Non-destructive spatial characterization of buried interfaces in multilayer stacks via two color picosecond acoustics

Abstract

We demonstrate the ability to construct wide-area spatial mappings of buried interfaces in thin film stacks in a non-destructive manner using two color picosecond acoustics. Along with the extraction of layer thicknesses and sound velocities from acoustic signals, the morphological information presented is a powerful demonstration of phonon imaging as a metrological tool. For a series of heterogeneous (polymer, metal, and semiconductor) thin film stacks that have been treated with a chemical procedure known to alter layer properties, the spatial mappings reveal changes to interior thicknesses and chemically modified surface features without the need to remove uppermost layers. These results compare well to atomic force microscopy scans showing that the technique provides a significant advantage to current characterization methods for industrially important device stacks.

Elastic and thermo-elastic characterizations of thin resin films using colored picosecond acoustics and spectroscopic ellipsometry

“…From compressive to extensive, the strain pulse then propagates back towards the substrate. The sign change of the strain pulse induces a reflectivity step, whose amplitude is sensitive to the laser wavelength [15,26]. This contribution allows us to measure the acoustic time-of-flight in the resin layer and to deduce its thickness from measured velocity.…”

“…This was recently used to investigate elastic properties [12] and the glass transition of ultra-thin PMMA films [13]. BO has also been used to investigate elastic properties of polymers [14,15].…”

Principles and advances in ultrafast photoacoustics; applications to imaging cell mechanics and to probing cell nanostructure

“…Ultrafast dynamics have mainly been studied in metals, semiconductor or dielectric materials used in sub-micrometric films, multilayered structures and other nanostructures. One major application field of ultrafast photoacoustics is the micro-electronics industry, which requires an accurate means of measuring thicknesses [5] , [6] , [7] and controlling bonding [8] , [9] , [10] , [11] and electron transport [12] at a nanometer scale, which the PU technique can provide.…”

Selective Excitation of Higher Harmonic Coherent Acoustic Phonons in a Graphite Nanofilm

“…Over the past decades, the study of femtosecond-laser-excited coherent acoustic phonons in the gigahertz to terahertz regime has attracted considerable interest and already led to the development of a wide range of applications as a versatile probing technique. In the field of picosecond ultrasonics for example, coherent strain waves excited in bulk material have been used to study the properties of buried nanostructures , and developments such as damage-free acoustic imaging of cells , or ultrafast magnetoacoustics , further demonstrate the exciting possibilities, while also underscoring the importance of the availability and development of tailored coherent acoustic phonon sources. Since the advent of two-dimensional van der Waals materials in the early 2000s, sparked by the development of the mechanical exfoliation technique (scotch tape method) , and the associated easy availability of high-quality single-crystal thin-film samples in a wide thickness range between tens of nanometers to atomic monolayers, the study of coherent acoustic phonons has also been extended to this class of materials.…”