We are evaluating the resolution capability of character projection (CP) exposure method using a Multi Colum Cell
Proof of Concept (MCC-POC) tool. Resolving of 14nm half pitch (HP) 1:1 line and space (LS) patterns are confirmed
with fine openings of a DNP fabricated CP mask for 10:1
de-magnification ratio. CP exposure has been proven to exhibit
high resolution capabilities even under the most challenging optimization conditions that are required for throughput
enhancement. As a result of evaluating the resolution capability of CP technology, it became apparent that the CP
technology has strong potentials to meet future challenges in two areas. One is where an increased number of CP with
variable illumination technology gives a higher throughput which has been the main objective behind the development of
this technology, and the other is to achieve higher resolution capability that is one of the strengths of CP exposure
method. We also evaluated the resolution on Quartz mask blanks instead of Si wafers and obtained 18nm HP 1:1
resolution with CP exposure.
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.
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.
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.
Nanoimprint lithography is a candidate for lithography for the hp32nm and hp22nm nodes. Molds or templates
for it are being developed on the basis of the process of making phase-shift photomasks. The combination of a 50
kV-VSB (variable shaped beam) EB writer and a chemically amplified resist (CAR) does not have a resolution sufficient
for 1X patterning. On the other hand, a combination of a 100 kV-SB (spot beam) EB writer and a non-CAR satisfies the
resolution requirement, but this combination leads to an extremely low throughput due to low resist sensitivity.
To increase the throughput, we have examined double patterning and double exposure with hybrid use of two
different types of writers, a 50 kV-VSB writer, JBX-9000MV, for delineating fine features and a 100 kV-SB writer,
JBX-9300FS, for delineating rough features. Overlay accuracy is a key item in such hybrid writing. The results of an
overlay accuracy evaluation together with a throughput improvement will be reported in this paper. An estimation of the
time for writing a gate layer has given a good example; the writing time for hybrid writing is reduced to about half of the
time for 100kV-SB writing. The overlay accuracy for double patterning is found to be 20nm (3σ). However, we are
confident that we will be able obtain an overlay accuracy of 10nm (3σ) by improving the image placement accuracy of
the JBX-9300FS. An example of double exposure is also shown.
EB lithography has a potential to successfully form hole patterns as small as 80 nm with a stencil mask. In a previous paper we proposed a technique using a HOLON dual-mode critical dimension (CD) SEM ESPA-75S in the transmission mode for CD measurement of line-and-space patterns on a stencil mask. In this paper we extend our effort of developing a CD measurement technique to contact hole features and determine it in comparison of measured values between features on mask and those printed on wafer. We have evaluated the width method and the area methods using designed 80-500 nm wide contact hole patterns on a large area membrane mask and their resist images on wafer printed by a LEEPL3000. We find that 1) the width method and the area methods show an excellent mask-wafer correlation for holes over 110 nm, and 2) the area methods show a better mask-wafer correlation than the width method does for holes below 110 nm. We conclude that the area calculated from the transmission SEM image is more suitable in defining the hole dimensions than the width for contact holes on a stencil mask.
KEYWORDS: Photomasks, Distortion, Semiconducting wafers, Data corrections, Image analysis, Data processing, Electron beams, Electron beam lithography, Projection lithography, Metrology
200-mm stencil masks for electron beam projection lithography (EPL) have been developed. Since they are not so rigid as photomasks because of their structure, 200-mm wafers with about 8,000 membrane windows, new metrological techniques dedicated to stencil masks have be introduced. Image placement (IP) accuracy of an EPL mask is evaluated with a suspension-type electrostatic chuck introduced to a Leica LMS IPRO. The dynamic repeatability of global IP measurements was 27 nm (3σ). It was confirmed that global IP errors were reduced to 60 nm (3σ, max) by linear-term and gravity corrections.
Electron beam projection lithography (EPL) has been developed for application to 65 nm node devices and beyond. 200-mm EPL masks have also been developed keeping pace with the exposure tool. Image placement (IP) accuracy is a necessary quality assurance item to bring masks into production. A suspension type electrostatic chuck designed for EPL mask measurement for an IP metrology tool Leica LMS IPRO was prepared for measurement of local IP errors, defined for each subfiled. The chuck holds the mask on its membrane-side surface right side up. Three 200-mm stencil masks with tensile membrane stresses of 8, 18, and 43 MPa were fabricated. The IP error is found to increase as the stress increases. Marks in the area of a high pattern density with a void fraction of 0.2 moved toward the area of a low pattern density with a void fraction of 0.016. The IP errors did not strongly depend on the kinds of dummy patterns (either hole or L&S) having the same void fraction of 0.25 and macroscopic uniformity. If the stress is less than 10 MPa, the IP error (3 sigma) is less than 10 nm, satisfying the EPL mask requirement. Local CD accuracy was also evaluated for a mask with a membrane stress of 8 MPa.
200-mm electron-beam projection lithography (EPL) masks were fabricated starting from stress-controlled silicon-on-insulator (SOI) substrates. The internal stress of the SOI layer is controlled to be ca. 10 MPa by B doping. The blank fabrication process has been established by the Bosch deep trench etch process. EB patterning was done on a JEOL JBX9000MVII with a positive-tone chemically amplified resist of 400-nm thickness. Resist image of 200-nm wide lines-and-spaces pattern was transferred to 2-um thick SOI layer by a shallow trench etching. A dual-mode critical dimension (CD)-SEM was implemented, and used for mask characterization. Preliminary results on uniformity of CD-shift in the dry etching and final CD were reported. 200-mm EPL masks with a gate layer of a system-on-chip device pattern were fabricated.
Scanning-electron microscopes designed for critical dimension (CD) measurement (CD-SEMs), which operate in a reflection mode, are commonly used in photomask quality assurance. However, such CD-SEMs are not always suitable for CD measurement of electron beam (EB) stencil masks such as electron-beam projection lithography (EPL) masks and low-energy electron-beam proximity projection lithography (LEEPL) masks. A dual-mode CD-SEM, which can operate in a transmission mode besides in a reflection mode, was recently developed by HOLON. The performance of the tool will be reported. Two EPL test masks with a 2-μm-thick Si scatterer and one LEEPL test mask with about 1-μm-thick absorber were prepared. The EPL masks have 1:1 lines-and-spaces (L&S) patterns and isolated spaces, all varying from 200 to 1000 nm in designed size. The LEEPL mask has 1:1 L&S patterns ranging from 80 to 550 nm. The masks were observed at an acceleration voltage of 5.5 kV with no bias voltage and a current of 10 pA. The dual-mode CD-SEM is found to have the following characters: (1) short-term repeatability and long-term repeatability less than 2 nm in both modes, (2) compatibility with a photomask CD-SEM in the reflection mode, (3) coincidence of the CDs measured in the transmission mode from the front side and back side within 3.0 nm for stencil patterns with a sidewall angle larger than 89.8 deg, and (4) capability of measurement at least down to 80 nm. Therefore we conclude that the dual-mode CD-SEM is applicable for measurement of CDs of EB stencil masks.
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