5 research outputs found
Fe-Centers in GaN as Candidates for Spintronics Applications
ABSTRACT The potential use of Fe doped GaN for spintronics applications requires a complete understanding of the electronic structure of Fe in all of its charge states. To address these issues, a set of 400 µm thick freestanding HVPE grown GaN:Fe crystals with different Fe-concentration levels ranging from 5×1
Fast scatterometric measurement of periodic surface structures in plasma-etching processes
To satisfy the continuous demand of ever smaller feature sizes, plasma etching technologies in microelectronics processing enable the fabrication of device structures with dimensions in the nanometer range. In a typical plasma etching system a plasma phase of a selected etching gas is activated, thereby generating highly energetic and reactive gas species which ultimately etch the substrate surface. Such dry etching processes are highly complex and require careful adjustment of many process parameters to meet the high technology requirements on the structure geometry. In this context, real-time access of the structure's dimensions during the actual plasma process would be of great benefit by providing full dimension control and film integrity in real-time. In this paper, we evaluate the feasibility of reconstructing the etched dimensions with nanometer precision from reflectivity spectra of the etched surface, which are measured in real-time throughout the entire etch process. We develop and test a novel and fast reconstruction algorithm, using experimental reflection spectra taken about every second during the etch process of a periodic 2D model structure etched into a silicon substrate. Unfortunately, the numerical simulation of the reflectivity by Maxwell solvers is time consuming since it requires separate time-harmonic computations for each wavelength of the spectrum. To reduce the computing time, we propose that a library of spectra should be generated before the etching process. Each spectrum should correspond to a vector of geometry parameters s.t. the vector components scan the possible range of parameter values for the geometrical dimensions. We demonstrate that by replacing the numerically simulated spectra in the reconstruction algorithm by spectra interpolated from the library, it is possible to compute the geometry parameters in times less than a second. Finally, to also reduce memory size and computing time for the library, we reduce the scanning of the parameter values to a sparse grid
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Fast scatterometric measurement of periodic surface structures plasma-etching processes
To satisfy the continuous demand of ever smaller feature sizes, plasma
etching technologies in microelectronics processing enable the fabrication of
device structures with dimensions in the nanometer range. In a typical plasma
etching system a plasma phase of a selected etching gas is activated, thereby
generating highly energetic and reactive gas species which ultimately etch
the substrate surface. Such dry etching processes are highly complex and
require careful adjustment of many process parameters to meet the high
technology requirements on the structure geometry. In this context, real-time
access of the structures dimensions during the actual plasma process would be
of great benefit by providing full dimension control and film integrity in
real-time. In this paper, we evaluate the feasibility of reconstructing the
etched dimensions with nanometer precision from reflectivity spectra of the
etched surface, which are measured in real-time throughout the entire etch
process. We develop and test a novel and fast reconstruction algorithm, using
experimental reflection spectra taken about every second during the etch
process of a periodic 2D model structure etched into a silicon substrate.
Unfortunately, the numerical simulation of the reflectivity by Maxwell
solvers is time consuming since it requires separate time-harmonic
computations for each wavelength of the spectrum. To reduce the computing
time, we propose that a library of spectra should be generated before the
etching process. Each spectrum should correspond to a vector of geometry
parameters s.t. the vector components scan the possible range of parameter
values for the geometrical dimensions. We demonstrate that by replacing the
numerically simulated spectra in the reconstruction algorithm by spectra
interpolated from the library, it is possible to compute the geometry
parameters in times less than a second. Finally, to also reduce memory size
and computing time for the library, we reduce the scanning of the parameter
values to a sparse grid
Lithium related deep and shallow acceptors in Li-doped ZnO nanocrystals
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Applied Physics 107, 024311 (2010) and may be found at https://doi.org/10.1063/1.3275889.We study the existence of Li-related shallow and deep acceptor levels in Li-doped ZnO nanocrystals using electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. ZnO nanocrystals with adjustable Li concentrations between 0% and 12% have been prepared using organometallic precursors and show a significant lowering of the Fermi energy upon doping. The deep Li acceptor with an acceptor energy of 800 meV could be identified in both EPR and PL measurements and is responsible for the yellow luminescence at 2.2 eV. Additionally, a shallow acceptor state at 150 meV above the valence band maximum is made responsible for the observed donor-acceptor pair and free electron-acceptor transitions at 3.235 and 3.301 eV, possibly stemming from the formation of Li-related defect complexes acting as acceptors.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement
Fast scatterometric measurement of periodic surface structures in plasma-etching processes
To satisfy the continuous demand of ever smaller feature sizes, plasma etching technologies in microelectronics enable the fabrication of device structures in the nanometer range. To control these processes, real-time access to the structure’s dimensions is needed. We develop a special method of optical critical dimension metrology and evaluate the feasibility of reconstructing the etched dimensions from experimental reflectivity spectra of the surface, taken about every second. For a periodic 2D model structure etched into a silicon, we develop and test a fast algorithm.
To reduce the computing time, we generate a library of spectra before the etching. We demonstrate that, by replacing the numerically simulated spectra in the reconstruction algorithm by spectra interpolated from the library, it is possible to compute the geometry parameters in times less than a second. Finally, to also reduce memory size and computing time for the library, we reduce the scanning of the parameter values to a sparse grid