International Technology Roadmap for Semiconductors 2003の要求清浄度について － シリコンウエハ表面と雰囲気環境に要求される清浄度, 分析方法の現状について －

The ability to manufacture a nanogap in between two electrodes has proven a powerful catalyst for scientific discoveries in nanoscience and molecular electronics A wide range of bottom-up and top-down methodologies are now available to fabricate nanogaps that are less than 10 nm wide However, most available techniques involve time-consuming serial processes that are not compatible with large-scale manufacturing of nanogap devices The scalable manufacturing of sub-10 nm gaps remains a great technological challenge that currently hinders both experimental nanoscience and the prospects for commercial exploitation of nanogap devices Here, available nanogap fabrication methodologies are reviewed and a detailed comparison of their merits is provided, with special focus on large-scale and reproducible manufacturing of nanogaps The most promising approaches that could achieve a breakthrough in research and commercial applications are identified Emerging scalable nanogap manufacturing methodologies will ultimately enable applications with high scientific and societal impact, including high-speed whole genome sequencing, electromechanical computing, and molecular electronics using nanogap electrodes

Scalable Manufacturing of Nanogaps

An electron beam (EB) lithography method using inedible cellulose-based resist material derived from woody biomass has been successfully developed. This method allows the use of pure water in the development process instead of the conventionally used tetramethylammonium hydroxide and anisole. The inedible cellulose-based biomass resist material, as an alternative to alpha-linked disaccharides in sugar derivatives that compete with food supplies, was developed by replacing the hydroxyl groups in the beta-linked disaccharides with EB-sensitive 2-methacryloyloxyethyl groups. A 75 nm line and space pattern at an exposure dose of 19 μC/cm2, a resist thickness uniformity of less than 0.4 nm on a 200 mm wafer, and low film thickness shrinkage under EB irradiation were achieved with this inedible cellulose-based biomass resist material using a water-based development process.

Inedible cellulose-based biomass resist material amenable to water-based processing for use in electron beam lithography

Recent Low k1 era requires aggressive OPC technology with advanced lithography technology. The aggressive OPC
contains the rounded pattern and a lot of assistant pattern which are the main source to increase the shot division. We
have defined the shot complexity, which is defined by the ratio of number of shot between the interested pattern and the
1:1 L/S pattern. Based on shot complexity parameter, we have estimated the writing time as the device node decreases.
We expect that the aggressive OPC and the high dose could generate severely the writing time issue in 32nm node era.

E-beam Shot Count Estimation at 32 nm HP and Beyond

The mechanism of image drift in the observation of a boundary between a metal and an insulator by scanning electron microscope (SEM) is clarified by electron-trajectory simulation and experiment In the region involving a straight boundary between a large-area metal layer and an insulating substrate, the largest image drift is expected to be observed owing to an asymmetric charging on the sample surface The simulation result shows that a metal–insulator boundary in the SEM image shifts toward the metal part over several seconds, which is induced by a positively charged area outside of the irradiation region in the insulator part This simulation result is confirmed to qualitatively coincide with the experimental one In addition, we demonstrate that the direction and magnitude of the image drift can be controlled by changing the charging voltage of the insulating substrate by applying a bias voltage to the anode facing the sample surface

https://iopscience.iop.org/article/10.1143/JJAP.51.06FB11/pdf

Study on Image Drift Induced by Charging during Observation by Scanning Electron Microscope

ArF immersion lithography combined with double patterning has been used for fabricating below half pitch 40nm devices However, when pattern size shrinks below 20nm, we must use new technology like quadruple patterning process or next generation lithography (NGL) solutions Moreover, with change in lithography tool, next generation mask production will be needed According to ITRS 2013, fabrication of finer patterns less than 15nm will be required on mask plate in NGL mask production 5 years later [1] In order to fabricate finer patterns on mask, higher resolution EB mask writer and high performance fabrication process will be required In a previous study, we investigated a potential of mask fabrication process for finer patterning and achieved 17nm dense line pattern on mask plate by using VSB (Variable Shaped Beam) type EB mask writer and chemically amplified resist [2][3] After a further investigation, we constructed higher performance mask process by using new EB mask writer EBM9000 EBM9000 is the equipment supporting hp16nm generation's photomask production and has high accuracy and high throughput As a result, we achieved 155nm pattern on mask with high productivity Moreover, from evaluation of isolated pattern, we proved that current mask process has the capability for sub-10nm pattern These results show that the performance of current mask fabrication process have the potential to fabricate the next-generation mask

/pdf/high-performance-mask-fabrication-process-for-the-next-27jufd978y.pdf

High performance mask fabrication process for the next-generation mask production

We achieved highly accurate Local CD in the vicinity of 1nm with the newly developed low sensitivity
chemically amplified resist (CAR) for the e-beam reticle writer, EBM-6000. We applied shot noise model to
estimate Line Edge Roughness (LER). According to the estimation result, LER is improved by increasing the
threshold dosage. We evaluated the performance of newly developed low sensitivity CAR. Local CD
accuracy, LER, pattern resolution and drawing time are evaluated. We concluded that the performance with
the low sensitivity CAR was good enough to produce photomasks for 45nm half pitch (HP) devices.

1nm of local CD accuracy for 45nm-node photomask with low sensitivity CAR for e-beam writer

The requirement for image placement accuracy on photomask has been rising The ITRS road map says that we need
to achieve 43nm accuracy in 2012 for HP 36nm device with single exposure process, further more we must achieve
30nm accuracy if double patterning process is selected
Fig1 shows the today's performance of image placement accuracy Some sample photomasks which have same pattern
shape are produced during 3 months, and the mask to mask overlay accuracy of them was measured The average of
them was 36nm This data shows the possibility to achieve the accuracy of photomask for HP 36nm devices The image
placement accuracy of actual device pattern during same period is showed in Fig2 The image placement accuracy of
actual device pattern is worse than that showed before We categorized these data according to the pattern density, low
density pattern and the high density pattern The density of the test pattern is categorized into very low density pattern
The results are showed in Fig3 We can see the degrading of image place accuracy according to the pattern density
This degrading of image placement accuracy is caused by resist charging effect In photomask production process,
electron beam writer is mainly used as lithography tool Each pattern on photomask is formed by step by step exposure
of electron beam The surface of resist film will be charged with exposed electron beam, and electric field will be
generated around that charged area So the orbit of electron beam for next exposure will be bended by the electric field
which generated by previous beam shot, and image placement accuracy will degrade To achieve the demanded image
placement accuracy, we need to remove the error caused by this phenomenon
We researched in resist charging effect for correcting it, and we studied that this phenomenon have so complex feature
After that we tried to research in it on EBM-7000, newly developed electron beam writer, and we found out the reduction
of the image placement error caused by the resist charging effect on EBM-7000

Reduction of resist charging effect by EB reticle writer EBM-7000

To investigate the possibility to catch up the NGL mask pattern size scaling strategy which indicated in ITRS2012, the performance of conventional mask fabricating process was examined. Current EB resist used for mask fabrication doesn’t have enough performance to resolve below hp20nm pattern. With newly developed CAR resist, the resolution limit reached to hp18nm pattern. Furthermore by using higher performance EB writer, the possibility to resolve up to hp16nm pattern was showed. The impact of proximity effect to the resist performance was examined. The resist damage induced by proximity effect degrades the resolution limit about 2nm. This is a serious problem for NGL mask manufacturing. Reducing the impact of proximity effect is one of the major challenges for developing higher resolution EB resist.

https://www.jstage.jst.go.jp/article/photopolymer/27/4/27_511/_pdf

The Performances and Challenges of Today’s EB Lithography and EB-resist Materials

Photomask used for optical lithography has been developed for purpose of fabrication a pattern along with finer
designed rules and increase the productivity. With regard to pattern fabrication on mask, EB (Electron beam) mask
writer has been used because it has high resolution beam. But in producing photomask, minimum pattern size on mask is
hits a peak around 40nm by the resolution limit of ArF immersion systems. This value is easy to achieve by current EB
writer. So, photomask process with EB writer has gotten attached to increase turnaround time.
In next generation lithography such as EUV (Extreme ultraviolet) lithography and Nano-imprint lithography, it is
enable to fabricate finer pattern beyond the resolution limit of ArF immersion systems. Thereby the pattern on a mask
becomes finer rapidly. According to ITRS 2012, fabrication of finer patterns less than 20nm will be required on EUV
mask and on NIL template. Especially in NIL template, less than 15nm pattern will be required half a decade later. But
today’s development of EB writer is aiming to increase photomask’s productivity, so we will face a difficulty to fabricate
finer pattern in near future.
In this paper, we examined a potential of mask production process with EB writer from the view of finer pattern
fabrication performances. We succeeded to fabricate hp (half-pitch) 17nm pattern on mask plate by using VSB (Variable
Shaped Beam) type EB mask writer with CAR (Chemically Amplified Resist). This result suggests that the photomask
fabrication process has the potential for sub-20nm generation mask production.

Kunihiro Ugajin

Papers

High performance mask fabrication process for the next-generation mask production

1nm of local CD accuracy for 45nm-node photomask with low sensitivity CAR for e-beam writer

Reduction of resist charging effect by EB reticle writer EBM-7000

The Performances and Challenges of Today’s EB Lithography and EB-resist Materials

Potential of mask production process for finer pattern fabrication