Identification of sub-20 nm EUV defects with nano-IR PiFM

Abstract

With the advent of 45nm and below technology nodes and EUV lithography, the need to identify the chemical composition of defects is of paramount importance. The defects of concern range from 10nm to 500nm, which the current batch of molecular analytical tools cannot address adequately since the indications are that most of the defects detected on photomasks are organic in nature. In this paper, a relatively new nanoscale technique called infrared photoinduced force microscopy (IR PiFM), which combines atomic force microscopy (AFM) and infrared (IR) spectroscopy with ~ 5 nm spatial resolution, is introduced. By utilizing a state-of-the-art tunable broadband IR laser (tunable from ~550 to < 4000 cm^-1 with ~ 3 cm^-1 spectral width over the entire range), truly nanoscale PiF-IR spectra that agree with bulk FTIR spectra can be acquired; PiF-IR spectra can be used to search the existing IR database to unambiguously identify the different chemical species (both organic and inorganic molecules) of sub-20 nm defects and monolayer residues via their IR signatures. PiFM images at fixed wavenumbers associated with the different chemical species provide chemical mapping in real space with ~ 5 nm spatial resolution, clearly illuminating multi-component defects and existence of residues. The paper will show how the nanoscale hyperspectral PiFM data can provide unambiguous and speedy feedback to process engineers engaged in advanced lithography.