To realize higher resolution in optical inspection systems is typically using shorter wavelengths including UV light and a higher NA of the objective lens. Extreme performances of illumination and imaging systems in well-matched situations are inevitable with further effort put on the development of an effective optical system for inspecting microscopic defects on patterned wafers.
For this study, we focus on the dark-field illumination system for index-matched near-field microscope using an aplanatic solid immersion lens (A-SIL). We present dark-field illumination that has illumination channels on the side of the A-SIL to overcome the issue of deficient space. The table-top experiments are conducted to show a feasibility of a dark-field imaging method for the near-field condition before verifying the performance of the optical system.
The tutorial describes essential features of moiré patterns, as well as the circumstances, when the moiré patterns appear and how to estimate their characteristics (parameters) such as the orientation and period. The moiré effect is described in two domains, the image space (spatial domain) and in the spectral domain using the complex numbers. The tutorial covers the indicial equation method, the coplanar and noncoplanar sinusoidal gratings, the moiré effect in a spatial object (a cylinder), as well as explains the moiré wave vector, the moiré spectra, the spectral trajectories, and summarizes behavior of the visible patterns in moved/rotated gratings.
General approaches to realize higher sensitivity in optical inspection system are using shorter wavelength including UV and higher NA for objective lens. Extreme performances of imaging and illumination systems in a situation of wellmatched to each other are inevitable for the further effort on an effective optical detection of fine defects in patterned wafer. This study focused on the dark-field illumination method in near-field condition with simple modification of far-field imaging and illumination system which is designed by anamorphic optics and the potential of it is derived from experimental methods.
General approaches to realize higher sensitivity in optical inspection system are using shorter wavelength including UV and higher NA for objective lens. Extreme performances of imaging and illumination systems in a situation of wellmatched to each other are inevitable for the further effort on an effective optical detection of fine defects in patterned wafer. This study focused on the dark field illumination systems satisfying hi areal uniformity and concentration efficiency for the specific conditions of non-symmetric illumination area and critical slanted angle. Three different types of anamorphic dark field illumination systems namely, Far-field Areal Illumination (FAI), Near-field Areal Illumination (NAI) and Farfield Linear Illumination (FLI), are designed and evaluated by brightness, uniformity and concentration efficiency of beam intensity.
In General, OLED, LCD, TSP Glass TFT Pattern consists of multi-layer of electrodes separated by a thin insulating film and layers are very close to each other. The inspection of electrode pattern and defect in multilayered devices by using visible light (550nm around) image is too much difficult to define its critical shape among layers, because of deep depth range in conventional optics of moderate numerical aperture (NA). To increase image contrast between materials and layers, this study uses UV wavelength that has larger selective differences of reflectance than visible light. Newly developed optical system and image analysis units are focused to the proper inspection wavelength at the specific UV range to clearly define a top electrode layer and reduce image processing time. To detect defects on the electrode, the resolution of the optical system should be much higher than the spatial frequency of the electrode size. After considering system requirements, two types of different magnification systems (1.2X and 3X) are developed. Direct side illumination is available in 1.2X system which has large back focal length, however, 3X system needs on axis illumination. Line beam illumination from the multi-point LED source (custom made) is used to increase the light efficiency and decrease noise(4). Illumination beam passing through the common objective lens (in front of imaging optics) and illumination optics (including cylinder lens) can realized uniform intensity of one dimensional Fourier plane on the surface of target electrode. Electric units for high speed data processing and transfer and image processing algorithm are also developed. For processing large capacity image data (8 GB) synchronized with moving sensors in real time, embedded system with hardware optimizing design and FPGA module camera are adopted. Final image shows good selective contrast and resolution between layers even in the high depth condition followed by required NA for the target resolution. This inspection system can be used in inspection of PCB Pattern, LCD, OLED and Mobile Glass including many other film and glass.
KEYWORDS: Charge-coupled devices, Molybdenum, Digital holography, Holography, Holograms, Microscopes, 3D image reconstruction, 3D metrology, Optical engineering, 3D image processing
Holography has a considerable advantage of retrieving three-dimensional information of an object from only one interference recording. However, twin images always appear in the reconstruction for the reason of symmetry. Especially, twin images significantly deteriorate the quality of the reconstructed information in on-axis configuration. A solution of the twin-image problem in a digital holographic microscope by using symmetry with quadrantal masks is suggested in this study. This method is effective to most of the measured area without any additional implements, and restrictions on sample or iterations, and is demonstrated by the simulation and experimental results. The ratio of the disturbed area by a twin-image to the total measured area is reduced to the value of 0.82% in a specific case.
We study the tolerance characteristic of SIAX and suggest a newly designed SIL-Axicon system for the better tolerances.
Methods for checking beam quality, optimization and remaining problems are suggested. SIL-Axicon system shows
more tolerances in the uniformity of beam incident angle. Bessel beam (BB) with SIL can be used for multi layer high
density data storage systems. We study the tolerance characteristic of SIAX and suggest a newly designed SIL-Axicon
system for the better tolerances.
Digital holography (DH) has a big advantage to retrieve the
three-dimensional (3D) information of the object from only
one interference recording. Especially, the digital holographic microscope (DHM) using a microscope objective (MO)
has been researched for 3D microscopy. The researches have progressed for compensation of aberrations and
improvement of the resolution in the optical system in recent years. Most of small aberrations caused by a MO are
compensated through various researches. However, the measured phase is distorted in the optical system, which has the
significant wavefront deformation in illuminating wave larger than number of wavelengths. In this paper, the relation
between illuminating wave and the reconstructed phase is studied based on the wave optics and the analysis is confirmed
by the simulations. The analysis of the wavefront compensation is applied to a super-resolution DHM in theory and the
technique for retrieving the distribution of the intensity and phase is demonstrated in simulation.
The digital holographic microscope (DHM) has emerged as a useful tool for verifying the three-dimensional structure of an object. A dual-type inline DHM that can be used with both transmission and reflection imaging in a single device is developed. The proper modes (between transmission and reflection imaging) can be easily changed according to the characteristics of the object in this system. The optimum condition for retrieving the correct phase information is illuminating a plane wave to an object. In contrast to the transmission imaging, it is difficult to illuminate an object using a plane wave without deformations in the reflection imaging. We developed an adequate relay lens module for illumination that can be adapted to any type of microscope objective without significant aberrations in the reflection imaging. The relationship between the illuminating condition and the measured phase based on the wave optics is analyzed. A specially designed and manufactured phase mask is observed in this system, and an alternative method for overcoming the limitation of phase unwrapping is introduced for the inspection of that object.
Axicon produces a deep focused Bessel beam whose transverse focal spot is smaller than the size of an airy disk
produced by conventional lens with the same numerical aperture. Rieko Arimoto et al. applied axicon to a beamscanning
system and established the beam-scanning imaging system which is free from need of precise positioning.
Meanwhile, the allowed amount of rotation is severely restricted due to the unwanted tilt in the focused ring. We analyze
the tilt in the focused ring quantitatively and suggest an appropriate method of designing the aberration corrected lens.
An exemplary lens design for 1° tilt in the scanning mirror is presented and it is shown that the amount of degradation is
clearly suppressed in the optimized system.
Holography has a considerable advantage to retrieve the three-dimensional (3D) information of an object from only one
interference recording. For several decades, the technology of digital holography (DH), which uses numerical
reconstruction as opposed to illuminating the reference beam to the hologram plate, has progressed with the assistance of
improvements in 2D array detectors and computers. In this paper, a dual-type inline digital hologram microscope (DHM)
system that can be used with both transmission imaging and reflection imaging in a single device is developed. The
proper method depending on the modes (transmission imaging or reflection imaging) can be changed easily in this
system according to the characteristics of the object. Illumination with a plane wave is the necessary condition for
retrieving the correct phase information. In the case of reflection imaging, unlike in transmission imaging, a special relay
lens in addition to the microscope objectives (MOs) is needed to meet the needs of this condition. However, the quality
of the 3D information can deteriorate significantly due to the overlapping twin image that is inherent in holography. This
study suggests an effective and convenient method for eliminating the twin image that is entangled in the reconstructed
information. The proposed method does not require extra components, numerical iterations, and restrictions on the
object.
According to the ITRS roadmap, DRAM half pitch (hp) will reach to 32 and 20 nm in 2012 and 2017
respectively. However, it is difficult to make sub-40 nm node by single exposure technology with currently
available 1.35 numerical aperture (NA) ArF immersion lithography. Although it is expected to enable 32 nm hp
with either double patterning technology or extreme ultra-violet lithography, there are many problems to be
solved with cost reduction. Thus, the study of high-index fluid immersion technology should be pursued
simultaneously. ArF water immersion systems with 1.35 NA have already introduced for 40 nm hp production.
ArF immersion lithography using high-index materials is being researched for the next generation lithography.
Currently, many studies are undergoing in order to increase NA with higher index fluid and lens in immersion
technology. The combination of LuAG (n=2.14) and third-generation fluid could be used to make 1.55 NA. This
combination with 0.25 k1, 32 nm hp can be obtained by single exposure technology. In order to check the
realization of this process and to check the possible process hurdles for this high NA single exposure technology,
32 nm hp with 1:1 line and space patterning is tried. Various illumination conditions are tried to make 1:1 32 nm
hp and the exposure and develop conditions are varied to check whether this single exposure can give
processible window. As a result, 32 nm hp can be obtained by single exposure technology with 1.55 NA.
Patterning of contact hole is always the most difficult process among many types of pattern formations. Specially
for the Extreme Ultra-Violet Lithography (EUVL), it will be even more difficult to make perfectly circled contact hole
due to the shadow effect. The shape of contact hole will be elliptical because the vertical axis opening is different from
the horizontal axis opening. We studied this behavior for 22 nm node contact hole patterns. We varied the pitch of the
regular contact hole array. The dependency of the position and density is studied for the random array. In addition to that
the thickness of the absorber and the reflectivity of the multilayer are varied to see non-circular contact hole. In order to
make desired circular contact hole with uniform width, direction dependent mask bias is applied in addition to the
normal optical proximity correction.
The crystal growth and haze formation on the reticle continue to be significant problems for the semiconductor industry. Recently, a pattern size has gradually reduced to enhance the integration of semiconductor device. As minimum linewidth has shrunk, the exposure wavelength has also progressively shrunk. The exposure wavelengths have been reduced progressively from g-line (436 nm), i-line (365 nm), KrF (248 nm), to ArF (193 nm). However, expose wavelength shrink caused some serious problems. One of the problems to be solved is growing defect in the reticle during the process. This growing defect on the reticle is called the haze. The haze is formed on both sides of the reticle, on the quartz side of the mask and on the chrome side of the mask. In this investigation, we varied the local haze defect size and the characteristics of the haze defect. And we get the critical dimension and the exposure latitude variation as the haze transmission changes and the haze phase shifts.
Pattern collapse for line widths under 32 nm printed by extreme ultra-violet lithography (EUVL) is investigated by using commercial tools. Pattern collapse phenomenon occurs very often in actual process. Pattern collapse means that pattern is bending, peel-off, and break of the resist, thus it affects the production and yield of semiconductor. In this paper, we newly defined and investigated the critical aspect ratio. Pattern collapse happens if the critical aspect ratio is smaller than aspect ratio. Because EUV resist has smaller adhesive strength than currently available DUV and ArF resists, EUV resist easily collapse more easily than DUV resist does. This phenomenon is successfully modeled.
Making a sub-100 nm contact hole pattern is one of the difficult issues in semiconductor process. Compared with
another fabrication process, resist reflow process is a good method to obtain very high resolution contact hole. However
it is not easy to predict the actual reflow result by simulation because very complex physics and/or chemistry are
involved in resist reflow process. We must know accurate physical and chemical constant values and many fabrication
variables for better prediction. We made resist reflow simulation tool to predict approximate resist reflow as functions of
pitch, temperature, time, array, and so on. We were able to see the simulated top view, side view and the changed hole
size. We used Navier-Stokes equation for resist reflow. We had varied the reflow time, temperature, surface tension, and
3-dimensional volume effect for old model. However the photoresist adhesion is another very important factor that was
not included in the old model. So the adhesion effect was added on Navier-Stokes equation and found that there was a
distinctive difference in reflowed resist profile and the contact hole width compared to the case of no adhesion effect.
The desired minimum feature size is decreasing for the future technology nodes. Immersion lithography has been actively pursued as a method of extending the resolution of optical lithography beyond 65 nm mode. Immersion lithography and hyper NA impact the selection and optimization of the various resolution enhancement techniques (RET). These can be selected as appropriate for each mask pattern. As the line width on target is narrower, the fine-line structure will no longer be discernible. Then this is the resolution limit of the system. Until recent times, the traditional means of determining the quality of an optical element or system of elements was to evaluate its limit of resolution. A useful parameter in evaluating the performance of a system is the modulation transfer function and this is analyzed for the hyper NA immersion lithography.
It is expected that technological needs will increase to create tinier patterns, since the information communication society requires the massive capacity semiconductor. Reducing the wavelength of the light source is the most powerful method for improving ever-decreasing the minimum feature size of the semiconductor device. 193 nm ArF excimer laser source will be followed by 157 nm F2 excimer laser source for the next generation device down to 32 nm line width. Also, it is predicted that the technology of 157 nm ultra vacuum violet light for super fine pattern formation will be essentially used in memory or logic semiconductor manufacturing, their parts and process development. 157 nm interference imaging lithography system will be built with direct support of 157 nm resist and its process development. A circumstance that reduces the absorption rate due to air, water, O3, and other gases must be made. So, the entire system is enclosed in a N2 purged. The optical interference system was constructed after investigating various optical materials, and it enabled us to test various chemical materials to produce a real pattern by implementing the existing optical system. By using the illumination system that uses Lloyd's mirror interference type, simple interference line and space pattern was obtained.
Resolution enhancement technology will play a crucial role in the future of optical lithography. The only question is how much the resolution limit can be extended. The better critical dimension (CD) uniformity is demanded as pattern size is decreased. In our previous work, we had made a simulation tool which can find the optimum illumination system such as numerical aperture, wavelength, and illumination shape for best CD control. In order to improve better CD control, the mask size, assist feature size and placement are modified by the simulated annealing (SA) algorithm. However, in this method, the effects of post exposure bake or development process are not considered to predict the real CD, since the results are obtained only with the aerial image which can be precisely calculated. To consider these elements that affect CD profile, threshold energy resist model (TERM) model was suggested previously. However, TERM model still has a weak point in extracting necessary parameters for the transfer function. Therefore, we made a simulation tool using Monte Carlo method that extracts the necessary parameters with the experimental data. The experimental data include the exposure energy, measured line CD on a mask, wafer line CD after development. Finally, the predicted line CDs are compared to the empirical data under a different optical system condition to verify the extracted parameters. The simulation results matching the actual process can be obtained by using these methods.
Three different versions of high numerical aperture 0.3 degree field diffraction limited WHAM lens systems are designed for hi-density data storage by using over-hemi- cylinder surfaces. A prototype WHAM lens with NAi equals 1.23 is also discussed. Detail of unique tolerance issue is presented.
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.