UHV STM nanofabrication: progress, technology spin-offs, and challenges

A brief review of scanned probe nanofabrication is presented followed by an in-depth discussion of ultrahigh vacuum (UHV) scanning tunneling microscope (STM) nanofabrication on hydrogen passivated silicon surfaces. In this latter case the UHV STM functions as a nanolithography tool by selectively desorbing hydrogen from silicon surfaces. Patterns of clean Si, down to atomic dimensions, are achieved as well as detailed information about the H-desorption mechanisms. At higher sample voltages direct electron stimulated desorption occurs, whereas, at lower voltages, vibrational heating of the Si-H bond leads to desorption. The chemical contrast between clean and H-passivated silicon enables a wide variety of spatially selective nanoscale chemical reactions. Results are presented in which these templates are used for selective oxidation, nitridation, and metallization by chemical vapor deposition. An unexpected byproduct of this research was the discovery that deuterium is about two orders of magnitude more difficult to desorb from silicon than hydrogen. This served as the basis for the idea of treating CMOS transistors with deuterium to reduce their susceptibility to hot carrier degradation effects. Tests have now shown that the lifetimes of CMOS transistors increase by factors of 10 to 50 when deuterium treatment is substituted for the traditional hydrogen processing.