Anodization of Ti by high electric fields at the tip of a scanned probe can be used to produce nanoscale features consisting of oxides of Ti. In this manner, Ti can be used as a sacrificial resist for nanoscale lithography by exploiting the etching selectivity differences between Ti and anodized Ti. The anodization was accomplished with an atomic force microscope using Ticoated silicon nitride cantilevers. The anodizing bias voltage is applied to the tip and is independent of the feedback, unlike the scanning tunneling microscope. With this setup we were able to fabricate sub-40 nm lines by direct anodization of Ti. It is also shown that once tip and sample are brought into hard contact, subsequent bending of the cantilever has little effect on the linewidth or thickness of the anodized material.

The direct modification of silicon and other semiconductor and metal surfaces by the process of anodization using the electric field from a scanning probe microscope in conjunction with the absorbed water from the atmosphere as the electrolyte is one promising method of accomplishing direct write lithography for the electron device fabrication using scanning probe microscopes. Both scanning tunneling microscopes and conductive-tip atomic force microscopes have been used for anodization with the work reported here primarily accomplished with a conductive-tip atomic force microscope. We have found that the terminating thickness of the scanning probe microscope induced oxide is governed by the diffusion limited electric field at the surface ͑which in this case is a function of the scanning probe microscope tip potential͒, with many similarities to liquid electrolyte anodization process. In particular, when using atmospheric water as the electrolyte on a silicon substrate and a conductive-tip atomic force microscope with a Ϫ7 to Ϫ10 V tip potential, the terminating electric field that is reached as the silicon dioxide thickness increases is to its final value of 80 Å is ϳ1ϫ10 7 V/cm. This is consistent with the diffusion limited electric field that is observed in many other anodization processes and the native oxidation of silicon ͑Mott-Cabrera process͒.

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In this experiment the ultrahigh vacuum environment of a molecular-beam epitaxy reactor equipped with ammonia was used to thermally nitride silicon. The resulting thin silicon nitride films were incorporated as gate insulators of metal-insulator-semiconductor field-effect transistors. The fabrication of field-effect transistors enabled very accurate interface state characterization of the silicon–silicon nitride interface by the charge pumping technique. The ammonia nitridation of silicon was also investigated as a surface passivation technique for scanning probe microscope (both conductive tip atomic force microscope and scanning tunneling microscope) lithography techniques.