Bull. Hiroshima Inst. Tech. Research Vol. 55（2021）95-100

ReportReview of HIT - IE-BAS joint research during the last 25 years

Takeshi TANAKA ＊ and Katia VUTOVA ＊＊（Received Oct. 31, 2020）

Abstract
The Department of Electronics and Computer Engineering, Hiroshima Institute of Technology(EC-HIT) started the international joint research with the Laboratory“Physical Problems ofElec-tron Beam technologies”of the Institute of Electronics, Bulgarian Academy of Sciences (IEBAS) in 1994. More than 30 papers, included a book chapter, were published by implementing
the international joint research under 7 Agreements for Academic Cooperation and Exchange
between HIT and IE-BAS. Our international joint research is getting the important positionin joint research between Japan and Bulgaria. The semiconductor fabrication process such asthin ﬁlm deposition, Electron and Ion Lithography, Etching, Ion implantation, Plasma treatment,
etc., evaluation technique such as X-ray photo-electron spectroscopy, optical spectroscopy,
X-ray diffraction, etc., and their simulation technology were used for application in industry,
medical service, medicine manufacture, biotechnology, dental, etc. By providing further steps
for developing and extending our bilateral relations, this research partnership between theHiroshima Institute of Technology and the Institute of electronics at the Bulgarian Academy ofSciences can become more stable in the future.
Key Words: joint research, Institute of electronics at the Bulgarian Academy of Sciences,
Hiroshima

Institute of Technology

materials, electron and ion beam technologies,

1. INTRODUCTION

process modelling and simulations, technology

The international joint research and collaboration

optimization for application in industry, inbetween the Department of Electronics andmedicine, new approaches in education, etc.

Computer Engineering, Hiroshima InstituteIn this review, the main results and selectedof Technology (EC-HIT), and the Laboratory

activities for the last 25 years of our successful“Physical Problems of Electron Beam technologies”

joint research and collaboration are presented.

of the Institute of Electronics, Bulgarian Academy

2. CONTENTSof Sciences (IE-BAS) started in 1994. Up to now
the joint research is in the framework of seven

The research results obtained for this period

Agreements for Academic Cooperation and(1994-2019) have been published in more than

Exchange between HIT and IE-BAS in the fields ofmore than 30 common publications, a significant

physical electronics, nanotechnologies, electronics

part of them in prestigious international scientific＊＊＊

Department of Electronics and Computer Engineering, Hiroshima Institute of Technology, Hiroshima, Japan
Institute of Electronics, Bulgarian Academy of Sciences, Sofia, Bulgaria― 95 ―

Takeshi TANAKA and Katia VUTOVA

journals such as Microelectronic Engineering,development and optimization of applications ofSurface and Interface Analysis, Mathematics andelectron beams in nanotechnology, biotechnology,Computers in Simulation, IOP Journal of Physics:

etc.

Conference Series, Vacuum, Metals, etc., a book

As a result of our long-term scientificchapter [1-21]. The results have been also reported

cooperation, a model for computer simulationin many international scientific forums such asof the signal formation at surface and thin film

IEEE International Spring Seminar on Electronics

analysis by electron spectroscopy was developed

Technology, International Conferences on Electron[2-6], (Fig.1). A Bulgarian-Japanese Center for

Beam Technologies (EBT), The Minerals, Metals

Modification of Materials with electron and& Materials Society (TMS), Education andion beams was established with the Hiroshima

Research Workshop of Electronic Devices, Circuits,

Institute of Technology.

Illuminations, and Systems (EDCIS), International
scientific conferences“High Technologies. Business.
Society”,International Summer School on Vacuum,
Electron and Ion Technologies (VEIT), etc.
In 2019, three important anniversaries werecelebrated in the history of the bilateral relations
between Japan and Bulgaria, namely - 110 years
since the official bilateral contacts began, 80 years

Fig. 1since the establishment of diplomatic relations

Book“Photoelectron signal simulation

at surface analysis”[6].

between the two countries and 60 years of theirrecovery.

At using the most powerful beams for theIn 2019, we were celebrating 150 years fromproduction of pure metals and for recycling of

the establishment of the Bulgarian Academy

metal technogenic materials in vacuum, refiningof Sciences. Established in 1869, the Bulgarianand heat processes are studied, and specificAcademy of Sciences (BAS) is the oldest

technologies for electron beam melting (EBM)

institution in modern Bulgaria. Nowadays, theare developed. Computer modeling of processes is

BAS is the largest scientific institution in Bulgaria

applied and on this basis the process peculiarities

with proven international authority. It carries out

are investigated and the purity of the obtained

scientific work in accordance with the universal

metals is optimized. High-purity metals andvalues, national traditions and interests.

their alloys have wide spectrum of applications

Electron beam technologies (EBT) celebrate

in electronics, medicine, transport, nuclear andnow 70 years from the first machines andchemical industry, special alloys, etc.

industrial technologies based of application ofElectron beam melting method has proven its

intense electron beams in vacuum. EB technologies

advantages as an effective, environmental-friendly

and devices are high-tech, environmental,

method and it plays an important role in theresource-saving methods and devices, key for theproduction of ultrapure sputtering target materials

development of competitive products with highand electronic alloys, in metal regeneration from

quality and to achieve sustainable development

waste products, in the metallurgical-grade silicon

based on knowledge. They are the foundation ofpurification for the photovoltaic industry, etc.

technical progress in micro- and nano-electronics,

The recycling of metal scrap enables obtaining

in the production of new materials and creating

new materials with improved characteristics

new designs of instruments and precision(composition and structure) and suitable properties

machinery. They are becoming more widely(magnetic, resistance, etc.) for responsible

used in the industries of the advanced industrial

application. Each one of the metals, processing

countries and in new research areas concerning

by EBM, is made in a unique way aiming to― 96 ―

Review of HIT - IE-BAS joint research during the last 25 years

achieve the superior level of refining of unwanted

sub-100 nm structures using EBL is a very

inclusions. Therefore, there is a need to look forsensitive process determined by various factors,

specific technological regimes for e-beam refining

starting with the choice of polymer resist material

for specific raw materials.

and ending with the development process.

The e-beam method provides obtaining metals

Limitations of different positive and negative

and alloys processing both natural raw materials

EB lithography resists such as PMMA, CSAR,

and technogenic materials containing these

SU-8, and HSQ for advanced research andmetals or their alloys in the case of lack of suchmany applications in sensors and microsystems

natural raw sources. The global recourses of many

development, surface science applications, etc. arevaluable metals are exceedingly limited and at thestudied [7,9,10,15]. Various process parameters,same time, there are some large amounts of metal

which determine the accuracy of the profiles inwastes collected.

the resists and the size of structures, such as

Theoretical and experimental investigations

exposure dose, resist thickness, solubility rates,

dealing with the relations of melting processdependences of the linewidth on the dose, etc.

parameters (such as melting power, the refining

and their influence on the limitations of e-beamtime, etc.) and impurities removal at refining oflithography, are investigated. Experimental anddifferent metals, including non-ferrous and rare

theoretical investigations are performed aiming

metals, refractory and reactive ones are performed

to improve the resolution of the nano-dimensioned

aiming to improve the composition and quality of

EBL using different resist materials and somethe produced metals and to optimize the processapplication results are also obtained (for gas[11,13,17,21].

sensors development, for photonic application, etc.).

Data of practical importance are obtained andPlasma-based ion implantation (PBII) method

recommendations for proper process parameters

is used to perform surface modification by theare formulated for processing of various metals

sample in the plasma and applying a high voltage

such as titanium, tantalum, nickel, etc. The

negative pulse voltage. It has been applied toobtained results are important for studying andsurface modification industrial machinery parts,

increasing the efficiency of e-beam melting of

metal material, and medical technology. PBII withmetal materials, optimizing the purity, structureself-ignited plasma (SIP) generated by only pulsedand properties of the metals obtained and show

voltages to the test specimen has been applied topossible applications of the method.

the sterilization process [18,19].

Electron beam lithography (EBL) evolved

Rapid globalization requires for students,

to one of the most important techniques forteachers, and researchers to have good education,

nanofabrication. EBL is one of the few“top-down”

logical thinking, problem-solving, comparative, andmethods and is becoming increasingly widespread

research skills, excellent expressiveness, and broadin R&D and small volume production due to its

scientific knowledge. The latest main projects

flexibility and mask-less nature, very high (sub-related to international education in Japan and10 nm) resolution and accuracy, maturity andsome specific approaches in HIT, based on projects

affordable price of equipment and in many cases

promoted by MEXT, were discussed. Some of thee-beam lithography is the only possible alternative.

newest and most important approaches and trends

Resist materials are crucial elements in EBL andin the universities’education system aiming attheir performance determines the final results ofachieving better results and some examples ofthe structures patterning.

good practices related to the application of these

Application range of EBL is wide, i.e. theapproaches in the education in Japan, Bulgaria anddevelopment of sensors, nanophotonic devices, highthe United States were also presented [12,14,20].

frequency electronics, spintronics, quantum dots,
nanowires, nanomechanical devices, etc. Achieving― 97 ―

Takeshi TANAKA and Katia VUTOVA

eds.: M.Nemtanu, M.Brasoveanu, publ.

3. CONCLUSION

Research Signpost/Transworld Research

By providing further steps for developing andNetwork, pp. 235-254 (2011).

extending our bilateral relations, this research(7) K.Vutova, G.Mladenov, T.Tanaka, K.Kawabata,partnership between the Hiroshima Institute of“Simulation of the energy absorption andTechnology and the Institute of electronics at thethe resist development at sub-150 nm ion

Bulgarian Academy of Sciences can become morelithography,”Microelectronic Engineering, v.

stable in the future.

78-79, pp. 533-539 (2005).
(8) T.Tanaka, K.Vutova, E.Koleva, G.Mladenov,Acknowledgements

T.Takagi, “Surface modification of plastic

The authors express gratitude to HIT and IE-films by charged particles,”Polymer Surface

BAS for their support of the joint research andModification: Relevance to Adhesion, K.L.Mittal

the successful cooperation between the Institute of(Ed.), VSP/Brill, Leiden, v. 5, pp. 96-106, (2009).

Electronics at the Bulgarian Academy of Sciences,(9) K.Vutova, E.Koleva, G.Mladenov, I.Kostic,Sofia, Bulgaria and the Hiroshima Institute ofT.Tanaka, “Computer simulation of resist

Technology, Hiroshima, Japan during all 25 years.

profiles at electron beam nanolithography,”

K.Vutova would also like to express gratitude toMicroelectronics Engineering, 87, pp. 1108-1111

the BNSF under the project DN17/9.

(2010).
(10) K.Vutova, G.Mladenov, E.Koleva, I.Kostic,

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Appendix

Insitute of Electronics, BASFig. A1

Hiroshima Institute of Technology

Logo mark of Institute of Electronics, BAS and Hiroshima Institute of Technology

Fig. A2Fig. A3

Bulgarian Academy of Sciences logo mark2019 Japan-Bulgaria Triple Anniversary Commemorative logo markFig. A4 International scientific conference“High Technologies. Business. Society”,
March 2018, Borovetc― 100 ―