In-process measuring procedure for sub-100 nm structures

Abstract

Fast and nondestructive laser light scattering measurements characterize the quality of surfaces with sub-100 nm structures during the production process. The aim is to detect defective surface structures. The measurement procedure is based on a primary comparison of measured speckle patterns with a multitude of numerically calculated speckle patterns caused by defect-free and defective surface structures. The comparison shows characteristic light scattering effects, which have to be detected by the in-process measurement setup. An efficient rigorous algorithm, implemented on a graphics processing unit, calculates the scattered light intensity distributions within reasonable computing times. The measurements are performed with an angle resolved light scattering measurement setup. The measuring procedure is applied to zinc oxide nanograss surfaces.

Scatterometric defect measurements – uncertainty assessment by means of a virtual instrument and a statistical analysis

“…An analytical study on light scattering from micrometer range surfaces showed that the out-ofplane scattering signatures of particulate contamination, subsurface defect, and surface microroughness differ significantly [18]. Another study on the scatterometric defect evaluation of ZnO nanograss surface compared numerical simulation results with experimental results from two different setups [10]. This demonstrated that a numerical simulation of modelled nanostructures having randomized spatial distributions, which are approximated from real samples, yields qualitatively similar light scattering results to that of the experiments.…”

“…the evaluation of scattered light, that works fast, non-invasive and is applicable also inprocess, has the potential to meet the time resolution and robustness requirements of a mass production line. It analyses the intensity distribution of laser light scattered from surfaces, in order to retrieve topography information, including structural defects [10,11].…”

“…For scatterometric measurements of nano-surfaces with randomly distributed structures or stochastic defects, the solution of the inverse problem becomes much more complicated because of the lack of clearly distinguishable light diffraction patterns [10]. Due to the fact that these nano-surfaces have a stochastic nature in terms of nanostructure element shape and/or the elements' distribution, there exist several surfaces with a different topography for a specific statistical feature value such as a defect grade.…”

“…The dipole size is chosen as 20 nm in the virtual samples used in this study. The discretization process and model specifications including dipole size have been previously used in other publications [10,11,23]. In the previous studies, using ZnO nanograss samples with similar dimension specifications, the appropriate dipole size according to the sample's edge length had been tested [23].…”

Advances in ultrafast laser structuring of materials at the nanoscale

“…A plethora of thermomechanical effects were indicated with the emergence of pressure waves [132] in the aftermath of plasma relaxation close to microexplosion conditions [133]. Alternative methods are based on scattering and diffraction techniques with capabilities to observe nanoscale structures, as first applied on surfaces [134,135]. Direct diffraction techniques were used either to steer open optimization loops on bulk nanogratings [136] or to detect the dynamic onset of a diffractive response of laserinduced regular structures [137].…”