Mechanisms of surface anodization produced by scanning probe microscopes

Abstract

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.

Predictive model for scanned probe oxidation kinetics

“…There has been considerable recent interest in interpreting experimental kinetic data for SPM oxidation [4][5][6][7][8][9][10][11][12] and general agreement has emerged on the dependence of oxide height, h(t), width, W(t), and aspect ratio, h/W, on exposure parameters, i.e., voltage applied between SPM tip and substrate, V ͓Ϸ5 -20 V͔, and the pulse duration, t͓Ϸ10 Ϫ3 -10 3 s͔. In 1995 Gordon 7 suggested that Cabrera-Mott theory 13 was appropriate, with significant progress in this direction reported in 1997 by Stievenard 8 and Avouris. 9 Stievenard arrived at the inverse-log form, 1/h(t)ϭk(V)Ϫlog t, beginning with the Cabrera-Mott assumptions and by introducing a thickness-dependent cutoff field E L ϭV/h L .…”

Characterization of grain boundaries in multicrystalline silicon with high lateral resolution using conductive atomic force microscopy

“…The oxidation process leads to a significant change in current flow, thus, resulting in rather poor repeatability of consecutive I/V measurements performed at the same position. The phenomenon of anodic oxidation occurring when the sample is positively biased with respect to the AFM tip is well described in many publications (e.g., Dagata et al, 27 Gordon et al, 28 and Sti evenard et al…”

Nanoscaled Electrical Characterization

“…Finally, the applied bias between tip and sample induces a high electric field under the tip that can affect the results. A notorious case is the tip oxidation induced by a positively biased tip in presence of adsorbed water and therefore OH − groups [16]. Similarly, by reversing the bias, if the sample is prone to oxidation the high field could induce surface modification (hillocks or bumps).…”