The Cherenkov Telescope Array (CTA) project aims to implement the world’s largest next generation of Very High Energy gamma-ray Imaging Atmospheric Cherenkov Telescopes devoted to the observation from a few tens of GeV to more than 100 TeV. To view the whole sky, two CTA sites are foreseen, one for each hemisphere. The sensitivity at the lowest energy range will be dominated by four Large Size Telescopes, LSTs, located at the center of each array and designed to achieve observations of high red-shift objects with the threshold energy of 20 GeV. The LST is optimized also for transient low energy sources, such as Gamma Ray Bursts (GRB), which require fast repositioning of the telescope. The overall design and the development status of the first LST telescope will be discussed.
We evaluated a new FIB-GAE (Focused Ion Beam-Gas Assisted Etching) repairing process for the absorber defects on
EUVL mask. XeF<sub>2</sub> gas and H<sub>2</sub>O gas were used as etching assist agent and etching stop agent respectively. The H<sub>2</sub>O gas
was used to oxidize Ta-nitride side-wall and to inactivate the remaining XeF<sub>2</sub> gas after the completion of defect repair.
At the Photomask Japan 2008 we had reported that side-etching of Ta-nitride caused CD degradation in EUVL. In the
present paper we report on the performance of defect repair by FIB, and of printability using SFET (Small Field
Exposure Tool). The samples evaluated, were in form of bridge defects in hp225nm L/S pattern. The cross sectional
SEM images certified that the newly developed H<sub>2</sub>O gas process prevented side-etching damage to TaBN layer and
made the side-wall close to vertical. The printability also showed excellent results. There were no significant CD
changes in the defocus characterization of the defect repaired region. In its defect repair process, the FIB method showed
no signs of scan damage on Cr buffered EUV mask. The repair accuracy and the application to narrow pitched pattern
are also discussed.
EUV mask damage caused by Ga focused ion beam irradiation during the mask defect repair was studied. The
concentration of Ga atom implanted in the multilayer through the buffer layer and distributions of recoil atoms were
calculated by SRIM. The reflectivity of the multilayer was calculated from the Ga distribution below the capping layer
surface. To validate the calculation, Ga focused ion beam was irradiated on the buffer layer. The EUV reflectivity was
measured after the buffer layer etching process. The measured reflectivity change was considerably larger than the one
predicted from the absorption of light by the implanted Ga. The large reflectivity loss was primarily due to the absorption
of light by chromium silicide residue which was generated by the intermixing of the buffer and the capping layer. Both
lowering of the acceleration voltage and using thicker buffer layer were found to be effective in reducing this intermixing.
The reduction of the reflectivity loss by using thicker buffer layer was confirmed by our experiments. An aerial image of
patterns with etching residue formed by the intermixing was simulated. When the thickness of the intermixed layer
happened to be 8 nm and the size of the resulting residue was larger than 100 nm, then the impact of the estimated
absorption by the residue on the linewidth of 32 nm hp line pattern became more than 5 %.
We utilized a newly developed low acceleration voltage FIB (Focused Ion Beam) system and evaluated the process for
repairing the absorber layer on EUVL mask.
During the etching of the absorber layer, which is a step in conventional repair technique, a phenomenon of side-etching
of Ta-nitride layer with XeF<sub>2</sub> gas was observed. This phenomenon was considered to be caused by the isotropic
etching of the Ta-nitride layer with XeF2 gas. We then added another gas for etching and evaluated the new process to
prevent the side-etching of Ta-nitride layer.
In this paper, we will report four evaluation results of EUVL mask pattern defect repair using FIB-GAE (Gas Assisted
Etching). The first one is the problem of pattern topography after conventional repairing process and the reaction
mechanism of gas assisted etching of Ta based absorber. The second evaluation result is addressed in two parts. One is
the evaluation of a new gas assisted etching process that employs an additional gas that has an ability to control the
etching rate of absorber layer. The second part addresses the repairing accuracy of EUVL mask pattern. The third is the
basic etching performance e.g. etching rate of Ta based absorber, Cr based buffer, and Si based capping layer. The fourth
and the last evaluation is the application of the newly developed gas assisted etching process on programmed bridge
defect in narrow pitched L/S patterns.
EUV mask damage caused by Ga focused ion beam irradiation during the mask defect repair was studied. The
concentration of Ga atom implanted in the multilayer through the buffer layer was calculated by SRIM. The reflectivity
of the multilayer was calculated from the Ga distribution below the capping layer surface. To validate the calculation, a
multilayer sample was irradiated with Ga FIB, and then EUV reflectivity was measured. The measured reflectivity
change was in good agreement with the calculated value. An aerial image of patterns with Ga implanted region was
simulated. The impact of the estimated Ga absorption on the linewidth of 32 nm hp line pattern was found to be less than
In order to go through the transition term from GDSII to OASIS successfully, the aid of the verification tools between
OASIS and GDSII is necessary. In general, we have two methods of OASIS file verification. One is a hierarchical method
that checks between GDSII and OASIS by each cell level. The other is a flat method that merges each pattern through its
hierarchy into a flat level and compares the flattened geometry one by one.
We did the experiments of comparison between two methods for OASIS to GDSII verification. The software tool called
'ogdiff' has been used for a hierarchical verification experiment. We used SmartMRC for the flat method experiment. In this
paper, we show the experimental results of comparison and we also address the pros and cons of each method. Then we
suggest which method is preferable for specific cases.
Association of Super-Advanced Electronics Technologies (ASET) has started a project called "Mask Design, Drawing
and Inspection Technology (MaskD2I)" with the sponsorship from The New Energy and Industrial Technology Development Organization (NEDO) since 2006. SIINT has joined the MaskD2I project and we have been developing MRC software considering DFM information for more effective data verification. By converting design level information
called as "Design Intent" to the priority information of mask manufacturing data called as "Mask Data Rank (MDR)", the
MRC process based on the importance of reticle patterns is possible. Our main purpose is to build a novel data checking
flow with the priority information of mask patterns extracted from the design intent. In this paper, we address the effectiveness of MRC technologies which have been widely applied in many mask data
fields. Then we present the current status of the new MRC development, its experimental results so far and the future
outlook using further Design Aware Manufacturing (DAM) information.
For almost a decade Nanomachining application has been studied and developed to repair next generation of
photomasks. This technique, based on Atomic Force Microscopy (AFM), applies a mechanical removing of the defects
with almost negligible quartz-damage, high accuracy of the edge-placement and without spurious depositions (stain,
implanted elements, etc.) that may affect the optical transmission. SII NanoTechnology Inc. (SIINT) is carrying out a
joint-development project with DNP Photomask Europe S.p.A. (DPE) that has allowed the installation in <i>DPE</i> of the
next generation state-of-the-art AFM based system SPR6300 to meet the repair specifications for the 65 nm Node.
Drift phenomena of the AFM probe represent one of the major obstacles for whichever kind of nano-manipulation
(imaging and material or pattern modification). AFM drift undermines the repeatability and accuracy performances of
the process. The repair methodology, called <i>NewDLock</i>, implemented on SPR6300, is a semi-automated procedure by
which the drift amount, regardless of its origin, is estimated in advance and compensated during the process. Now AFM
Nanomachining approach is going to reveal properties of repeatability and user-friendly utilization that make it suitable
for the production environment.
We have reported the FIB repair system with low acceleration voltage is applicable to 65nm generation photomasks. Repair technology beyond 65nm generation photomasks requires higher edge placement accuracy and more accurate shape. We developed two new functions, "Two Step Process" and "CAD Data Copy". "Two Step Process" consists of primary process and finishing process. The primary process is conventional process, but the finishing process is precise process to control repaired edge position with sub-pixel order. "Two Step Process" achieved edge placement repeatability less than 3nm in 3sigma. At "CAD Data Copy", defects are recognized with comparison between shape captured from a SIM image and that imported from a CAD system. "CAD Data Copy" reproduced nanometer features with nanometer accuracy. Thus the FIB repair system with low acceleration voltage achieves high performance enough to repair photomasks beyond 65nm generation by using "Two Step Process" and "CAD Data Copy".
Repair technology for 65nm generation photomasks requires more accurate shape and transmittance. The objective of this study is to evaluate FIB repair process with low acceleration voltage. The evaluation items were imaging impact, defect visibility, repaired shape, through focus behavior, repeatability of edge placement and controllability of repair size. In conclusion, we confirmed that FIB repair process with low acceleration voltage is applicable to 65nm generation photomasks.
Since 2001, we have been improving the hp65nm generation photomask repairing systems, the SIR7000. FIB repair stains quartz substrate with Ga ions. We process the repaired area using two parameters: edge bias and over-etching depth to recover transmission loss. The simulation shows that smaller over-etching makes the lithography process window larger. The dependence of Ga density in quartz with on FIB acceleration voltages shows that the Ga-doped area is smaller according as acceleration voltage is lower. It is found that the over-etching depth should be below 15nm, and a new FIB repairing system should have a low acceleration column. In order to confirm the effect of low acceleration voltage, we investigated the transmittance and the over-etching depth as a feasibility study. As the result, lower acceleration voltage repair gives higher transmittance and lower over-etching depth. We confirmed that the FIB with low acceleration voltage is the most promising technology for the hp65nm generation photomask repairing.
The 65nm photomasks have to meet tight specifications and improve the production yield due to high production cost. The 65nm optical lithography was thought to have two candidates, 157nm and 193nm. However, at the advent of immersion lithography, it is certain that 193nm lithography will be adopted. Therefore, we decided to develop the FIB machine, SIR7000FIB, proior to the EB machine. We optimized repair conditions of FIB system, SIR7000FIB, and evaluated this system. First, we demonstrated minute defect repair using about 15nm defect mask. Then, we confirmed that the repeatability of repair accuracy was below 7nm on a MoSi HT mask patterned 360nm and 260nm L&S patterns with opaque and clear defects by AFM. Consequently, we have achieved the target specifications of this system.
The 65nm photomasks have to meet tight specifications and improve the production yield due to high production cost. The 65nm optical lithography has two candidates, 157nm and 193nm, and we are developing two types of experimental photomask repair systems, FIB and EB, for the 65nm generation. We designed and developed experimental EB and FIB system that are beta systems. The construction of these systems was the same design except the each column. The platforms of beta systems consist of anti-vibration design to reduce outer disturbance for repair accuracy. Furthermore, we developed a new CPU control system, especially the new beam-scanning control system that makes it possible to control the beam position below nanometer order. These developments will suppress transmission loss and improve repair accuracy of the systems. We also adopt the 6-inch mask SMIF pod system and the CAD data linkage system that matches the EB mask data image with the SED image to search defects in photomasks with sophisticated patterns such as OPC patterns. We evaluated the EB and FIB beta systems with AIMS, LWM and AFM. EB and FIB beta systems were able to deposit carbon film and etch chrome, quartz, and MoSi. Furthermore, We confirmed that repair accuracy is 3σ below 10nm and transmission is over 97%. We also confirmed that CAD linkage was able to repair sophisticated pattern completely. In this paper, we report the photomask defect repair experimental systems for the 65nm generation.
The 65nm photomasks have to meet tight specifications and improve the production yield due to high production cost. The 65nm optical lithography has two candidates, 157nm and 193nm, and we are developing two types of experimental photomask repair systems, FIB and EB, for the 65nm generation. We designed and developed FIB and EB beta systems. The platforms of beta systems consist of anti-vibration design to reduce outer disturbance for repair accuracy. Furthermore, we developed a new CPU control system, especially the new beam-scanning control system that makes it possible to control the beam position below nanometer order. These developments will suppress transmission loss and improve repair accuracy of the systems. We also adopt the 6-inch mask SMIF pod system and the CAD data linkage system that matches the EB mask data image with the SED image to search defects in photomasks with sophisticated patterns such as OPC patterns. We evaluate the EB repair process, and confirm that it generates carbon film, which has possibility to generate the same quality as that of FIB. Furthermore, we confirmed that EB and FIB repair systems were able to deposit carbon film and etch chrome, quartz, and MoSi. In this paper, we report the photomask defect repair experimental systems and the feasibility study on photomask defect repair for the 65nm generation.
We have studied stencil mask repair technology with focused ion beam and developed an advanced mask repair tool for electron projection lithography. There were some challenges in the stencil mask repair, which were mainly due to its 3-dimensional structure with aspect ratio more than 10. In order to solve them, we developed some key technologies with focused ion beam (FIB). The transmitted FIB detection technique is a reliable imaging method for a 3-dimensional stencil mask. This technique makes it easy to observe deep patterns of the stencil mask and to detect the process endpoint. High-aspect processing can be achieved using gas-assisted etching (GAE) for a stencil mask. GAE enables us to repair mask patterns with aspect ratio more than 50 and very steep sidewall angle within 90±1°precisely. Edge placement accuracy of the developed tool is about 14nm by manual operation. This tool is capable to achieve less than 10nm by advanced software. It was found that FIB technology had capability to satisfy required specifications for EPL mask repair.
The SIR5000 mask repair system was developed with an FIB system featuring new ion optics, modified SED detectors, new platform software and optimized repair processes to repair 130nm/ArF generation masks. Thereafter we have continuously improved it for 90nm/ArF lithography and evaluated its performance such as edge placement repeatability, lithography simulation and printing tests.
The transmittance of FIB imaging area is more than 95% over 70 times scans, and the printing result data also shows that the imaging damage by FIB scans little affect CD until around 70 times. The ED windows of both repaired clear and opaque defects almost overlap non repaired reference ones, and they show that the printing performance of repaired mask does not have any printing issues. Consequently, we demonstrated that the improved SIR5000 capability has reached the 90nm node mask technology requirement.
Photomask is a key factor to support the lithography technology. Defect repairing technology has become more important than ever to keeping the photomasks' integrity in the manufacturing processes. The SIR5000 is a photomask defect repair system for ArF/90 nm generation lithography. In this work, the repaired masks by the SIR5000 were evaluated by an Aerial Imaging Microscope System (AIMS) and Atomic Force Microscope (AFM). These test results do not show actual printing condition on wafer, but rather a simulated lithography image. In this paper, we present the imaging damage, the edge placement repeatability, the repair area's transmission and the printing performance on wafer. An ArF scanner was employed for the tests on the imaging damage and the printing performance. The transmission of imaged area is more than 95% after 70 scanning frames. The edge placement has shown the 90 nm node repair capability. The transmission of repaired area is no issue by AIMS193 analysis. The actual printing result on wafer has shown there is no printing issue. The SIR5000 is well suited for ArF generation lithography.
The satisfactory data have been confirmed on the photomask repairing performance for 100nm-node/ArF-generation lithography with the model SIR5000 photomask repair system. In this report, the repairing ability is presented with transmittance and edge placement data. The edge placement was almost 15nm(3sigma) on binary and MoSi-HT masks, and there isn’t any transmittance loss in the AIMS193 data.
The design rule of the semiconductor devices is getting dramatically tighter as the progress of lithography technology. Photomask is a key factor to support the lithography technology. Defect repairing technology becomes more important than ever for keeping the photomasks' integrity in the manufacturing processes. When using conventional FIB, however, there are issues of transmission loss due to riverbed and gallium stain for opaque defect repairs as well as the problem raised by halo around repair areas for clear defect repairs. Because of these issues, it is necessary to develop the new FIB mask repairing system for 130nm node. We have been developing the new FIB mask repair system since 1998 and have been testing the repairing performance. The results were published at both PMJ2000 and BACUS2000. This time, we introduce the prototype system's outline, and report preliminary data of imaging damage and repair accuracy for the first time in public.
It is well known that focused ion beam (FIB) has been employed widely in photomask manufacturing process because the feature of this system is the high accuracy to observe small defect, to determine the repairing position, to remove opaque defect, and to deposit repairing film for clear defect. But it is required to improve the functions and the performance of the current FIB mask repair system for the next generation masks, which the smaller pattern width and the shorter lithography wavelength have been raising the pattern printability issue of the area repaired by FIB. So, the initial evaluation has been done by using the experimental machine which was remodeled the SIR series FIB photomask Repair System of Seiko Instruments Inc. The system adopts new ion beam column from which the beam size is reduced to 2/3 or less than conventional machine with the ion beam current of 15pA, FOV (field of view) of 10?pm, and the new deposition film to have thin but sharp edge. Substrate damage by scanning ion irradiation was evaluated by Aerial Image Monitoring System (MSM193 @193nm). Optical intensity is affected by the ion beam irradiation, but there is no critical issue in usual operation. The transmission loss of glass substrate is less than 50% with 5 times scan frame. Under these conditions, the ion dosage is 2.40 x 1014 [ions/cm2] for 10mm x 10mm FOV. The new deposition film was confirmed that the carbon halo was reduced, optical density was enough to shade the ArF laser, though the film thickness was decreased to 1/3 of conventional film, and the durability of the ArF laser irradiation was enough to 3 years in mass production. Wafer printability of clear and opaque defect was evaluated by using ArF scanner. No significant problem was observed. In addition to that, basic experiment of MoSi-based attenuated phase shift mask repair is demonstrated.
New ion beam column was used for mask repair. The ion irradiation was 15pA for the probe current and 31nm for the pixel size. The imaging damage was evaluated from the optical intensity value with MSM193. Optical intensity have the change within 5 percent in case of the repetition image in scanning until five times. The carbon film was formed with a new hydrocarbon gas which change into the pyrene. It is a film that the halo is small and the optical density is about three times higher. The durability to the ArF laser of the carbon film was done by method of measuring the transmittance with MPM193. The carbon film has the durability that exchange in the transmittance is within 0.3 percent by ArF laser irradiation of 30KJ cm-2. The program defects formed to the L and S pattern was repaired by these new conditions. The repaired pattern was printed with ArF scanner on the wafer. The reported pattern was not transferred defect on the wafer.