Glow-discharge optical spectroscopy as a diagnostic of sputtered permalloy film composition and saturation magnetostriction

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Abstract
We show that the composition and saturation magnetostriction of sputtered permalloy films can be correlated with the relative intensities of iron and nickel atomic emissions from a 13.56-MHz rf glow discharge. Wavelength-resolved emission spectra as a function of discharge pressure were recorded while sputtering iron and permalloy targets. Intensities of some emission lines were highly correlated, so that their ratios were nearly independent of argon pressure. This occurred in spite of a ∼50-fold change in the brightness of the glow over the pressure range studied, and suggested that the stoichiometry of the sputtering target and the sputtered permalloy film can each be assessed during the sputtering process. The selection of appropriate emission lines is discussed, along with considerations of the type of equilibrium distribution prevalent in a sputtering discharge. We used five sputtering targets with different Ni/Fe ratios to grow films. The films were analyzed in terms of composition, stress, and saturation magnetostriction. Film stress was not observed to vary significantly with sputtering target composition. A high degree of correlation was observed between Fe/Ni emission intensity ratio, target composition, film composition, and saturation magnetostriction.