Direct detection of polystyrene equivalent nanoparticles with a diameter of 21 nm (∼λ/19) using coherent Fourier scatterometry.

D Kolenov,R C Horsten,I E Zadeh,S F Pereira

doi:10.1364/oe.421145

Abstract

Coherent Fourier scatterometry (CFS) has been introduced to fulfil the need for noninvasive and sensitive inspection of subwavelength nanoparticles in the far field. The technique is based on detecting the scattering of coherent light when it is focused on isolated nanoparticles. In the present work, we describe the results of an experimental study aimed at establishing the actual detection limits of the technique, namely the smallest particle that could be detected with our system. The assessment for particles with a diameter smaller than 40 nm is carried out using calibrated nano-pillars of photoresist on silicon wafers that have been fabricated with e-beam lithography. We demonstrate the detection of polystyrene equivalent nanoparticles of diameter of 21 nm with a signal-to-noise ratio of 4 dB using the illuminating wavelength of 405 nm.

Highlights

Large scale integrated circuits [1,2], neuromorphic computing [3], bio-sensing monitoring [4], optical networks [5] and optical image processing [6] require the fabrication and associated metrology to be done at the nanoscale
The technique is based on detecting the scattering of coherent light when it is focused on isolated nanoparticles
We describe the results of an experimental study aimed at establishing the actual detection limits of the technique, namely the smallest particle that could be detected with our system

Summary

Introduction

Large scale integrated circuits [1,2], neuromorphic computing [3], bio-sensing monitoring [4], optical networks [5] and optical image processing [6] require the fabrication and associated metrology to be done at the nanoscale. Coherent Fourier Scatterometry (CFS) had been suggested as a metrology technique for high-accuracy retrieval of shape parameters of periodic gratings [10,11]. The field that is reflected from the surface is collected by the same focusing lens and directed to a split photodetector, where a differential photocurrent value is obtained point per point of the scan. This scheme allows the use of low power lasers (as compared to darkfield techniques) and is suitable for detection of low optical contrast subwavelength nanoparticles. One can determine the position of the particles with high accuracy as well as classify their sizes.

Methods

Results

Conclusion