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Damage characterization of ion beam exposed metal-oxide-semiconductor varactor cells by charge to breakdown measurements

: Brünger, W.H.; Buchmann, L.-M.; Naumann, F.; Friedrich, D.; Finkelstein, W.; Mohondro, R.


Journal of vacuum science and technology B. Microelectronics and nanometer structures 13 (1995), Nr.6, S.2561-2564
ISSN: 0734-211X
ISSN: 1071-1023
International Conference on Electron, Ion, and Photon Beam Technology and Nanofabrication <39, 1995, Scottsdale>
Fraunhofer ISIT ()
electric breakdown; ion beam effects; ion beam lithography; MOS capacitors; varactors

Damage in thin (10 nm) oxide layers of metal-oxide-semiconductor varactor cells caused by exposures with ions, electrons, and X-rays has been electrically characterized by constant-current stress time-dependent dielectric breakdown and capacitance-voltage measurements. The time-dependent dielectric breakdown investigations show measurable damage if the ions (H+; 74 keV) are allowed to penetrate the resist (300 nm PMMA) and the poly-Si layer (250 nm) to reach the oxide. This is not the case if the ions (H2+; 74 keV) are stopped inside the poly-Si layer by use of a thicker (450 nm) resist. Also for electrons and X-rays the exposure with lithographic doses did not change the time-dependent dielectric breakdown curves. The capacitance-voltage measurements demonstrate that electrons and X-rays which do penetrate the gate oxide cause a flatband voltage shift of nearly 400 mV. This shift could not be observed if the H2+ ions were stopped in the poly-Si buffer layer. Ions seem to create no sec ondary effects like X-ray generation which reach beyond the penetration depth. The measurements were performed in the unannealed state to detect all possible damage effects including those which can be removed by annealing.