Resist-on-silicon sub-50-nm critical dimension targets have been investigated using a 193 nm angle-resolved
scatterfield microscope (ARSM). The illumination path of this microscope allows customization of the conjugate
back focal plane (CBFP) while separate collection paths permit both high-magnification and Fourier-plane
imaging. Aspects of the calibration of this microscope are presented. Full-field, Fourier-plane images are collected
as individual targets are illuminated using a field-of-view smaller than the target size; the range of incident polar
angles corresponds to the numerical aperture (NA) of the objective, NA = 0.08 to 0.74. Next, angle-resolved
scatterfield high-magnification imaging of these same targets are acquired in a conical mounting configuration
by scanning the 12 mm diameter CBFP with a 1 mm diameter aperture. The results of these measurements and
the prospects for quantitative, simultaneous measurement of multiple targets are discussed.
New techniques recently developed at the National Institute of Standards and Technology using bright-field optical tools
are applied to signal-based defect analysis of features with dimensions well below the measurement wavelength. A key
to this approach is engineering the illumination as a function of angle and analysis of the entire scattered field. In this
paper we demonstrate advantages using this approach for die-to-die defect detection metrology. This methodology,
scatterfield optical microscopy (SOM), is evaluated for defect inspection of several defect types defined by Sematech on
the Defect Metrology Advisory Group (DMAG) intentional defect array (IDA) wafers. We also report the systematic
evaluation of defect sensitivity as a function of illumination wavelength.
Theoretical simulations are reported that were carried out using a fully three-dimensional finite difference time domain
(FDTD) electromagnetic simulation package. Comprehensive modeling was completed investigating angle-resolved
illumination to enhance the detection of several defect types from the IDA wafer designs. The defect types covered a
variety of defects from the IDA designs. The simulations evaluate the SOM technique on defect sizes ranging from
those currently measurable to those the industry considers difficult to measure. The simulations evaluated both the 65
nm IDA metal-1 M1 trench and the polysilicon stack and more recent 13 nm linewidth logic cells.
The current photomask linewidth Standard Reference Material (SRM) supplied by the National Institute of
Standards and Technology (NIST), SRM 2059, is the fifth generation of such standards for mask metrology.
The calibration of this mask has been usually done using an in house NIST ultra-violet transmission microscope
and an Atomic Force Microscope (AFM). Recently, a new optical reflection scatterfield microscope has been
developed at NIST for wafer inspection, Critical Dimension (CD) and overlay metrology purposes.
Scatterfield microscopy relies on illumination engineering at a sufficiently large Conjugate Back Focal Plane
(CBFP) of the microscope.1 Our new scatterfield reflection microscope uses 193 nm excimer laser light as well as
sophisticated configurations to allow measurement of both the image plane and the Fourier plane using full-field
and angle-resolved illumination. By reducing the wavelength compared to many current metrology tools that
work in the visible light and near ultra-violet range, we have made substantial improvements in image resolution2
and commensurate gains in sensitivity to geometrical parameters.
We present a preliminary study on the use of this new microscope to calibrate and measure features of this SRM
photomask. The 193 nm scatterfield microscope is used in full-field mode with a NA range from 0.12 to 0.74
using our scatterfield imaging method. Experimental results obtained on isolated lines for different polarization
states of the illumination are presented and discussed. Pitch measurements are compared to the measurements
done on our NIST Ultra-Violet (UV) transmission microscope.
In preparation for the international Nano1 linewidth comparison on photomasks between nine national metrology institutes,
the National Institute of Standards and Technology (NIST) and the Physikalisch-Technische Bundesanstalt (PTB),
initiated a bilateral linewidth comparison in 2008, independent of and prior to the Nano1 comparison in order to test the
suitability of the mask standards and the general approach to be used for the Nano1 comparison. This paper reports on
the current status of the bilateral comparison. In particular the methods for linewidth metrology applied at NIST and
PTB and its major uncertainty contributions will be discussed based on actual measurements results for both of the mask
standards chosen for the bilateral comparison.
An angle-resolved scatterfield microscope (ARSM) featuring 193 nm excimer laser light was developed for measuring
critical dimension (CD) and overlay of nanoscale targets as used in semiconductor metrology. The microscope is
designed to have a wide and telecentric conjugate back focal plane (CBFP) and a scan module for resolving Köhler
illumination in the sample plane. Angular scanning of the sample plane was achieved by linearly scanning an aperture
across the 12 mm diameter CBFP, with aperture size as small as 0.4 mm for some scans. For each aperture, the sample
was illuminated over a range of angles from 12° to 48°, corresponding to a numerical aperture of 0.2 to 0.74. Angleresolved
measurement results are presented for grating targets with nominal linewidths down to 50 nm.
We have developed a set of techniques, referred to as scatterfield microscopy, in which the illumination is
engineered at a sufficiently large Conjugate Back Focal Plane (CBFP) of the microscope. A primary advance of
our new scatterfield microscope is the use of 193 nm excimer laser light. Sophisticated configurations have been
implemented to allow measurement of both the image plane and the Fourier plane using full-field and angleresolved
illumination. Here, the microscope is primarily used in an angular mode by engineering the CBFP to
enable angle-resolved scatterometer measurements with a numerical aperture (NA) range from 0.08 to 0.74.
Electromagnetic models - the Finite Element Method (FEM) and the Modal Method of Fourier Expansion
(MMFE) were used to model the experimental light scattering and evaluate the sensitivity to the geometrical
parameters and correlations.
In addition, experimental results obtained on line gratings for unpolarized illumination will be presented and
A scatterfield microscope using 193 nm laser light was developed that utilizes angle-resolved illumination for high
resolution optical metrology. An angle scan module was implemented that scans the illumination beam in angle space at
the sample by linearly scanning a fiber aperture at a conjugate back focal plane. The illumination light is delivered
directly from a source laser via an optical fiber in order to achieve homogeneous angular illumination. A unique design
element is that the conjugate back focal plane (CBFP) is telecentric allowing the optical axis of the fiber to be scanned
linearly. Initial results from full field and angle-resolved illumination are presented and potential applications in
semiconductor metrology are described.
In preparation of the international Nano1 linewidth comparison on photomasks between 9 national metrology institutes,
NIST and PTB have started a bilateral linewidth comparison in 2008, independent of and prior to the Nano1 comparison
in order to test the suitability of the mask standards and the general approach to be used for the Nano1 comparison. This
contribution describes the rationale of both comparisons, the design of the mask comparison standards to be used and the
measurement methods applied for traceable photomask linewidth metrology at NIST and PTB.
During the last five years scatterometry measurement using ellispometry and reflectometry has met a great interest in nano and microelectronics fab. Today, this technology of measurement is used to control lot production and has become mature for 1D-grating measurements. Nevertheless, some aspects of this method of measurement are always under research studies. This paper focuses on one of these aspects: the evaluation of the influence of the "real-life 1D-structure" (linewidth variations along the lines and line to line, roughness, defect inside the grating) on spectroscopic signatures and on scatterometry measurement methods. The measurements have been carried out on KLA-TENCOR ellispometer and on Nanometrics reflectometer in order to compare the two methods of measurement. The simulations have been done with MMFE (Modal Method of Fourier Expansion) software developed by LETI labs. To control defect characteristics and defect distributions, one wafer was printed using electron beam lithography. The aim is the evaluation of the impact of defects in the grating on the spectroscopic signatures and its influence on extracted geometrical parameters by fitting the experimental curves. Different deviations to real-life structures have been studied. First we focus on the influence of typical defects of lithography processes such as bridging and partial destruction of lines and on the influence of CD distribution values inside the grating. Then, we study the influence and the possibilities of measuring Line Edge Roughness (LER). For LER measurements different targets have been also exposed on e-beam tool. Simulations and experimental measurements have been carried out. All the results obtained have been compared with imaging standard tool: top down SEM measurement.
This paper focuses on the capability of the spectroscopic scatterometry method to determine holes features parameters from experimental 3D-target. Scatterometry uses optical tools for spectra recording as ellipsometer form KLA TENCOR and a MMFE (Modal Method of Fourier Expansion) software tool including an advanced electromagnetic simulator and an optimization loop for data extraction.
This study reports on 3D-MMFE regression of different dense holes square and rectangular matrix structures on the simplest structure-resist on silicon-to extract diameter, height of the holes. The holes diameter is from 90nm to 500nm, and the duty ratio is from 1:1 to 2:2 (CD/Space). To be close to real production stack the same matrices have been studied on more complex stack (close to via level with different dielectric material: FSG, dense SiOC).
Finally this study is focused on an analysis on simulation and experiment of the relative sensitivity position of a hole inside the basic element of diffraction. That shows the possibility of scatterometry measurement in detecting via shift.
Spectroscopic scatterometry is an optical metrology technique based on light scattering aiming at measuring geometrical dimensions, such Critical Dimension (CD) but also height or depth, side-wall angle and even more tiny details in a line profile. Scatterometry tool measures and analyzes the spectrum scattered or diffracted from a periodic target patterned on a wafer. Scatterometry is strongly considered as an alternative or as a complementary technique to CDSEM for 90 nm and below technology nodes. Like other optical metrology techniques, scatterometry measurements are rapid, non-destructive and highly repeatable. Actual tools have been assessed for dense to semi-isolated lines CD metrology and profiling. Developments are now targeting hole measurement. 2D-scatterometry (scatterometry on 3D patterns) becomes mature and begins to be used in advanced fab for CD control after lithography. This paper focuses on the capability of the spectroscopic scatterometry method to determine holes features and to try to give theoretical limits of method. Scatterometry uses an optical tool for spectra recording and a software tool including an advanced electromagnetic simulator and an optimization loop for data extraction. The first part of this study reports on the influence of bi-periodic structures in the experimental analysis of holes measurements. Then a limitation in holes density is defined. The second part of this study is a theoretical analysis based on simulation of the sensitivity of scatterometry with respect to various holes parameters. Following parameters are generally taken into account: holes diameter, holes ellipticity (elliptical ratio), holes roundness, holes depth and tilt angle for non-circular holes. We determine the respective influence of these parameters on ellipsometric spectra.