We have studied MVM (Multi Vision Metrology) -SEM<sup>®</sup> E3630 to measure 3D shape of defects. The four detectors
(Detector A, B, C and D) are independently set up in symmetry for the primary electron beam axis. Signal processing
of four direction images enables not only 2D (width) measurement but also 3D (height) measurement. At last PMJ,
we have investigated the relation between the E3630’s signal of programmed defect on MoSi-HT and defect height
measured by AFM (Atomic Force Microscope). It was confirmed that height of integral profile by this tool is
correlated with AFM. It was tested that E3630 has capability of observing multilayer defect on EUV. We have
investigated correlation with AFM of width and depth or height of multilayer defect.
As the result of observing programmed defects, it was confirmed that measurement result by E3630 is well
correlated with AFM. And the function of 3D view image enables to show nm order defect.
The required measurement precision for multilayered EUV mask metrology is set below 0.4 nm three
sigma. In addition to limited precision of CD-SEM, there are fundamental physical factors that deteriorate
the accuracy of the measurements, the most important of which is charging. It is widely believed that
EUV masks are conductive. However, experiments have revealed noticeable charging in CD-SEM
measurements of EUV masks that cannot be ignored. In this work, the results of the experiments and
simulations of the SEM signals are presented. It was shown that charging affects the metrology in a few
ways. The SEM signal shifts at each frame, changes with beam current and also depends on the wall
angle of the absorber. The results of the simulations are compared to experimental results.
Proc. SPIE. 8441, Photomask and Next-Generation Lithography Mask Technology XIX
KEYWORDS: Metrology, Detection and tracking algorithms, Sensors, Image segmentation, Atomic force microscopy, Scanning electron microscopy, 3D metrology, Photomasks, Signal detection, 3D image processing
As feature sizes of semiconductor device structures have continuously decreased, needs for metrology tools with high
precision and excellent linearity over actual pattern sizes have been growing. And it has become important to measure
not only two-dimensional (2D) but also three-dimensional (3D) shapes of patterns at 22 nm node and beyond. To meet
requirements for 3D metrology capabilities, various pattern metrology tools have been developed. Among those, we
assume that CDSEM metrology is the most qualified candidate in the light of its non-destructive, high throughput
measurement capabilities that are expected to be extended to the much-awaited 3D metrology technology. On the basis
of this supposition, we have developed the 3D metrology system, in which side wall angles and heights of photomask
patterns can be measured with high accuracy through analyzing CDSEM images generated by multi-channel detectors.
In this paper, we will discuss our attempts to measure 3D shapes of defect patterns on a photomask by using
Advantest's "Multi Vision Metrology SEM" E3630 (MVM-SEM™ E3630).
In next generation lithography (NGL) for the 22nm node and beyond, the three dimensional (3D) shape
measurements of side wall angle (SWA) and height of the photomask pattern will become critical for controlling the
exposure characteristics and wafer printability. Until today, cross-section SEM (X-SEM) and Atomic Force
Microscope (AFM) methods are used to make 3D measurements, however, these techniques require time consuming
preparation and observation.
This paper presents an innovative technology for 3D measurement using a multiple detector CDSEM and reports its
accuracy and precision.
A new metrology method for CD-SEM has been developed to measure the side wall angle of a pattern on photomask. The
height and edge width of pattern can be measured by the analysis of the signal intensity profile of each channel from multiple
detectors in CD-SEM.
The edge width is measured by the peak width of the signal intensity profile. But it is not possible to measure the accurate
edge width of the pattern, if the edge width is smaller than the primary electron beam diameter. Using four detectors, the
edge width can be measured by the peak width which appears on the subtracting signal profile of two detectors in opposition
to each other. Therefore, the side wall angle can be calculated if the pattern height is known.
The shadow of the side wall appears in the signal profile from the detector of the opposite side of the side wall.
Furthermore, we found that there was the proportional relation between pattern height and the shadow length of the signal on
This paper describes a method of measuring the side wall width of a pattern and experimental results of the side wall angle
The Multiple Detector CD-SEM acquires the secondary electron from pattern surface at each detector. The 3D shape
and height of mask patterns are generated by adding or subtracting signal profile of each detector. In signal profile of the
differential image formed in difference between left and right detector signal, including concavo-convex information of
mask patterns. Therefore, the 3D shape of mask patterns can be obtained by integrating differential signal profile. This
time, we found that proportional relation between pattern height and shadow length on one side of pattern edge. In this
paper, we will report experimental results of pattern height measurement. The accuracy of measurement and side wall
angle dependency are studied. The proposal method is applied to OMOG masks.
Influence of the prominent charging effect on the precision of measuring EUV mask features using CD-SEM was studied.
The dimensions of EUV mask features continuously measured by CD-SEM gradually varied because of the charging.
The charging effect on the measured CD variation mainly consists of three factors: 1) shift of the incident points of
primary electrons deflected by the surface charge, 2) distortions of the profiles of secondary electron signal intensity
caused by the deflection of the secondary electrons, 3) deviation of the maximum slope points of the secondary electron
signal intensity due to the variation of the image contrast. For those three factors described above, how the material
constant affect the CD variation measured by CD-SEM is discussed.
In order to analyze small reticle defects quantitatively, we have developed a function to measure differences in two
patterns using contour data extracted from SEM images. This function employs sub-pixel contour data extracted with high
accuracy to quantify a slight difference by ΔCD and ΔArea. We assessed the measurement uncertainty of the function with a
test mask and compared the sizes of programmed defects by each of conventional and proposed methods. We have also
investigated a correlation between measured minute defects in high MEEF (Mask Error Enhancement Factor) regions and
aerial images obtained by AIMS (Aerial Image Measurement System) tool. In this paper, we will explain the Contour
Comparison Measurement function jointly developed by Toppan and Advantest and will show its effectiveness for photomask
The verification of not only two-dimensional feature but also three-dimensional feature, sidewall angle (SWA), has
been becoming increasingly important in NGL mask fabrication. The OMOG (Opaque MoSi on Glass) mask for ArF
immersion lithography with double patterning and the reflective type mask for EUV (Extreme Ultra- Violet) lithography
are especially in need of it.
There are several metrology tools e.g. SEM, AFM, and Scatterometry for sidewall angle (SWA) measurement. We
evaluated a new SWA measurement method using white-band width (WBW), which is equivalent to mask pattern edge
width, by CD-SEM. In general, WBW correlates with SWA. It narrows as SWA becomes steeper. However, the
correlation deteriorates when SWA is vertically near. This is due to the resolution limit of electron beam diameter used
for measurement. We analyzed the new approach to measure SWA by CD-SEM to solve this problem. And the analysis
revealed that WBW changes proportionately electron beam current value. The amount of width change depends on
In this paper, we will describe the new SWA measurement method and its evaluation results as well as SWA
measurement results of OMOG and EUV masks.