The physical dimensions of nanoscale objects are an important indicator of their functionality. However, measuring
feature size from a SEM image is difficult not only because of fundamental considerations, such as the nature of beam
interactions and the information transfer properties of the microscope, but because the magnification of the SEM image
from which a measurement will be made is completely uncalibrated and additionally is subject to local distortions and
variations. Nano-gauges fabricated by electron beam lithography - one or two dimensional structures on the size scale of
the objects of interest - provide a local length standards within the image field from which the relative size of features
can be accurately determined. In order to provide an absolute measurement of size the dimensions of the nano-gauge
structure must themselves be calibrated against some primary standard. Because there are no convenient standards of
appropriate scale available we propose that this can be done using a moiré fringe technique to bridge the gap between the
nanoscale and common length standards such as ruled diffraction gratings.
With the semiconductor industry moving into the 65nm technology node, the metrology of the critical dimension (CD)
becomes an important part for the industry. Metrology relies not only on the precision, but also on the accuracy of the
tools like the high performance CD-SEMs. A major area of concern affecting the accuracy of the high performance CD-SEMs
is the magnification calibration. The purpose of the research is to address this area of concern by fabrication of
magnification calibration artifact by using direct write electron beam lithography. A calibration artifact has been
fabricated in negative resist Hydrogen Silsesquioxane (HSQ) onto a silicon substrate, thereby decreasing the
contamination on the substrate. The design of the artifact has been corrected for the proximity effects, giving a 2-D dense
grid structure with 100nm pitch. Pitch determination using optical metrology tools and the inbuilt laser interferometer in
the electron beam lithography tool is being evaluated for making the artifact traceable to some national standards. Once
the traceability is achieved, mass production at low cost using Nanoimprint technology is feasible.
Proc. SPIE. 6152, Metrology, Inspection, and Process Control for Microlithography XX
KEYWORDS: Signal to noise ratio, Electron beam lithography, Fourier transforms, Image resolution, Interference (communication), Image analysis, Scanning electron microscopy, Image enhancement, Spatial resolution, Zone plates
It is important to be able to quantify the imaging performance of CD-SEMs for such purposes as verifying the specification, rechecking after a routine maintenance, or for tool matching. To perform tests such as these it is necessary to have both appropriate software for image analysis and suitable test samples. A package of 2-D Fourier transform and analysis software, designed as a plug-in for the shareware IMAGE-Java program, has been developed and is freely available on line. The requirement for a reproducible and well characterized sample has been met by using direct-write electron beam lithography to fabricate suitable Fresnel zone plate structures.