Atomic-force lithography with interferometric tip-to-substrate position metrology

Inadequacies in lateral tip stability and registration presently limit lithographic applications of scanning probes. The authors describe a tool they constructed to write sub-10-nm features with 1 nm pattern registration. The tool utilizes an interferometric metrology technique called interferometric-spatial-phase imaging (ISPI) to continuously measure tip position relative to a substrate. Direct tip-to-substrate position measurement permits correction for the multitude of error sources encountered in the long mechanical path between a tip and a substrate. Experimental results indicate that the lateral tip position is stabilized by ISPI to 3 sigma=0.3 nm, and pattern placement accuracy in a two-dimensional (2D) grid array is 3 sigma=0.2 nm. According to ISPI measurements, 2D closed figures written in a polymer are overlaid to < 1 nm. Analysis of patterns written by the tip while under ISPI control provides an error bound that is in good agreement with the ISPI measurements. (c) 2007 American Vacuum Society.