for a sputtering voltage of 880 V at an argon pressure of 1.3×10 −3 mbar. This study confirmed the results of the former empirical optimisation. By revealing the existence of several sets of optimum parameters it opens up a further parameter to adjust other properties like stress. The interface layer on top of the FeCo layer is 16% thicker than the one on top of the Si layer due to the larger roughness of the FeCo layers.

In situ fast kinetic ellipsometry, X-ray and polarized neutron scattering are used to investigate the growth of sputtered Fe Co –Si multilayers with atomic resolution and to determine interface thickness and composition.The values of these 89 11 properties depend on the sputtering parameters.Under the conditions of minimal thickness of the interface layers we find on top of the silicon layer 15 A (Fe Co ) Si and on top of the iron cobalt layer 19 A (Fe Co ) Si .During the growth of the 89 11 0.5 0.5 89 11 0.67 0.33 ˚˚ iron cobalt layer a phase transition occurs.After the formation of the interface layer on top of the silicon layer the iron cobalt alloy starts to grow in an amorphous phase until a thickness of 25 A is reached.Then it crystallizes down to the interface layer ˚ whereby it shrinks to 18.5 A, the atomic density changes nearly proportionally to the imaginary part of the index of refraction. ˚ As will be shown, the growth of the layers and the formation of the interface layers can be followed on an atomic scale. 2003 Elsevier Science B.V. All rights reserved.