Stress modification of Ni–Fe films by ion bombardment concurrent with film growth by alloy evaporation

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Abstract
A technique is described for selectively modifying, by ion bombardment during film growth, the state of internal stress of thin films on flexible polymer substrates. A laser-monitoring system is used to measure strain-induced deflections of the simply supported substrate prior to, during, and after the deposition without disturbing the film–substrate system. Sensitivity of the in situ measured bending force per unit width is ∼130 dyn/cm. The result is a composite view of the ‘‘frozen-in’’ thin-film internal stress including postdeposition relaxation. Permalloy (83% Ni–17% Fe) is deposited on Kapton at room temperature by electron beam evaporation simultaneous with Ar+ bombardment of current densities j=10 to 1000 μA/cm2 and ion energies E=150, 300, 750, and 1500 eV/ion. In the absence of ion bombardment, the average internal stress is tensile with a value of 11 Gdyn/cm2 for deposition rate =0.5 nm/s. Transition from tensile to compressive stress is a strong function of j and a rather weak function of E.

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