New results for dimensional measurements of nanostructures obtained using the method of defocusing of the SEM electron probe are presented. The method is extended to nanostructures representing the protrusions of the trapezoidal form with the small size of the top base and the features (protrusions and trenches) with nearly vertical sidewalls. It is also shown that the method can be applied for measurements of geometric parameters of features located on resist masks as well as of individual nanoparticles.
KEYWORDS: Oxides, Silicon, Transmission electron microscopy, Crystals, Calibration, Chemical elements, Distance measurement, Temperature metrology, Electron microscopes, Phosphorus
The study was performed on a test step relief structure of monocrystalline silicon. There was experimentally measured the thickness of the natural oxide on this structure consisting of a set of elements (protrusions) with a trapezoidal profile and 2.0 μm step size, upper base about 10 nm, height about 500 nm. The tilt angle of side face with respect to the lower base was 54.7°. The entire structure was covered with a natural oxide film that appeared at room temperature, the thickness of which is being measured using a transmission electron microscope with atomic resolution by the observed pattern in the direct mode resolution of the crystal structure. In order to calibrate the measurements a distance between {111} planes was used. It was shown experimentally, that in the area of this bottom the natural oxide thickness increases from 2.3 ± 0.2 nm in the middle of the bottom to 3.0 ± 0.2 nm and 4.5 ± 0.2 nm at the left and right edges of the bottom, respectively.
KEYWORDS: Calibration, Electron microscopes, Silicon, Transmission electron microscopy, Scanning electron microscopy, Crystals, Ions, Silica, Scanning transmission electron microscopy, Carbon
We propose a new type of reference material as a magnification standard of transmission electron microscope and a
scanning transmission electron microscope. The reference material represents a thin cross-section of a silicon relief
structure with certified sizes of its elements. It is fabricated using ion milling. Such reference material can be used for
high microscope magnifications (by direct observation of the lattice), as well as for moderate magnifications (around
30,000 times).
We consider features and restrictions of ellipsometry as applied to the system consisting of a silicon dioxide film on
silicon, which is widely used in nanoelectronics. A method is developed for ellipsometric determination of the presence
or absence of the "film-substrate" interfacial layer. Contributions of various factors into the total measurement
uncertainty are analyzed, including the factors related to the ellipsometer characteristics.
KEYWORDS: Scanning electron microscopy, Calibration, Electron beams, Atomic force microscopy, Stereolithography, Microscopes, Silicon, Solids, Electron microscopes, Atomic force microscope
Test objects for calibration of scanning electron microscopes (SEMs) and atomic force microscopes (AFMs) operating in
the nanometer range are analyzed. All the test objects can be divided into three groups: (a) structures with right-angled
profiles; (b,c) structures with trapezoidal profiles and small/large angles of sidewalls inclination. Calibration methods for
SEMs and AFMs, based on such structures, are presented. Structures with trapezoidal profiles and large angles of
sidewall inclination offer the most broad range of calibration opportunities for SEMs and AFMs.
We are describing a method of measuring thickness of a native silicon dioxide film using a scanning electron
microscope. The method consists of etch removal of native silicon dioxide from the surface of trenches in silicon with a
right-angled profile, with a subsequent measurement of an increase in trench width. The thickness of a native silicon
dioxide film measured with the help of this method turned out to be 2.39 ± 0.12 nm.
KEYWORDS: Scanning electron microscopy, Atomic force microscopy, Calibration, Interferometry, 3D imaging standards, Stereolithography, 3D metrology, Crystals, Standards development, Dimensional metrology
We discuss the formation of the system of nanoscale dimensional measurements in Russia. The traceability of the
nanoscale measurements to the primary standard of the unit of length (the meter) is shown. Russian state standards that
provide the standardization basis for such dimensional measurements are discussed.
Two types of test objects for automated measurements of critical dimensions with scanning electron microscopes
(SEMs) are described. The first type can be used for SEM calibration along two coordinates in a wide range of
magnifications (to perform dimensional measurements in the range from 10 nm to 100 μm without making
recalibration), including determination of the electron beam diameter. The second type is recommended for embedding
into the integrated circuits (ICs) to monitor the focusing of the SEM electron beam in the course of dimensional
measurements of IC elements. Measurement and monitoring of the SEM magnification and electron beam diameter is
necessary to measure the linewidth (the sizes of the upper and lower bases of the IC trapezoidal relief elements) in the
nanometer range.
KEYWORDS: Calibration, Scanning electron microscopy, Atomic force microscopy, Standards development, Nanotechnology, Microscopes, Metrology, Atomic force microscope, Electron microscopes, Video
In order to provide the uniformity of measurements at the nanoscale, seven national standards have been developed in
the Russian Federation. Of these seven standards, three standards specify the procedures of fabrication and certification
of linear measures with the linewidth lying in the nanometer range. The other four standards specify the procedures of
verification and calibration of customer's atomic force microscopes and scanning electron microscopes, intended to
perform measurements of linear dimensions of relief nanostructures. For an atomic force microscope, the following four
parameters can be deduced: scale factor for the video signal, effective radius of the cantilever tip, scale factor for the
vertical axis of the microscope, relative deflection of the microscope's Z-scanner from the orthogonality to the plane of a
sample surface. For a scanning electron microscope, the following two parameters can be deduced: scale factor for the
video signal and the effective diameter of the electron beam. The standards came into force in 2008.
KEYWORDS: Scanning electron microscopy, Silicon, Photomasks, Electron microscopes, Integrated circuits, Nanostructures, Electron beams, Etching, Sensors, Atomic force microscopy
We studied the effect of focusing of the electron probe of a scanning electron microscope (SEM), operating in the mode
of collection of slow secondary electrons, on the form of a signal obtained when scanning elements of nanorelief of two
kinds of objects with electron probe: (a) resist masks, and (b) protrusions and trenches on silicon. The shift of the
positions of the points of reference, the distance between which is usually used to determine the size of the relief
elements, was observed. The linear dependence of such distance on the size of the electron probe was found. We
propose a method to measure the width of the nanorelief element, based on the extrapolation of this linear dependence to
the zeroth size of the electron probe. With the help of this method, we measured the widths of nanorelief elements of
resist masks, as well as of protrusions and trenches on silicon.
We propose a method of calibration of a scanning electron microscope (SEM) in a wide range of magnifications. We
also describe a method of SEM measurements of linear dimensions of relief elements of micro- and nanostructures
without performing a special calibration of SEM magnification, which can lie in a wide range. The methods are based on
the use of the marker of the SEM as a measure of length. In order to do it, the marker has to be certified in special
experiments. We present a method for such certification, based on the use of a test object of trapezoidal profile and large
angles of sidewall inclination. We studied the dependence of the marker characteristics on the SEM working distance
and the nominal marker size declared by the microscope manufacturer. We determined periodicity of performing marker
calibration for the SEM being used. The methods are developed for the calibration of SEMs incorporated into the
integrated circuit production line, whose magnification may vary considerably in the course of operation, depending on
dimensions to be measured.
Comparison is made for parameters and properties of test objects based on the relief structures with right-angled and
trapezoidal profiles, which are used for calibration of scanning electron microscopes (SEMs) and atomic force
microscopes (AFMs). Methods of calibration of SEMs and AFMs with help of this test objects are presented.
Comparative analysis has shown that trapezoidal structures with large angles of sidewall inclination, created by
anisotropic etching of silicon with the (100) orientation of its surface, possess the most universal characteristics. Such
structures could be used for development of internationally recognized measures of length in the nanometer range for
calibration of SEMs and AFMs.
A method for objective monitoring of the quality of fabrication of test objects with a trapezoidal profile and large angles
of inclination of the sidewalls is proposed. The test objects are created by anisotropic etching of silicon. The method is
based on the correlation analysis of the results of experiments performed with scanning electron microscopes (SEMs)
and atomic force microscopes (AFMs). In the course of such analysis, coefficients of correlation between the test points
on the SEM or AFM signals are calculated. These points correspond to the coordinates of the upper and lower bases of
trapezoidal protrusions of a test object structure. The closeness of the correlation coefficients to unity is indication of
high quality of the created test object.
Results of investigations in the field of measurements of geometrical characteristics of the electron beam of a scanning
electron microscope (SEM) are presented. Methods for determining the electron beam diameter are developed and tested
on various microscopes. Besides, methods for obtaining the dependence of the electron beam diameter on the beam
current, the energy of the primary electrons, and the focusing of the beam are also developed. Finally, method for
determining the electron density distribution in the electron beam is proposed.
KEYWORDS: Scanning electron microscopy, Atomic force microscopy, Calibration, Silicon, Electron beams, Atomic force microscope, Electron microscopes, Anisotropic etching, Crystals, Video
The results of the study of a test object on scanning electron microscopes and atomic force microscopes are presented.
The test object presents a relief on a monosilicon surface, and it is fabricated by the anisotropic etching of monosilicon.
The relief elements have a trapezoidal profile with large angles of inclination of the sidewalls. The sides of the relief
elements coincide with the crystallographic planes {100} and {111} of silicon. The test object is intended for calibration
of scanning electron microscopes and atomic force microscopes.
The results of the study of image formation in atomic force microscope (AFM) are presented. Effects of the radius and
the angular characteristics of the cantilever tip, as well as of the relief of the surface being studied, on the signal shape
are discussed. Methods of AFM calibration, including the calibration of all three scales with the use of only one certified
size of a test object and the measurement of the cantilever tip radius, are presented. Formulas are obtained that relate the
sizes of trapezoidal structures to the sizes of the control intervals chosen in the AFM signals.
KEYWORDS: Scanning electron microscopy, Electron beams, Calibration, Electron microscopes, Microscopes, Silicon, Chemical elements, Metrology, Distance measurement, Optical testing
We present results of the study of forming the image in a scanning electron microscope (SEM). The effects of the
electron beam energy and of the beam diameter on the signal profile are demonstrated. Methods of SEM calibration
including the measurement of the electron beam diameter are presented. The formulas relating the size of the trapezoidal
structures to the length of the reference portions of the SEM signals are presented. Examples of measurements of linear
sizes of relief structures are given.
The present state of Stark plasma spectroscopy is discussed. The possibilities of measurements of electric field and related plasma parameters are considered. A brief theory of linear and nonlinear Stark effect is outlined. The specific features of Stark effect — shifts, splitting and related line broadening, forbidden transitions — are described for the electric fields of differing nature — correlated external static and alternative fields, plasma turbulence fields, microfields generated by charged particles. Techniques based on classical emission spectroscopy, and novel linear and nonlinear laser techniques are considered. It is shown that the application of recently developed coherent laser spectroscopic methods radically improves the possibilities of electric fields measurements for the high pressure range.
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