Low-temperature Deposition Process Research Articles

나노물질의 선택적 레이저소결을 이용한 유연전기소자 구현 연구현황

대부분의 유연전기소자는 플라스틱, 옷감, 종이와 같이 고온에 민감한 물질이기 때문에 열에 민감한 기판 위에 금속을 증착하고 패터닝할 수 있는 저온 공정의 개발이 필요하다. 최근 기존의 광식각과 진공증착 방법을 이용하지 않고 액상으로 금속 나노입자의 박막을 형성하고 선택적 레이저 소결을 이용하여 플라스틱에 열적손상을 최소화하고 고해상도의 금속 패터닝을 방법이 많은 연구가 활발히 진행되고 있다. 본 논문에서는 본 연구실에서 활발히 수행중인 나노물질의 선택적 레이저소결법을 이용하여 유연 디스플레이와 유연태양전지와 같은 유연전기소자의 개발 동향에 대해 알아보고 앞으로의 발전방향에 대해 논의한다.

Low-temperature atomic layer deposition of ZnO thin films: Control of crystallinity and orientation

Low-temperature atomic layer deposition (ALD) processes are intensely looked for to extend the usability of the technique to applications where sensitive substrates such as polymers or biological materials need to be coated by high-quality thin films. A preferred film orientation, on the other hand, is often required to enhance the desired film properties. Here we demonstrate that smooth, crystalline ZnO thin films can be deposited from diethylzinc and water by ALD even at room temperature. The depositions were carried out on Si(100) substrates in the temperature range from 23 to 140°C. Highly c-axis-oriented films were realized at temperatures below ~80°C. The film crystallinity could be further enhanced by post-deposition annealing under O2 or N2 atmosphere at 400–600°C while keeping the original film orientation intact.

The application of dry photoresists in fabricating cost-effective tapered through-silicon vias and redistribution lines in a single step

In this paper, we report a simple and cost-effective technique to fabricate a partially electroplated tapered through-silicon via (TSV) and redistribution line (RDL)-like structures on the field in a single process step using dry laminated photoresists. An array of 100 µm deep positively tapered silicon vias was etched by a three-step non-Bosch plasma etching process. Insulation, diffusion barrier and seed layers were deposited by low-temperature plasma-enhanced chemical vapor deposition and sputtering processes, respectively. A 15 µm thick dry MXA115 photoresist was laminated on the wafer by a roller-less vacuum lamination process. The dry resist allows a satisfactory patterning of the RDL-like structures by eliminating the chances of resist residuals falling in the etched TSVs. Direct-current (dc) electroplating was used to deposit 10 µm thick copper layers on the via sidewalls as well as on the field. Therefore, the electroplating not only partially fills the vias but also forms the RDL structures at the same time. Since both TSVs and RDLs are fabricated together in a single process step, several conventional process steps such as over-burden polishing, lithography, and metal etching were avoided. Compared to the conventional TSV fabrication processes, this dry resist lithography-based method turned out to be simple and very cost-effective in making complex TSV interconnects.

Fabrication and characterization of plastic-based flexible dye-sensitized solar cells consisting of crystalline mesoporous titania nanoparticles as photoanodes

We fabricated a highly efficient (with a solar-to-electricity conversion efficiency (η) of 5.51%), plastic-based, flexible dye-sensitized solar cell (DSSC). The photoanode was made of a crystalline mesoporous TiO2 film using a low-temperature electrophoretic deposition (EPD) process and compression treatment. The crystalline mesoporous TiO2 film was composed of secondary mesoporous TiO2 nanoparticles (MTNs, ca. 260 nm in size), synthesized by an aggregation of primary TiO2 nanocrystallites. In contrast to commercial TiO2 nanoparticles (i.e., P90, ca. 15.9 nm in size) that are widely used in DSSCs, the synthesized MTN-based film exhibited a higher surface area and porosity that increased dye adsorption, promoted effective electron transport, and enhanced light scattering, as evidenced by analysis of reflectance and absorbance spectra, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). We also optimized the compression pressure for MTN- and P90-based DSSCs in order to achieve maximum efficiency. We further systematically investigated the cause for the enhanced conversion efficiency of MTN-based DSSCs by measuring incident photon-to-electron conversion efficiency (IPCE) curves and electrochemical impedance spectra (EIS). IPCE results explained the increase in the short-circuit photocurrent density (JSC) for MTN-based DSSCs, and EIS results indicated that MTN-based DSSCs exhibited a larger diffusion coefficient (Deff), longer effective diffusion length (Ln), longer electron lifetime (τe), and lower charge transfer resistance (Rk), resulting in a higher power conversion efficiency. The MTN-based DSSC fabricated in the study showed great potential for application in plastic-based DSSCs using room temperature procedures.

Piezoresistive polysilicon film obtained by low-temperature aluminum-induced crystallization

A low-temperature deposition process employing aluminum-induced crystallization has been developed for fabrication of piezoresistive polycrystalline silicon (polysilicon) films on low cost and flexible polyimide substrates for force and pressure sensing applications. To test the piezoresistive properties of the polysilicon films, prototype pressure sensors were fabricated on surface-micromachined silicon nitride (Si 3N 4) diaphragms, in a half-Wheatstone bridge configuration. Characterization of the pressure sensor was performed using atomic force microscope in contact mode with a specially modified probe-tip. Low pressure values ranging from 5 kPa to 45 kPa were achieved by this method. The resistance change was found to be − 0.1% to 0.5% and 0.07% to 0.3% for polysilicon films obtained at 500 °C and 400 °C, respectively, for the applied pressure range.

Highly efficient blue organic light-emitting devices with indium-free transparent anode on flexible substrates

Indium-free transparent conducting oxides (TCOs) may provide a lower cost solution for the transparent anode in large area displays and solid-state lighting. Low temperature deposition processes are essential for manufacturing compatible with flexible substrate materials. We report herein a near room temperature sputtering process for generating an indium-free TCO coating on a flexible substrate. Specifically, we deposited gallium-doped zinc oxide (GZO) uniformly over a 12″ diameter area at nominally room temperature on polyethylene terephthalate (PET), without any noticeable damage to the PET substrate. The GZO films exhibit excellent physical, optical and electrical properties: roughness ∼7 nm, transmittance >85% and resistivity ∼10 −3 ohm cm. Phosphorescent blue organic light-emitting devices (OLEDs) were fabricated on these substrates with comparable performance (16% external quantum efficiency and 33 lm/W power efficiency at 1 mA/cm 2) to that of devices fabricated on glass with GZO or indium tin oxide (ITO) as the anodes. These results demonstrate the utility of using GZO instead of the higher cost material ITO on PET for flexible displays and solid-state lighting.

Preparation and mechanical property of polymer-based biomaterials

The porous polymer-based biomaterial has been synthesized from PLGA, dioxane and tricalcium phosphate (TCP) by low-temperature deposition process. The deformation behaviours and fracture mechanism of polymer-based biomaterials were investigated using the compression test and the finite element (FE) simulation. The results show that the stress-strain curve of compression process includes linear elastic stage I, platform stage II and densification stage III, and the fracture mechanism can be considered as brittle fracture.

Cryogenic inductively coupled plasma etching for fabrication of tapered through-silicon vias

Vertical interconnects pose an interesting method for heterogeneous integration of electronic technologies allowing three-dimensional (3D) stacking of microelectromechanical systems devices and integrated circuit components. The vertical interconnects, referred to as through-silicon vias, begin with the formation of blind vias in silicon that are eventually exposed by mechanically lapping and polishing the wafer back side. Inductively coupled plasma (ICP) etching using SF6∕O2 gas chemistry at cryogenic temperatures has been investigated as a way to form vias with a tapered sidewall. The point in creating a controlled taper is so that subsequent thin films can be deposited along the sloped sidewall that line the via with insulation, barrier, and seed films. This tapering is necessary if the via lining processes do not provide adequate conformal coverage, a common problem for conventional low temperature deposition processes. In our process for lining the via sidewall, plasma enhanced chemical vapor deposited silicon dioxide is used to insulate vias from the surrounding silicon. Both Ti and Cu are sputter deposited and provide protection from copper migration and a seed film for Cu electrodeposition, respectively. After etching and lining, the vias are filled by reverse pulse plating of Cu. Vias are 20–25μm in diameter and etched using different masking materials. The effect of changing gas flow rates, chamber pressure, ICP power, and substrate temperature on etch rate, via profile, and sidewall morphology will be presented. These parameters are critical in the optimization of an etch process for vias of specific dimensions to be used in 3D integration.

Loading effects of self-biased magnetic films on patch antennas with substrate/superstrate sandwich structure

From materials perspective, it has been challenging to achieve relative permeability mr . 1i n self- biased antenna substrates at gigahertz frequencies. In this study, self-biased microwave NiCo ferrite films were deposited with a low-temperature spin spray deposition process. Novel antenna designs with self-biased NiCo- ferrite films were investigated at 2.1 GHz. These magnetic antennas with several micrometers thick ferrite films show an enhanced antenna performance over the unloaded patch antenna. With ferrite loading of the alumina substrate, the resonant frequency shows a down shift of 30 - 50 MHz. The radiation efficiency is increased from 41% for the non-magnetic antenna to 76% for the ferrite films loaded antenna, together with an antenna gain enhancement greater than 1 dB over the non-magnetic antenna. The combination of these self-biased ferrite films and alumina substrates can lead to miniature antennas with enhanced performance at gigahertz frequencies.

Biocompatible Interface Films Deposited within Porous Polymers by Atomic Layer Deposition (ALD)

Ultrathin ceramic films were deposited throughout highly porous poly(styrene-divinylbenzene) (PS-DVB) particles using a low-temperature atomic layer deposition (ALD) process. Alumina and titania films were deposited by alternating reactions of trimethylaluminum and H2O at 33 degrees C and of titanium tetrachloride and H2O2 (50 wt % in H2O) at 100 degrees C, respectively. Analytical characterization revealed that conformal alumina and titania films were grown on internal and external polymer surfaces. The improved bioactivity of the polymer substrates was revealed on the basis of the formation of hydroxyapatite (HA) in simulated body fluid. The accelerated formation of HA on the ALD-modified polymer surface was caused by the negatively charged surface provided by the ultrathin ceramic interface. The potential for ALD films to support cell attachment was demonstrated.

Fabrication of an Apatite/Collagen Composite Coating on the NiTi Shape Memory Alloy through Electrochemical Deposition and Coating Characterisation

To improve the biocompatibility and bioactivity of NiTi shape memory alloy (SMA), apatite/collagen composite coatings were fabricated on the surface of NiTi SMA at room temperature using the electrochemical deposition technique. Spherical apatite particles and fibrous collagen that formed the composite coating were visible under scanning electron microscope (SEM). The Ca/P ratio of the apatite component in the coating, as determined by energy dispersive X-ray spectroscopy (EDX), was about 1.38 which is slightly higher than that of octocalcium phosphate (OCP). X-ray diffraction result showed that the apatite was amorphous, which was due to the low temperature (i.e., room temperature) deposition process. The structure of the composite coatings was further characterized using Fourier transform infrared reflection spectroscopy (FTIR). It was also found that, compared to bare NiTi SMA samples, the wettability of as-deposited samples was increased because of the formation of the composite coating.

Proton related defects in α-BaTiO 3:H films based MIM capacitors

Hydrogenated barium titanate film based metal–insulator–metal (MIM) systems show high dielectric constant and have therefore been proposed as solid state supercapacitors. Hydrogen was incorporated in the dielectric layer during the low temperature deposition process. An investigation of the electrical properties has revealed that hydrogen contributes to the conduction process as mobile ionic species as well as donor trap levels.

Integration of High Aspect Ratio Tapered Silicon Via for Silicon Carrier Fabrication

This paper provides a detailed overview of silicon carrier-based packaging for 3-D system in packaging application. In this work the various critical process modules that play a vital role in the integration and fabrication of silicon carrier with high aspect ratio tapered through-silicon interconnections have been explained and discussed with experimental data. A method of fabricating tapered deep silicon via in a three-step approach has been developed and characterized which controls via depth, sidewall profile, and surface roughness effectively. A low-temperature dielectric deposition process is also developed that has minimum residual stress and good dielectric coverage on the via sidewall. The above processes were then integrated with back-end processes like seed metallization, copper electroplating, chemical mechanical polishing, and wafer thinning to realize a fully integrated silicon carrier fabrication technology. The silicon carriers were finally assembled and tested for through silicon interconnection.

Atomic Layer Deposition Al$_{2}$O$_{3}$ Films for Permanent Magnet Isolation in TMR Read Heads

Al2O3 films made with atomic layer deposition (ALD) have been developed for use as isolation layers in CPP tunneling magnetoresistive readers. A low-temperature deposition process was developed to permit integration with a self-aligned patterning scheme. The resulting films show excellent thickness uniformity ( 9 MV/cm). TEMs of sub-100 nm TMR readers fabricated using these processes show>95% conformality on junction sidewalls, indicating nonselective growth of ALD Al2O3 on the various stack and bottom shield surfaces. Permanent magnets with well-controlled junction grain structure and coercivities in excess of 2500 Oe have been deposited with existing processes. FEM modeling shows the effective stabilizing field from the magnets at the junction edge scales inversely with ALD layer thickness, in agreement with device-level free layer stability metrics showing improvements at lower ALD thicknesses. As the conformal ALD layer thickness is easily tuned, this technology provides flexibility in trading off reader amplitude and stability that should support scaling of the abutted TMR design out to 1 Tb/in2 and beyond.

Role of rf power on the properties of undoped SnO x films deposited by rf-PERTE at low substrate temperature

Transparent and conductive undoped tin oxide (SnO x ) thin films were deposited at low substrate temperature (< 140 °C) by radio frequency (rf) plasma enhanced reactive thermal evaporation (rf-PERTE) of tin (Sn) in the presence of oxygen The undoped SnO x films were not submitted to any post-annealing treatments. The influence of rf power variation on the optical, electrical and structural properties of the as-grown films is presented. A variation in the films' structure was verified with the increase of rf power. Undoped SnO x films, 90 nm average thick, deposited at rf power range of 60–70 W are nanocrystalline, show a conductive behaviour, an average visible transmittance of ≥ 80% and a maximum electrical conductivity of about 34.6 (Ω cm) − 1 . Films deposited at lower values of rf power (40 W) are amorphous and exhibit a semiconductive behaviour, showing an electrical conductivity of about 7.54 × 10 − 1 (Ω cm) − 1 . As a low substrate temperature deposition process is used, SnO x thin films can be obtained on a wide range of substrates.

Flexible Cu(In, Ga)Se2 Thin-Film Solar Cells on Polyimide Substrate by Low-Temperature Deposition Process

The electrical and structural properties of polycrystalline Cu(In,Ga)Se2 films grown on polyimide (PI) substrates below 400° C via one-stage and three-stage co-evaporation process have been investigated by x-ray diffraction spectra (XRD), scanning electron microscopy (SEM) and Hall effect measurement. As shown by XRD spectra, the stoichiometric CIGS films obtained by one-stage process exhibit the characteristic diffraction peaks of the (In0.68Ga0.32)2Se3 and Cu(In0.7Ga0.3)2Se. It is also found that the film structures indicate more columnar and compact than the three-stage process films from SEM images. The stoichiometric CIGS films obtained by three-stage process exhibit the coexistence of the secondary phase of (In0.68Ga0.32)2Se3, Cu2-xSe and Cu(In0.7Ga0.3)2Se. High net carrier concentration and sheet conductivity are also observed for this kind of film, related to the presence of Cu2-xSe phase. As a result, when the CIGS film growth temperature is below 400° C, the three-stage process is inefficient for solar cells. By using the one-stage co-evaporation process, the flexible CIGS solar cell on a PI substrate with the best conversion efficiency of 6.38% is demonstrated (active area 0.16 cm2).

Industrially-scaled room-temperature pulsed laser deposition of Ti-TiN multilayer coatings

The aim of the current work is the transfer of multilayer design knowledge on the Pulsed Laser Deposition (PLD) technique for industrially-scaled room-temperature growth of titanium–titanium nitride (Ti–TiN) structures. Because almost all PVD and CVD coating techniques require substrate temperatures >200°C for sufficiently adhering and dense coatings, there is high demand for the development of large-area and high-rate low-temperature vacuum deposition process like the PLD, e.g. for the coating of temperature-sensitive or shape-distortion-sensitive materials and substrates. A pulsed Nd:YAG laser (wavelength: 1064 nm) was used for depositing alternately Ti and TiN layers in Ar and N2 atmosphere, resp., forming nearly particulate-free, very smooth and dense 1 μm thick coatings. Starting from single layers, in multilayers with thicker individual layers hardness and scratch resistance (critical load in scratch tests) is decreased, but this trend is reversed in multilayers of very thin (<100 nm) individual layers. In contrast, the compressive growth stress is dropping down continuously in the multilayers of increasing period numbers.

Low-temperature plasma-enhanced atomic layer deposition growth of WNxCy from a novel precursor for barrier applications in nanoscale devices

A low-temperature plasma-enhanced atomic layer deposition (PEALD) process has been developed for the growth of ultrathin WNxCy films, using a halide-free W precursor. A 32-nm-thick PEALD WNxCy film deposited using this process at 250 °C possesses a composition of W72C20N5, resistivity of ∼250 μΩ·cm, a root-mean-square (rms) surface roughness of 0.23 nm, and a thickness conformality of more than 80% on trench structures with a width of 120 nm and an aspect ratio of 11. The WNxCy films exhibited excellent thermal stability, whereby resistivity, thickness, surface roughness, and crystal structure were stable after 30 min anneals in 700 Torr, forming gas ambient at temperatures up to 700 °C. Copper diffusion barrier performance measurements show that a 9 nm thick WNxCy film could prevent copper diffusion after a 30 min anneal at 700 °C, while a 2-nm-thick film could prevent copper diffusion after a 30 min anneal at 500 °C.

Numerical studies on up scaling of metal organic PACVD processes used for tribological coating in automotive industry

In this research, a numerical simulation of the plasma-assisted CVD coating process for low-temperature deposition of a TiN layer using TDMAT: Tetrakis(dimethylamino)titanium was performed. Despite the tremendous demands for coated applications, most coating processes remain on a laboratory scale. To apply the results for a laboratory-size chamber to an industrial-size chamber, simulation studies were focused on a pilot plant as an intermediate step. On the whole, the tendency of deposition on a substrate was shown to be dependent on the process parameters of flow rate, heating temperature, pressure and process gas composition. The simulation technique would apply to an up-scaled industrial chamber.

Metallorganic Chemical Vapor Deposition of Hafnium Silicate Thin Films Using a Dual Source Dimethyl-alkylamido Approach

A low-temperature metallorganic chemical vapor deposition process has been developed for the growth of hafnium silicate thin films for advanced gate dielectric applications. In this process, a metallorganic hafnium precursor, tetrakis(dimethylamino)hafnium, and a metallorganic silicon precursor, tris(dimethylamino)silicon, were employed, using as a co-reactant. Films were deposited at a substrate temperature in the range of . The films were subsequently annealed in oxygen and forming gas ambients to assess thermal stability. The resulting films were characterized by Auger electron spectroscopy to determine composition and X-ray diffraction to determine microstructure. Electrical test structures were fabricated with as-deposited and annealed hafnium silicate films, and C-V and J-V measurements were performed. As-deposited dielectric constant values ranging from 6.9 to 12.9 were achieved depending on processing conditions and resulting film composition. Leakage current density at flatband voltage minus for a thick as-deposited film was measured to be and was shown to decrease following an anneal. The performance of these hafnium silicate films was also compared to hafnium oxide films deposited using the same Hf precursor and oxidizer approach.