A metrology approach to detect nanoscale asymmetries in structures on a silicon wafer is being introduced through simulation investigations. The simulations were performed based on a rigorous coupled-wave analysis. A structured spot focused on the wafer with a high-numerical aperture (NA=0.7) has been scanned over the wafer. Having access to the complex amplitude of the wavefront over the field, both the intensity and the phase profile of the spot have been investigated in the far-field image plane. To show the proof of concept, we considered a 10-nm asymmetry that appears in the radius of the bottom roundings of a trench on the wafer. The results have been compared to the case of using a conventional spot and it has been shown that the structured illumination provides more sensitivity to the presence of asymmetry. In both illumination cases, the phase distribution along the spot was shown to be more sensitive to the changes due to the presence of asymmetry in the wafer.
Scatterometry is a well-established optical metrology method used in research as well as in industrial applications to
precisely characterize small structures. The method is based on a comparison of the measured scattered light field to the
rigorously simulated scattered light field based on a model of the real structure. Although in recent time this method has
been steadily improved and extended to characterize structures down to sub-lambda size, the sensitivity towards the
parameters of interest is generally decreasing for smaller structures, which makes the characterization more and more
difficult. Opposed to other efforts based on changing the measurement configuration or combining different
measurement methods, we have chosen to address the fundamental cause of this loose of information: As known from
theory the electromagnetic near field is directly dominated by currents and charge-separations in the illuminated
structure, while the far field is produced by its corresponding near field and is not directly linked to the charges and
currents induced in the structure. For that reason the transition from the near field to the far field, which is accessible in
a scatterometric measurement, causes information loss about the structure. In our approach we directly influence the near
field with the introduction of additional structures in the direct vicinity of the sub-lambda grating to be characterized.
With rigorous electromagnetic simulations we optimize the design of these near field structures to increase the
information content of the scatterometric signatures which can be detected in the far field region. We show the
optimization of scatterometric signatures for a silicon line grating and compare the gain of information obtained by the
near field design. Understanding the influence of the near field on the scatterometric signatures can help to address the increasing demand on quality management caused by the constant miniaturization in industrial applications.
Recently Fourier-Scatterometry has become of increasing interest for quantitative wafer metrology. But also in other
fields the fast and precise optical characterization of periodical gratings of sub 100 nm size is of great interest. We
present the application of Fourier-Scatterometry, extended by the use of the coherent properties of white light for the
characterization of sub-wavelength periodic gratings of photosensitive material structured by two-photon polymerization.
First a simulation-based sensitivity comparison of Fourier-Scatterometry at one fixed wavelength, Fourier-Scatterometry
using a white light light source and also additionally using a reference-branch for white-light-interference has been
carried out. The investigated structures include gratings produced by two-photon polymerization of photosensitive
material and typical semiconductor test gratings. The simulations were performed using the rigorous-coupled-waveanalysis
included in our software package MicroSim. A sensitivity comparison between both methods is presented for
the mentioned structure types. We also show our experimental implementation of the measurement setup using a whitelight-
laser and a modified microscope with a high-NA (NA: 0.95) objective as well as a Linnik-type reference branch
for the phase sensitive measurements. First measurements for the investigation of the performance of this measurement
setup are presented for comparison with the simulation results.
Proc. SPIE. 7271, Alternative Lithographic Technologies
KEYWORDS: Lithography, Electron beams, Metrology, Cadmium, Scatterometry, Line width roughness, Critical dimension metrology, Line edge roughness, Electron beam direct write lithography, Semiconducting wafers
Electron beam direct write (EBDW) can be utilized for developing metrology methods for future technology nodes. Due
to its advantage of high resolution and flexibility combined with suitable throughput capability, variable-shaped E-Beam lithography is the appropriate method to fabricate sub 40nm resist structures with accurately defined properties, such as critical dimension (CD), pitch, line edge roughness (LER) and line width roughness (LWR). In this study we present results of exposure experiments intended to serve as an important instrument for testing and fitting various metrology
and defect density measurement methods for future technology nodes. We successfully fabricated sub 40nm gratings with varying CD, pitch, programmed defects and LER/LWR. First metrology measurements by means of optical scatterometry on these dense structures show that variation of the signal response is sufficient to detect sub 10nm fluctuations with a satisfying repeatability.