Tantalum Film Capacitors with Improved AC Properties

Tantalum thin-film capacitors have been fabricated from magnetron sputtered tantalum films with different nitrogen concentrations. Capacitors made from film containing between 13 and 22 atom percent nitrogen and heat treated at temperatures between 250°C and 350°C show lower ac losses and TCC, and improved capacitance stability, when compared to standard capacitors based on tantalum containing 3 atom percent nitrogen. In addition, the dc properties of the improved capacitors are equivalent or better than those of the standard product. It is proposed that in capacitors containing over 13 atom percent nitrogen, the nitrogen fills interstitial vacancies in the tantalum lattice. A barrier is therefore produced to substantial oxygen diffusion from the dielectric into the underlying tantalum film during exposure to temperature between 250° and 350°C. In addition, results at 200°C suggest that a second mechanism for improved characteristics is the removal of water or citrate molecules, incorporated during anodization, from the hulk of the dielectric.