Full-field and contact-less topography of nanometric thin films based on multiwavelength interferometry

Abstract

This paper discusses a method to measure the thickness of thin layers deposited on a reflective substrate. A Michelson type interferometer with three wavelengths produces color interferences. A color sensor records the tint that is produced. The color interferences are approximated by a model based on the measurement of the laser intensities obtained with the reference mirror only. An iterative process leads to unambiguous algorithmic convergence and high accuracy thickness measurement. This method is simple, robust, compact, and single shot. The method does not need for angular scanning over the field of measurement (about 75mm 2 ). The measurement on the surface yields a histogram of the thickness distribution and there is no requirement for any reference points (e.g. no need to make a groove or a walk on the layer). A thickness measurement performance of 50nm was demonstrated for homogenous polymer films deposited on silicon wafer. Set-up and digital image processing are discussed.

Alternative Strategy Based on Scanning Probe Lithography for Patterning Complex Metallic Nanostrutures on Rigid or Flexible Substrates

“…After deposition, the films were dried under vacuum for 2 h at 50 °C . Detailed procedure for film deposition is described elsewhere …”

“…As illustrated in Figure , the proposed fabrication process can be divided into four main steps: spin‐coating, SPL, gold deposition, and transfer. The first step consists of depositing a flat poly(methyl)methacrylate (PMMA) thin film of several hundred nanometers on a silicon substrate using the widely described spin‐casting method . The desired micro–nano patterns are engraved into the PMMA layer by the AFM tip with a controlled load force.…”

“…With SPL, since the indentation depth depends on the mechanical properties of the material and on the applied load, the structure heights of the metallic structures can be monitored with a nanometer resolution . As an example, various nanothick gold squares with differents heights (14 and 19 nm) were created on silicon substrate ( Figure a) in order to obtain a height reference sample for the calibration of optical metrology techniques …”

Multi-colour microscopic interferometry for optical metrology and imaging applications

“…The high frequency of the fringes sets a limitation due to speckle de-correlation for quantitative analysis, (iii) it cannot reveal the shape of a rough surface, (iv) it cannot resolve the discontinuities between polished and unpolished surfaces. The approaches adopted to overcome the problems associated with single-wavelength are based on scanning white light interferometry [33][34][35], spectrally resolved white light interferometry [36][37][38][39] and multiple-wavelength interferometry [17,[40][41][42][43][44][45][46].…”