We have developed a new focused ion beam (FIB) technology using a gas field ion source (GFIS) for mask repair.
Meanwhile, since current high-end photomasks do not have high durability in exposure nor cleaning, some new
photomask materials are proposed. In 2012, we reported that our GFIS system had repaired a representative new material
“A6L2”. It is currently expected to extend the application range of GFIS technology for various new materials and
various defect shapes. In this study, we repaired a single bridge, a triple bridge and a missing hole on a phase shift mask
(PSM) of “A6L2”, and also repaired single bridges on a binary mask of molybdenum silicide (MoSi) material “W4G”
and a PSM of high transmittance material “SDC1”. The etching selectivity between those new materials and quartz were
over 4:1. There were no significant differences of pattern shapes on scanning electron microscopy (SEM) images
between repair and non-repair regions. All the critical dimensions (CD) at repair regions were less than +/-3% of those at
normal ones on an aerial image metrology system (AIMS). Those results demonstrated that GFIS technology is a reliable
solution of repairing new material photomasks that are candidates for 1X nm generation.
The next generation EUVL masks beyond hp15nm are difficult to repair for the current repair technologies including
focused ion beam (FIB) and electron beam (EB) in view of the minimum repairable size. We developed a new FIB
technology to repair EUVL masks. Conventional FIB use gallium ions (Ga+) generated by a liquid metal ion source
(LMIS), but the new FIB uses hydrogen ions (H2+) generated by a gas field ion source (GFIS). The minimum reaction
area of H2+ FIB is theoretically much smaller than that of EB. We investigated the repair performance of H2+ FIB. In the
concrete, we evaluated image resolution, scan damage, etching rate, material selectivity of etching and actinic image of
repaired area. The most important result is that there was no difference between the repaired area and the non-repaired
one on actinic images. That result suggests that the H2+ GFIS technology is a promising candidate for the solution to
repair the next generation EUVL masks beyond hp15nm.
At the Photomask Japan 2010, we reported on the cleaning process durability and the EUV light shielding capability of
FIB- and EB-CVD film based on carbon, tungsten and silicon containing precursors. The results were that the tungsten
based FIB-CVD film showed no loss of film thickness after dry cleaning process, and the calculation showed that 56nm
thick was sufficient for repairing clear defects on EUV mask with 51nm thick of absorber layer. On the other hand,
carbon based FIB-CVD film suffered considerable loss in its film thickness and needed more than 180nm thick even if
the 10nm thick of buffer layer between the CVD films and the capping layer supported the EUV light shield.
In this paper, we will report on a newly developed repair method of clear defects on EUV mask using an FIB technique.
The clear defects were repaired by removing or damaging the reflective ML (multi layer) underlying the clear defect area
instead of applying the conventional FIB-CVD (Focused Ion Beam-Chemical Vapor Deposition) films. After removing
the ML, the cross sectional pattern angle was approximately 83 degree and the sidewalls were covered with 15nm thick
of Si and Mo mixing layer caused by Ga ions exposure. The performance of defect repair was evaluated by SFET (Small
Field Exposure Tool) printability test. The exposure results showed that the ML etched area behaved as low reflection
area and the printed CDs were proportional to the mask opening CDs. The study also revealed that the ML etched pattern
was not sensitive to 50nm of focus error.
In this paper, we will report on the cleaning process durability and light shielding capability of FIB- and EB-CVD
(Chemical Vapor Deposition) films which, are applied to repair clear defects on EUV mask. We evaluated tungsten
containing, and silicon containing precursors in addition to carbon based precursor. For the conventional photomasks, the
carbon based precursor is applied for repairing the clear defects because the reconstructed patterns by the carbon based
precursor have excellent printability. However, under the condition of EUV lithography, the optical property of carbon
deposited film is quite different.
From the stand point of beam, FIB-CVD films showed better cleaning process durability and light shielding capability
than EB-CVD film did. These differences are attributed to chemical components of the CVD films, especially with the
tungsten based FIB-CVD film that contains 44 atomic % of tungsten and 24 atomic % of gallium. The tungsten based
FIB-CVD film showed no loss of film thickness after dry cleaning, and the calculation showed that 56nmt was sufficient
for repairing clear defects on EUV mask with 51nmt of absorber layer. On the other hand, carbon based FIB-CVD film
suffered considerable loss in the film thickness and needed more than 180nm.
We evaluated a FIB-CVD (Focused Ion Beam-Chemical Vapor Deposition) process for repairing clear defects on EUV
masks. For the CVD film, we selected Carbon material. Our simulation result showed that the properties of wafer-prints
depended on the density of the carbon films deposited for repairing the clear defects. Especially, when the density of
carbon film was higher than that of graphite the properties of the wafer-prints came out to be almost same as obtained
from Ta-based absorbers. For CVD, in this work we employed typical carbon based precursor that has been routinely
used for repairing photomask patterns. The defects created for our evaluation were line-cut defects in a hp225nm L/S
pattern. The performance of defect repair was evaluated by SFET (Small Field Exposure Tool) printability test. The
study showed that the focus characteristic of repaired region deteriorated as the thickness of the deposition film
decreased, especially when the thickness went below the thickness of the absorber. However, when the deposition film
thickness was same as that of the absorber film, focus characteristic was found to be excellent. The study also revealed
that wafer-print CDs could be controlled by controlling the CDs of the deposition films. The durability of deposition
films against the buffer layer etching process and hydrogen radical cleaning process is also discussed.
We evaluated a new FIB-GAE (Focused Ion Beam-Gas Assisted Etching) repairing process for the absorber defects on
EUVL mask. XeF2 gas and H2O gas were used as etching assist agent and etching stop agent respectively. The H2O gas
was used to oxidize Ta-nitride side-wall and to inactivate the remaining XeF2 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 H2O 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 XeF2 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
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.
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.
In this paper we present new development of intellectual properties(IP) protection software using OASIS format. By taking advantage of repetition presentation of OASIS, it becomes possible to express arrayed patterns without any generation of new cells, which also brings less overhead and further compaction of the result file. As a result, we could rebuild the hierarchy without cell generation and reduce the output file size. The experimental results show that there are no redundant cells generated and the file size has become 5 to 8 times smaller than conventional methods.
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.
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 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.
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.
OPC and other complicated geometric structures are increasingly common on production masks. These features may be small, have highly irregular shapes and may not be repeated in a nearby region. These features make it difficult for a repair operator to know where the defect stops and the desired pattern begins. We are increasingly called upon to write masks with these complicated patterns, high densities and long write times. In order to meet our customers demand for shorter turnaround times and high throughput, it makes sense to implement new, more sophisticated repair techniques. We have recently acquired a new, state of the art Seiko SIR3000 FIB (focused ion beam) mask repair system. This system is a sophisticated secondary ion mass spectrometer (SIMS) that uses a focused primary beam of gallium ions to both image and repair mask defects. Both opaque and clear defects can be reconstructed by the gallium beam. The SIR3000 system uses a proprietary material (alpha-gas) to reduce glass damage caused by the sputtering process. We have performed some preliminary measurements to determine the extent of the glass damage and performed some introductory work into methods of reducing the damage further. We present some of the data we use to monitor its performance, a number of examples illustrating its utility and our expectations for the tool in the near future.
Until recently, opaque defects on photomask have been removed by laser evaporation. However there are several disadvantages in this repair technique. First an operator must visually align the laser irradiation spot and pattern edge, so high repair accuracy can not be obtained. Also when the area to be repaired is large the laser sputters the surrounding surfaces and the evaporation tends to redeposit on pattern edges causing them to swell thus increasing the probability of detection by inspection equipment. Additionally the laser repair technique has proven to be very difficult if the pattern defect is any complex geometry. The repair using Focused Ion Beam (FIB) has been developed to solve some of these issues, however this method has not yet been applied to the production line because of degradation of transmission rate and the damage to the glass substrate. This paper reports the evaluation on the performance of the FIB repair using a newly developed gas assisted etching (GAE) technique and the status of using FIB with GAE in the production line. By using GAE, the degree of glass damage has been reduced by a factor of ten as compared with the FIB repairs without GAE. A transmission rate of 94% (i-line) could be obtained on a conventional mask and 92% (i-line) on the Halftone Phase Shift mask (HT-PSM). Furthermore, by applying the post-treatment after the repair, the transmission rate of the repaired area could be recovered to the same level as the normal glass area. The printing characteristics for i-line of the GAE repaired in both conventional mask and HT-PSM has been also good, showing that the GAE FIB repair is applicable in the normal photolithographic process window and that this method can achieve the similar printing result in comparison with non- repaired area.
To improve the depth of focus (DOF) of isolated lines, attenuated assist feature (AAF) technique has been proposed; AAFs having more than 20% transmittance were located around an isolated line. In this mask, the transmittance and phase shift angle of AAF as well as its position and width have effects on lithographic performance. In particular, the phase shift angle has strong effect on focus latitude. The performances of two AAF masks (65% transmittance/28 degree phase shift and 40% transmittance/54 degree phase shift) were evaluated by using an NA equals 0.6, sigma- in)/(sigma) out equals 0.42/0.7, i-line stepper. The focus latitude of 0.3 micrometer isolated line became flat around the best focus position with 28 degree phase shift AAFs. In conclusion, we can obtain wide DOF for isolated lines by selecting optimum phase shift angle of AAF.