Conventional RF Magnetron Sputtering Research Articles

Enhancement in structural, morphological and optical features of thermally annealed zinc oxide nanofilm

This paper presents the study of surface morphological, optical and microstructural features of zinc oxide (ZnO) nanofilm layered upon p-type Si substrate of <100> orientation by employing conventional RF magnetron sputtering system at different annealing temperatures. The effect of annealing on the nano-film is examined using different characterization techniques such as Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), FTIR (Fourier Transform Infrared Spectroscopy), UV-vis spectroscopy and Raman spectroscopy. The sharp diffraction peak at (002) orientation is seen by the XRD spectra which signifies a better growth of single crystalline thin film along the z-axis with the hexagonal wurtzite crystal structure. The surface morphological study shows that the grain size of the thin film intensifies from 22.06 nm to 36.77 nm when the annealing temperature is increased whereas there is a decrease in the values of lattice constants (a=b, c), FWHM (full width at half maximum), residual stress, lattice strain and dislocation density by increasing annealing temperature. The enhancement in the grain size makes the thin film appropriate for MEMS device applications including piezoelectric energy harvesters, gas sensors, etc. The optical bandgap of the ZnO thin film is estimated using Kubelka-Munk (KM) approach and it decreases from 3.23 to 3.16 eV for As-deposited, 400 °C, 600 °C and 800 °C respectively which makes the annealed thin film apposite for optoelectronic device applications. The intensity of the Raman peaks strengthens with the annealing temperature. These results prove that the annealing extensively enhances the crystallinity, structural, morphological and optical features of ZnO thin film and hence becomes suitable for nanoelectronic device applications.

Transparent and Conducting Oxide Films: SiO₂-Doped ZnO.

(SiO₂)x(ZnO)100-x films with x = 2, 3, 4, and 5 wt.% were deposited on slide glass substrates at room temperature by the conventional Rf magnetron sputtering method. Their resistivities were investigated as a function of SiO₂ content. The lowest resistivity of 4.5×10-3 Ω.· cm was obtained for the (SiO₂)x(ZnO)100-x film with x = 2 wt.%. This film showed an excellent average transmittance of 85% in the visible range with a wide band gap over 3.4 eV and a high refractive index of 2.1. In addition, the electrical conductivity of the films was improved by annealing at a temperature films decrease range from 100 °C to 400 °C in vacuum. The resistivities of (SiO₂)x(ZnO)100-x with increasing annealing temperature. In particular, SZO film with x = 2 wt.% shows a minimum resistivity of ~10-3 Ω.cm after the heat treatment for 30 min at 300 °C in vacuum. Thus, we suggest that (SiO₂)x(ZnO)100-x films being sufficiently transparent and having a high conductivity, are suitable for application as transparent and conductive oxide films.

Preparation and characterization of high quality diamond like carbon films on Si microspheres

High quality diamond like carbon (DLC) films are urgent demanded for inertial confinement fusion (ICF) experiments. DLC films with excellent qualities were deposited on Si microspheres by coupling anode-layer ion source and RF magnetron sputtering. The obtained films were characterized by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray Reflectivity (XRR) and nanoindentation techniques. The films deposited under coupling anode-layer ion source and RF magnetron sputtering exhibit denser microstructure and smoother surface with lower surface roughness. Meanwhile, the mechanical properties and mass density of these films experience an improvement compared to those only prepared by either conventional RF magnetron sputtering or anode-layer ion source. DLC films deposited by coupling anode-layer ion source and RF magnetron sputtering can be a better candidate for ICF experiments.

SiGe layer thickness effect on the structural and optical properties of well-organized SiGe/SiO2 multilayers

In this work, we report on the production of regular (SiGe/SiO2)20 multilayer structures by conventional RF-magnetron sputtering, at 350 °C. Transmission electron microscopy, scanning transmission electron microscopy, raman spectroscopy, and x-ray reflectometry measurements revealed that annealing at a temperature of 1000 °C leads to the formation of SiGe nanocrystals between SiO2 thin layers with good multilayer stability. Reducing the nominal SiGe layer thickness (tSiGe) from 3.5–2 nm results in a transition from continuous SiGe crystalline layer (tSiGe ∼ 3.5 nm) to layers consisting of isolated nanocrystals (tSiGe ∼ 2 nm). Namely, in the latter case, the presence of SiGe nanocrystals ∼3–8 nm in size, is observed. Spectroscopic ellipsometry was applied to determine the evolution of the onset in the effective optical absorption, as well as the dielectric function, in SiGe multilayers as a function of the SiGe thickness. A clear blue-shift in the optical absorption is observed for tSiGe ∼ 2 nm multilayer, as a consequence of the presence of isolated nanocrystals. Furthermore, the observed near infrared values of n = 2.8 and k = 1.5 are lower than those of bulk SiGe compounds, suggesting the presence of electronic confinement effects in the nanocrystals. The low temperature (70 K) photoluminescence measurements performed on annealed SiGe/SiO2 nanostructures show an emission band located between 0.7–0.9 eV associated with the development of interface states between the formed nanocrystals and surrounding amorphous matrix.

Effect of ITO film deposition conditions on ITO and CdS films of semiconductor solar cells

Inorganic metal chalcogenide compounds based thin-film solar cells are regarded as most promising candidates for film power modules due to their high efficiencies with low cost. From top to bottom, the semiconductor thin film solar cell is made up of a metal layer, an absorber material, a buffer layer, and a transparent conducting oxide (TCO). Indium tin oxide (ITO) is a common material for transparent conducting films used as a front contact layer on solar cells. Although extensive studies have been performed on the deposition and properties of ITO films, few studies focused on the effect of the sputtering deposition conditions of ITO on the buffer layer. In this study, ITO thin films were deposited on soda-lime glass (SLG) by conventional RF-magnetron sputtering. The dependence of the electrical and crystalline properties on different substrate temperature, different RF power and different introducing rate of oxygen was investigated. The deposition conditions of ITO not only have influences on the structure and properties of ITO but also affect the buffer layer underneath. Therefore, we investigated the effect of ITO deposition parameters on the crystallization and electrical and optical properties of sputtered CdS films and, in turn, on the resulting device characteristics.

Thermally activated ionic conduction and local structure in solid LiPON thin films

Compact lithium phosphorous oxynitride (LiPON) thin films, as a solid-state electrolyte for all solid-state Li batteries and electrochromic (EC) devices, with the high ratio of the triply coordinated –N< (Nt) over the doubly coordinated –N= (Nd) structural units was deposited by a conventional reactive RF magnetron sputtering of a Li3PO4 target at a low pure N2 pressure. The effect of heat treatment from 200 to 500 °C on the ionic conductivity and local structure of LiPON thin films were investigated by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) core level analysis. A dramatical improvement of ionic conductivity from 1.1 to 3.28 μS/cm and microstructure changes were happened on the LiPON thin films while annealed for 1 h at 300 °C, which was linked to structural differences with a highest ratio of –N< over –N= structural units. The work proves that a proper heat treatment on LiPON thin film can effectively improve its ionic conductivity and change its microstructure.

Defect-Free Amorphous Indium Gallium Zinc Oxide Deposition Process By Magnetic Field Shielded Sputtering

The amorphous InGaZnO (a-IGZO) is widely accepted as a promising channel material for thin-film transistor (TFT) applications owing to their outstanding electrical properties [1, 2]. However, a-IGZO TFTs have still suffer from their bias instability with illumination [1-4]. Up to now, many researchers have studied the sub-gap density of states (DOS) as the root cause of instability. It is well known that defect states can influence on the performances and stabilities of a-IGZO TFTs. The defects states should be closely related with the deposition condition, including sputtering power, and pressure. Nevertheless, it has not been reported how these defects are created during conventional RF magnetron sputtering. In general, during conventional RF magnetron sputtering process, negative oxygen ions (NOIs) can be generated by electron attachment in oxygen atom near target surface and then accelerated up to few hundreds eV by a self-bias; at this time, the high energy bombardment of NOIs induce defects in oxide thin films. Recently, we have reported that the properties of IGZO thin films are strongly related with effects of NOIs which are generated during the sputtering process [5]. From our previous results, the electrical characteristics and the chemical bonding states of a-IGZO thin films were depended with the bombardment energy of NOIs. And also, we suggest that the deep sub-gap states in a-IGZO as well as thin film properties would be influenced by the bombardment of high energetic NOIs during the sputtering process.In this study, we have studied the gate bias instability and their density of states (DOSs) of a-IGZO TFTs as depending on the bombardment of NOIs during conventional magnetron sputtering. Finally, we will introduce our novel technology named as Magnetic Field Shielded Sputtering (MFSS) process to prevent the NOIs bombardment effects and present how much to be improved the instability of a-IGZO TFTs by this new deposition method. 1. M.G. Kim, M.G. Kanatzidis, A. Facchetti, and T.J. Marks, Nat. Mater. 10, 382 (2011). 2. K.K. Banger, Y. Yamashita, K. Mori, R.L. Peterson, T. Leedham, J. Rickard, and H. Sirringhaus, Nat. Mater. 10, 45 (2011). 3. M.D.H. Chowdhury, P. Migliorato, and J. Jang, Appl. Phys. Lett. 98, 153511 (2011). 4. X. Xiao, W. Deng, S. Chi, Y. Shao, X. He, L. Wang, and S. Zhang, IEEE Trans. Electron Devices 60, 4159 (2013). 5. D.H. Kim, J.N. Jang, S.B. Yoon, and MunPyo Hong, Appl. Phys. Express 7, 031401 (2014).

이종 접합 구조를 갖는 TiO&lt;sub&gt;2&lt;/sub&gt;/WO&lt;sub&gt;3&lt;/sub&gt; 이중 박막의 광유기 친수 특성

The photoinduced hydrophilicity of double layer films was fabricated by using a conventional rf-magnetron sputtering method. The photoinduced hydrophilic reaction of the surface was enhanced by the presence of under the layer by irradiation of a 10 W cylindrical fluorescent light bulb. However, when the and layers were separated by an insulating layer, the surface did not appeared high hydrophilic, under the same light bulb. The enhanced photoinduced hydrophilic reaction can be explained by the charge transfer between and layers. It was also demonstrated that visible light passing through the layer could excite . Thus, visible light can be used for the hydrophilic reaction in the present system.

Microstructural and optical properties tuning of BiFeO3 thin films elaborated by magnetron sputtering

Multiferroic BiFeO3 thin films were deposited using a conventional RF magnetron sputtering technique on Si substrate. The influence of the microstructure of BiFeO3 thin films on their optical properties was investigated through an extensive characterization. Using X-ray diffraction and atomic force microscopy, the structure and crystalline quality of the films were studied with regard to the effect of oxygen partial pressure during the deposition and to post annealing treatment. Stoichiometric films with the crystallographic perovskite structure required for multiferroic behaviour were obtained. It is demonstrated that films annealed at 700 °C in oxygen at atmospheric pressure are highly (100) perovskite orientated and free of the undesired phases. This perovskite phase is observed only for a narrow range of oxygen partial pressure The refractive index and extinction coefficient were obtained using variable angle spectroscopic ellipsometry. The optical characteristics of the films are directly correlated to their microstructural properties. Ellipsometry analysis showed that we can tune the optical constants of BiFeO3 films by controlling the oxygen partial pressure during deposition.

Photoinduced hydrophilicity of TiO2/WO3 double layer films

The photoinduced hydrophilicity of TiO2/WO3 double layer films fabricated by conventional RF magnetron sputtering was evaluated. The photoinduced hydrophilic reaction at the TiO2 surface during irradiation by a 10W cylindrical fluorescent light bulb was enhanced by the presence of WO3 under the TiO2 layer. However, when the TiO2 and WO3 layers were separated by an insulating layer, the surface did not become highly hydrophilic under the same light conditions. The enhanced photoinduced hydrophilic reaction can be explained by charge transfer between the TiO2 and WO3 layers. TiO2/WO3 double layer films may be applied as coatings on indoor products requiring antifogging and self-cleaning properties because the films produce a highly hydrophilic surface even with indoor lights.

Preparation of Transparent Metal Films, Gallium-Doped Zinc-Oxide (Ga2O3)x (ZnO)100-x Films by Using Facing Target Sputtering System

(Ga2O3)x(ZnO)100-x, x = 3, 5, 7, 9 wt.%, (GZO) films were prepared at room temperature by using a conventional rf-magnetron sputtering method. Their electrical resistivity was investigated as a function of the Ga2O3 content. The GZO film with x = 7 wt.%, shows the lowest resistivity of 1.5×10−3Ω. cm. This GZO films were also prepared at various substrate temperatures from room temperature to 400°C, Their electrical resistivity was found to be improved as the substrate temperature was increased, A very low resistivity of 4.5×10−4Ω.cm was obtained in the film prepared at the substrate temperature of 300°C. In addition, we found that the GZO films prepared by using facing target sputtering (FTS) system showed a dramatically improved conductivity as compared with that of the film prepared by the conventional sputtering system. In particular, we also found that the lowest resistivity of 2.8×10−4Ω.cm that is almost comparable with that of ITO film was obtained in the GZO films prepared at the substrate temperature of 300°C by using the facing target sputtering (FTS) system.

Effects of the Bombardment of Negative Oxygen Ions on Gate Bias Stability of InGaZnO Thin Film Transistors

Amorphous InGaZnO (α-IGZO) thin-film transistors (TFTs) are very promising due to their potential use in thin film electronics and display drivers. However, the stability of AOS-TFTs under the various stresses has been issued for the practical AOSs applications. Up to now, many researchers have studied to understand the sub-gap density of states (DOS) as the root cause of instability. Nomura et al. reported that these deep defects are located in the surface layer of the α-IGZO channel. Also, Kim et al. reported that the interfacial traps can be affected by different RF-power during RF magnetron sputtering process. It is well known that these defect states can influence on the performances and stabilities of α-IGZO TFTs. Nevertheless, it has not been reported how these defects are created during conventional RF magnetron sputtering. In general, during conventional RF magnetron sputtering process, negative oxygen ions (NOI) can be generated by electron attachment in oxygen atom near target surface and accelerated up to few hundreds eV by a self-bias of RF magnetron sputter; the high energy bombardment of NOIs generates bulk defects in oxide thin films and can create the defects of α-IGZO thin films. The a-IGZO TFTs have been fabricated with different dc biases (200 V, 300V, and 400V). Figure 1 shows that the transfer characteristics of the a-IGZO TFTs with a positive bias stress (PBS in (a)), a negative bias stress (NBS in (b)), and a negative bias illumination stress (NBIS in (c)). It is observed that the changes of the transfer characteristics with PBS, and NBS are not depended on different dc biases. However, a huge shift of a threshold voltage on a-IGZO TFTs is observed under NIBS condition. In this study, we have investigated that the NOIs accelerated by dc self-bias were one of the dominant causes of instability in α-IGZO TFTs when the channel layer was deposited by conventional RF magnetron sputtering system. Finally, we will introduce our novel technology named as Magnetic Field Shielded Sputtering (MFSS) process to prevent the NOIs bombardment effects and present how much to be improved the instability of α-IGZO TFTs by this new deposition method.

아르곤 플라즈마를 이용하여 유리기판에 증착된 PTFE 박막의 초친수 특성 연구

An excellent hydrophobic surface has a high contact angle over 147 degree and the contact angle hysteresis below <TEX>$5^0$</TEX> was produced by using roughness combined with hydrophobic PTFE coatings, which were also confirmed to exhibit an extreme adhesion to glass substrate. To form the rough surface, the glass was etched by Ar-plasma. A very thin PTFE film was coated on the plasma etched glass surface. Roughness factors before or after PTFE coating on the plasma etched glass surface, based on Wensel's model were calculated, which agrees well with the dependence of the contact angle on the roughness factor is predicted by Wensel's model. The PTFE films deposited on glass by using a conventional rf-magnetron sputtering. The glass substrates were etched Ar-plasma prior to the deposition of PTFE. Their hydrophobicities are investigated for application as a anti-fouling coating layer on the screen of displays. It is found that the hydrophobicity of PTFE films mainly depends on the sputtering conditions, such as rf-power, Ar gas content introduced during deposition. These conditions are closely related to the deposition rate or thickness of PTFE film. Thus, it is also found that the deposition rate or the film thickness affects sensitively the geometrical morphology formed on surface of the rf-sputtered PTFE films. In particular, 1,950-nm-thick PTFE films deposited for 30 minute by rf-power 50 watt under Ar gas content of 20 sccm shows a very excellent optical transmittance and a good anti-fouling property and a good durability.

Pseudo-binary alloying system of ZnO-AgGaO2 reducing the energy band gap of zinc oxide

Pseudo-binary oxide semiconductor alloy films of (1-x)ZnO-x(AgGaO2)1/2 were fabricated using a conventional rf-magnetron sputtering. The wurtzite-type single phases were obtained in the wide composition range of x ≤ 0.33 because the terminal β-AgGaO2 that corresponds to the composition with x = 1 possesses a wurtzite-derived β-NaFeO2 structure. The energy band gap of ZnO decreased with increasing AgGaO2 concentration, falling to 2.55 eV at x = 0.33. This alloy system enables to use ZnO-based semiconductors in optoelectronic devices working in visible region.

High‐density remote plasma sputtering of high‐dielectric‐constant amorphous hafnium oxide films

Abstractmagnified imageHafnium oxide (HfOx) is a high dielectric constant (k) oxide which has been identified as being suitable for use as the gate dielectric in thin film transistors (TFTs). Amorphous materials are preferred for a gate dielectric, but it has been an ongoing challenge to produce amorphous HfOx while maintaining a high dielectric constant. A technique called high target utilization sputtering (HiTUS) is demonstrated to be capable of depositing high‐k amorphous HfOx thin films at room temperature. The plasma is generated in a remote chamber, allowing higher rate deposition of films with minimal ion damage. Compared to a conventional sputtering system, the HiTUS technique allows finer control of the thin film microstructure. Using a conventional reactive rf magnetron sputtering technique, monoclinic nanocrystalline HfOx thin films have been deposited at a rate of ∼1.6 nm min−1 at room temperature, with a resistivity of 1013 Ω cm, a breakdown strength of 3.5 MV cm−1 and a dielectric constant of ∼18.2. By comparison, using the HiTUS process, amorphous HfOx (x = 2.1) thin films which appear to have a cubic‐like short‐range order have been deposited at a high deposition rate of ∼25 nm min−1 with a high resistivity of 1014 Ω cm, a breakdown strength of 3 MV cm−1 and a high dielectric constant of ∼30. Two key conditions must be satisfied in the HiTUS system for high‐k HfOx to be produced. Firstly, the correct oxygen flow rate is required for a given sputtering rate from the metallic target. Secondly, there must be an absence of energetic oxygen ion bombardment to maintain an amorphous microstructure and a high flux of medium energy species emitted from the metallic sputtering target to induce a cubic‐like short range order. This HfOx is very attractive as a dielectric material for large‐area electronic applications on flexible substrates.

Structural and electrical studies of ultrathin layers with Si0.7Ge0.3 nanocrystals confined in a SiGe/SiO2 superlattice

In this work, SiGe/SiO2 multi-layer (ML) films with layer thickness in the range of a few nanometers were successfully fabricated by conventional RF-magnetron sputtering at 350 °C. The influence of the annealing treatment on SiGe nanocrystals (NCs) formation and crystalline properties were investigated by Raman spectroscopy and grazing incidence x-ray diffraction. At the annealing temperature of 800 °C, where well defined SiGe NCs were observed, a thorough structural investigation of the whole ML structure has been undertaken by Rutherford backscattering spectroscopy, grazing incidence small angle x-ray scattering, high resolution transmission electron microscopy, and annular dark field scanning transmission electron microscopy. Our results show that the onset of local modifications to the ML composition takes place at this temperature for annealing times of the order of a few tens of minutes with the formation of defective regions in the upper portion of the ML structure. Only the very first layers over the Si substrate appear immune to this problem. This finding has been exploited for the fabrication of a defect free metal-oxide-semiconductor structure with a well-defined single layer of SiGe NCs. A memory effect attributed to the presence of the SiGe NCs has been demonstrated by high frequency capacitance-voltage measurements.

Effects of substrate temperature on the properties of transparent conducting AZO thin films and CIGS solar cells

Chalcopyrite CuInGaSe2 (CIGS) based thin-film solar cells are regarded as most promising candidates for film power modules due to high efficiencies and low cost. Aluminum doped zinc oxide (ZnO:Al, AZO) is a common material for transparent conducting films used as a front contact layer on CIGS solar cells. In this study, AZO thin films were deposited on soda-lime glass (SLG) by conventional RF-magnetron sputtering using a commercial ceramic target. The dependence of the electrical and crystalline properties on the substrate to target position at different substrate temperature was investigated. The result shows that adjusting the substrate temperature could develop better transparent conducting thin films. However, the plasma ion-bombardment producing from the magnetron sputtering method makes significant effects on the distribution of electric conductive uniformity. When the substrate is placed on the appropriate position and the deposition process is carried out at higher substrate temperature, highly conductive AZO films with the average transmittance >90% would be obtained. The transparent conducting AZO films are also utilized as the front contact to fabricate (Cu(In,Ga)Se2, CIGS) thin-film solar cells at different substrate temperature. The results find that the CIGS solar cells show better efficiencies at lower temperature even if high conductive AZO films are obtained at higher substrate temperature. It shows that the substrate temperature significantly affects the properties of CIGS solar cells.

Thermal Instability of La_(0.6)Sr_(0.4)MnO_3 Thin Films on Fused Silica

<TEX>$La_{0.6}Sr_{0.4}MnO_3$</TEX> (LSMO) thin films, which are known as colossal magnetoresistance materials, were prepared on fused silica thin films by conventional RF magnetron sputtering, and the interfacial reactions between them were investigated by rapid thermal processing. Various analyses, namely, X-ray diffraction, transmission electron microscopy combined with energy adispersive X-ray spectrometry, and secondary ion mass spectrometry, were performed to explain the mechanism of the interfacial reactions. In the case of an LSMO film annealed at <TEX>$800^{\circ}C$</TEX>, the layer distinction against the underplayed <TEX>$SiO_2$</TEX> was well preserved. However, when the annealing temperature was raised to <TEX>$900^{\circ}C$</TEX>, interdiffusion and interreaction occurred. Most of the <TEX>$SiO_2$</TEX> and part of the LSMO became amorphous silicate that incorporated La, Sr, and Mn and contained a lot of bubbles. When the annealing temperature was raised to <TEX>$950^{\circ}C$</TEX>, the whole stack became an amorphous silicate layer with expanded bubbles. The thermal instability of LSMO on fused silica should be an important consideration when LSMO is integrated into Si-based solid-state devices.

Laser annealing of thin film electroluminescent devices deposited at a high rate using high target utilization sputtering

This paper presents the photoluminescent (PL) and electroluminescent (EL) characteristics of ZnS:Mn deposited at room temperature using high target utilization sputtering (HiTUS). Significant improvements in PL intensity are seen when ZnS:Mn is deposited using HiTUS instead of conventional RF magnetron sputtering. When incorporated as part of a complete EL device with yttrium oxide forming the dielectric layers and indium tin oxide used as the top contact electrode, localized laser annealing of the ZnS:Mn phosphor layer is shown to provide enhancement of the EL characteristics.

고주파 마그네트론 스퍼터링 방법을 사용하여 유리 기판 위에 증착된 PTFE 박막의 발수 특성

The polytetrafluoroethylene (PTFE) films are deposited on glass using conventional rf-magnetron sputtering method. Their hydrophobic properties are investigated for application as an anti-fouling coating layer on the screen of displays. It is found that the hydrophobicity of PTFE films largely depends on the sputtering conditions, such as Ar gas flow and deposition time during sputtering process. These conditions are closely related to the deposition rate or thickness of PTFE film. Thus, it is also found that the deposition rate or the film thickness affects sensitively the geometrical morphology formed on surface of the rf-spluttered PTFE films. In particular, the PTFE film with 1950 nm thickness deposited for 30 minute at rf-power 50 W shows a very excellent optical transmittance of over 90% and a good anti-fouling property and a good durability.