AVS 50th International Symposium
    High-k Gate Dielectrics and Devices Topical Conference Monday Sessions
       Session DI-MoA

Paper DI-MoA6
Post Deposition Stability of High-k Dielectrics to Air Exposure and its Implications to Interface Reactivity

Monday, November 3, 2003, 3:40 pm, Room 317

Session: High-k Dielectric Stability
Presenter: T. Gougousi, North Carolina State University
Authors: T. Gougousi, North Carolina State University
D. Niu, North Carolina State University
R.W. Ashcraft, North Carolina State University
G.N. Parsons, North Carolina State University
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Post-deposition stability of the gate oxide is an important issue for advanced gate stacks. For this study, group III and IV high-k dielectrics films are deposited on Si by PECVD or by metal sputtering and ex-situ oxidation in N@sub 2@O. After deposition the dielectrics are permitted to react with ambient H@sub 2@O and CO@sub 2@ for extended periods and their stability is monitored as a function of time using FTIR. We find that group III (Y and La) based-films are generally susceptible to reactions with H@sub 2@O and CO@sub 2@ forming hydride and carbonate species. For PVD La films, the oxidation temperature affects the film stability significantly. Films oxidized at 600°C show signs of reaction within minutes of air exposure while films oxidized at 900°C are stable for exposures up to two weeks. Y@sub 2@O@sub 3@ CVD films deposited at 400°C also show high reactivity with H@sub 2@O. Post deposition inert anneals at 900°C in N@sub 2@ improves the film stability significantly. In-situ capping of the Y@sub 2@O@sub 3@ films with 500Å of a-Si reduces greatly the amount of OH detected in the films. Group IV (Hf and Zr) based film exhibit superior stability as compared to the group III films, however. Carbonate formation is verified for both HfO@sub 2@ and ZrO@sub 2@ films. OH is practically undetectable in the films even after ambient exposure for six months. The effect of the OH incorporation on the interface stability will be discussed, and examples of OH promoted reactions between the dielectric film and the Si substrate or polysilicon gate metal will be presented.