Positive charge effect in atomic force microscope anodization lithography using self-assembled monolayers of metal phosphate as resists

Abstract

Various metal phosphate monolayers prepared as resists on silicon substrates were prepared for atomic force microscope (AFM) anodization lithography. The metal phosphate monolayers were prepared by binding tetravalent (Zr4+, Hf4+) or divalent (Ca2+, Mg2+) metal ions on a phosphorylated Si substrate. The presence of the metal ions on a phosphorylated Si substrate was confirmed using Auger electron spectroscopy. Since the divalent and tetravalent metal ions are changed to be neutral and divalent, respectively, after binding on phosphorylated substrates, the role of a positive ion in the monolayer structure in AFM anodization lithography was systematically investigated. The presence of positively charged metal ions in case of Zr4+ and Hf4+ enhances the electron transfer from a tip to a substrate under a tip negative bias. In addition to the effect of lowering a bias for anodization process, the lithographic scan speed was also enhanced by the order of magnitude in the presence of the positive ions. After patterning of protruding lines on Zr2+ phosphate monolayer, the etching process was also accomplished.