Quantitative secondary ion mass spectrometry imaging of self-assembled monolayer films for electron beam dose mapping in the environmental scanning electron microscope

Abstract

Fluorinated alkanethiol self-assembled monolayers (SAM) films immobilized on gold substrates have been used as electron-sensitive resists to map quantitatively the spatial distribution of the primary electron beam scattering in an environmental scanning electron microscope (ESEM). In this procedure, a series of electron dose standards are prepared by exposing a SAM film to electron bombardment in well-defined regions at different levels of electron dose. Microbeam secondary ion mass spectrometry (SIMS) using Cs+ bombardment is then used to image the F- secondary ion signal from these areas. From the reduction in F- intensity as a function of increasing electron dose, a calibration curve is generated that allows conversion of secondary ion signal to electron dose on a pixel-by-pixel basis. Using this calibration, electron dose images can be prepared that quantitatively map the electron scattering distribution in the ESEM with micrometer spatial resolution. The SIMS imaging technique may also be used to explore other aspects of electron-surface interactions in the ESEM.