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3D push–pull heterodyne interferometer for SPM metrology

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Applied Optics
Authors:
Tatiana Kazieva at National Research Nuclear University MEPhI
Tatiana Kazieva
K. L. Gubskii at National Research Nuclear University MEPhI
K. L. Gubskii
A. P. Kuznetsov
A. P. Kuznetsov
A. P. Kuznetsov
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V. N. Reshetov at National Research Nuclear University MEPhI
V. N. Reshetov
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Abstract and Figures

A three-coordinate heterodyne laser interferometer has been developed to measure the displacement of the probe microscope scanner with a subnanometer resolution that provides traceability of measurements to the standard of meter through the wavelength of a stabilized He–Ne laser. Main sources of errors are investigated, and their influence is minimized so that the resulting measurement uncertainty of the system does not exceed 0.2 nm, and the resolution is 0.01 nm. The investigation of metrological characteristics of the three-coordinate interferometer was carried out with a scanning probe microscopy (SPM) NanoScan-3D using TGZ-type calibration gratings. The values measured with SPM fell within the 95% confidence interval given by Physikalisch-Technische Bundesanstalt (PTB) (Germany). SPM equipped with a laser interferometer was used to measure the characteristics of dynamic etalons of geometric dimensions.
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3D push–pull heterodyne interferometer
for SPM metrology
T. V. KAZIEVA,* K. L. GUBSKIY,A.P.KUZNETSOV,AND V. N. RESHETOV
National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow 115409, Russia
*Corresponding author: glizerogen@gmail.com
Received 4 February 2019; revised 15 April 2019; accepted 16 April 2019; posted 16 April 2019 (Doc. ID 359583); published 16 May 2019
A three-coordinate heterodyne laser interferometer has been developed to measure the displacement of the probe
microscope scanner with a subnanometer resolution that provides traceability of measurements to the standard of
meter through the wavelength of a stabilized He–Ne laser. Main sources of errors are investigated, and their
influence is minimized so that the resulting measurement uncertainty of the system does not exceed 0.2 nm,
and the resolution is 0.01 nm. The investigation of metrological characteristics of the three-coordinate interfer-
ometer was carried out with a scanning probe microscopy (SPM) NanoScan-3D using TGZ-type calibration
gratings. The values measured with SPM fell within the 95% confidence interval given by Physikalisch-
Technische Bundesanstalt (PTB) (Germany). SPM equipped with a laser interferometer was used to measure
the characteristics of dynamic etalons of geometric dimensions. © 2019 Optical Society of America
https://doi.org/10.1364/AO.58.004000
Scanning probe microscopy (SPM) is associated with a
wide range of modern methods for studying local properties
of a solid surface with high spatial resolution. SPM methods
enable transition from simple visualization toward qualitative
measurements of the surface topology of samples. These meth-
ods do not require complicated preliminary preparation of the
samples and allow working in a wide range of external condi-
tions: from high to ultralow temperatures, in vacuum, in air,
or in a controlled gas medium [1]. However, in this case,
one needs to measure both the scanning probe displacement
and the object position independently with an uncertainty
of ∼1·10−10 m. Currently, to measure the position of the ob-
ject under investigation with respect to the scanning probe,
SPMs are complemented with capacitive sensors included in
the feedback loop [2]. However, the presence of nonlinearities
and the lack of direct traceability of measurements to the meter
standard do not allow existing sensors to completely solve the
problem of metrological reliability of linear displacement
measurements made with the SPM scanner [3].
The only way to realize the traceability to the reference
length and to measure the displacement of the SPM scanner
with subnanometric uncertainty, is to incorporate laser interfer-
ometers into the existing SPM designs, with a stabilized laser as
a radiation source. To characterize the change in the object
position, different schemes of multiaxis interferometers can
be used in the SPMs [4–12].
The existing commercially available interferometers do not
allow one to achieve subnanometric measurement uncertainties
in three orthogonal directions. The best characteristics thus far
have been demonstrated by the instruments produced in
metrological institutes, but their large dimensions hinder
them from integration into the mass-produced SPMs, and
no method to reduce the dimensions has been found due to
specificity of the optical circuits and the associated systems that
neutralize the influence of external factors [5–7]. Combining
SPMs with multiaxis interferometers is tricky as well because
the scanners, whose displacements are to be measured, are ar-
ranged in such a way that bonding each of them with several
reflective elements for every interferometer is extremely difficult.
The authors developed a single-chassis laser interferometer
designed to measure the displacement of an SPM piezoelectric
table in real time, with measurement uncertainty as low as
1·10−10 m, and a resolution of 1·10−11 mthat allows
measuring displacements in three orthogonal coordinates.
This system is based on the heterodyne method for the forma-
tion of interference signals. In contrast with homodyne inter-
ferometry, where the information of the optical length change is
contained in the amplitude of the photoelectric signal, in
heterodyne methods the “shift-phase”transformation is per-
formed, and the processing of the measurement information
is reduced to high-precision phase measurements. Transfer
of the interference signal to the intermediate frequency makes
it possible to reduce the measurement uncertainty of phase
shifts and to provide noise immunity by using radio engineer-
ing methods of narrowband signal extraction from noises of
various nature.
4000 Vol. 58, No. 15 / 20 May 2019 / Applied Optics Research Article
1559-128X/19/154000-07 Journal © 2019 Optical Society of America
... However, all these methods do not have direct traceability to the primary standard of length; therefore, they are not metrological. For metrologically correct measurement of the function of the surface area of the tips of the probes of nanohardness testers, a method was proposed for measuring the function of the surface of the tip using a three-axis linear displacement interferometer coupled with an atomic force microscope [6]. ...
... Structural changes, such as the removal of the radiation source from the optical unit, the design of the triple prism holder and the compactization of the optical scheme, made it possible to reduce or completely eliminate the influence of such noise sources as thermal drift, non-orthogonality of the interferometer axes, and Abbe error. A detailed description of the optical scheme can be found in [6] ...
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