Fundamental science and lithographic applications of scanning probe oxidation

Abstract

Local oxidation of metal, semiconductor, and insulating surfaces by a scanning probe microscope (SPM) is a promising approach for nanoelectronics device prototyping. Voltage applied between a conductive SPM tip and (positively biased) substrate, results in the formation of a highly non-uniform electric field. The electric field attracts a stable water meniscus to the tip-sample junction, creates oxyanions from water molecules, and transports these oxyanions through the growing oxide film. This leads to oxidation of the substrate on a scale determined by the dimensions of the water meniscus. Experimental studies have shown that almost every material oxidizes under the extremely high electric-field conditions at the tip-substrate junction, including some noble metals, diamond, and nitrides of silicon, titanium, and zirconium. This chapter organizes fundamental relationships between oxide volume growth, current flowduring exposure, and the resulting electrical and structural properties of the oxide. The underlying transport and reaction kinetics within the electrochemical nanocell is presented in a self-consistent manner in terms of dispersive kinetic theory through time-dependent rate constants. Key signatures of scanning probe oxidation, extreme simplicity and flexibility, become apparent when local oxidation is combined with standard device processing techniques. Nanodevices fabricated using this method include superconducting quantum interference devices, single-electron tunneling transistors, and antidote lattices in a wide variety of materials, such as titanium, Nb/NbN, GaAs/AlGaAs 2-D electron gas, SrTiO3, and SiGe thin films. Examples of some of these devices will be reviewed in terms of the kinetic and materials insights revealed by fundamental studies. © 2007 Springer Science+Business Media, LLC.