Preparation, Characterization and Diffusion Barrier Application in Cu Metallization of Reactively Sputtered Tantalum Zirconium Nitride Thin Films
| Autor: | Jian-LongRuan, 阮建龍 |
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| Rok vydání: | 2012 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 As semiconductor device technology approached the deep sub-micron process requirements, copper has replaced aluminum in the interconnect metallization due to its excellent electrical conductivity and superior electromigration resistance as compared to Al. However, with a higher diffusivity than Al, Cu diffused easily through the dielectrics, and then, the performance of devices was degraded by the introduction of deep-level acceptor. Moreover, Cu silicides were easily formed at temperatures as low as 200 °C. Therefore, it is necessary to introduce a diffusion barrier between Cu and the underlying dielectrics to suppress Cu diffusion. In this study, ZrN films were prepared by reactive magnetron sputtering. The effects of process parameters (nitrogen flow rate and negative substrate bias) on the composition, microstructure, electrical property and Cu barrier performance of ZrN films were investigated. In addition, TaZrN films were also prepared by reactive magnetron sputtering using dual target co-sputtering system based on the optimum process parameters of ZrN films (nitrogen flow rate: 3 SCCM and negative substrate bias: -200 V). The effects of Ta addition on the microstructure, electrical property and Cu barrier performance of TaZrN films were also intensively studied in this work. Results indicated that the formation of compound on the target surface with increasing nitrogen flow rate not only led to a reduction in deposition rate but also influenced the composition of the film. The existence of residual oxygen in the ZrN films was ascribed to the relatively high base pressure attained in the present work. The slightly larger lattice constant of ZrN films compared with the ideal value of ZrN compound demonstrated the presence of residual oxygen atoms in the films. The residual oxygen atoms in the ZrN films may possibly substitute the nitrogen atoms or occupy the interstitial positions in the ZrN lattice, causing that so called near-stoichiometric films and the delay of occurrence for over-stoichiometric films in the N/Zr ratio evolution with nitrogen flow rate. The electron scattering effects due to impurity atoms may be enhanced by the incorporation of residual oxygen atoms and were responsible for the overall raise in the resistivity of ZrN films as a function of nitrogen flow rate, comparing with the value reported by previous studies. The composition, microstructure, resistivity and diffusion barrier properties of ZrN films, with respect to substrate bias, were studied in this work. Results showed that the deposition rate and impurity oxygen content of ZrN films were substantially influenced by the resputtering effects due to the ion bombardment on the film surface. The competition between surface energy and strain energy made the preferred orientation of ZrN films change from (111) to (200) and then back to highly (111) preferred orientation as a function of substrate bias. The application of negative substrate bias could effectively decrease the electrical resistivity due to the decrease of impurity oxygen content and the densification of films, resulting from the moderate-energy ion irradiation. The biased ZrN films could successfully be used as a diffusion barrier layer, between Cu and SiO2, even up to the high temperature of 800 °C for 30 minutes. The effects of Ta content on the microstructure, composition, electrical and diffusion barrier properties of TaZrN films were also investigated in this study. Results indicated that the TaZrN films with different Ta content were crystallized in NaCl-type structure. In addition, the lattice constant of TaZrN films decreased with the increase of Ta content due to the smaller ionic radius of Ta5+ comparing with that of Zr4+. The decreasing lattice constant of TaZrN films with Ta content evidenced the successful substitution of Zr with Ta and then the formation of TaZrN solid solution. The electrical resistivity of TaZrN films showed a minimum value of 78 μΩ-cm at Ta content of 3.5 at. % and then increased with the increase of Ta content. Hall measurements indicated that the electrical conduction of films was essentially due to electrons (n-type). And the increase of carrier density and mobility at Ta content of 3.5 at. %, caused by the extra d valence electron of Ta and the less electron scattering of grain boundaries, was responsible for the further decreasing of resistivity from pure ZrN films. A sputter-prepared Cu (100 nm)/TaxZr1-xN (10 nm)/SiO2 (100 nm)/Si stacked structure was fabricated for the evaluation of diffusion barrier performance of TaZrN films. Results showed that the little incorporation of Ta (3.5 at. %) into the ZrN films significantly improved the barrier performance against Cu diffusion at high temperature annealing due to the slightly distorted lattices and higher packing density attributed to the addition of Ta elements into ZrN films. In this study, the TaZrN films with 3.5 at. % of Ta could be successfully used as a potential diffusion barrier layer in Cu metallization even up to the high temperature of 900 °C, while the ZrN films failed at the same situation. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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