The detection and management of mask defects which are transferred onto wafer becomes more important day by day.
As the photomask patterns becomes smaller and more complicated, using Inverse Lithography Technology (ILT) and
Source Mask Optimization (SMO) with Optical Proximity Correction (OPC).
To evaluate photomask quality, the current method uses aerial imaging by optical inspection tools. This technique at
1Xnm node has a resolution limit because small defects will be difficult to detect.
We already reported the MEEF influence of high-end photomask using wide FOV SEM contour data of "E3630
MVM-SEM<sub>®</sub>" and lithography simulator "TrueMask<sub>®</sub> DS" of D2S Inc. in the prior paper .
In this paper we evaluate the correlation between our evaluation method and optical inspection tools as ongoing
Also in order to reduce the defect classification work, we can compose the 3 Dimensional (3D) information of defects
and can judge whether repairs of defects would be required.
Moreover, we confirm the possibility of wafer plane CD measurement based on the combination between E3630
MVM-SEM<sub>®</sub> and 3D lithography simulation.
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.
To evaluate photomask quality, the current method uses spatial imaging by optical inspection tools. This technique at 1Xnm node has a resolution limit because small defects will be difficult to extract. To simulate the mask error-enhancement factor (MEEF) influence for aggressive OPC in 1Xnm node, wide FOV contour data and tone information are derived from high precision SEM images. For this purpose we have developed a new contour data extraction algorithm with sub-nanometer accuracy resulting in a wide Field of View (FOV) SEM image: (for example, more than 10um x 10um square). We evaluated MEEF influence of high-end photomask pattern using the wide FOV contour data of "E3630 MVM-SEM<sup>TM</sup>" and lithography simulator "TrueMask<sup>TM</sup> DS" of D2S, Inc. As a result, we can detect the "invisible defect" as the MEEF influence using the wide FOV contour data and lithography simulator.
As an alternative to EUV lithography, ArF immersion multiple patterning lithography has been heavily employed in
semiconductor fabrication. This situation has led to increase use of bright-field photomasks with floating small patterns.
Latest CDSEMs are equipped with various charge compensation features and applicable for devices with conductive
and insulating material. However, there remain some difficulties when floating small patterns are to be measured. One
of the specific examples is a floating dot on a via mask, dimension of which is around 200nm at the 45 nm process
node, scaling down to 100nm at the 22nm process node. Since the dot has very small capacitance, it is easily charged by
electron beam irradiation, and discharged in a short period. This kind of temporary voltage variation can affect the
secondary electron yield, causes degradation of the SEM image contrast. We have analyzed that the "edge effect",
which is the principle of SEM, has a primary role in small dot charging, and interchanging of scan line effectively
suppresses the voltage variation. Based on this concept, we have developed a new scan technology for our "Multi
Vision Metrology SEM" E3630, and improved the performance of image-based measurement. In this paper, the new
scan technology and evaluation results are presented.
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.
Thin film hardmasks with 10nm or less are used in double patterning techniques to generate fine
patterns for 32nm-node and beyond. Using a conventional Mask CDSEM for ultra accurate
measurement of patterns on these thin film hardmasks is difficult due to weakness of the edge
profiles generated by a scanning electron beam. Additionally, the tones of a SEM image can be
reversed due to a charging phenomenon, which causes false recognition of lines and spaces. This
paper addresses ultra accurate measurement of thin film hardmasks using a new measurement
algorithm that is applied to profiles obtained from multiple detectors.
The application of Mask CD-SEM for process management of photomask using two dimensional measurements as
photomask patterns become smaller and more complex, . Also, WPI technology application using an optical Mask
inspection tool simulates wafer plane images using photomask images .
In order to simulate the MEEF influence for aggressive OPC and High-end photomask patterns in 32nm node and
beyond, a requirement exists for wide Field of View (FOV) GDS data and tone information generated from high
precision SEM images.
In light of these requirements, we developed a GDS data extraction algorithm with sub-nanometer accuracy using wide
FOV images, for example, greater than 10um square. As a result, we over come the difficulty of generating large contour
data without the distortion that is normally associated with acquired SEM images. Also, it will be shown that the
evaluation result can be effective for 32 nm applications and beyond using Mask CD-SEM E3620 manufactured by
On the other hand, we investigate the application example of the wide FOV GDS data.
In order to easily compare the acquired GDS data with design data, we explain the separate algorithm with three layer
structures for Tri-tone (Ternary) photomask pattern, consisting of an outer pattern and another pattern.
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
In the UV-NIL template fabrication sequence usually four 65×65mm<sup>2</sup> templates are fabricated at once using a 6025 mask
blank. After finishing all patterning processes and the etching of the imprint pedestals the templates are separated by
dicing and polishing. This technique offers the advantage to use standard mask tools for the majority of the production
steps. In order to check the imprint pattern on the mask CD measurements of quartz features are necessary. To control
the fabrication process more effectively the additional measurement of resist features would be helpful. When the
template is used for imprinting, repeated cycles of anti-adhesion layer deposition and cleaning after multiple imprints
might change the CD of the quartz features. The metrology steps have to be performed on 1X features and are therefore
more challenging, compared to those for 4X photomasks. For this purpose we evaluated the capability of Vistec's CDSEM
LWM90xx for line-width measurements of nanoimprint templates. After optimization of hardware and software
settings, the measurement capability for different feature sizes has been characterized. Finally, the evaluated results have
been compared with the ITRS requirements for the 22nm node in order to address possible future needs.
KEYWORDS: Electron beams, Metrology, Image resolution, Electron microscopes, Scanning electron microscopy, Process control, Photomasks, Critical dimension metrology, Beam controllers, OLE for process control
Measurement of resist critical dimensions (CDs) utilizing a scanning electron microscope (SEM)
based metrology system causes the resist to change due to irradiation effects of the electrons. A new
and novel scanning approach has been developed in an effort to minimize the effects electron
irradiation and exposure during the measurement process. This technique is especially pertinent in
view of the tightening requirements for process control to achieve single digit CD uniformity on
leading edge photo masks being produced today. The measurement of OPC features necessitates
utilization of SEM based metrology due to resolution requirements, but the effects of high
magnification imaging presents unique challenges. By controlling the scanned region of interest
(ROI) it is possible to reduce exposure and irradiation effects. This paper will detail this new
approach as it is utilized on the LWM9045 SEM Metrology system. The LWM9000SEM mask CD
SEM was introduced earlier.