Post-deposition Processing Research Articles

Amorphous oxide channel TFTs

Thin film transistors (TFTs) using amorphous oxides of post-transition metals: indium, gallium, and zinc for the channel materials are fabricated with radio-frequency magnetron sputtering methods for the deposition of the channel and the gate insulator layers, at room temperature with no high-temperature post-deposition annealing process. The TFTs operate as n-channel field-effect transistors with various structures of top/bottom gate and top/bottom source-and-drain contact including the inverse-stagger types, and with various materials for the gate insulators, the electrodes, and the substrates. The TFTs having smoother channel interfaces show the better performance at the saturation mobility beyond 10 cm2 V−1 s−1 and the on-to-off current ratio over 108 than the rough channel interfaces. The ring oscillator circuits operate with five-stage inverters of the top-gate TFTs or the inverse-stagger TFTs. Organic light-emission diode cells are driven by a simple circuit of the TFTs. It is also found by a combinatorial approach to the material exploration that the TFT characteristics can be controlled by the composition ratio of the metals in the channel layers. The amorphous oxide channel TFTs fabricated with sputtering deposition at low temperature could be a candidate for key devices of large-area flexible electronics.

Excimer laser processing of inkjet-printed and sputter-deposited transparent conducting SnO 2:Sb for flexible electronics

The feasibility of low-temperature fabrication of transparent electrode elements from thin films of antimony-doped tin oxide (SnO 2:Sb, ATO) has been investigated via inkjet printing, rf magnetron sputtering and post-deposition excimer laser processing. Laser processing of thin films on both glass and plastic substrates was performed using a Lambda Physik 305i excimer laser, with fluences in the range 20–100 mJ cm − 2 reducing sheet resistance from as-deposited values by up to 3 orders of magnitude. This is consistent with TEM analysis of the films that shows a densification of the upper 200 nm of laser-processed regions.

Structure and magnetic properties of high-energy product Nd-Fe-B/Nd-O thin films

Nd2Fe14B/Nd-O thin films with high-energy product (BH)max = 33.9 MGOe are fabricated by a one-step sputtering process, i.e. dc magnetron sputtering on a Si substrate heated at 600–650 °C, without a post-deposition annealing process. The highly anisotropic Nd-Fe-B/Nd-O thin film with high-energy product is realized immediately after the deposition, owing to the anisotropic growth of both the Nd-O and the Nd2Fe14B phases. The coexistence of the nanoscale Nd2Fe14B and Nd-oxide phases in the thin films is confirmed by means of x-ray diffraction, high-resolution transmission electron microscopy (HRTEM) and energy-filtered transmission electron microscopy. The boundaries between the buffer layer and the Nd-Fe-B layers and the different phases are investigated by HRTEM.

Refractive index properties of SiN thin films and fabrication of SiN optical waveguide

SiN thin films having excellent surface morphology for the optical device application were synthesized using a plasma enhanced chemical vapor deposition (PECVD) method at low temperature (350∘C) using silane (SiH4) and nitrogen (N2). The effects of the SiH4/N2 flow ratio, rf power and annealing on the SiN films were investigated. The optical and structural properties of SiN films were characterized using an ellipsometry, a fourier-transform infrared spectroscopy (FT-IR), and an atomic force microscope (AFM). The refractive index increased from 1.6 to 2.3 as the SiH4/N2 ratio was increased from 0.17 to 1.67. The rms surface roughness decreased from 14.1 to 3.6A after post-deposition annealing process performed at 800∘C for 1hr in an air ambient. We could fabricate straight waveguides based on a three layer structure and have no problems with step coverage.

Electrical Characterization of Semiconducting Nanowire and Its Application to a Chemical Sensor

Semiconducting oxide nanowire devices were fabricated using more convenient way to combine photolithography and e-beam lithography, and their electrical properties were studied. To realize the reliable device operation which is a key factor for a chemical sensor, the contact resistance should be optimized. Here, we studied the contact resistance problem under post-deposition annealing or etching process using scanning probe microscopic tool to analyze IV spectroscopic and surface potential behaviors. And, its performance as a chemical sensor was also studied for several gas specie

Slowdown in development of self-assembled InAs∕GaAs(001) dots near the critical thickness

By strain relaxation measurements using reflection high-energy electron diffraction, it is observed that development of the self-assembled InAs∕GaAs(001) dots continues after In deposition is stopped just above the critical thickness under As4 atmosphere. Transmission electron microscope and photoluminescence measurements reveal that dot size increases considerably during this postdeposition process. On the other hand, the dot size increases only slightly during the postdeposition if the amount of In is greater than the critical thickness. Energetics within a finite surface area for a dot shows that the energy barrier for the transformation from the metastable InAs wetting layer to the optimum dot on the thinner wetting layer is high and suppresses the transformation near the critical thickness. Development of the dot density is also illustrated by calculating the nucleation rate from the thickness-dependent barrier height.

High efficiency ultra-thin sputtered CdTe solar cells

Abstract Large scale manufacturing of CdTe PV modules at the GW/yr level may be constrained due to the limited availability of the relatively rare (Te) element and the volume of potentially hazardous (Cd) material being used in the typically 3–8 μm thick CdTe absorber layer. However, we find that it is possible to reduce the CdTe layer thickness without much compromise in efficiency. The CdS/CdTe solar cells were fabricated using magnetron sputtering with ultra-thin CdTe layers in the range of 0.5–1.28 μm. The ultra-thin films and cells were characterized using X-ray diffraction (XRD), optical transmission, scanning electron microscopy (SEM), current–voltage and quantum efficiency measurements. These results were compared with those of standard 2.3 μm thick CdTe sputtered cells. Different post-deposition processing parameters were required for cells with ultra-thin and standard CdTe thicknesses to achieve high efficiency. Ultra-thin CdTe cells showed crystallographic texture and CdTe1−xSx alloy formation after CdCl2 treatment very similar to standard CdTe cells. Optimization of the post-deposition CdCl2 treatment and back-contact processing yielded cells of 11.2% efficiency with 0.7 μm CdTe compared to 13.0% obtained with standard 2.3 μm CdTe cells.

Influence of fabrication process on the final properties of natural-rubber latex tubes for vascular prosthesis

We report a process of fabrication of latex tubes using the dip-coating technique. We investigated centrifuged latex, with different original viscosities, extracted from the Hevea brasiliensis. The influence of the main deposition parameters (dip-coating velocity, mold material, mold diameter and number of coatings) and post-deposition drying process parameters (temperature and time) on the properties of the final samples are investigated and discussed. Additional investigation about the elastic behavior of the tubes is presented for strain values up to rupture. The rupture occurred at 120 mm for tubes 15 mm-long, which represents an elongation of 800%. The tubes presented two distinct elastic mechanisms, with the most elastic one being observed below an elongation of about 500%. During a cycled strain experiment with strain values below the rupture point, a hysteretic-like curve was observed, which was related to the uncurling and recurling of the polymeric chains.

Indium doping in nanostructured ZnO through low-temperature hydrothermal process

Abstract ZnO nanostructures of rod-like morphology were synthesized through a low-temperature hydrothermal process. Incorporation of indium in the nanostructures during synthesis was not successful due to the formation of In(OH) 3 phase. A post-deposition thermal annealing process in inert atmosphere resulted effective for the dissociation of In(OH) 3 phase and doping of indium into the nanostructures. Effect of indium doping on the structure, morphology and optical absorption of the nanostructures are studied. Beyond a certain concentration, the incorporated indium form phase separated oxide instead of being doped. Incorporated indium occupy the zinc sites in the nanostructures.

Fabrication of clean carbon nanotube field emitters

We have developed a method for fabricating a good carbon nanotube (CNT) field emitter using electrophoretic deposition and fissure formation techniques. A thin film of CNTs was deposited on a Ti substrate, by electrophoresis, from an aqueous mixture of CNT and detergent, dried naturally, and then pressed on the surface to make it smooth. By firing, it was changed to numerous microsized islands. As a result very clean CNT tips were generated from the fissures formed. The film showed good field emission properties. Our method affords a process of simple steps and does not need any postdeposition or activation process for field emission.

Challenges of Ultra Low-k Dielectric Measurement and Plasma Damage Assessment

AbstractThe implementation of porous low-k and ultra-low k dielectrics to reduce RC delay in integrated circuit interconnect wiring has been fraught with numerous challenges. The obvious challenges of materials design and preservation of the desired electrical and mechanical properties upon subsequent processing have been significant. The vulnerability of these films to damage from fast ion and radiation damage will be discussed in the context of post-deposition processing (including low-k cure and plasma processing damage). This paper attempts to review the challenges associated with destructive and non-destructive measurement of low k dielectric films with respect to underlying physical principles of the metrology. Metrology techniques, assumed to be non-destructive based on experience with dense silicon dioxide, will be discussed with regards to newer and more fragile low-k dielectric films.

In situ grown epitaxial YBa2Cu3O7−x thin films by pulsed laser deposition under reduced oxygen pressure during cool-down time

We report novel pulsed laser deposition conditions that were used to obtain superconducting epitaxial YBCO thin films, grown in situ using an oxygen pressure lower than the usual one during the cool-down time. We studied the influence of the PLD conditions as substrate temperature, oxygen pressure, laser fluence, and number of laser pulses on the crystallographic and morphological features, and on the superconducting properties of the films. Good superconducting properties were obtained without a high temperature post-deposition annealing process. A maximum critical temperature of 88.6 K was obtained.

Molecular Ordering in Monolayers of an Alkyl-Substituted Perylene-Bisimide Dye by Attenuated Total Reflectance Ultraviolet—Visible Spectroscopy

Surface-relative orientational parameters were determined for monolayer films of N, N'-ditridecylperylenetetracarboxylic dianhydridediimide (C13-PTCDI) in terms of the relative electronic transition dipole strengths, providing a three-dimensional view of the absorption dipole distribution. In order to obtain a macroscopically ordered film, C13-PTCDI was deposited by (1) horizontal Lang-muir-Blodgett (LB) transfer onto methyl- and phenyl-silanized glass, and (2) vapor deposition onto oriented films of poly(tetrafluoroethylene) (PTFE) on glass. Films of LB-deposited C13-PTCDI were found to be completely isotropic prior to annealing. After annealing, these films remained isotropic in the plane of the substrate while the out-of-plane anisotropy was significantly enhanced. In contrast, films of C13-PTCDI vapor deposited onto oriented poly(tetrafluoroethylene) (PTFE)-modified substrates yielded films with a high degree of both in- and out-of-plane anisotropy. Atomic force microscopy (AFM) images of both the LB- and vapor-deposited films show substantial differences in film morphology and long-range order. These results demonstrate that molecular orientation in C13-PTCDI films can be controlled by varying substrate surface chemistry and post-deposition processing.

Comparison of<tex>$rm YBa_2rm Cu_3rm O_7-delta$</tex>Precursors Made Using TFA-MOD and<tex>$rm BaF_2$</tex>Ex-Situ Processes and Their Post-Deposition Processing Under Low Pressure Conditions

Two ex-situ techniques including metal-organic deposition using solution from trifluoroacetates (TFA-MOD) and electron beam co-evaporation using BaF/sub 2/ are regarded as promising candidates for fabricating long-length, uniform, high critical current density (J/sub c/) YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) superconducting films for practical applications. It is generally accepted that the precursors made by these two methods and their post-deposition processing are basically similar. Typical MOD-TFA and e-beam BaF/sub 2/ precursors were made and then annealed in our low-pressure processing system. It was found that the conditions required for the conversion of these two types of precursors are quite different. The precursors were compared in terms of the differences in their composition and pre-conversion structure. The conversion behaviors were studied by structure characterization and property measurement. The effect of composition, especially the fluorine content on the conversion reaction is discussed.

Advantages of HfAlON gate dielectric film for advanced low power CMOS application

There are a number of challenges against an actual employment of high-k films in the production, but ultra-thin SiON films cannot survive for low power application anymore. On the other hand, any new materials introduced into ULSI fabrication processes are required to be used for a couple of device generations, so the material selection should be carefully made. We have investigated HfAlON film as a high-k material in perspective of the equivalent oxide thickness (EOT)=1nm, and has newly developed a layer-by-layer deposition and annealing (LL-D&A) method for the film growth technique and a high temperature oxygen annealing (HiTOA) for the post-deposition annealing process, in order to overcome intrinsic challenges of deposited films. This paper describes recent progress of HfAlON gate stack technology, and discusses advantages of those approaches for advanced low power CMOS from scalability viewpoints of material and film growth technique as well as from experimental results of gate leakage current reduction, mobility improvement and threshold voltage control.

MBE growth and properties of epitaxial metal oxides for high- [formula omitted] dielectrics

Aggressive reduction in the thickness of SiO 2-based gate dielectrics in ULSI devices brings about a number of fundamental problems, the most critical ones being reduced dielectric reliability and exponentially increasing leakage (tunneling) current with decreasing oxide thickness. This has induced an urgent search for alternative dielectric materials (high- κ dielectrics). The common approach has involved amorphous materials with higher dielectric constants, such as metal oxides and their silicates. The problem here is to keep the material amorphous even after post-deposition high-temperature processing. A different approach is based on the development of epitaxial metal oxides grown directly on silicon surfaces. An epitaxial oxide involves more effort, but it has the advantages of enabling defined interface engineering and higher thermal stability. MBE is known for its superior capability in atomic level engineering and interface control, and is one of the techniques being investigated for the epitaxial growth of various high- κ materials.

Wear behaviour of CrN coatings MEVVA ion implanted with Zr

CrN films deposited by a commercial physical vapour deposition (PVD) process were implanted with Zr ions by metal vapour vacuum arc (MEVVA) implantation at an energy of 40 keV and with doses ranging from 6×10 16 to 2×10 17 ion/cm 2. The films were characterised by glancing incident angle X-ray diffraction (GIXRD), optical microscopy and scanning electron microscopy (SEM). Friction and wear tests were carried out using a pin-on-disc tribometer with a 6 mm diameter ruby pin. X-ray photoelectron spectroscopy (XPS) results show the formation in the implanted zone (IZ) of ZrN/CrZrN. X-ray diffraction (XRD) shows evidence of crystal damage, which increases with dose. The post-deposition process has induced only small changes in the friction behaviour of the CrN film, and overall the tribological properties were not enhanced. Nano-hardness measurements show that implantation has caused softening of the IZ layer. The tribological behaviour is explained in view of these results.

High critical current density Y Ba2Cu3O7−δ thin films fabricated by ex situ processing at low pressures

There is interest in probing the feasibility and possible advantages of making uniform andcost-effective long-length coated conductors through a low-pressure processing approach.The low-pressure approach, eliminating the boundary layer and gas flow considerations,consumes much less of the processing gases and offers the possibility of improveduniformity and faster growth rate of superconducting films. Here, we have fabricatedY Ba2Cu3O7−δ (YBCO) epitaxialfilms of thickness 0.1–1.0 µm on SrTiO3 single crystal substrates using ex situ post-deposition processing of co-evaporated Y,BaF2 and Cuprecursors in a controlled low-pressure gas mixture of oxygen and water vapour. Partial pressures of oxygen(PO2) and watervapour (PH2O) as low as 10 and 0.1 mTorr, respectively, were used. X-ray diffraction and scanning electron microscopyinspection were conducted for structure characterization of the films. High critical current densities(Jc) of at 77 K in self-field were obtained, yielding properties comparable to those ofin situ films and ex situ films processed under atmospheric pressure condition.

Measurement of the mechanical properties of electroplated gold thin films using micromachined beam structures

We have measured the Young’s modulus, residual stress, and stress gradient of electroplated gold thin films using surface micromachined beam structures. Cantilever and bridge beam structures of different lengths were fabricated using UV-LIGA surface micromachining and dry-release methods. The Young’s modulus and residual stress of the fabricated beams were determined from the resonance frequencies of electrostatically excited beams, and the stress gradient was evaluated from the self-deformation of released cantilevers. The observed Young’s modulus was smaller than the bulk Young’s modulus, and showed small changes depending on the deposition current density. The average residual stress was found to be tensile in nature, and the observed residual stresses showed no differences, regardless of the current density. However, the stress gradient increased with increasing current density. The deformation of the cantilever beam after release was dependent on the plasma ashing time used. This result implies that additional thermal effects from the post-deposition process may have an influence on the final performance of fabricated micro electro mechanical systems (MEMS) devices.

Stable trapping of electrons and holes in deposited insulating oxides: Al2O3, ZrO2, and HfO2

Charge trapping in high-permittivity metal oxides (Al2O3, ZrO2, and HfO2) grown on (100)Si using various types of chemical vapor deposition (CVD) was studied using generation of electron-hole pairs in the oxide by 10 eV photons. For most of the CVD methods, thin (≈5 nm) oxide films exhibit positive charging suggesting hole trapping as most efficient charge trapping process. Negative charge is observed only in as-deposited nitrogen-containing films grown from Hf(NO3)4. The trapped positive charge depends only weakly on the HfO2 thickness indicating that holes are trapped in a silicon oxide interlayer grown between the Si and HfO2 during deposition, which is further affirmed by enhanced positive charging after additional oxidation of the samples at high temperatures. The work function of the metal electrode material has a large influence on hole trapping in thin oxides, indicating electron exchange between the metal and defect states in the oxide. In addition, trapping of positive charge correlates with liberation of atomic hydrogen during electron-hole pair generation pointing to a considerable contribution of protonic species to the charge. Electron trapping increases with thickness of oxide layers and appears strongly sensitive to both the method of oxide deposition and post-deposition processing. This suggests the electron traps to be related to defects and/or impurities incorporated into the oxide film during deposition.