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Delaying Breakdown of Gate Oxides by Reverting the Electric Field in the Oxide

IP.com Disclosure Number: IPCOM000013757D
Original Publication Date: 2001-Apr-14
Included in the Prior Art Database: 2003-Jun-18

Publishing Venue

IBM

Abstract

The further scaling of MOSFETs is endangered by the early breakdown of smaller devices, when the gate oxide reaches a thickness of 1-2 nm. By reverting the polarity of the electric field acting on the oxide during "rest'' times, the processes resulting in breakdown can be reverted and dielectric breakdown can be delayed. The result is an increased life span of MOSFETs. Calculations indicate that breakdown is due to hydrogen-induced electro migration, which causes roughening of the anode interface of the oxide: Protrusions of silicon pointing into the oxide are preferentially reduced, if they are negatively charged, as the increase electric field attracts positive defects that are silicon-rich. The protrusions can grow into dendrites extending throughout the oxide and forming conducting pathways for electrons. In contrast a cathode is being smoothened as any protrusions are oxidized by attracting negative defects that are oxygen rich. Thus protrusions at the cathode are being oxidized and the interface is smoothened. By reverting the voltage, any silicon protrusions formed at the anode interface, are oxidized again, and the formation of silicon dendrites is reverted while the process is causing protrusions at the opposite interface. However, the overall growth of silicon protrusions on both sides is reduced. This process delays breakdown of MOSFETs, by exploiting the rest times of a transistor to heal out the processes that may cause early breakdown of the oxide the life span of MOSFETs is extended. 1