Proc. SPIE. 7272, Metrology, Inspection, and Process Control for Microlithography XXIII
KEYWORDS: Electron beams, Edge detection, Electron microscopes, Feature extraction, Atomic force microscopy, Scanning electron microscopy, 3D metrology, Atomic force microscope, Line edge roughness, 3D image processing
Emerging three-dimensional (3D) transistor structures have increased the demand for an easy and practical method to
measure pattern feature metrics (such as CD, line-edge roughness, etc.) as a function of height (z coordinate). We have
examined 3D pattern-profile extraction from a top-view image obtained using a critical-dimension scanning electron
microscope (CD-SEM). An atomic force microscope (AFM) was used to measure 3D pattern profiles as a reference. In
this examination, line-edge positions were firstly obtained from a CD-SEM image at various threshold levels, and the
result was compared with the reference profile measured using the AFM. From this comparison, a mapping function
from threshold levels of CD-SEM image-processing to z coordinates is obtained. Using this mapping function, 3D
pattern profiles were reconstructed from CD-SEM signal profiles, and the obtained profiles were similar to the directly
obtained cross-sectional profile. Put simply, a 3D pattern-profile was extracted from a top-view image successfully.
Though the results are not sufficient to confirm the validity of our method yet, the method may feasibly be introduced
for quick and easy 3D measurement.
We have developed a new measurement techniques employing digital probing with AFM (Atomic Force
Microscope) that can examine sidewalls of fine patterns. This new technique employs digital probing operations, such
sample-tilt step-in operation, tilt-step-in operation with a sharpened tilted tip, and multi-angle step-in operation with a
flared tip. First, we examined the validity of digital probing operation using a carbon nanotube (CNT) tip, showing the
measurement repeatability of approximately 1 nm (3σ) on a fine trench pattern with 50 nm width and 300 nm depth.
After the slip calculation between the tilted-tip and the sidewall for the new sidewall measurement technique, we
measured a perpendicular reference sidewall with two types of operations, namely, tilt-step-in and multi-angle step-in
operations. We then obtained 3D images of ArF resist patterns that involved measurement of sidewall surface
roughness. Finally, we demonstrated a possibility of extending the technique for measuring denser trench patterns by
using sample-tilt method and a tilted CNT tip.
A critical-dimension atomic force microscope system equipped with an ultra-high resolution, three-axis laser interferometer was constructed and tested. The MIRAI (Millennium Research for Advanced Information Technology) project has been improving the precision of critical dimension measurements with atomic force microscopy (AFM) by implementing modularized laser interferometers, to meet requirements for dimensional measurement in 45 nm technology node. The stability of the cross-sectional profile of an AFM image for a rectangular cross-section was greatly improved by optimizing interferometer linearity and resolution with DSP signal processing and reducing the angular motion and mechanical vibration of the monolithic three-dimensional probe scanner with a unique parallel spring mechanism. The repeatability of linewidth measurement of a nominal 100 nm linewidth along the same scanned line showed a standard deviation of 0.5-1.0 nm (3-sigma). This shows AFM to be one of the most promising metrological tools for next-generation nanodevice fabrication processes. Instrumentation, measurement results, and precision will be discussed.