Kimio Itoh

PROGRESS OF NIL TEMPLATE MAKING

Nano-imprint lithography (NIL) has been counted as one of the lithography candidates for hp32nm node and beyond and has showed excellent resolution capability with remarkable low line edge roughness that is attracting many researchers in the industry who were searching for the finest patterning technology. Therefore, recently we have been focusing on the resolution improvement on the NIL templates with the 100keV acceleration voltage spot beam (SB) EB writer and the 50keV acceleration voltage variable shaped beam (VSB) EB writer. The 100keV SB writers have high resolution capability, but they show fatally low throughput if we need full chip writing. Usually templates for resolution pioneers needed just a small field (several hundred microns square or so), but recently requirements for full chip templates are increasing. For full chip writing, we have also started the resolution improvement with the 50keV VSB writers used in current 4X photomask manufacturing. The 50keV VSB writers could generate full chip pattern in a reasonable time though resolution limits are inferior to that with the 100keV SB writers. In this paper, we will show latest results with both the 100keV SB and the 50keV VSB EB writers. With the 100keV SB EB writer, we have achieved down to hp15nm resolution for line and space pattern, but found that to achieve further improvement, an innovation in pattern generation method or material would be inevitable. With the 50keV VSB EB writer, we have achieved down to hp22nm resolution for line and space pattern. Though NIL has excellent resolution capability, solutions for defect inspection and repair are not clearly shown yet. In this paper, we will show preliminary inspection results with an EB inspection tool. We tested an EB inspection tool by Hermes Microvision, Inc. (HMI), which was originally developed for and are currently used as a wafer inspection tool, and now have been started to seek the application for mask use, using a programmed defect template.

Dry etch technology development for NIL template

Nano-imprint lithography (NIL) is expected as one of the candidates for 32nm node and below. We reported in PMJ2005 that we could achieve 30nm resolution for isolated spaces and 50nm resolution for dense features with tools used in commercial mask shops today, and with modification of widely used resist. We also reported that the CD had shifted non-negligibly from the resist to quartz trench, due to the not-vertical pattern profile of the resist. In this paper, we review the resolution limit with current photomask manufacturing tools and the 100keV spot beam writer, and investigate the pattern line edge roughness. We also report our improvement in quartz dry-etch, in particular the improvement in the pattern profile and the etch depth linearity. We found by using the spot beam writer, we can potentially achieve 10nm isolated space and 35nm dense features, but we need to optimize the resist process.

NIL template making and imprint evaluation

Nano-imprint lithography (NIL) is expected as one of the candidates for hp32nm to hp22nm technology nodes. NIL needs 1X patterns on masks and a transit from 4X to 1X means a big and hard technology jump for the mask industry. We have reported in previous papers that the resolution limit with 50keV acceleration voltage VSB (variable shaped beam) electron beam writer, which are used in current 4X photomask manufacturing, was around 65nm. And we have also reported that to reach the required resolution for hp32nm node, the usage of a 100keV acceleration voltage spot beam writer would be inevitable. Recently, we have installed a 100keV spot beam EB writer adjacent to our photomask manufacturing line. In this paper, we will present our initial results with the tool. We have confirmed, after tuning of our process, a stable resolution capability compatible for hp32nm. With this process, we have begun sample template manufacturing, and initial imprint results are also presented. Templates with hp28nm dense line patterns were fabricated and were well imprinted.

Developing Quartz Wafer Mold Manufacturing Process for Patterned Media

Recently, patterned media have gained attention as a possible candidate for use in the next generation of hard disk drives (HDD). Feature sizes on media are predicted to be 20-25 nm half pitch (hp) for discrete-track media in 2010. One method of fabricating such a fine pattern is by using a nanoimprint. The imprint mold for the patterned media is created from a 150-millimeter, rounded, quartz wafer. The purpose of the process introduced here was to construct a quartz wafer mold and to fabricate line and space (LS) patterns at 24 nmhp for DTM. Additionally, we attempted to achieve a dense hole (HOLE) pattern at 12.5 nmhp for BPM for use in 2012. The manufacturing process of molds for patterned media is almost the same as that for semiconductors, with the exception of the dry-etching process. A 150-millimeter quartz wafer was etched on a special tray made from carving a 6025 substrate, by using the photo-mask tool. We also optimized the quartz etching conditions. As a result, 24 nmhp LS and HOLE patterns were manufactured on the quartz wafer. In conclusion, the quartz wafer mold manufacturing process was established. It is suggested that the etching condition should be further optimized to achieve a higher resolution of HOLE patterns.

Si-mold fabrication for patterned media using high-resolution chemically amplified resist

Nanoimprint lithography (NIL) is one promising candidate for fabricating a patterned media to be used in the next generation of hard disk drives. It is expected that the pitch, characterizing the feature size of the media will become as low as 40-50 nm for Discrete-Track Media (DTM) by 2010 and 25 nm for Bit-Patterned Media (BPM) by 2012. Electron beam lithography is usually employed for fabricating the nanoimprint mold used for nanoimprint lithography. ZEP520A, the high-resolution resist that is commonly used for this fabrication has a low throughput; caused by the low sensitivity when used at the high acceleration voltage of 100 kV. To solve this problem, we evaluated a new high-resolution, chemically amplified resist (CAR) developed by TOKYO OHKA KOGYO Co., LTD., that was specifically developed for high resolution, instead of high sensitivity, with over twice the sensitivity of ZEP520A and a resolution of 50 nm pitch or less. A spot-electron beam (EB) writer with an acceleration voltage of 100 kV (100 kV-SB) was employed and the new CAR and ZEP520A were compared for resolution and sensitivity. Results indicated that the new CAR patterns were resolved down to a 48 nm pitch, but were collapsed even at a64 nm pitch. To prevent the collapse, we attempted to optimize the baking conditions and examined the primers as promoters of the adhesion between the resist patterns and the substrate surface. As a result, a resist pattern as low as a 48 nm pitch was obtained. We report on the performance of the new CAR and the fabrication of the Si mold by using the new CAR.

UV-NIL templates for the 22nm node and beyond

NIL (nano-imprint lithography) is expected as one of the lithographic candidates for 32nm node and beyond. Recently, the small line edge roughness (LER) as well as the potentially high resolution that will ensure no-OPC mask feature is attracting many researchers. However, the NIL needs 1X patterns on template and a transit from 4X to 1X is a big and hard technology jump for the mask industry. The fine resolution pattern making on the template is one of the most critical issues for the realization of NIL. In this paper, as a continuation of our previous works1-5, we have achieved further resolution by optimizing the materials, their thicknesses, the developing and the etching processes, as well as the writing parameters of the 100keV SB (spot beam) writer. At the best resolved point on the template, resolutions down to hp (half pitch) 18nm on dense line patterns, hp20nm on dense hole patterns, and hp26nm on dense dot patterns were confirmed. Concerning stable pattern resolution over a certain field area, we evaluated pattern resolution through over a 250um square area, which we think would be adequate for initial imprint tests. For the 250μm square area, we confirmed pattern resolution of hp24nm for dense line patterns and hp32nm for dense hole patterns. In addition, we have studied resolution limit of the 50keV VSB (variable shaped beam) photomask production writing tools, which have been commonly used tools in the 4X photomask manufacturing for larger field size patterning. Materials, process conditions and parameters acquired through the 100keV SB process were implanted, and we could fabricate templates with hp32nm dense line patterns, with acceptable full chip uniformity and writing time. We also studied the imprint capability, and fabricated a template with fine features and imprinted it onto a wafer. As a result, we could transfer hp24nm dense line patterns, hp24nm dense hole patterns, and hp32nm dense dot patterns onto the wafer.

Photomask process development for next generation lithography

For the coming technology nodes, lithography options that use 1X masks are becoming practical candidates. Especially the nano-imprint lithography (NIL) is expected as one of the candidates for 32nm node and below, because of its potential low lithography cost. Naturally, 1X masks require features finer than those on todays 4X masks, and for mask making this means a big and hard technology jump. From the mask making point of view, even the 1X mask is still a candidate, it would be a technology driver in terms of patterning process development for the coming nodes. In this paper, we focused on the NIL mold (or mask) making evaluation. Among the important factors dominating the resolution of the mask making process, we studied particularly on the resist and the dry etch. We found that with tools currently used in the commercial mask shops today, and by modification of resists, we could achieve 30nm isolated spaces and 50nm dense lines and holes. We also discuss about our initial results of mask EB writing method evaluation. We found that, to improve the resolution further, the implementation of high resolution EB tools into the mask manufacturing line is inevitable to made molds for 32nm or 22nm technology nodes.

6-inch circle template fabrication for patterned media

Nanoimprint lithography (NIL) is one promising candidate for fabricating a patterned media to be used in the next generation of hard disk drives (HDD). It is expected that the pitch, characterizing the feature size of the media will become as small as about 40-50 nm for discrete-track recording (DTR) in 2011 or 2012. There are two major issues, one is fine groove formation and the other is long e-beam writing time. Writing time is estimated more than one week if we use ZEP520A-resist. To solve these problems, master template fabrication processes using combination of silicon substrate and new chemically amplified resist (CAR) were demonstrated by using a rotary stage e-beam writer and 50 nm pitch DTR patterns. Estimated writing speed is three times higher. Also it was demonstrated that silicon master template can be applicable for J-FIL quartz replica process.

6-inch circle template fabrication for patterned media using a conventional resist and new chemically amplified resists

Nanoimprint lithography (NIL) is one promising candidate for fabricating a patterned media to be used in the next generation of hard disk drives. It is expected that the pitch, characterizing the feature size of the media will become as small as about 50 nm for discrete-track recording (DTR) in 2010 or 2011. There are two major issues, one is fine groove formation and the other is long e-beam writing time. Writing time is estimated more than one week if we use ZEP520A-resist. To solve these problems, master template fabrication processes using combination of silicon substrate and new CAR were evaluated. As a result, the capability of 1:2 groove and land ratio 50 nm pitch LS pattern formation with new CAR which sensitivity is approximately 2.5 times higher than ZEP520A was shown.