Magnetic Materials for Three-Dimensional Damascene Metallization: Void-Free Electrodeposition of Ni and Ni70Fe30 Using 2-Mercapto-5-benzimidazolesulfonic Acid

Abstract

Superconformal filling of submicrometer trenches with electrodeposited Ni is demonstrated using a electrolyte containing 2-mercapto-5-benzimidazolesulfonic acid (MBIS). The process offers the ability to build three-dimensional magnetically active structures that may be easily integrated with other state-of-the-art metallization schemes. MBIS acts to inhibit Ni(Fe) electrodeposition, although under certain conditions rapid, autocatalytic breakdown accompanies the onset of Ni deposition. Optimal trench filling is associated with the positive feedback process, moderated by electrolyte internal-resistance losses, and manifests as a hysteretic voltammetric response on planar electrodes for an MBIS concentration . On freshly immersed substrates, trench filling is characterized by an initial period of uniform growth followed by the development of a v-notch geometry associated with transient depletion of MBIS within the recessed feature. Interestingly, the finest submicrometer features are filled while only minimal deposition occurs on the neighboring free surface. Continued growth of the MBIS derived v-notch geometry also results in void-free filling of the larger features by geometrical leveling. The same behavior is observed for soft magnetic alloys, such as Ni-rich Ni–Fe alloys. Preliminary experiments indicated that MBIS does not significantly perturb the low coercivity of Ni–Fe alloys, an important attribute for prospective technical applications.