As the design rule becomes continuously smaller, the Hard OPC is being applied to pattern design in semiconductor
production. Controllability of hard OPCed pattern’s quality directly affects to the performance of the device and yields of
production. Critical Dimension Scanning Electron Microscopy (CD-SEM) is used to accurately confirm the Critical
Dimension (CD) quality of the photomask. CD-SEM makes the pattern’s shape image by using secondary electrons
information directly from the Mask surface and can measure CD values. Classically the purpose of CD-SEM
measurement was to get one dimensional CD values. However it is difficult to guarantee complex hard OPCed pattern’s
quality by using only one dimensional CD values because complexity of pattern design has been increased.
To confirm and control the quality of hard OPCed pattern, the quality of pattern fidelity must be measured
quantitatively. In order to overcome this difficulty we developed a new method to quantitatively evaluate the quality of
pattern fidelity using EPE (Edge Placement Error) distance from the overlay between Target Design GDS and SEM GDS
contour which is extracted from CD-SEM image. This paper represents how to define and analyze quantitatively the
quality of complex hard OPCed pattern.
The 1Xnm technology node lithography is using SMO-ILT, NTD or more complex pattern. Therefore in mask defect inspection, defect verification becomes more difficult because many nuisance defects are detected in aggressive mask feature. One key Technology of mask manufacture is defect verification to use aerial image simulator or other printability simulation. AIMS™ Technology is excellent correlation for the wafer and standards tool for defect verification however it is difficult for verification over hundred numbers or more.
We reported capability of defect verification based on lithography simulation with a SEM system that architecture and software is excellent correlation for simple line and space.[1]
In this paper, we use a SEM system for the next generation combined with a lithography simulation tool for SMO-ILT, NTD and other complex pattern lithography. Furthermore we will use three dimension (3D) lithography simulation based on Multi Vision Metrology SEM system. Finally, we will confirm the performance of the 2D and 3D lithography simulation based on SEM system for a photomask verification.
In a Photomask manufacturing process, mask defect inspection is an increasingly important topic for 193nm optical lithography. Further extension of 193nm optical lithography to the next technology nodes, staying at a maximum numerical aperture (NA) of 1.35, pushes lithography to its utmost limits. This extension from technologies like ILT and SMO requires more complex mask patterns. In mask defect inspection, defect verification becomes more difficult because many nuisance defects are detected in aggressive mask features. One of the solutions is lithography simulation like AIMS. An issue with AIMS, however, is the low throughput of measurement, analysis etc.
KEYWORDS: 3D metrology, Sensors, Atomic force microscopy, 3D image processing, Scanning electron microscopy, Algorithm development, Photomasks, Metrology, Transmission electron microscopy, Time metrology
In next generation lithography (NGL) for the 1x nm node and beyond, the three dimensional (3D) shape measurements such as side wall angle (SWA) and height of feature on photomask become more critical for the process control. Until today, AFM (Atomic Force Microscope), X-SEM (cross-section Scanning Electron Microscope) and TEM (Transmission Electron Microscope) tools are normally used for 3D measurements, however, these techniques require time-consuming preparation and observation. And both X-SEM and TEM are destructive measurement techniques. This paper presents a technology for quick and non-destructive 3D shape analysis using multi-channel detector MVM-SEM (Multi Vision Metrology SEM), and also reports its accuracy and precision.
As design rules of lithography shrink: accuracy and precision of Critical Dimension (CD) and controllability of hard OPCed patterns are required in semiconductor production. Critical Dimension Scanning Electron Microscopes (CD SEM) are essential tools to confirm the quality of a mask such as CD control; CD uniformity and CD mean to target (MTT). Basically, Repeatability and Reproducibility (R and R) performance depends on the length of Region of Interest (ROI). Therefore, the measured CD can easily fluctuate in cases of extremely narrow regions of OPCed patterns. With that premise, it is very difficult to define MTT and uniformity of complex OPCed masks using the conventional SEM measurement approach. To overcome these difficulties, we evaluated Design Based Metrology (DBM) using Large Field Of View (LFOV) of CD-SEM. DBM can standardize measurement points and positions within LFOV based on the inflection/jog of OPCed patterns. Thus, DBM has realized several thousand multi ROI measurements with average CD. This new measurement technique can remove local CD errors and improved statistical methodology of the entire mask to enhance the representativeness of global CD uniformity. With this study we confirmed this new technique as a more reliable methodology in complex OPCed patterns compared to conventional technology. This paper summarizes the experiments of DBM with LFOV using various types of the patterns and compares them with current CD SEM methods.
KEYWORDS: Atomic force microscopy, 3D image processing, 3D metrology, Sensors, Semiconducting wafers, Metrology, Reticles, Line edge roughness, Scanning electron microscopy
A new SEM technology is becoming available that allows image-based 3D profile metrology of nanoscale features. Using patented multi-channel detector technology, this system can acquire information of surface concave and convex features, and sidewall angle (SWA) and height of profiles, quickly and non-destructively for nanoscale structures such as fin field-effect transistors (FinFETs), using electron beam technology with its well-known long probe lifetime, stability and small probe size. Here we evaluate this new technology and demonstrate its applicability to contemporary advanced structures such as FinFETs, including not only CD, but also profile, SWA, top corner rounding (TCR) and bottom corner rounding (BCR).
KEYWORDS: 3D metrology, Sensors, 3D image processing, Atomic force microscopy, 3D vision, 3D acquisition, Extreme ultraviolet, Scanning electron microscopy, Phase measurement, Electron beams
We have studied MVM (Multi Vision Metrology) -SEM® 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.
For multi-purpose applications such as advanced LSIs, photonics, MEMS, and other nano- fabrications, it is important
for electron beam (EB) writers that handle the various substrates with their own single mechanical platform. We have
been developing the adjusting pallet function both 200mm and 300mm bases to satisfy this requirement. By analyzing
actual examples of adjusting pallets we proved their effectiveness to their applications. The combination of adjusting
pallet function, 1Xnm resolution column and character projection technologies will enable the next generation EB writer
“F7000” to fit from Fab to Lab applications.
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®" and lithography simulator "TrueMask® DS" of D2S Inc. in the prior paper [1].
In this paper we evaluate the correlation between our evaluation method and optical inspection tools as ongoing
assessment.
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® and 3D lithography simulation.
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-SEMTM" and lithography simulator "TrueMaskTM 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.
Character projection (CP) exposure has some advantages compared with variable shaped beam (VSB) system; (1) shot count reduction by printing complex patterns in one e-beam shot, (2) high pattern fidelity by using CP stencil.
In this paper we address another advantage of CP exposure, namely the shape correction of CP stencil for cancelling the pattern deformation on the substrate. The deformation of CP printings is decomposed into some elements. They are CP stencil manufacturing error, proximity effect, beam blur of the e-beam writer and resist blur. The element caused by beam blur of e-beam writer can be predicted by measuring the total beam blur obtained from CD-dose curves. The pattern deformation was corrected by applying the shape correction software system of D2S. The corrected CP stencil of 22nm-node standard cell was manufactured and standard cell patterns were exposed. We confirmed that our shape correction method is the appropriate solution for correcting deformation issue of CP openings. The beam blur required for the 1X nm dimensions was predicted from the exposure results of standard cell patterns with applying shape correction and CD-dose curves. We simulated the optical system to realize the required beam blur. As a result, the next electron optics has the resolving capability of 1X nm dimension.
KEYWORDS: Scanning electron microscopy, Photomasks, Metrology, Electron beam lithography, Line scan image sensors, Electron beams, Lithography, Semiconductors, Capacitance, Absorption
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.
KEYWORDS: Sensors, Signal detection, 3D metrology, Photomasks, Atomic force microscopy, Lithography, Scanning electron microscopy, Image sensors, Edge detection, Extreme ultraviolet
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.
KEYWORDS: Sensors, Signal detection, Photomasks, Algorithm development, 3D metrology, Polonium, Metrology, Scanning electron microscopy, Electron beams, Detection and tracking algorithms
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
one side.
This paper describes a method of measuring the side wall width of a pattern and experimental results of the side wall angle
measurements.
KEYWORDS: Sensors, Atomic force microscopy, Signal detection, Photomasks, Etching, 3D metrology, Tantalum, Critical dimension metrology, Scanning electron microscopy, Extreme ultraviolet
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, [1]. Also, WPI technology application using an optical Mask
inspection tool simulates wafer plane images using photomask images [2].
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
Advantest.
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
defect analyses.
In the UV-NIL template fabrication sequence usually four 65×65mm2 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: Scanning electron microscopy, Photomasks, Critical dimension metrology, Electron beams, Metrology, Electron microscopes, Process control, OLE for process control, Image resolution, Beam controllers
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.
As the design rule of lithography becomes smaller, accuracy and precision in Critical Dimension (CD) and
controllability of pattern-shape are required in semiconductor production. Critical Dimension Scanning Electron
Microscope (CD SEM) is an essential tool to confirm the quality of the mask such as CD control, CD uniformity and CD
mean to target (MTT). Unfortunately, in the case of extremely rounded region of arbitrary enclosed patterns, CD
fluctuation depending on Region of Interest (ROI) is very serious problem in Mask CD control, so that it decreases the
yield. In order to overcome this situation, we have been developing 2-dimensonal (2D) method with system makers and
comparing CD performance between mask and wafer using enclosed arbitrary patterns. In this paper, we summarized the
results of our evaluation that compare error budget between 1-dimensonal (1D) and 2D data using CD SEM and other
optical metrology systems.
For next generation photomask lithography, improved resolution and precision are required to monitor lithography tools and photomask processes. The newly developed LWM9000 SEM Critical Dimension Scanning Electron Microscope (CD-SEM) for photomask applications will be presented. Its proprietary electron optics technology combined with an improved detection system leads to sub-nanometer CD measurement repeatability by almost completely eliminating the effect of charging and contamination. In an effort to minimize integration into production environments and to facilitate the ease of use the new CD-SEM utilizes a graphical user interface and data evaluation software based on Leica Microsystems’ LMS IPRO / LMS IPRO2. Presented in this paper is data showing leading edge CD measurement repeatability performance on chrome on glass substrates (COG), different types of phase shift masks (PSM), and resist plates. The virtual lack of charging in conjunction with a laser controlled stage, dramatically reduces the need for local feature alignment prior to CD measurement in most cases. The lack of need for local pattern alignment leads to increased throughput and high reliability during the measurement process. The standard system can be configured for manual loading or SMIF handling.
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