| 摘要 |
Very thin tunnel oxides are used in conventional non-volatile memories to obtain a sufficiently strong tunnelling current to or from the floating gate . Usual thicknesses of the tunnel oxide lie in the 8-10 nm range. The invention renders it possible to use tunnel oxides of a much greater thickness, for example of the order of 20 nm, for comparable tunnelling current values. According to the invention, the tunnelling effect is enhanced by implantation of a heavy, high-energy ion, for example As, into a comparatively thin poly layer of the oxide. Duri ng this, Si atoms are propelled from the polylayer into the oxide, so that the oxide is enriched with Si, which causes a major change in the tunnelling characteristics. The same oxide which functions as a gate oxide elsewhere may be used for the tunnel oxide. An important advantage of the invention is that direct contact between the tunnel oxide a nd photoresist layers necessary during the process is avoided, so that the properties of th e tunnel oxide are not or at least substantially not impaired by the photoresist.
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