Field induced oxidation of silicon by SPM: study of the mechanism at negative sample voltage by STM, ESTM and AFM

Abstract

Nanometer scale oxidation of silicon surfaces by STM and AFM is an important subject in the SPM community, and its application for nanofabrication has been demonstrated by several groups. Most published work show that the surface can only be oxidized if a positive sample voltage is applied to the sample with respect to the tip (anodization). In the present work we have studied the oxidation mechanism at negative sample voltage with STM and AFM in air and with an electrochemical STM in HF solution. It is demonstrated that two oxidation mechanisms exist, and that the frontier between both oxidation mechanisms is the voltage at which the surface is in the flat band condition. The influence of the electrical field is evaluated and a mechanism for the cathodic oxidation is proposed.Since the first experiments of Dagata et al. in 1990 [1], several groups have been studying the local oxidation of the surface of semiconductors and metals with nanometer lateral resolution by means of scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The first work by Dagata et al. [1], Nagahara et al.[2] and our group [3] used a negative voltage applied to the sample with respect to the tip to induce the oxidation of silicon surfaces, and the maximum resolution of 10 nm was soon achieved [4]. Sugimura's group produced local oxidation at both polarities [5], observing that the oxidation rate was higher at positive sample bias (anodization). In addition, breakthroughs towards the practical application of the technique were introduced in 1993 by Day and Allee [6], who used AFM with a metallized tip instead of STM to oxidize silicon surfaces locally, and by Snow et al. [7], who locally oxidized H-passivated silicon surfaces using AFM. Other relevant results that should be mentioned are those of Fay et al. [8], who demonstrated that the STM-oxidized regions appear as depressed areas when imaged with STM but as raised areas when imaged with AFM, and the dependence of the oxidation on the air humidity as * Corresponding author found by several authors [9]. It has also been demonstrated that photons from the probe of a scanning near-field optical microscope (SNOM) induce local oxidation of an amorphous Si-H film [10]. It was also demonstrated that, in the absence of light, the electrostatic field between the sample and the tip is enough to induce oxidation of the surface.Probably due to their greater applicability for nanolithography [11], modifications produced at positive sample voltages have been studied in more detail, and as a consequence a good understanding of the mechanism that produces them has been achieved. The dependencies of the dimensions of the modifications on the tunneling current [12], electrical field [13-16], tip-sample voltage or relative air humidity, and also the relationship between the threshold voltage for modification and substrate doping [15], indicate that the anodic modifications are produced by an anodization electrochemical reaction [17]. In contrast, the mechanism related to modifications at n...

Mechanism of laser-induced nanomodification on hydrogen-passivated Si(100) surfaces underneath the tip of a scanning tunneling microscope

“…Then, O Ϫ and OH Ϫ drift across the oxide layer under the influence of the high electric field produced by the voltage between the tip and the sample, increasing oxide thickness. 7,8 At positive sample-tip bias, which is in the regime of anodic oxidation, the electric field not only enhances OH Ϫ formation but also enhances the diffusion of OH Ϫ through the oxide layer. At negative sample-tip bias, which was in the regime of cathodic oxidation, the electric field only enhances the OH Ϫ formation.…”

Scanning tunnelling microscopy imaging and modification of hydrogen-passivated Ge(100) surfaces

“…4. The dependence of apparent depth on modification voltage This is because of the different mechanism for these two cases [24,25]. Modifications at positive sample voltages and negative sample voltages are due to anodic and cathodic oxidation, respectively.…”

Modifying single crystalline silicon by Tribo nanolithography for pulsed hybrid electrochemical nanolithography applications

“…Snow and co-workers [12,13] have shown the possibility of nano-patterning lines below 10nm in width using a metal tip as a tool. In addition, Perez-Murano and coworkers [14,15] have introduced nano-patterning process on Al-coated silicon wafer using a conductive AFM tip in electrochemical environment, and tried to apply this technique to the mass sensor on CMOS. Gwo et al [16,17] introduced the nano-scale SiO 2 fabrication process on Si and Volume 5 C 978-1-4244-5586-7/10/$26.00 2010 IEEE Si 3 N 4 wafer.…”