Abstract
Surface patterning technologies represent a worldwide growing industry, creating smart surfaces and micro/nanoscale device. The advent of large-area, high-speed imprinting technologies has created an ever-growing need for rapid and non-destructive dimensional metrology techniques to keep pace with the speed of production. Here we present a new real-time optical scatterometry technique, applicable at the mesoscale when optical inspection produces multiple orders of diffraction. We validate this method by inspecting multiple silicon gratings with a variety of structural parameters. These measurements are cross-referenced with FIB, SEM and scanning stylus profilometry. Finally, we measure thermally imprinted structures as a function of imprinting temperature in order to demonstrate the method suitable for in-line quality control in nanoimprint lithography.
Highlights
Smart surfaces with nano- and micro- scale features find application in a wide variety of sectors in modern society: electronics[1], security[2], photonics[3], micro-optics, micro- fluidics[4] and biomedicine[5]
For micro-scale nanoimprint lithography (NIL) applications where multiple orders of diffraction exist, as is the case for diffractive optical elements or smart medical surfaces[5], we present a scatterometry method, advanced upon our previous work[28,29], which analyses the diffraction efficiency of all collected diffractive orders simultaneously and compares this data to a finite-difference frequency-domain (FDFD) EM library
The technique works on the principle that the optical diffraction pattern can be used to determine the unit cell critical dimensions via inverse problem-solving whereby an imaged diffraction pattern is compared to a theoretically computed library and a χ2 minimisation process is used to predict the www.nature.com/scientificreports structural parameters in real-time
Summary
Smart surfaces with nano- and micro- scale features find application in a wide variety of sectors in modern society: electronics[1], security[2], photonics[3], micro-optics, micro- fluidics[4] and biomedicine[5]. Traditional powerful CD technologies such as scanning electron microscopy (SEM) and atomic force microscopy (AFM) have serious drawbacks for such an application They are hard to insert into a production, comparatively slow, require precise alignment and are potentially destructive. For this reason, a variety of non-imaging optical technologies are used for inspection having the advantage of being fast and non-destructive. Scatterometry techniques use scattered light from a surface as a function of a variable such as angle-of-incidence or wavelength This surface scattering response is compared to a library of simulated data created by electromagnetic (EM) modelling techniques to fit the measured response to a computational prediction a method known as inverse problem solving. The aforementioned structural parameters for measurement are indicated along with the grating period, Λ, which remains constant in the simulations
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