Low RMS Roughness Research Articles

In‐situ stress suppression of hydrogenated a‐CNx film prepared via Ar gas introduction

Evolution of hydrogenated amorphous carbon nitride films was investigated with an introduction of Ar gas in the deposition. The results showed that compressive stress of the films decreased versus an increase of Ar flow rate. Especially, at an Ar flow rate of 5 sccm the film exhibited lower compressive stress, higher hardness and lower root‐mean‐square (rms) roughness than the films deposited without Ar gas introduction. Structural analysis showed that the films with higher hardness, low compressive stress and lower rms roughness had relatively high sp2 and nitrogen content. It was attributed to the assistance of Ar plasma, which can cause N atom to enter graphite ring easily and form curved graphite microstructure. Copyright © 2016 John Wiley & Sons, Ltd.

Annealing effects on polycrystalline GaN using nitrogen and ammonia ambients

This paper describes effects of using post-annealing treatment in different conditions on the properties of polycrystalline GaN layer grown on m-plane sapphire substrate by electron beam (e-beam) evaporator. Without annealing, GaN surface was found to have a low RMS roughness with agglomeration of GaN grains in a specific direction and the sample consisted of gallium oxide (Ga2O3) material. When the post-annealing treatment was carried out in N2 ambient at 650 °C, initial re-crystallization of the GaN grains was observed while the evidence of Ga2O3 almost disappeared. As the NH3 annealing was conducted at 950 °C, more effect of re-crystallization occurred but with less grains coalescence. Three dominant XRD peaks of GaN in (101¯0), (0002) and (101¯1) orientations were evident. Near band edge (NBE) related emission in GaN was also observed. The significant improvement was attributed to simultaneous recrystallization and effective reduction of N deficiency density. The post-annealing in a mixture of N2 and NH3 ambient at 950 °C was also conducted, but has limited the effectiveness of the N atoms to incorporate on the GaN layer due to ‘clouding’ effect by the inert N2 gas. Further increase in the annealing temperature at 980 °C and 1100 °C, respectively caused severe deteriorations of the structural and optical properties of the GaN layer. Overall, this work demonstrated initial potential in improving polycrystalline GaN material in simple and inexpensive manner.

Surface modification of reverse osmosis membranes with zwitterionic coating for improved resistance to fouling

Copolymer films of poly(4-vinylpyridine-co-ethylene glycol diacrylate) (p(4-VP-co-EGDA)) were synthesized and first deposited on various substrates via initiated chemical vapor deposition (iCVD). As-deposited copolymer films were converted to surface zwitterionic structures containing poly(carboxybetaine acrylic acetate) (pCBAA) units by a quaternization reaction with 3-bromopropionic acid (3-BPA). Conversion to a zwitterionic structure was confirmed by FTIR and high-resolution XPS N1s scans. Biopolymer adsorption of the deposited copolymer coatings was investigated by quartz crystal microbalance with dissipation (QCM-D) using a model foulant‐bovin serum albumin (BSA). The optimized copolymer films were then deposited onto commercial RO membranes and with subsequent zwitterionicalization. Inertness to bacterial adhesion of the modified membranes was investigated by counting the number of Escherichia coli and Pseudomonas aeruginosa cells attached on the membrane surface under static conditions. Bacterial adhesion studies revealed an almost 98% reduction in micro-organism attachment onto the surface of modified membranes compared to bare membranes, which clearly demonstrates the effectiveness and superior performance of the zwitterionic coating against bacterial adhesion. The salt rejection performance of the modified membranes resulted in improved salt rejection (98%); however, permeate flux was slightly compromised compared to virgin membranes. AFM analysis demonstrated that modified membranes showed lower RMS roughness compared to virgin membranes.

Precursor Concentration and Substrate Effects on High Rate Dip-Coated Vanadium Oxide Thin Films

Uniform thin films of vanadium pentoxide were dip-coated from a high-concentration vanadium oxytriisopropoxide precursor which is shown to be resistant to the dewetting processes which can form surface pinhole defects. Through appropriate withdrawal speed choice, the thin films have a smooth uniform surface morphology with a low rms roughness of <1 nm in both their amorphous and crystallized states. The structure of the thin films follows that of bulk vanadium pentoxide but in a nanostructured form. The deposition methods shown can be applied to prepare thin films upon a variety of different substrates and other alkoxide based metal oxide materials.

Effect of a ZTO buffer layer on the structural, optical, and electrical properties of IGZO thin films

Transparent and conducting InGaZnO4 (IGZO) thin films were deposited by RF magnetron sputtering on zinc tin oxide (ZTO) coated glass substrates to investigate the effect of the ZTO buffer layer on the structural, optical, and electrical properties of the IGZO/ZTO films.X-ray diffraction (XRD) analysis revealed that although all the films were in the amorphous phase, IGZO 90nm/ ZTO 10nm bi-layered films had a lower resistivity (1.1×10−2Ωcm) than the other films prepared in this study. The enhanced optical transmittance of IGZO 80nm/ZTO 20nm films (85.5%) was attributed to the two-fold lower RMS roughness of these films than that of IGZO single films, because a flat surface reduces optical scattering and absorption at the film surface.These results indicate that a ZTO thin film is an effective buffer layer that can enhance the optical transmittance and electrical conductivity of the IGZO upper film.

High quality relaxed germanium layers grown on (110) and (111) silicon substrates with reduced stacking fault formation

Epitaxial growth of Ge on Si has been investigated in order to produce high quality Ge layers on (110)- and (111)-orientated Si substrates, which are of considerable interest for their predicted superior electronic properties compared to (100) orientation. Using the low temperature/high temperature growth technique in reduced pressure chemical vapour deposition, high quality (111) Ge layers have been demonstrated almost entirely suppressing the formation of stacking faults (&amp;lt; 107 cm−2) with a very low rms roughness of less than 2 nm and a reduction in threading dislocation density (TDD) (∼ 3 × 108 cm−2). The leading factor in improving the buffer quality was use of a thin, partially relaxed Ge seed layer, where the residual compressive strain promotes an intermediate islanding step between the low temperature and high temperature growth phases. (110)-oriented layers were also examined and found to have similar low rms roughness (1.6 nm) and TDD below 108 cm−2, although use of a thin seed layer did not offer the same relative improvement seen for (111).

바코팅 공정을 이용한 유기 발광 다이오드 특성 향상

Solution processed conjugated molecules enable to manufacture various electronic devices by unconventional and cost effective patterning methods as screen or gravure printing. Spin-coating is the most popularly used method to form conjugated polymeric film for various electronic devices. The coating method has certain disadvantages such as a large amount of unwanted wastes, difficulty forming a film with a large area, and impossible to apply roll-to-roll manufacturing. We present here a promising alternative coating method, bar-coating for conjugated polymer film and OLED with the bar coated light emitting layer. In this papers, we show atomic force microscope images of spin- and bar-coated Poly[(9,9-di-n-octylfluorenyl-2,7- diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT) films on substrate. The bar-coated film showed a slight lower RMS roughness (1.058 [nm]) than spin-coated film (1.767 [nm]). It means the barcoating is suitable method to form light emitting layers in OLEDs. By using bar-coating process, an OLED obtained with 4.7 [cd/A] in maximum current efficiency.

Effect of β-cyclodextrin and Citric Acid on Chemical Mechanical Polishing of Polycrystalline Ge2Sb2Te5 in H2O2 Containing Slurry

The effect of citric acid (CA) and β-cyclodextrin (CD) used as chelating agents on the chemical mechanical polishing (CMP) process of polycrystalline Ge2Sb2Te5 (pc-GST) film was investigated for a H2O2 containing slurry. CD would be better used in slurry than CA in pc-GST CMP, because a higher polishing rate of over 1000 Å/min as well as a low RMS roughness of 0.44 nm for a pc-GST film would be possible. A very smooth surface with a passive film was formed after the pc-GST film was polished with the addition of CD. According to a surface analysis conducted using scanning electron microscopy and X-ray photoelectron spectroscopy, there was only negligible formation of chemical oxides with an increase in CA in the H2O2 containing slurry, while they were formed continuously for CD. The potentiodynamic curves measured for the CA addition showed that there was insufficient oxidizing power for the forming the passive film. However, the oxidizing power of the slurry containing H2O2 with CD was sufficient enough to form the passive film due to the sufficient evolution of O2 on the surface of the pc-GST film. The additions of CA and CD largely affected the anodic and cathodic polarization, respectively.

Strong Electro-Absorption in GeSi Epitaxy on Silicon-on-Insulator (SOI)

We have investigated the selective epitaxial growth of GeSi bulk material on silicon-on-insulator substrates by reduced pressure chemical vapor deposition. We employed AFM, SIMS, and Hall measurements, to characterize the GeSi heteroepitaxy quality. Optimal growth conditions have been identified to achieve low defect density, low RMS roughness with high selectivity and precise control of silicon content. Fabricated vertical p-i-n diodes exhibit very low dark current density of 5 mA/cm2 at −1 V bias. Under a 7.5 V/µm E-field, GeSi alloys with 0.6% Si content demonstrate very strong electro-absorption with an estimated effective ∆α/α around 3.5 at 1,590 nm. We compared measured ∆α/α performance to that of bulk Ge. Optical modulation up to 40 GHz is observed in waveguide devices while small signal analysis indicates bandwidth is limited by device parasitics.

Synthesis and characterization of sol–gel derived gallium-doped zinc oxide thin films

Gallium-doped ZnO (GZO) semiconductor thin films were prepared by a sol–gel spin coating process. The effects of Ga dopant concentrations on the microstructure, electrical resistivity, optical properties, and photoluminescence (PL) were studied. XRD results showed that all the as-prepared GZO films had a wurtzite phase and a preferred orientation along the [002] direction. ZnO thin films doped with Ga had lower electrical resistivity, lower RMS roughness, and improved optical transmittance in the visible region. The lowest average electrical resistivity value, 2.8×102Ωcm, was achieved in the ZnO thin films doped with 2% Ga, which exhibited an average transmittance of 91.5%. This study also found that the optical band gap of Ga-doped films was 3.25eV, slightly higher than that of undoped samples (3.23eV), and the PL spectra of GZO films showed strong violet-light emission centers at about 2.86eV (the corresponding wavelength of which is about 434nm).

Growth of preferentially-oriented AlN films on amorphous substrate by pulsed laser deposition

Preferentially-oriented aluminum nitride (AlN) films are grown directly on natively-oxidized Si (100) substrate by pulsed laser deposition (PLD) in nitrogen (N2) environment. The AlN preferential orientation changes from (002) to (100) with increasing N2 pressure. Such different behaviors are discussed in terms of deposition-rate-dependent preferential orientation, kinetic energy of depositing species and confinement of laser plume. Finally, sample deposited at 0.9 Pa is proved to have the highest (002) peak intensity, the lowest FWHM value, the highest deposition rate and a relatively low RMS roughness (1.138 nm), showing the optimal growth condition for c-axis-oriented AlN growth at this N2 pressure.

Effect of sol temperature on the structure, morphology, optical and photoluminescence properties of nanocrystalline zirconia thin films

Transparent nanocrystalline zirconia thin films were prepared by sol–gel dip coating technique using Zirconium oxychloride octahydrate as source material on quartz substrates, keeping the sol at room temperature (SET I) and 60 °C (SET II). X-ray diffraction (XRD) pattern shows the formation of mixed phase [tetragonal (T) + monoclinic (M)] in SET I and a pure tetragonal phase in SET II ZrO2 thin films annealed at 400 °C. Phase transformation from tetragonal to monoclinic was achieved in SET II film annealed at 500 °C. Atomic force microscopy analysis reveals lower rms roughness and skewness in SET II film annealed at 500 °C indicating better optical quality. The transmittance spectra gives a higher average transmittance >85% (UV–VIS region) in SET II films. Optical spectra indicate that the ZrO2 films contain direct—band transitions. The sub- band in the monoclinic ZrO2 films introduced interstitial O−defect states above the top of the valance band. The energy bandgap increased (5.57–5.74 eV) in SET I films and decreased (5.74–5.62 eV) in SET II films, with annealing temperature. This is associated with the variations in grain sizes. Photoluminescence (PL) spectra give intense band at 384 and 396 nm in SET I and SET II films, respectively. A twofold increase in the PL intensity is observed in SET II film. The “Red” shift of SET I films and “Blue” shift of SET II films with annealing temperature, originates from the change of stress of the film due to lattice distortions.

Adsorption of organic layers over electrodeposited magnetite (Fe 3O 4) thin films

The formation of monolayers of two organic compounds (oleic acid and dodecanethiol) over magnetite films was studied. Magnetite films ranging from 80 nm to 3.75 μm-thick were electrodeposited on Au on glass substrates under galvanostatic control, with deposition parameters optimized for minimum surface roughness. Films were characterised by SEM and AFM, showing granular deposits with a low rms roughness of 5–40 nm measured over an area of 1 μm 2. The growth rate was estimated by measuring cross-sections of the thin films. Pure magnetite with an fcc structure is observed in XRD diffractograms. The adsorption of both oleic acid and dodecanethiol on the magnetite films was tested by immersing them in ethanol solutions containing the organic molecules, for different deposition time, temperature and cleaning procedure. Monolayer formation in both cases was studied by contact angle and voltammetric measurements, as well as XPS.

Thermal transformation of solvent-processable organosilicon compounds into inorganic silicone-based thin films

In this study, a solution-processable precursor, decaphenycyclopentasilane (DPCPS) was synthesized and successfully converted into an inorganic thin film through the heat treatment process. When the DPCPS coating was heat-treated at various temperatures up to 900 °C, the organic DPCPS was converted into an inorganic compound composed of Si, C and O atoms in the form of SiCxOy. The relative compositions of Si, C, and O changed with the heat-treatment temperatures changing the carbon content, for example, from 88.9% for the pristine DPCPS to 3.0% for the specimen heat-treated over 700 °C, consequently becoming SiC0.05O1.7. The dielectric constant of the heat-treated DPCPS could be tailored with the heat treatment temperatures from high- to low-dielectric materials, i.e., 10.8 at 300 °C and 2.3 at 900 °C, providing tunable dielectric properties for various optoelectronic applications. The resulting inorganic thin films had excellent coating characteristics with low RMS roughness (<1.0 nm).

InP substrate evaluation by MOVPE growth of lattice matched epitaxial layers

InP substrates form the starting point for a wide variety of semiconductor devices. The surface morphology produced during epitaxy depends critically on the starting substrate. We evaluated (1 0 0)-oriented InP wafers from three different vendors by growing thick (5 μm) lattice-matched epilayers of InP, GaInAs, and AlInAs. We assessed the surfaces with differential interference contrast microscopy and atomic force microscopy. Wafers with near singular (1 0 0) orientations produced inferior surfaces in general. Vicinal substrates with small misorientations improved the epitaxial surface for InP dramatically, reducing the density of macroscopic defects while maintaining a low RMS roughness. GaInAs and AlInAs epitaxy step-bunched forming undulations along the miscut direction. Sulfur-doped wafers were considered for singular (1 0 0) and for 0.2° misorientation toward (1 1 0). We found that mound defects observed for InP and GaInAs layers on iron-doped singular wafers were absent for singular sulfur-doped wafers. These observations support the conclusion that dislocation termination at the surface and expansion of the step spiral lead to the macroscopic defects observed.

Kinetics of the oxidation of Zn foils in air atmosphere

The formation kinetics of ZnO thin films grown by oxidation of polycrystalline Zn foils in air atmosphere at temperatures below the melting point is reported. Previous to the oxidation process the Zn foils were polished to produce mirror-like finished surfaces. The growth rate of the ZnO films was monitored by ellipsometric measurements. The growth rate of the ZnO films under 100 nm follows a linear and parabolic behavior in accordance with previously reported studies. The thicknesses of the films strongly influence the appearance of the final produced ZnO surface. The ZnO films surfaces with thicknesses less than 100 nm resulted uniform with low rms roughness. However as the films become thicker the rms roughness increased and a uniform distribution of whiskers was observed. X-ray diffraction and photoluminescence (PL) studies were done on the ZnO films to find out their structural and optical characteristics. PL spectra on the films are composed by two main bands; a weak near-band gap in the ultraviolet region and a strong but well defined green band. A discussion is included on the origins of the observed PL spectra.

Growth of High Quality Strained-Si on Ultra-Thin SiGe-on-Insulator Substrate

Ultra-thin and near-fully relaxed SiGe substrate is fabricated using a modified Ge condensation technique, and then a 25-nm-thick biaxially tensile strained-Si with a low rms roughness is epitaxially deposited on a SiGeon-Insulator (SGOI) substrate by ultra high vacuum chemical vapor deposition (UHVCVD). High-Resolution cross-sectional transmission electron microscope (HR-XTEM) observations reveal that the strained-Si/SiGe layer is dislocation-free and the atoms at the interface are well aligned. Furthermore, secondary ion mass spectrometry (SIMS) results show a sharp interface between layers and a uniform distribution of Ge in the SiGe layer. One percent in-plane tensile strain in the strained-Si layer is confirmed by ultraviolet (UV) Raman spectra, and the stress maintained even after a 30-s rapid thermal annealing (RTA) process at 1000°C According to those results, devices based on strained-Si are expected to have a better performance than the conventional ones.

Er:YAB nanoparticles and vitreous thin films by the polymeric precursor method

The synthesis of Y0.9Er0.1Al3(BO3)4 crystalline powders and vitreous thin films were studied. Precursor solutions were obtained using a modified polymeric precursor method using d-sorbitol as complexant agent. The chemical reactions were described. Y0.9Er0.1Al3(BO3)4 composition presents good thermal stability with regard to crystallization. The Y0.9Er0.1Al3(BO3)4 crystallized phase can be obtained at 1,150 °C, in agreement with other authors. Crack- and porosity-free films were obtained with very small grain size and low RMS roughness. The films thickness revealed to be linearly dependent on precursor solution viscosity, being the value of 25 mPa s useful to prepare high-quality amorphous multi-layers (up to ∼ 800 nm) at 740 °C during 2 h onto silica substrates by spin coating with a gyrset technology.

Exploration of waveguide fabrication from thermally evaporated Ge–Sb–S glass films

Waveguides from thermally evaporated Ge23Sb7S70 films have been fabricated using both plasma etching and lift-off techniques. The two methods have been compared in their ability to provide high quality, low-loss waveguides for microphotonics applications. We have demonstrated in this paper that low-loss 3μm and 4μm wide channel waveguides can be fabricated using CHF3 and SF6 plasma etching, and lift-off, respectively. Additionally, lift-off does not change the structure of the waveguide during the fabrication whereas the structure of the plasma etched waveguide differs slightly from that of the films. Finally, channel waveguides fabricated using lift-off leads to a low RMS roughness of 10±2nm, compared to those fabricated by a plasma etching process which lead to a higher RMS roughness of 17–20nm. As-fabricated waveguides have been found to exhibit optical propagation losses of 3–5dB/cm at 1550nm. These high losses are attributed to scattering by sidewall roughness and defects arising from the fabrication process.

Achieving Low Sheet Resistance from Implanted P-Type Layers in 4H-SiC Using High Temperature Graphite Capped Annealing

Low resistance p-layers are achieved in this paper using a graphite cap to protect SiC surface from out-diffusion of Si during high temperature post-implantation annealing, which is carried out to maximize the activation of Al dopant in 4H-SiC. With a graphite layer converted from photoresist, as high as 1700 and 1800oC post-implantation annealing is able to be used. Low RMS roughness of surface after high temperature annealing shows the effectiveness of the graphite cap. Small sheet resistance and resistivity are also achieved from the high temperature annealing. At room temperature, sheet resistances of 9.8 and 1.3 k/□, and the corresponding resistivities of 235 and 31 m-cm are obtained from 1700 and 1800oC annealed samples, respectively. The Al ionization energy extracted from Arrhenius plot is also close to the typical reported values. Therefore, it can be concluded that, using graphite cap could help to activate the Al dopant effectively during high temperature annealing.