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.
Recently, most of defects on high-end masks are repaired with electron beam (EB). The minimum repairable dimension
of the current state-of-the-art repair systems is about 20-30 nm, but that dimension is not small enough to repair the next
generation masks. Meanwhile, new molybdenum silicide (MoSi) films with high cleaning durability are going to be
provided for an alternative technology, but the etching selectivity between new MoSi and quartz under EB repair process
is not high enough to control etching depth. We developed the focused ion beam (FIB) technology that uses light ions
emitted from a gas field ion source (GFIS). In this study, the performance of our developed GFIS mask repair system
was investigated by using new MoSi (HOYA-A6L2). Specifically, the minimum repairable dimension, image resolution,
imaging damage, etching material selectivity and through-focus behavior on AIMS were evaluated. The minimum
repairable dimension was only 11 nm that is nearly half of that with EB. That result suggests that GFIS technology is a
promising candidate for repairing the next generation masks. Meanwhile, the etching selectivity between A6L2 and
quartz was 6:1. Additionally, the other evaluations on AIMS showed good results. Those results demonstrate that GFIS
technology is a reliable solution of repairing new MoSi masks with high cleaning durability.
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 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.