Fabrication of a gold pattern with a nanoscale edge by using heptanethiol self-assembled monolayers and a metastable helium beam

By exposure to a metastable helium beam, latent images of the patterns were formed in the heptanethiol (HT) self-assembled monolayer (SAM) resists on Au(1 1 1) films, and then the patterns were transferred to the underlying gold films by wet chemical etching. Negative patterns, as well as positive patterns with lower doses, were fabricated with higher exposures to a metastable-atom beam. The smallest width of edge, ∼40 nm, among alkanethiol SAM resists was achieved in the condition of negative pattern formation. According to the metastable-atom-stimulated desorption (MSD) measurement of alkanethiol SAMs on Au(1 1 1), the SAMs were damaged under the irradiation of metastable-atom beam losing either H atoms or CH3 groups. Thus, the highly concentrated energy deposition by a metastable-atom beam, which induced crosslinking of the main molecular chain in the SAM resists and increased the resistance to etching, could lead to the negative pattern formation at higher doses.