Removal of ion-implanted photoresists on GaAs using two organic solvents in sequence

Oh, E.,Na, J.,Lee, S.,Lim, S. New York] ; North-Holland 2016 APPLIED SURFACE SCIENCE - Vol.376 No.-

Organic solvents can effectively remove photoresists on III-V channels without damage or etching of the channel material during the process. In this study, a two-step sequential photoresist removal process using two different organic solvents was developed to remove implanted ArF and KrF photoresists at room temperature. The effects of organic solvents with either low molar volumes or high affinities for photoresists were evaluated to find a proper combination that can effectively remove high-dose implanted photoresists without damaging GaAs surfaces. The performance of formamide, acetonitrile, nitromethane, and monoethanolamine for the removal of ion-implanted ArF and KrF photoresists were compared using a two-step sequential photoresist removal process followed by treatment in dimethyl sulfoxide (DMSO). Among the various combinations, the acetonitrile+DMSO two-step sequence exhibited the best removal of photoresists that underwent ion implantation at doses of 5x10<SUP>13</SUP>-5x10<SUP>15</SUP> atoms/cm<SUP>2</SUP> on both flat and trench-structured GaAs surfaces. The ability of the two-step process using organic solvents to remove the photoresists can be explained by considering the affinities of solvents for a polymer and its permeability through the photoresist.

SnO₂ thin films grown by atomic layer deposition using a novel Sn precursor

Choi, M.J.,Cho, C.J.,Kim, K.C.,Pyeon, J.J.,Park, H.H.,Kim, H.S.,Han, J.H.,Kim, C.G.,Chung, T.M.,Park, T.J.,Kwon, B.,Jeong, D.S.,Baek, S.H.,Kang, C.Y.,Kim, J.S.,Kim, S.K. New York] ; North-Holland 2014 APPLIED SURFACE SCIENCE - Vol.320 No.-

SnO<SUB>2</SUB> thin films were grown by atomic layer deposition (ALD) with dimethylamino-2-methyl-2-propoxy-tin(II) (Sn(dmamp)<SUB>2</SUB>) and O<SUB>3</SUB> in a temperature range of 100-230<SUP>o</SUP>C. The ALD window was found to be in the range of 100-200<SUP>o</SUP>C. The growth per cycle of the films in the ALD window increased with temperature in the range from 0.018 to 0.042nm/cycle. Above 230<SUP>o</SUP>C, the self-limiting behavior which is a unique characteristic of ALD, was not observed in the growth because of the thermal decomposition of the Sn(dmamp)<SUB>2</SUB> precursor. The SnO<SUB>2</SUB> films were amorphous in the ALD window and exhibited quite a smooth surface. Sn ions in all films had a single binding state corresponding to Sn<SUP>4+</SUP> in SnO<SUB>2</SUB>. The concentration of carbon and nitrogen in the all SnO<SUB>2</SUB> films was below the detection limit of the auger electron spectroscopy technique and a very small amount of carbon, nitrogen, and hydrogen was detected by secondary ions mass spectroscopy only. The impurity contents decreased with increasing the growth temperature. This is consistent with the increase in the density of the SnO<SUB>2</SUB> films with respect to the growth temperature. The ALD process with Sn(dmamp)<SUB>2</SUB> and O<SUB>3</SUB> shows excellent conformality on a hole structure with an aspect ratio of ~9. This demonstrates that the ALD process with Sn(dmamp)<SUB>2</SUB> and O<SUB>3</SUB> is promising for growth of robust and highly pure SnO<SUB>2</SUB> films.

RF plasma based selective modification of hydrophilic regions on super hydrophobic surface

Lee, J.,Hwang, S.,Cho, D.H.,Hong, J.,Shin, J.H.,Byun, D. New York] ; North-Holland 2017 APPLIED SURFACE SCIENCE - Vol.394 No.-

Selective modification and regional alterations of the surface property have gained a great deal of attention to many engineers. In this paper, we present a simple, a cost-effective, and amendable reforming method for disparate patterns of hydrophilic regions on super-hydrophobic surfaces. Uniform super-hydrophobic layer (Contactangle; CA>150<SUP>o</SUP>, root mean square (RMS) roughness ~0.28nm) can be formed using the atmospheric radio frequency (RF) plasma on top of the selective hydrophilic (CA~70<SUP>o</SUP>, RMS roughness ~0.34nm) patterns imprinted by electrohydrodynamic (EHD) jet printing technology with polar alcohols (butyl carbitol or ethanol). The wettability of the modified surface was investigated qualitatively utilizing scanning electron microscopy (SEM), atomic force microscopy (AFM), and wavelength scanning interferometer (WSI). Secondary ion mass spectroscopy (SIMS) analysis showed that the alcohol addiction reaction changed the types of radicals on the super-hydrophobic surface. The wettability was found to depend sensitively on chemical radicals on the surface, not on surface morphology (particle size and surface roughness). Furthermore, three different kinds of representative hydrophilic samples (polystyrene nano-particle aqueous solution, Salmonella bacteria medium, and poly(3,4-ethylenediocythiophene) ink) were tested for uniform deposition onto the desired hydrophilic regions. This simple strategy would have broad applications in various research fields that require selective deposition of target materials.

Electrical, electronic and optical properties of amorphous indium zinc tin oxide thin films

Denny, Y.R.,Lee, K.,Seo, S.,Oh, S.K.,Kang, H.J.,Yang, D.S.,Heo, S.,Chung, J.G.,Lee, J.C. New York] ; North-Holland 2014 APPLIED SURFACE SCIENCE - Vol.315 No.-

The electrical and optical properties of amorphous indium zinc tin oxide (a-IZTO) thin films were examined as a function of chemical composition. Effects of Sn/Zn composition ratio and In content on the electrical and optical properties of a-IZTO thin films are discussed. The electron mobility of thin film transistors with higher Sn/Zn composition ratio was dramatically improved due to a shorter zinc-zinc separation distance. The thin film transistor with the composition of In:Zn:Sn=20:48:32 exhibits a high mobility of 30.6cm<SUP>2</SUP>V<SUP>-1</SUP>s<SUP>-1</SUP> and a high on-off current ratio of 10<SUP>9</SUP>.

Interface sulfur passivation using H₂S annealing for atomic-layer-deposited Al₂O₃ films on an ultrathin-body In_0.53Ga_0.47As-on-insulator

Jin, H.S.,Cho, Y.J.,Lee, S.M.,Kim, D.H.,Kim, D.W.,Lee, D.,Park, J.B.,Won, J.Y.,Lee, M.J.,Cho, S.H.,Hwang, C.S.,Park, T.J. New York] ; North-Holland 2014 APPLIED SURFACE SCIENCE - Vol.315 No.-

Atomic-layer-deposited Al<SUB>2</SUB>O<SUB>3</SUB> films were grown on ultrathin-body In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As substrates for III-V compound-semiconductor-based devices. Interface sulfur (S) passivation was performed with wet processing using ammonium sulfide ((NH<SUB>4</SUB>)<SUB>2</SUB>S) solution, and dry processing using post-deposition annealing (PDA) under a H<SUB>2</SUB>S atmosphere. The PDA under the H<SUB>2</SUB>S atmosphere resulted in a lower S concentration at the interface and a thicker interfacial layer than the case with (NH<SUB>4</SUB>)<SUB>2</SUB>S wet-treatment. The electrical properties of the device, including the interface property estimated through frequency dispersion in capacitance, were better for (NH<SUB>4</SUB>)<SUB>2</SUB>S wet-treatment than the PDA under a H<SUB>2</SUB>S atmosphere. They might be improved, however, by optimizing the process conditions of PDA. The PDA under a H<SUB>2</SUB>S atmosphere following (NH<SUB>4</SUB>)<SUB>2</SUB>S wet-treatment resulted in an increased S concentration at the interface, which improved the electrical properties of the devices.

Dependence of adhesion strength between GaN LEDs and sapphire substrate on power density of UV laser irradiation

Park, J.,Sin, Y.G.,Kim, J.H.,Kim, J. New York] ; North-Holland 2016 APPLIED SURFACE SCIENCE - Vol.384 No.-

Selective laser lift-off (SLLO) is an innovative technology used to manufacture and repair micro-light-emitting diode (LED) displays. In SLLO, laser is irradiated to selectively separate micro-LED devices from a transparent sapphire substrate. The light source used is an ultraviolet (UV) laser with a wavelength of 266nm, pulse duration of 20ns, and repetition rate of 30kHz. Controlled adhesion between a LED and the substrate is key for a SLLO process with high yield and reliability. This study examined the fundamental relationship between adhesion and laser irradiation. Two competing mechanisms affect adhesion at the irradiated interface between the GaN LED and sapphire substrate: Ga precipitation caused by the thermal decomposition of GaN and roughened interface caused by thermal damage on the sapphire. The competition between these two mechanisms leads to a non-trivial SLLO condition that needs optimization. This study helps understand the SLLO process, and accelerate the development of a process for manufacturing micro-LED displays via SLLO for future applications.

Low-cost laser printable photomask: One-step, photoresist-free, fully solution processed high-grade photolithography mask

Yun, J.,Kim, J.,Yang, M.,Kang, B. New York] ; North-Holland 2017 APPLIED SURFACE SCIENCE - Vol.394 No.-

Owing to the short life cycle of present-day microelectronics, conventional method of photomask fabrication should be replaced in order to improve the resultant agility and productivity of photolithography. To fulfill these requirements, we suggest a fully solution-based one-step fabrication method of a high-grade photomask, without the use of a photoresist, vacuum deposition, and etching process. The photomask is fabricated via the laser-induced instantaneous thermochemical metallization of an optically catalyzed hybrid complex synthesized in-situ from a low-cost particle-free organometallic solution. This reaction yields a masking layer whose high selectivity of less than 1μm, self-generated retroreflective structure, and excellent optical surface are comparable to those of masks fabricated by vacuum depositions. In addition, the complexity of the process is minimized owing to the solution deposition of all the constituent layers. A series of evaluations and the application of this method to an actual photolithography process confirm that this approach constitute a next-generation photomask fabrication method by satisfying both improved agility and productivity of microelectronics manufacturing.

Fabrication and design of bioactive agent coated, highly-aligned electrospun matrices for nerve tissue engineering: Preparation, characterization and application

Lee, S.J.,Heo, M.,Lee, D.,Heo, D.N.,Lim, H.N.,Kwon, I.K. New York] ; North-Holland 2017 APPLIED SURFACE SCIENCE - Vol.424 No.3

In this study, we designed highly-aligned thermoplastic polycarbonate urethane (PCU) fibrous scaffolds coated with bioactive compounds, such as Poly-l-Lysine (PLL) and Poly-l-Ornithine (PLO), to enhance cellular adhesion and directivity. These products were characterized by scanning electron microscope (SEM) analysis which demonstrated that highly aligned fiber strands were formed without beads when coated onto a mandrel rotating at 1800rpm. During in vitro cell test, PLO-coated, aligned PCU scaffolds were found to have significantly higher proliferation rates than PLL coated and bare PCU scaffolds. Interestingly, dental pulp stem cells (DPSCs) were observed to stretch along the longitudinal axis parallel to the cell direction on highly aligned scaffolds. These results clearly confirm that our strategy may suggest a useful paradigm by inducing neural tissue repair as a means to remodeling and healing of tissue for restorative procedures in neural tissue engineering.

Dominantly epitaxial growth of graphene on Ni (111) substrate

Fogarassy, Z.,Rummeli, M.H.,Gorantla, S.,Bachmatiuk, A.,Dobrik, G.,Kamaras, K.,Biro, L.P.,Havancsak, K.,Labar, J.L. New York] ; North-Holland 2014 APPLIED SURFACE SCIENCE - Vol.314 No.-

Graphene was grown on a Ni (111) thin layer, used as a substrate. The Ni layer itself was grown on single crystal sapphire (0001). Carbon was deposited by chemical vapor deposition using a mixture of methane, argon and hydrogen at atmospheric pressure implementing a constant gas flow (4.8-5l/min) varying both the gas composition and the deposition temperature (900-980<SUP>o</SUP>C) and cooling rate (8-16<SUP>o</SUP>C/min) in the different experiments. Formation of uninterruptedly grown epitaxial single layer graphene was observed over the Ni (111) thin film substrate. Epitaxial growth was proven through STM measurements. Electron diffraction studies, also confirmed by STM, demonstrated that only one dominant orientation exists in the graphene, both results providing evidence of the epitaxial growth. On top of the, continuous, large area graphene flakes were also observed with sizes varying between 10nm and 10μm. Most of the top flakes are turbostratically related to the continuous underlying epitaxial graphene layer. The formation of the graphene layer with constant dominant orientation was observed over millimeter wide areas. Large areas (~20-40μm in diameter) of continuous, epitaxial graphene, free of additional deposits and flakes were obtained for the best set of growth parameters.

Low temperature magneto-transport properties in bilayered magnetic anti-dot mircoarrays

Deshpande, N.G.,Hwang, J.S.,Seo, M.S.,Yoo, Y.J.,Rhee, J.Y.,Kim, K.W.,Shao, Y.C.,Chen, K.H.,Pong, W.F.,Lee, Y.P. New York] ; North-Holland 2014 APPLIED SURFACE SCIENCE - Vol.314 No.-

Magneto-transport study on the photolithographically-patterned anti-dot micro-arrays of cobalt upper-layer over a uniform thin nickel under-layer has been carried out. Circular anti-dots in rhomboidal symmetry were fabricated. The magnetoresistance (MR) curves were recorded for magnetically-easy and -hard axes of the bilayer structure at various temperatures. In addition to anisotropic MR, at low temperatures, the MR data shows anomalous behavior with several kinks and plateau regions, indicating complex reversal phenomena. Further, decrease in temperature results in increase of MR average peak height, double splitting of MR peaks and broadening of MR peaks. Additionally, the exchange bias behavior was found in the transverse MR curve; while no significant exchange effect was seen in the longitudinal MR curve. Using energy dispersive spectrum and X-ray absorption spectra taken at Co L<SUB>3,2</SUB>-edge, the presence of CoO layer over the bilayer structure was detected; while the Ni under-layer remained deoxidized.