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<sup>+</sup>) generated by a liquid metal ion source
(LMIS), but the new FIB uses hydrogen ions (H<sub>2</sub>+) generated by a gas field ion source (GFIS). The minimum reaction
area of H<sub>2</sub><sup>+</sup> FIB is theoretically much smaller than that of EB. We investigated the repair performance of H<sub>2</sub><sup>+</sup> 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 H<sub>2</sub><sup>+</sup> GFIS technology is a promising candidate for the solution to
repair the next generation EUVL masks beyond hp15nm.
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 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 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.