Local oxidation

Here, we focus on our recent work on the local oxidation of semiconductors and thin metal films under ambient conditions. The capability to oxidize metals and semiconductors with nanometer-scale resolution opens a variety of possibilities to improve current electronic devices such as field-effect transistors and allows the fabrication of novel electronic devices such as single-electron transistors.

The atomic-force microscope (AFM) image above gives an example where oxide lines of about 20 nm width were used to define the silicon dioxide pattern "IBM NANO" on a silicon wafer.

The AFM-tip induced oxidation process is based on negatively biasing the tip with respect to the substrate under ambient conditions, which can be either a semiconductor or a metal. The substrate locally oxidizes upon moving the tip in contact mode across the surface. The oxidant for the chemical reaction is provided by OH^- ions in the water droplet that is formed between the tip and the sample. Thus, the lateral resolution of the AFM oxidation process depends strongly on the humidity in the air. As an example, silicon dioxide lines have been written into silicon at two different humidities (see below). The lines written at 61% ambient humidity (left) are much wider than those formed at 14% (right).