Effects of molecular structure and interfacial ligation on the precision of Cu-bound alpha,omega-mercaptoalkanoic acid "molecular ruler" stacks.

Nanolithography processes based on designed, precision thickness multilayer thin films (molecular rulers) have been reported that enable patterning of features on surfaces from a few to the hundred nanometer range. These strategies are unique in their potential ability to enable wafer scale patterning of features of just a few nanometers. If these techniques could be developed to be sufficiently precise and generally applicable, they would fill a long-standing need in nanoscience. In this study a systematic and detailed analysis of the growth mechanisms and molecular layer structures has been carried out for the mercaptoalkanoic acid-copper ion multilayer thin film system currently used as the standard nanolithography resist. Our results show these films form via a redox reaction of thiol groups with surface-ligated Cu(II) ions to form adlayers at only approximately 50% coverage with islanding of the alkyl chains, thereby leading to rough topographies and less than theoretical thicknesses based on a 1:1 ideal adlayer. Strategies are suggested to help overcome these issues for molecular resist applications in nanolithographic processing.