• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.367.2-367.2
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• 2016

그 동안 열화학 기상 증착법으로 고결정의 그래핀을 합성하는 연구가 많이 진행되었다. 더불어 그래핀을 소자로 이용하기 위해서는 합성하는 과정에서 그래핀의 모양 및 형태를 제어하는 방법이 필요하기 때문에 이와 관련된 연구들 또한 진행되었다. 일반적으로 그래핀의 모양은 촉매의 모양에 의존하기 때문에 촉매 금속의 패터닝에 관심이 집중되었고, 보다 작은 크기의 구조를 완성하기 위해 포토리소그래피(photolithography)법을 이용하는 것이 보편화 되었다. 본 연구에서는 촉매 금속을 이용하여 그래핀을 합성시, 촉매 표면에 잔여하는 유기물(포토리소공정으로 인해 발생하는 잔여물)이 열화학 기상 증착법으로 그래핀을 합성하는 방법에 문제를 야기한다는 것을 확인하였다. 이를 해결하기 위해 플라즈마를 이용하여 잔여 유기물을 제거하였고, 그에 따라 합성된 그래핀의 결정성이 향상되는 것을 확인하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.197-197
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• 2012

Device 제작에 사용된 graphene은 일반적인 lithography 공정에서 resist residue에 의한 오염을 피할 수 없으며 이로 인하여 graphene의 pristine한 성질을 잃어버린다. 본 연구에서는 graphene을 저밀도의 argon inductively coupled plasma (Ar-ICP)를 통해 처리함으로서 graphene based back-gated field effect transistor (G-FET)의 특성변화를 유도한 결과에 대해서 보고한다. Argon capacitively coupled plasma (Ar-CCP)은 에 노출된 graphene은 강한 ion bombardment energy로 인하여 쉽게 planar C-C ${\pi}$ bonding (bonding energy: 2.7 eV)이 breaking되어 graphene의 defect이 발생되었다. 하지만 우리의 경우 저밀도의 Ar-ICP가 적용될 때 graphene의 defect이 제한되며 이와 동시에 contamination 만을 제거할 수 있었다. 소자의 전기적 측정 (Gsd-Vbg)을 통하여 contamination으로 인하여 p-doping된 graphene은 pristine 상태로 회복되었으며 mobility도 회복됨이 확인되었다. Ar-ICP를 이용한 graphene cleaning 방법은 저온공정, 대면적 공정, 고속공정을 모두 만족시키며 thermal annealing, electrical current annealing을 대체하여 graphene 기반 소자를 생산함에 있어 쉽고 빠르게 적용할 수 있는 강점이 있다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.446-446
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• 2010

탄소나노튜브(CNT, carbon nanotube)를 에미터 재료로 사용하여 전계방출 디스플레이 (FED, field emission display)용 캐소드(cathode)를 제작할 때 CNT paste를 구성하는 유기성 바인더를 제거하기 위한 열처리 공정은 필수적이며, 이후에 CNT의 돌출을 위한 표면처리 공정이 뒤따르게 된다. 이러한 표면처리에는 여러 가지 방법들이 있으며 캐소드 제작시 매우 중요한 부분이다. 그 이유는 열처리 과정을 거치게 되면 이물질들이 CNT를 감싸게 되는데 이는 전계방출을 방해하는 요소가 되기 때문에 이를 효과적으로 제거해주지 않으면 전계방출의 효율성이 떨어지기 때문이다. 본 연구는 스크린 인쇄법으로 제작한 CNT 캐소드의 표면처리에 관한 것으로 Tpae 방법을 이용하여 1차적으로 표면처리를 수행한 후 2차적으로 재열처리법을 이용하여 열처리 후 CNT를 감싸고 있는 이물질(ash, residue)등을 효과적으로 제거하였는지 전계방출 특성을 통하여 알아보았다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.375.2-375.2
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• 2016

그래핀(Graphene)은 원자 한 층 두께의 얇은 특성에 기인하여 우수한 투과도(~97.3%)를 나타내며, 높은 전자 이동도($200,000cm^2V^{-1}s^{-1}$)로 인하여 전기 전도도가 우수한 2차원 전자소재이다. 또한 유연하고 우수한 기계적 물성을 가지고 있어 실제로 다양한 소자에서 활용되고 있다. 그래핀을 이용하여 다양한 소자로 응용하기 위한 과정 중 하나인 포토리소그래피 공정(Photolithography process)은 원하는 패턴을 만들기 위해 제작하고자 하는 기판 위에 포토레지스트(Photoresist)를 코팅하는 과정을 거치게 된다. 하지만 이러한 과정은 소자 제작에 있어서 포토레지스트 잔여물을 남기게 된다. 그래핀 위에 남은 포토레지스트 잔여물은 그래핀의 우수한 전기적 특성을 저하시켜 소자특성에 불이익을 주게 된다. 본 연구에서는 수소 플라즈마를 이용하여 그래핀 위에 남은 중합체(Polymer) 잔여물을 제거한다. 사용한 그래핀은 화학 기상 증착법(Chemical vapor deposition)을 이용하여 성장시켰으며, PMMA(Poly(methyl methacrylate))를 이용하여 이산화규소(silicon dioxide) 기판에 전사하였다. 그래핀의 손상 없이 중합체 잔여물을 제거하기 위해 플라즈마 처리시간을 15초부터 1분까지 늘려가며 연구를 진행하였으며, 플라즈마 처리 시간에 따른 중합체 잔여물의 제거 정도와 그래핀의 보존 여부를 확인하기 위해 라만 분광법(Raman spectroscopy)과 원자간력현미경(Atomic force microscopy)을 사용하였다. 본 연구 결과를 통해 간단한 플라즈마 처리로 보다 나은 특성의 그래핀 소자를 얻게 됨으로써, 향상된 특성을 가진 그래핀 소자로 산업적 응용 가능성을 높일 수 있을 것이라 생각된다.

• Journal of the Korean Vacuum Society
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• v.6 no.4
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• pp.364-371
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• 1997

Silicon trench etching has been carried out using a magnetically enhanced reactive ion etching system in HBr plasma containing He-$O_2$, $CF_4$. The changes of etch rate and etch profile, the degree of residue formation, and the change of surface chemical state were investigated as a function of additive gas flow rate. A severe lateral etching was observed when pure HBr plasma was used to etch the silicon, resulted in a pot shaped trench. When He-$O_2$, $SiF_4$ additives were added to HBr plasma, the lateral etching was almost eliminated and a better trench etch profile was obtained. The surface etched in HBr/He-$O_2/SiF_4$ plasma showed relatively low contamination and residue elements compared to the surface etched in HBr/He-$O-2/CF_4$plasma. In addition, the etching characteristics including low residue formation and chemically clean etched surface were obtained by using HBr containing He-$O_2$ or $SiF_4$ additive gases instead of $CF_4$ gas, which were confirmed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM).

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.642-642
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• 2013

Graphene, two dimensional single layer of carbon atoms, has tremendous attention due to its superior property such as high electron mobility, high thermal conductivity and optical transparency. Especially, chemical vapor deposition (CVD) grown graphene has been used as a promising material for high quality and large-scale graphene film. Unfortunately, although CVD-grown graphene has strong advantages, application of the CVD-grown graphene is limited due to ineffective transfer process that delivers the graphene onto a desired substrate by using polymer support layer such as PMMA(polymethyl methacrylate). The transferred CVD-grown graphene has serious drawback due to remaining polymeric residues generated during transfer process, which induces the poor physical and electrical characteristics by a p-doping effect and impurity scattering. To solve such issue incurred during polymer transfer process of CVD-grown graphene, various approaches including thermal annealing, chemical cleaning, mechanical cleaning have been tried but were not successful in getting rid of polymeric residues. On the other hand, lithographical patterning of graphene is an essential step in any form of microelectronic processing and most of conventional lithographic techniques employ photoresist for the definition of graphene patterns on substrates. But, application of photoresist is undesirable because of the presence of residual polymers that contaminate the graphene surface consistent with the effects generated during transfer process. Therefore, in order to fully utilize the excellent properties of CVD-grown graphene, new approach of transfer and patterning techniques which can avoid polymeric residue problem needs to be developed. In this work, we carried out transfer and patterning process simultaneously with no polymeric residue by using a metal etch mask. The patterned thin gold layer was deposited on CVD-grown graphene instead of photoresists in order to make much cleaner and smoother surface and then transferred onto a desired substrate with PMMA, which does not directly contact with graphene surface. We compare the surface properties and patterning morphology of graphene by scanning electron microscopy (SEM), atomic force microscopy(AFM) and Raman spectroscopy. Comparison with the effect of residual polymer and metal on performance of graphene FET will be discussed.

• Applied Chemistry for Engineering
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• v.29 no.4
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• pp.468-473
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• 2018

In this study, the reforming reaction of vacuum residues (VR), high viscosity oil residues produced from vacuum distillation process of petroleum oil, was carried out using catalytic aquathermolysis reaction. VR showed a prone to decrease the amount of resins and asphaltenes in the constituents, and to increase saturates and aromatics when reacting with steam at 30 bar and above $300^{\circ}C$ for 24 h. When the amount of steam is not enough at this reaction, the asphaltene content in the products was rather increased after the reaction. As a result of the catalytic aquathermolysis using the metal oxide-zeolite catalyst with the decaline as a hydrogen donor, a 10% decrease in resin and asphaltene as well as a 10% increase in the aromatic hydrocarbon were observed. Consequently, the viscosity of VR decreased by 70% after the reaction. GC-Mass spectroscopy showed that the aquathermolysis of VR resulted in the decomposition of the resins and asphaltens into a low molecular weight material.

• Applied Chemistry for Engineering
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• v.28 no.4
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• pp.467-472
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• 2017

In this study, the reforming reaction of vacuum residue (VR) was carried out using aquathermolysis reaction. VR showed a prone to decrease the amount of resins and asphaltenes in the constituents, and to increase saturates and aromatics when reacting with steam at 30 bar and above $300^{\circ}C$ for 24 h. This tendency became more evident when the amount of steam used was excessive than the amount of VR. When the aquathermolysis reaction was performed at $300^{\circ}C$ and 30 bar for 48 h, the VR composition was changed from the initial state (S/A/R/A = 7.3%/43.7%/25.6%/23.5%) to final state (S/A/R/A = 6.8%/57%/12.2%/24.0%), and the contents of the resins decreased by 13% and the aromatic compounds increased by 13%. The viscosity decreased from 880,000 cp to 290,000 cp by 68%. When 10% of decalin, which is easy to provide hydrogen, was added, the viscosity decreased by 68% in 24 h. The VR composition showed a reduction in the contents of resins and asphaltenes from 49% to 17% from the initial state (S/A/R/A = 7.3%/43.7%/25.6%/23.5%) to the final state (S/A/R/A = 4.5%/63.5%/12.5%/20.0%), and the content of aromatics was maximized to 63.5%. The gas layer formed by the aquathermolysis reaction in the reactor chamber was collected and analyzed by GC-MS spectroscopy. As a result, various hydrocarbon compounds such as ethylbenzene, octane and dimethylbenzene were detected.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.629-629
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• 2013

Graphene is a carbon based material and it has intriguing features, such as phenomenally strong, thin, flexible, transparent and conductive, those make it attractive for a broad range of applications.Unfortunately, graphene is extremely sensitive to contamination. When we fabricate graphene devices, electrical properties of graphene are altered [1], and the charge carrier mobility drops accordingly by orders of magnitude. This significant impact on electron mobility occurs because any surrounding medium could act as a dominant source of extrinsic scattering, which effectively reduces the mean free path of carriers [2,3]. The dominant contaminant is generated through fabrication stage by polymethyl methacrylate (PMMA) [4], or photo resist (PR). Surface contamination by these residues has long been a critical problem in probing graphene's intrinsic properties. If we clearly solve this problem, we can get highly performed graphene devices. Here, we will report on graphene cleaning process by Induced Coupled Plasma (ICP). We demonstrated how much decomposition of residue impact on improving electrical properties of graphene.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.561-561
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• 2012

Graphene, two dimensional single layer of carbon atoms, has tremendous attention due to its superior property such as fast electron mobility, high thermal conductivity and optical transparency, and also found many applications such as field-effect transistors (FET), energy storage and conversion, optoelectronic device, electromechanical resonators and chemical sensors. Several techniques have been developed to form the graphene. Especially chemical vapor deposition (CVD) is a promising process for the large area graphene. For the electrically isolated devices, the graphene should be transfer to insulated substrate from Cu or Ni. However, transferred graphene has serious drawback due to remaining polymeric residue during transfer process which induces the poor device characteristics by impurity scattering and it interrupts the surface functionalization for the sensor application. In this study, we demonstrate the characteristics of solution-gated FET depending on the removal of polymeric residues. The solution-gated FET is operated by the modulation of the channel conductance by applying a gate potential from a reference electrode via the electrolyte, and it can be used as a chemical sensor. The removal process was achieved by several solvents during the transfer of CVD graphene from a copper foil to a substrate and additional annealing process with H2/Ar environments was carried out. We compare the properties of graphene by Raman spectroscopy, atomic force microscopy(AFM), and X-ray Photoelectron Spectroscopy (XPS) measurements. Effects of residual polymeric materials on the device performance of graphene FET will be discussed in detail.