The barrier properties and failure mechanisms for many diffusion barriers in high-density volatile and non-volatile capacitors were reviewed. Based on failure mechanisms of these barriers reported by others, we suggested the new design concept for a diffusion barrier and developed the new Ta + CeO2 and Ta + RuO2 barriers. Although both barriers were shown to exhibit good diffusion barrier properties, however, oxide-incorporated barriers result in the surface oxidation of the under-layer during deposition and/or post-thermal budgets, resulting in the degradation of capacitor performance. The design concept for a diffusion barrier should be changed to sacrificial oxygen diffusion barrier concept, and both the RuTiN and the RuTiO films, as new sacrificial oxygen diffusion barriers, were proposed. New RuTiN and RuTiO barriers showed the higher oxidation resistance and cell capacitance and the lower contact resistance up to high temperatures. Therefore, the design concept of a sacrificial diffusion barrier should be emphasized to achieve high-density dynamic and ferroelectric random access memory devices.
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In the present study, Ta+RuO 2 diffusion barriers deposited with 100 and 150 W rf power showed that Ta is significantly bound to oxygen in the as-deposited state, but RuO 2 is deconvoluted into Ru metallic and Ru–O binding states. With increasing annealing temperature, the Ta–O bonds slightly increased compared to the as-deposited state, whereas the Ru–O bonds increased much more. When the Ta film was deposited with 170 W rf power, however, the amount of metallic Ta–Ta bonds is larger than that of Ta–O bonds. With increasing annealing temperature, Ta, which is not bound to oxygen, changed into the tantalum oxide by reaction with the in-diffused oxygen from an air atmosphere. This is supported by the results of sheet resistance measurement and glancing angle XRD analysis. Correspondingly, the Ta+RuO 2 diffusion barrier involving a large amount of RuO 2 effectively prevented the in-diffusion of oxygen and increased its oxidation resistance up to 800 °C.
All Science Journal Classification (ASJC) codes
- Materials Science(all)