According to the ITRS Roadmap [1], 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 [2]. 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 [3], [4]. 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.
Grazing incidence small-angle x-ray scattering (GISAXS) is proposed as one of the candidates for characterizing cross
section of nanostructure line grating pattern. GISAXS is expected as useful nondestructive tool for characterizing cross
section. We developed GISAXS and evaluated the capability using the 4X nm resist line patterns and the 3X nm silicon
gate line patterns. The GISAXS results are compared with TEM images to evaluate the reconstruction ability in cross
section contour profile. The correlation is investigated between GISAXS and the reference tools such as CD-SEM and
TEM in the values of CD, height and bottom corner radius. The static repeatability is also evaluated by performing measurement ten times. We report the results of GISAXS capability as cross sectional metrology tool in actual device of 4X and 3X generation.
KEYWORDS: Scanning electron microscopy, Scatterometry, Metrology, Critical dimension metrology, Monte Carlo methods, Inspection, Stereolithography, Manufacturing, Time metrology, Optical proximity correction
Measurement characteristics in scatterometry and critical dimension-scanning electron microscopy (CD-SEM) for lot acceptance sampling of inline CD metrology were investigated by using a statistical approach with Monte Carlo simulation. By operation characteristics curve analysis, producer's risk and consumer's risk arising from sampling were clarified. Single use of scatterometry involves a higher risk, such risk being particularly acute in the case of large intrachip CD variation because it is unable to sufficiently monitor intrachip CD variation including local CD error. Substituting scatterometry for conventional SEM metrology is accompanied with risks, resulting in the increase of unnecessary cost. The combined use of scatterometry and SEM metrology in which the sampling plan for SEM is controlled by scatterometry is a promising metrology from the viewpoint of the suppression of risks and cost. This is due to the effect that CD errors existing in the distribution tails are efficiently caught.
KEYWORDS: Scatterometry, Critical dimension metrology, Metrology, Scanning electron microscopy, Monte Carlo methods, Inspection, Time metrology, Statistical analysis, Optics manufacturing, Line edge roughness
Measurement characteristics in scatterometry and CD-SEM for lot acceptance sampling of inline critical dimension (CD) metrology were investigated by using a statistical approach with Monte Carlo simulation. By operation characteristics curve analysis, producer's risk and consumer's risk arising from sampling were clarified. Single use of scatterometry involves a higher risk, such risk being particularly acute in the case of large intra-chip CD variation because it is unable to sufficiently monitor intra-chip CD variation including local CD error. Substituting scatterometry for conventional SEM metrology is accompanied with risks, resulting in the increase of unnecessary cost. The combined use of scatterometry and SEM metrology in which the sampling plan for SEM is controlled by scatterometry is a promising metrology from the viewpoint of the suppression of risks and cost. This is due to the effect that CD errors existing in the distribution tails are efficiently caught.
Scatterometry, a non-destructive optical metrology, provides information on cross-sectional pattern profiles, including pattern height, sidewall angle and linewidth. Compared with other non-destructive metrology tools, such as the atomic force microscope (AFM) and CD-SEM, scatterometry offers the advantages of high throughput and superior repeatability. We have applied scatterometry to the monitoring of the depth of Shallow Trench Isolation (STI) for the analysis of complicated stack. We obtained sufficient measurement accuracy by optimizing a model.
In addition, we propose the application of scatterometry to post-lithography monitoring for advanced process control (APC). A regression model was established to derive effective dose and focus from the change of photoresist profile monitored by means of scatterometry. In our experiment using an ArF scanner, we obtained sufficient measurement repeatability of dose and focus.
For advanced process control, a sampling plan for critical dimension measurement is optimized through empirical considerations concerning the nature of error and a statistical approach. The metric of the optimization is the accuracy of lot mean estimation. In this work, critical dimension errors are classified into static and dynamic components. The static component is defined as the error which repeats through lots while keeping its tendency, and the dynamic as the error whose tendency changes by lot. In the basic concept of our sampling plan, sampling positions and size are determined from the static and dynamic error, respectively. The balance of sampling number of wafer, field and pattern is obtained under the restriction of total sampling size by a statistical theory with some assumptions. Based on the concept, we could make a sampling plan for 65 nm CMOS lithography.
Reducing resist thickness easily and simultaneously decreases the k1 factor and increases the k2 factor in conventional Rayleigh equations, without changing the wavelength of the illumination light and NA of the optics. In this work, we investigated the effect of reduced resist thickness on process latitude and optical proximity effect (OPE) at the sub-quarter micron level. The experiment exposures were performed by a 0.6 NA KrF excimer step and scan system with an in-house chemically amplified positive resist in the thickness range of 0.6 micrometers to 0.25 micrometers . The results showed remarkable improvements in process latitude of both 0.175 micrometers L&S and 0.225 micrometers contact hole, as well as OPE such as a CD variation between different pitches and a feature deformation at isolation by reducing resist thickness.
Recently, resist edge roughness with reducing pattern size has become a serious problem. We investigated the roughness of chemically amplified, positive-tone resists, experimentally. To reduce the roughness, we added a quencher with strong basicity to the resist, and observed sub quarter micron nested lines. As a result, the roughness was improved with increasing the quencher concentration, especially in 0.15 micrometers nested line patterns. Adding quencher was not too much effective for the larger size patterns. The acid concentration in resist was increased by adding quencher, because the nominal dose became large by that. It was also indicated experimentally that generated acid concentration at pattern edge was nearly equal to that of quencher at nominal dose. The nominal dose was determined by quencher concentration. We defined effective acid concentration as remaining acid concentration after quenching. This effective acid concentration increased with increasing quencher concentration too. The roughness seemed to be generated when effective acid concentration profile was lowered. It is indicated that the resist edge roughness with reducing pattern size can be expected from its effective acid concentration profile.
At the first stage of defect repair on masks with focused ion beam (FIB), it is necessary to recognize defects by imaging. One of the problems in halftone mask imaging by FIB is that the contrast between halftone (HT) film and quartz (Qz) substrate is not sufficient to recognize material. We investigated the methods of the defect area distinction in deep UV silicon nitride (SiNx) single-layer halftone masks to avoid the transmittance decrease of masks induced by FIB irradiation. The cause of the difficulty in the area distinction is that the difference between the mean secondary electron intensity of HT area and that of Qz area is small in comparison with the width of the secondary electron intensity distributions. A conventional filter was found to be effective to narrow the intensity distributions and the area of defects on halftone masks could be recognized by means of the image filter in the images obtained with a low FIB dose.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.