Nanoimprint lithography (NIL) is promising technology for next generation lithography for the fabrication of semiconductor devices. The advantages of NIL are simpler process, less design rule restriction, which lead to lower cost-of-ownership, compared with conventional optical lithography. NIL is one to one lithography and contact transfer technique using template. Therefore template quality variations impact on wafer performance directly. To introduce NIL technology to high volume manufacturing (HVM) of semiconductor devices, improvement of template quality is very important. In the situation of pattern size shrinking, it is necessary to improve CD uniformity and defectivity to achieve the target of HVM. So that high accuracy QA (Quality Assurance) tools are required to qualify CD uniformity and defectivity which are key metrics on high-end template development. In this paper, we show the current status of template development for sub15nm NIL. For the template fabrication, double patterning technologies were applied to extend pattern resolution limit. Template replication was also implemented by template replication system Canon FPA1100-NR2. Finally we will show QA examples for high accuracy template by using key metrics such as CD uniformity, defectivity and Cross-sectional profile.
KEYWORDS: Signal to noise ratio, Deep ultraviolet, Inspection, Scanning electron microscopy, Photomasks, Extreme ultraviolet, Line width roughness, Extreme ultraviolet lithography, Critical dimension metrology
Deep Ultra Violet (DUV) inspection of Extreme Ultra Violet (EUV) mask has been known for high stability, high throughput, and low cost, since it has been used for a long time, even though sensitivity is thought to be insufficient for the EUV mask of under 20 nm half pitch (hp). We have been studying extendibility for 1X nm hp of the DUV inspection using optics named Super Inspection Resolution Improvement method for UnreSolved pattern (SIRIUS). In previous study, we demonstrated the DUV inspection has capability for the EUV mask of 17 nm hp Lines and Spaces (LS) on wafer. In this paper, the more extendibility for the DUV inspection of EUV masks under sub-15 nm on wafer was demonstrated by studying relationship of roughness and sensitivity. Firstly, an estimated model for effects of the EUV mask roughness to Signal Noise Ratio (SNR) of the inspection image was established, and simulation was carried out. Secondly, the SNR was evaluated using actual Line Width Roughness (LWR) improved masks. It was confirmed that the results are the same trend as the model and the simulation, and, the SNR is enhanced with the LWR improvement. Finally, the sensitivity of the LWR improved mask was evaluated. As a result, it becomes enough for the EUV mask over 13 nm hp on wafer. In conclusion, we confirm that the DUV inspection of the EUV mask by the SIRIUS can be extending to the 13 nm hp LS on wafer, this is around the limit of NA 0.33 EUV lithography, using the LWR improved mask.
It is generally said that conventional deep ultraviolet inspection tools have difficulty meeting the defect requirement for extreme ultraviolet masks of hp 1X nm. In previous studies, it has been shown that the newly developed optics and systems using deep ultraviolet, named Super Inspection Resolution Improvement method for UnreSolved pattern (SIRIUS), has high sensitivity for nanoimprint lithography templates with unresolved patterns which are the same scale as the wafer. In this paper, the capability of SIRIUS for the extreme ultraviolet mask of hp 1X nm lines and spaces pattern has been studied by evaluating the signal to noise ratio of inspection images and capture rates with 5 runs to the target defects which cause over 10% printed wafer critical dimension errors calculated by simulation. It was demonstrated that the signal to noise ratio was increased and the all target defects became detectable with the throughput of 120 min per 100 × 100 mm2 . Additionally, the printability of natural defects detected with SIRIUS was analyzed. It was confirmed that SIRIUS was able to detect natural defects under 10% of wafer critical dimension. In conclusion, we confirm that SIRIUS can be available for the extreme ultraviolet mask inspection of hp 1X nm lines and spaces pattern.
Recently, much attention has been paid on nanoimprint lithography (NIL) because of its capability for fabricating device
at a low cost without multiple patterning. It is considered as a candidate for next generation lithography technology. NIL
is one to one lithography and contact transfer technique using template. Therefore, the lithography performance depends
greatly on the quality of the template pattern. And there are some challenges to be solved for defect repair of template
because pattern size of template is as same as that of wafer.
In order to realize the defect repair of template using electron beam (EB) repair tools, it is necessary to control the EB
irradiated area and dose amount of EB repair process more accurately. By optimizing these conditions, EB repair process
for template has been improved.
In this paper, we evaluated etching repair of a master template and the imprinting to replica. Programmed missing defects
on master template were repaired by changing parameters of EB repair tool. It was confirmed that the relationship of
critical dimension (CD) and depth of etching repair process for master template and the influence on replica imprinting.
As a result, the repair process for master template with hole pattern enables the corresponding CD error of the replica
template to be less than ±10% of the target CD.
We summarize the metrology and inspection required for the development of nanoimprint lithography (NIL), which is recognized as a candidate for next-generation lithography. Template inspection and residual layer thickness (RLT) metrology are discussed. An optical-based inspection tool for replica template inspection showed sensitivity for defects below 10 nm with sufficient throughput. For the RLT control, in-die RLT metrology is needed. Because the metrology requires dense sampling, optical scatterometry is the best solution owing to its ability to measure profile features nondestructively with high throughput. For in-die metrology, we have developed a new hybrid metrology that can combine key information from these complex geometries with scatterometry measurements to reduce the impact on the RLT measurement due to the layers beneath the resist. The technologies discussed here will be important when NIL is applied for IC manufacturing, as well as in the development phases of those lithography technologies.
Mask inspection tool with DUV laser source has been used for Photo-mask production in many years due to its high sensitivity, high throughput, and good CoO. Due to the advance of NGL technology such as EUVL and Nano-imprint lithography (NIL), there is a demand for extending inspection capability for DUV mask inspection tool for the minute pattern such as hp4xnm or less. But current DUV inspection tool has sensitivity constrain for the minute pattern since inspection optics has the resolution limit determined by the inspection wavelength and optics NA.
Based on the unresolved pattern inspection capability study using DUV mask inspection tool NPI-7000 for 14nm/10nm technology nodes, we developed a new optical imaging method and tested its inspection capability for the minute pattern smaller than the optical resolution. We confirmed the excellent defect detection capability and the expendability of DUV optics inspection using the new inspection method. Here, the inspection result of unresolved hp26/20nm pattern obtained by NPI-7000 with the new inspection method is descried.
According to the road map shown in ITRS , the EUV mask requirement for defect inspection is to detect the defect
size of sub- 20 nm in the near future. EB (Electron Beam) inspection with high resolution is one of the promising
candidates to meet such severe defect inspection requirements. However, conventional EB inspection using the SEM
method has the problem of low throughput. Therefore, we have developed an EB inspection tool, named Model EBEYE
M※. The tool has the PEM (Projection Electron Microscope) technique and the image acquisition technique with TDI
(Time Delay Integration) sensor while moving the stage continuously to achieve high throughput .
In our previous study, we showed the performance of the tool applied for the half pitch (hp) 2X nm node in a production
phase for particle inspection on an EUV blank. In the study, the sensitivity of 20 nm with capture rate of 100 % and the
throughput of 1 hour per 100 mm square were achieved, which was higher than the conventional optical inspection tool
for EUV mask inspection -.
Such particle inspection is called for not only on the EUV blank but also on the patterned EUV mask. It is required after
defect repair and final cleaning for EUV mask fabrication. Moreover, it is useful as a particle monitoring tool between a
certain numbers of exposures for wafer fabrication because EUV pellicle has not been ready yet. However, since the
patterned EUV mask consists of 3D structure, it is more difficult than that on the EUV blank.
In this paper, we evaluated that the particle inspection on the EUV blank using the tool which was applied for the
patterned EUV mask. Moreover, the capability of the particle inspection on the patterned EUV mask for the hp 2X nm
node, whose target is 25 nm of the sensitivity, was confirmed. As a result, the inspection and SEM review results of the
patterned EUV masks revealed that the sensitivity of the hp 100 nm Line/Space (LS) was 25 nm and that of the hp 140-
160 nm Contact Hole (CH) was 21 nm. Therefore, we confirmed that particle inspection on the patterned EUV mask
using Model EBEYE M could be available for the EUV mask of the hp 2X nm node. In the future, we will try to inspect
the production mask of the hp 2X nm node, and try to confirm the performance for the EUV mask of the hp 1X nm node.
For sub-10nm lithography for semiconductor devices, inspection technologies for detecting nanometer size defects become quite important. In the case of optical inspection, it is difficult to detect a defect whose size is less than 23nm because of optical resolution limit. This paper describes a cost-effective inspection technology for detecting a nanometer size defect with the optical inspection technology using replicated soft template which is able to enlarge a defect size by expanding. Feasibility of detecting 9.6nm defect with optical inspection is reported.
Based on an acceptable wafer critical dimension (CD) variation that takes device performance into consideration, we
presented a methodology for deriving an acceptable mask defect size using defect printability -. The defect
printability is measurable by Aerial Image Measurement System (AIMSTM) and simulated by lithography simulation
without exposure. However, the defect printability of these tools is not always the same as the actual one. Therefore, the
accuracy of these tools is confirmed by fabricating the programmed defect mask and exposing this mask on wafer.
Advanced Binary Film (ABF) photomask has recently been studied as a substitute for the conventional MoSi phase shift
mask. For ABF photomask fabrication, mask performance for process and guarantee for mask defects by repair and
inspection are important. With regard to the mask performance, the ABF photomask has high performance in terms of
resolution of pattern making, placement accuracy, and cleaning durability . With regard to the guarantee for mask
defects, it has already been confirmed that the defect on the ABF photomask is repairable for both clear and opaque
defects. However, it has not been evaluated for inspection yet. Therefore, it is necessary to evaluate the defect
printability, to derive the acceptable mask defect size, and to confirm the sensitivity of mask inspection tool.
In this paper, the defect printability of the ABF photomask was investigated by the following process. Firstly, for opaque
and clear defects, sizes and locations were designed as parameters for memory cell patterns. Secondly, the ABF
programmed defect mask was fabricated and exposed. Thirdly, mask defect sizes on the ABF programmed defect mask
and line CD variations on the exposed wafer were measured with CD-SEM. Finally, the defect printability was evaluated
by comparing the correlation between the mask defect sizes and the wafer line CD variations with that of the AIMSTM
and the lithography simulation. From these results, the defect printability of AIMSTM was almost the same as the actual
one. On the other hand, the defect printability of the lithography simulation was relaxed from the actual one for the
isolated defect types for both clear and opaque defects, though the defect printability for the edge defect types was
almost the same. Additionally, the acceptable mask defect size based on the actual defect printability was derived and
the sensitivity of the mask inspection tool (NPI-7000) was evaluated. Consequently, the sensitivity of the NPI-7000 was
detectable for the derived acceptable mask defect size. Therefore, it was confirmed that the ABF photomask could be
guaranteed for mask defects.
We have developed a new photomask inspection method which has capability for inspecting 65nm technology node reticles using 257nm wavelength light source. This new method meets the requirement for the current mask inspection system using KrF inspection light source to be employed even in the fabrication of photomasks for 65nm technology node by the appearance of immersion technology using ArF wavelength. This paper discusses the detection capability of the 257nm wavelength inspection system for the defects on the 6% ArF attenuated phase shifting masks for 65nm node, using DSM based test pattern mask.
Binary (Chromium) and, KrF/ArF phase shift masks (PSM) were inspected by MC-3000, which uses DUV (257nm) light source, and an evaluated results of these sensitivities are shown. In the case of the chromium mask, sufficient detection sensitivity for 130nm-device inspection was obtained. For KrF and ArF phase shift masks, the detection sensitivities of the edge and the corner areas are practically equivalent to that of chromium. Though the detection sensitivity of a minute pinhole is slightly lower under the influence of the diffracted light. With an ArF phase shift mask, the contrast of absorber and a glass portion is low, and so improvement of the signal noise ratio of a sensor becomes essential for false-defect control. Additionally, the minute pinhole detection sensitivity will be higher, if a reflective inspection etc. is carried out.
Toshiba and Toshiba Machine have developed an advanced electron beam writing system EX-11 for next-generation mask fabrication. EX-11 is a 50 kV variable-shaped beam lithography system for manufacturing 4x masks for 0.15 - 0.18 micrometer technology generation. Many breakthroughs were studied and applied to EX-11 to meet future mask-fabrication requirements, such as critical dimension and positioning accuracy. We have verified the accuracy required for 0.15 - 0.18 micrometer generation.
In order to obtain a precise dose control for proximity effect correction, a fast beam blanking system has been developed which can make possible the fine control of the beam pulse width with precision of less than 1 nanosecond. The system consists of a high precision blanker driving circuit and a blanking structure suitable for fast operation. The blanker driving circuit controls the pulse width by selecting delay line logic with required delay. The pulse width control of less than 1 nanosecond and pulse rising time of less than 10 nanoseconds were achieved. A coaxial structure was adopted for the blanking structure. The simulation study has shown that a blanking structure with low reflectance in a few GHz range is achievable. The pulse passed through an experimental blanking structure without distortion in waveform.