Giyul Ham

Tuning the electronic structure of tin sulfides grown by atomic layer deposition.

In this study, tin sulfide thin films were obtained by atomic layer deposition (ALD) using Tetrakis(dimethylamino)tin (TDMASn, [(CH3)2N]4Sn) and hydrogen sulfide (H2S). The growth rate of the tin sulfides (SnSx) was shown to be highly dependent on the deposition temperature, and reaction times of 1 second for the TDMASn and H2S were required to reach the saturation regime. Surface morphologies were smooth or rectangular with rounded corners as observed by a field emission scanning electron microscope (FE-SEM) and were dependent on temperature. X-ray diffraction results confirmed that the crystal structure of SnSx can be tuned by changing the ALD temperature. Below 120 °C, SnSx films appeared to be amorphous. In addition, SnSx films were SnS2 hexagonal at 140 and 150 °C and SnS orthorhombic above 160 °C. Similarly, the values of the optical band gap and binding energy showed significant differences between 150 and 160 °C. The electronic structures of SnSx were extracted by UPS and absorption spectroscopy, and the unsaturated Sn 3d molecular orbital (MO) states in the band edge were found to be responsible for the great improvement in electrical conductivity. This study shows that TDMASn-H2S ALD is an effective deposition method for SnSx films, offering a simple approach to tune the physical properties.

Al2O3 multi-density layer structure as a moisture permeation barrier deposited by radio frequency remote plasma atomic layer deposition

Al2O3 films deposited by remote plasma atomic layer deposition have been used for thin film encapsulation of organic light emitting diode. In this study, a multi-density layer structure consisting of two Al2O3 layers with different densities are deposited with different deposition conditions of O2 plasma reactant time. This structure improves moisture permeation barrier characteristics, as confirmed by a water vapor transmission rate (WVTR) test. The lowest WVTR of the multi-density layer structure was 4.7 × 10−5 gm−2 day−1, which is one order of magnitude less than WVTR for the reference single-density Al2O3 layer. This improvement is attributed to the location mismatch of paths for atmospheric gases, such as O2 and H2O, in the film due to different densities in the layers. This mechanism is analyzed by high resolution transmission electron microscopy, elastic recoil detection, and angle resolved X-ray photoelectron spectroscopy. These results confirmed that the multi-density layer structure exhibits ver...

Moisture Barrier Properties of Al2O3 Films deposited by Remote Plasma Atomic Layer Deposition at Low Temperatures

We report the effect of process temperature on moisture permeation barrier properties of Al2O3 films deposited by remote plasma atomic layer deposition (RPALD) at various low temperatures from 50 to 200 °C. XPS analysis of O 1s peak reveals that the O–H ratio decreases with process temperature from 38.1% at 50 °C to 25.8% at 200 °C. The water transmission rates using electrical Ca degradation test indicates that the 100 nm Al2O3 film enhances the moisture barrier performance from 2.0×10-2 to 5.0×10-4 g m-2 day-1 with increasing the process temperature. This result indicates that increasing the process temperature improves the moisture permeation barrier properties significantly even in RPALD process. It is attributed to the increase in the Al2O3 mass density due to the decrease of relatively O–H ratio with increase in temperature as revealed by XPS O 1s peak deconvolution and FTIR analysis in the Al2O3 films.

Engineering the crystallinity of tin disulfide deposited at low temperatures

Tin disulfide (SnS2), which exhibits a two-dimensional (2D) layered structure, is considered to be a promising channel material for thin film transistors because of its high electrical performance and low temperature processibility. In this work, we deposited crystalline SnS2 at 150 °C using atomic layer deposition (ALD) which is compatible with current electronic device processing methods. And then, crystalline SnS2 films were annealed to investigate the change in crystallinity. We carried out sulfur annealing of the SnS2 films at temperatures of 250, 300 and 350 °C. The effects of sulfur annealing were investigated in a mixed gas atmosphere of 100 sccm argon (Ar) and 5 sccm hydrogen (H2). SnS2 samples were examined using XRD, TEM, XPS, UV-vis and PL. The crystallinity of the SnS2 films after annealing was improved, and its grain size became larger compared with the as-deposited SnS2 film. We also observed a clear two dimensional layered structure of SnS2 using high resolution TEM. The change in the optical properties of the SnS2 films was observed using UV-vis and PL.

원자층증착 기술: 개요 및 응용분야

Atomic layer deposition(ALD) is a promising deposition method and has been studied and used in many different areas, such as displays, semiconductors, batteries, and solar cells. This method, which is based on a self-limiting growth mechanism, facilitates precise control of film thickness at an atomic level and enables deposition on large and three dimensionally complex surfaces. For instance, ALD technology is very useful for 3D and high aspect ratio structures such as dynamic random access memory(DRAM) and other non-volatile memories(NVMs). In addition, a variety of materials can be deposited using ALD, oxides, nitrides, sulfides, metals, and so on. In conventional ALD, the source and reactant are pulsed into the reaction chamber alternately, one at a time, separated by purging or evacuation periods. Thermal ALD and metal organic ALD are also used, but these have their own advantages and disadvantages. Furthermore, plasma-enhanced ALD has come into the spotlight because it has more freedom in processing conditions; it uses highly reactive radicals and ions and for a wider range of material properties than the conventional thermal ALD, which uses H2O and O3 as an oxygen reactant. However, the throughput is still a challenge for a current time divided ALD system. Therefore, a new concept of ALD, fast ALD or spatial ALD, which separate half-reactions spatially, has been extensively under development. In this paper, we reviewed these various kinds of ALD equipment, possible materials using ALD, and recent ALD research applications mainly focused on materials required in microelectronics.

Thickness-dependent structure and properties of SnS2 thin films prepared by atomic layer deposition

Tin disulfide (SnS2) thin films were deposited by a thermal atomic layer deposition (ALD) method at low temperatures. The physical, chemical, and electrical characteristics of SnS2 were investigated as a function of the film thickness. SnS2 exhibited a (001) hexagonal plane peak at 14.9° in the X-ray diffraction (XRD) results and an A1g peak at 311 cm−1 in the Raman spectra. These results demonstrate that SnS2 thin films grown at 150 °C showed a crystalline phase at film thicknesses above 11.2 nm. The crystallinity of the SnS2 thin films was evaluated by a transmission electron microscope (TEM). The X-ray photoelectron spectroscopy (XPS) analysis revealed that SnS2 consisted of Sn4+ and S2− valence states. Both the optical band gap and the transmittance of SnS2 decreased as the film thickness increased. The band gap of SnS2 decreased from 3.0 to 2.4 eV and the transmittance decreased from 85 to 32% at a wavelength of 400 nm. In addition, the resistivity of the thin film SnS2 decreased from 1011 to 106 Ωcm as the film thickness increased.

Improved electrical properties of atomic layer deposited tin disulfide at low temperatures using ZrO2 layer

We report the effect of zirconium oxide (ZrO2) layers on the electrical characteristics of multilayered tin disulfide (SnS2) formed by atomic layer deposition (ALD) at low temperatures. SnS2 is a two-dimensional (2D) layered material which exhibits a promising electrical characteristics as a channel material for field-effect transistors (FETs) because of its high mobility, good on/off ratio and low temperature processability. In order to apply these 2D materials to large-scale and flexible electronics, it is essential to develop processes that are compatible with current electronic device manufacturing technology which should be conducted at low temperatures. Here, we deposited a crystalline SnS2 at 150 °C using ALD, and we then annealed at 300 °C. X-ray diffraction (XRD) and Raman spectroscopy measurements before and after the annealing showed that SnS2 had a hexagonal (001) peak at 14.9° and A1g mode at 313 cm−1. The annealed SnS2 exhibited clearly a layered structure confirmed by the high resolution tr...

Characteristics of layered tin disulfide deposited by atomic layer deposition with H2S annealing

Tin disulfide (SnS2) has attracted much attention as a two-dimensional (2D) material. A high-quality, low-temperature process for producing 2D materials is required for future electronic devices. Here, we investigate tin disulfide (SnS2) layers deposited via atomic layer deposition (ALD) using tetrakis(dimethylamino)tin (TDMASn) as a Sn precursor and H2S gas as a sulfur source at low temperature (150° C). The crystallinity of SnS2 was improved by H2S gas annealing. We carried out H2S gas annealing at various conditions (250° C, 300° C, 350° C, and using a three-step method). Angle-resolved X-ray photoelectron spectroscopy (ARXPS) results revealed the valence state corresponding to Sn4+ and S2- in the SnS2 annealed with H2S gas. The SnS2 annealed with H2S gas had a hexagonal structure, as measured via X-ray diffraction (XRD) and the clearly out-of-plane (A1g) mode in Raman spectroscopy. The crystallinity of SnS2 was improved after H2S annealing and was confirmed using the XRD full-width at half-maximum (FW...

Effect of ozone concentration on atomic layer deposited tin oxide

Tin dioxide (SnO2) thin films were deposited by atomic layer deposition (ALD) using tetrakis(dimethylamino)tin {[(CH3)2N]4Sn} and various concentrations of ozone (O3) at 200 °C. In order to characterize SnO2 thin films, the growth rate, thin film crystallinity, surface roughness, chemical bonding state, and electrical and optical properties were investigated. The growth rate of SnO2 increased slightly when the O3 concentration was increased. However, the growth rate was almost saturated above 300 g/m3 concentration of O3. Also, the x-ray diffraction patterns of SnO2 thin films become sharper when the O3 concentration increased. Specifically, the (101) and (211) peaks of SnO2 improved. In addition, the defects of the SnO2 thin films such as oxygen vacancy and hydroxyl group are related to the O3 concentration that was observed via x-ray photoelectron spectroscopy. As the O3 concentration is higher than 300 g/m3, the electrical Hall resistivity and mobility saturated 3.6 × 10−3 Ω cm and 9.58 cm2/V s, respectively. However, the carrier concentration slightly decreased to 3.22 × 1020 cm−3. It is assumed that the oxygen vacancies were filled with a high O3 concentration at ALD reaction. The optical bandgaps were larger than 3.5 eV, and the transmittance of all SnO2 thin films exceeded 90%. The O3 concentration below 200 g/m3 in the ALD process of SnO2 thin films is considered to be one of the factors that can affect the crystallinity, chemical bonding, and electrical properties.Tin dioxide (SnO2) thin films were deposited by atomic layer deposition (ALD) using tetrakis(dimethylamino)tin {[(CH3)2N]4Sn} and various concentrations of ozone (O3) at 200 °C. In order to characterize SnO2 thin films, the growth rate, thin film crystallinity, surface roughness, chemical bonding state, and electrical and optical properties were investigated. The growth rate of SnO2 increased slightly when the O3 concentration was increased. However, the growth rate was almost saturated above 300 g/m3 concentration of O3. Also, the x-ray diffraction patterns of SnO2 thin films become sharper when the O3 concentration increased. Specifically, the (101) and (211) peaks of SnO2 improved. In addition, the defects of the SnO2 thin films such as oxygen vacancy and hydroxyl group are related to the O3 concentration that was observed via x-ray photoelectron spectroscopy. As the O3 concentration is higher than 300 g/m3, the electrical Hall resistivity and mobility saturated 3.6 × 10−3 Ω cm and 9.58 cm2/V s, respec...

Effect of scan speed on moisture barrier properties of aluminum oxide using spatial atomic layer deposition

Atomic layer deposition (ALD) has been shown to produce high-quality thin films with superior moisture barrier performance on polymer substrates. However, the conventional time-sequenced mode is incompatible with industrial needs due to its low deposition rate. One solution to overcome this throughput issue is to use spatial ALD. Recently, various approaches have been reported. The authors also developed a fast spatial ALD system using an industrial 2G (370 × 470 mm2) glass substrate. Using this system, the authors investigated the effect of a scan speed on the moisture barrier properties of aluminum oxide (Al2O3) thin films. While the scan speeds were varied over a wide range of 100–800 mm/s, the water vapor transmission rate increased only slightly, from 1.4 × 10−3 to 3.0 × 10−3 g/m2/day. At a scan speed of 800 mm/s, the deposition rate was 70 A/min, which was about seven times higher than that of conventional ALD. Moreover, the physical and chemical properties of the thin films slightly worsened with t...