Kazuo Aita

Photomask repair technology by using gas field ion source

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.

Advanced FIB mask repair technology for 100 nm/ArF 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.

FIB mask repair technology for electron projection lithography

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.

Performance of gas-assisted FIB repair for opaque defects

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.

Development of focused ion-beam repair for opaque defects on MoSi-based attenuated phase-shift mask

Focused-ion beam (FIB) repair technique is one of the important technologies for quality and productivity of attenuated phase shift mask (HT-PSM),especially for KrF lithography. Mainly, accurate and low damage technique are necessary for HT-PSM repair. Such requirements are satisfied with the improvement of gas-assisted etching (GAE) technique for FIB. New SIR-3000 made by Seiko Instruments has been developed for applying MoSi material etching. Using GAE technique, the transmittance evaluated from AIMS at repaired area was more than 99% (i-line), and 96 - 97% (KrF) without post process (Qz reference: 100%). The results indicate the focused-ion beam repair is applicable without post process to MoSi-based HT-PSM for KrF lithography. This paper report the characterization results of opaque defect repair on MoSi-based HT-PSM using new SIR-3000.

Recent progress in repair accuracy of the focused ion-beam mask repair system

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.