High Resolution Patterning with the STM

Abstract

The use of low energy electrons for e-beam lithography in radiation sensitive materials is of interest because the detrimental effects of electron scattering can be eliminated. The scanning tunneling microscope (STM) is a convenient way to produce such electrons in a spatially localized beam. The STM has proved to be a valuable probe of resist materials and a viable method of lithography for high resolution patterning of semiconductor substrates. Thin layers of commercially available resist materials have been patterned and the patterns transferred into a substrate with a reactive ion etch. The absence of electron scattering is evidenced by the elimination of proximity effects and an improvement in resolution over that obtained with a tightly focussed 50 kV e-beam in identically prepared and processed resist films. Preliminary studies are also reported of STM lithography of ultrathin resists formed by self assembly techniques. The use of such thin films promises to increase further the resolution capability of STM based lithography. Issues related to the implementation of a low voltage lithography tool are discussed. A single tip instrument built with a fast STM like scanner appears viable for small scale nanolithography whereas a multiple tip approach is required for applications where throughput is an issue.