According to the ITRS Roadmap , within a few years the EUV mask requirement for defect will be detection of defect
size of less than 25 nm. Electron Beam (EB) inspection is one of the candidates to meet such a severe defect requirement.
EB inspection system, Model EBEYE M※1, has been developed for EUV mask inspection. Model EBEYE M employs
Projection Electron Microscope (PEM) technique and image acquisition technique to acquire image with Time Delay
Integration (TDI) sensor while the stage moves continuously . Therefore, Model EBEYE M has high performance in
terms of sensitivity, throughput and cost.
In a previous study, we showed the performance of Model EBEYE M for 2X nm in a development phase whose
sensitivity in pattern inspection was around 20 nm and in particle inspection was 20 nm with throughput of 2 hours in
100 mm square , . With regard to pattern inspection, Model EBEYE M for High Volume Manufacturing (HVM) is
currently under development in the production phase. With regard to particle inspection, Model EBEYE M for 2X nm is
currently progressing from the development phase to the production phase.
In this paper, the particle inspection performance of Model EBEYE M for 2X nm in the production phase was evaluated.
Capture rate and repeatability were used for evaluating productivity. The target set was 100% capture rate of 20 nm.
100% repeatability of 20 nm with 3 inspection runs was also set as a target. Moreover, throughput of 1 hour in 100 mm
square, which was higher than for Model EBEYE M for 2X nm in the development phase, was set as a target. To meet
these targets, electron optical conditions were optimized by evaluating the Signal-to-Noise Ratio (SNR). As a result,
SNR of 30 nm PSL was improved 2.5 times. And the capture rate of 20 nm was improved from 21% with throughput of
2 hours to 100% with throughput of 1 hour. Moreover, the repeatability of 20 nm with 3 inspection runs was 100% with
throughput of 1 hour. From these results, we confirmed that Model EBEYE M particle inspection mode could be
available for EUV mask production.
According to the ITRS Roadmap, the EUV mask requirement for 2X nm technology node is detection of defect size of
20 nm. The history of optical mask inspection tools involves continuous efforts to realize higher resolution and higher
throughput. In terms of productivity, considering resolution, throughput and cost, we studied the capability of EUV light
inspection and Electron Beam (EB) inspection, using Scanning Electron Microscope (SEM), including prolongation of
the conventional optical inspection. As a result of our study, the solution we propose is EB inspection using Projection
Electron Microscope (PEM) technique and an image acquisition technique to acquire inspection images with Time Delay
Integration (TDI) sensor while the stage is continually moving. We have developed an EUV mask inspection tool,
EBeyeM, whole design concept includes these techniques. EBeyeM for 2X nm technology node has the following targets,
for inspection sensitivity, defects whose size is 20 nm must be detected and, for throughput, inspection time for particle
and pattern inspection mode must be less than 2 hours and 13 hours in 100 mm square, respectively. Performance of the
proto-type EBeyeM was reported. EBeyeM for 2X nm technology node was remodeled in light of the correlation
between Signal to Noise Ratio (SNR) and defect sensitivity for the proto-type EBeyeM. The principal remodeling points
were increase of the number of incident electrons to TDI sensor by increasing beam current for illuminating optics and
realization of smaller pixel size for imaging optics.
This report presents the performance of the remodeled EBeyeM (=EBeyeM for 2X nm) and compares it with that of the
proto-type EBeyeM. Performances of image quality, inspection sensitivity and throughput reveal that the EBeyeM for
2X nm is improved. The current performance of the EBeyeM for 2X nm is inspection sensitivity of 20 nm order for both
pattern and particle inspection mode, and throughput is 2 hours in 100 mm square for particle inspection mode.
We are developing new electron beam inspection system, named EBeyeM, which features high speed and high
resolution inspection for EUV mask. Because EBeyeM has the projection electron microscope technique, the scan time
of EBeyeM is much faster than that of conventional SEM inspection system.
We developed prototype of EBeyeM. The aim of prototype system is to prove the concept of EBeyeM and to estimate
the specification of system for 2Xnm and 1Xnm EUV mask.
In this paper, we describe outline of EBeyeM and performance results of the prototype system. This system has two
inspection mode. One is particle inspection and the other is pattern defect inspection. As to the sensitivity of EBeyeM
prototype system, the development target is 30nm for the particle inspection mode and 50nm for pattern defect
inspection mode. The performance of this system was evaluated. We confirmed the particle inspection mode of the
prototype system could detect 30nm PSL(Polystyrene Latex) and the sensitivity was much higher than conventional
optical blank inspection system. And we confirmed that the pattern defect sensitivity of the prototype system was
around 45nm. It was recognized that both particle inspection mode and pattern defect inspection mode met the
development target. It was estimated by the performance results of the prototype system that the specification of
EBeyeM would be able to achieve for 2Xnm EUV mask. As to 1Xnm EUV mask, we are considering tool concept to
meet the specification.
As the candidates of factors to consider for accurate Monte Carlo simulation of SEM images, (1) the difference
of cross-section between an approximate shape for simple simulation and a real pattern shape, (2) the influence of native
oxide growing on a pattern surface, and (3) the potential distribution above the target surface are proposed. Each
influence on SEM signal is studied by means of experiments and simulations for a Si trench pattern as a motif. Among
these factors, native oxide of about 1nm in thickness has a significant influence that increases SEM signals at the top
edge and the slope. We have assumed and discussed models for the native oxide effect.
CD-SEM measurement is the main measuring tool of critical dimensions (CD). CD-measurements involve
systematic errors that depend on SEM set-up and the pattern. In addition to systematic errors, charging of a
wafer plays an important role in CD-SEM and defect inspection tools. Charging dependence of secondary
electron emission coefficient which is one of the major charging parameters, was studied. Timing
characteristics were measured and then simulated using Monte Carlo model. The measurements and
simulations were done for a multiple number of frames and for imaging of a contact hole using pre-charge of
a large area. The results of simulation confirmed the measured results. The understanding of the effect helps
in tuning the settings of CD-SEM.
In semiconductor manufacturing, control of hotspots by optical proximity correction (OPC) requires
accurate measurements of shapes and sizes of fabricated features. These measurements are carried
out using CD-SEM. In order to measure 2D shapes, edges of features should be clearly defined in all
directions. Positions of edges are often unclear because of charging. Depending on the SEM setup and
the pattern under measurement, the effect of charging varies. The influence of measurement conditions
can be simulated and optimized. A Monte Carlo electron-beam simulation tool was developed, which
takes into account electron scattering and charging. CD-SEM imaging of SiO<sub>2</sub> lines on Si were studied.
In experiment, an effect of contrast tone reversal was found, when beam voltage was varied. The same
effect was also found in simulations, where contrast reversal was similar to the experimental results. The
time dependence of contrast variation was also studied. A good agreement between simulation and
measurement was found. The simulation software proved reliable in predicting SEM images, which
makes it an important tool to optimize settings of electron-beam tools. Based on such simulations,
optimum conditions of SEM setup can be found.