New theoretical approach to the RF-dynamics of soft magnetic FeTaN films for CMOS components

A new approach to a theoretical description of the RF-behavior of magnetic films possessing an in-plane uniaxial anisotropy was carried out by combining the Landau-Lifschitz and Maxwell equations for modeling spin dynamics and eddy current loss, respectively, to a comprehensive mathematical expression. Because of that, it is possible to compute the complex permeability in a wide frequency range. The theory was utilized to describe the dynamic response of soft magnetic FeTaN films deposited by reactive RF-magnetron sputtering for microelectronic RF-components like micro-inductors. A 6-inch target consisting of Fe90Ta10 was used to grow the films on oxidized silicon substrates with a titanium seed layer for better film adhesion. The concentration of nitrogen could be adjusted by a flow control system. With regard to aluminum CMOS processes carried out at around 400degreesC and to induce an in-plane uniaxial anisotropy the films were annealed at this temperature in a static magnetic field of 50 mT. It was found that the nitrogen content of the films in conjunction with the needed temperatures played an important role to obtain a marked uniaxial anisotropy in the film plane. Consequently, an annealing procedure had to be elaborated to obtain the in-plane uniaxial anisotropy at the relevant CMOS temperatures. For the application in RF-components and in view of eddy current losses, the magnetic FeTaN films were investigated for different thicknesses which delivered information that slipped in a multilayer design. Multilayers, i.e. magnetic single layers with a sufficient thickness separated by insulating inter-layers made of Si3N4, were necessary to decrease eddy currents at radio frequencies. This led to an improved frequency behavior. The introduced theory was then compared satisfactorily with the frequency-dependent permeability of FeTaN films of various thickness. It is concluded that an optimum film thickness can be roughly calculated in advance to keep eddy currents at a minimum. (C) 2004 Elsevier B.V. All rights reserved.