Electron Cyclotron Resonance Oxygen Plasma Research Articles

Spectroscopic characterization of the plasmas formed during the deposition of ZnO and Al-doped ZnO films by plasma-assisted pulsed laser deposition

An oxygen-zinc plasma and an oxygen-zinc-aluminum plasma are formed by pulsed laser ablation of a Zn target or pulsed laser co-ablation of a Zn target and an Al target in an electron cyclotron resonance (ECR) discharge-generated oxygen plasma for the deposition of ZnO and Al-doped ZnO (AZO) films. The plasmas are characterized spectroscopically by time-integrated and time-resolved optical emission spectroscopy. Both the oxygen-zinc plasma and the oxygen-zinc-aluminum plasma contain excited species originally present in the working O2 gas and energetic species ablated from the targets. The optical emission of the oxygen-zinc-aluminum plasma is abundant in the emission bands of oxygen molecular ions and the emission lines of mono-atomic oxygen, zinc and aluminum atoms and atomic ions. The time-integrated spectra as well as the time-resolved spectra of the plasma emission indicate that the oxygen species in the ECR oxygen plasma experience additional excitation by the expanding ablation plumes, and the ablated species are excited frequently when traveling accompanying the plume expansion in the oxygen plasma, making the formed plasma highly excited and very reactive, which plays an important role in the reactive growth of ZnO matrix and the in-situ doping of Al into the growing ZnO matrix. The deposited ZnO and AZO films were evaluated for composition analysis by energy dispersive X-ray spectroscopy, structure characterization by X-ray diffraction and optical transmission measurement. The deposited ZnO is slightly rich in O. The Al concentration of the AZO films can be controlled and varied simply by changing the repetition rate of the laser used for Al target ablation. Both the ZnO and the AZO films are featured with hexagonal wurtzite crystal structure and exhibit high optical transparency in a wide spectral region. Al doping results in an improvement in the ultraviolet transparency, a blue shift in the absorption edge and a widening of the band gap.

Ge/Si Heterojunction Tunnel Field-Effect Transistors and Their Post Metallization Annealing Effect

Ge/Si heterojunction tunnel field-effect transistors (TFETs) with an Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> gate-stack are demonstrated. The high performances of steep subthreshold swing (SS) of 58 mV/decade and large I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ratio over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> are realized by a proper postmetallization annealing (PMA) process. We can obtain the high-quality Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /Ge interface with Dit of as low as ~1011 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> by electron cyclotron resonance oxygen plasma post oxidation. The electrical characteristics of the Ge/SOI TFETs are studied with changing PMA temperature from 200 °C to 400 °C. It is found that Dit between Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and the Si channel region is a critical factor for significantly reducing SS of Ge/Si heterojunction TFETs.

Combined In Situ XPS and UHV-Chemical Force Microscopy (CFM) Studies of the Plasma Induced Surface Oxidation of Polypropylene

Modification of the surface chemistry and correlated adhesive properties of polypropylene (PP) by means of an electron cyclotron resonance (ECR) oxygen plasma source is studied based on an in situ ultra-high-vacuum (UHV)-analytical approach. To determine the plasma induced chemical changes without exposure to atmosphere, X-ray excited valence band (VB) spectroscopy and core level X-ray photoelectron spectroscopy (XPS) are performed. Adhesive properties are characterized by means of UHV chemical force microscopy (UHV-CFM). Correlation of XPS and UHV-CFM data indicate that interactions between a SiO2-tip and the modified PP surface is dominated by hydrogen bonds between surface silanol groups on the tip and induced oxidized species on PP surface. Such interactions are maximized in the initial phase of surface oxidation.

Al 2 O 3 / GeO x / Ge gate stacks with low interface trap density fabricated by electron cyclotron resonance plasma postoxidation

An electron cyclotron resonance (ECR) plasma postoxidation method has been employed for forming Al2O3/GeOx/Ge metal-oxide-semiconductor (MOS) structures. X-ray photoelectron spectroscopy and transmission electron microscope characterizations have revealed that a GeOx layer is formed beneath the Al2O3 capping layer by exposing the Al2O3/Ge structures to ECR oxygen plasma. The interface trap density (Dit) of Au/Al2O3/GeOx/Ge MOS capacitors is found to be significantly suppressed down to lower than 1011 cm−2 eV−1. Especially, a plasma postoxidation time of as short as 10 s is sufficient to reduce Dit with maintaining the equivalent oxide thickness (EOT). As a result, the minimum Dit values and EOT of 5×1010 cm−2 eV−1 and 1.67 nm, and 6×1010 cm−2 eV−1 and 1.83 nm have been realized for Al2O3/GeOx/Ge MOS structures with p- and n-type substrates, respectively.

Effect of ECR etching conditions of (100)Ib diamond substrates on homoepitaxial low boron doped diamond layer quality

AbstractThe effect of oxygen electron cyclotron resonance (ECR) microwave plasma etching on the crystallinity of low boron doped thin diamond films grown on Ib (100)‐oriented diamond substrates by MPCVD has been investigated with respect to the main experimental conditions: microwave power and O2 pressure at a constant DC bias. The substrates were exposed to ECR oxygen plasma to remove from 0.8 μm to 3.5 μm (depending on the value of the microwave power). The optimization of these two parameters has been performed in order to get the lowest surfaces roughness. This study aims also at demonstrating that oxygen ECR plasma etching is a powerful tool to remove surface and subsurface defects of diamond substrates as polishing grooves, subsurface damaged zone (polishing process induced defects) and various substrate roughness according to the observed growth sector. Low boron doped layers ([acceptors] = 4 × 1016 atoms/cm3) were grown by MPCVD on either O2 ECR plasma etched or merely chemically prepared (100) Ib diamond substrates. Cathodoluminescence analysis showed, for specific substrate etching conditions, a decrease of the band A emission (2.8 eV) in a low boron doped layer deposited on an etched substrate compared to a layer grown on a chemically prepared one. The FWHM of the FETO excitonic line of all theses layers is comprised between 16 meV and 13 meV for the best ones at 5 K. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Structure, conductivity, and optical absorption of Ag 2− xO films

Evaporation of Ag in the presence of an electron cyclotron resonance (ECR) oxygen plasma was used to deposit Ag 2− x O films with a range of stoichiometries onto r-plane sapphire substrates. A quartz crystal oscillator (QCO) was used to accurately measure the silver and oxygen arrival rates and establish the O/Ag flux ratio needed to produce films with nominal Ag 2O stoichiometry. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis indicates that the Ag 2− x O films are not single phase but contain signatures of coexisting Ag 2O and AgO components. XRD shows that the lattice matching with the r-plane sapphire substrate causes the Ag 2O phase to grow with <002> heteroepitaxial crystallites coexisting with crystallites having <111> normal and random in-plane orientation. The AgO phase also forms with crystallites having <002> heteroepitaxy as well as crystallites with <111> normal and random in-plane orientation. The mixed phase Ag 2− x O films exhibit approximately 77% optical transmission over the visible range (500 nm to 700 nm) and have a single absorption edge near 3.3 eV. Four-point van der Pauw conductivity and Hall effect measurements indicate that the Ag 2− x O films are p-type with a conductivity on the order of 3 × 10 − 3 Ω − 1 cm − 1 .

Ground-to-Space Effective Atomic Oxygen Fluence Correlation for DC 93-500 Silicone

The objective of this research was to calibrate the ground-to-space effective atomic oxygen fluence for DC 93-500 silicone in a thermal energy electron cyclotron resonance (ECR) oxygen plasma facility. A technique has been developed at NASA Glenn Research Center to determine the equivalent amount of atomic oxygen exposure in an ECR ground-test facility to produce the same degree of atomic oxygen damage as in space. The approach used was to compare changes in the surface hardness of ground test (ECR)-exposed DC 93-500 silicone with DC 93-500 exposed to low Earth orbit (LEO) atomic oxygen as part of a shuttle flight experiment. The ground-to-space effective atomic oxygen fluence correlation was determined based on the fluence in the ECR source that produced the same hardness for the fluence in space. A nanomechanical measurement system operated in conjunction with an atomic force microscope (AFM) was used to determine the surface hardness of the silicones. Hardness vs contact depth measurements were obtained for five ECR-exposed DC 93-500 samples (ECR exposed for 18 to 40 h, corresponding to Kapton effective fluences of 4.2 × 10 20 to 9.4 × 10 20 atoms/cm 2 , respectively) and for space-exposed DC 93-500 from the Evaluation of Oxygen Interactions with Materials III (EOIM III) shuttle flight experiment, exposed to LEO atomic oxygen (2.3 × 10 20 atoms/cm 2 ). Pristine controls for the ECR tests and for the EOIM III flight sample were also evaluated. A ground-to-space correlation value was determined based on correlation values for four contact depths (150, 200, 250, and 300 nm), which represent the near-surface depth data. The results indicate that the Kapton effective atomic oxygen fluence in the ECR facility needs to be 2.64 times higher than in LEO to replicate equivalent exposure damage in the ground test silicone as occurred in the space exposed silicone.

Growth and structure of silver and silver oxide thin films on sapphire

The growth and epitaxy of Ag and Ag 2O films on r-cut sapphire surfaces is reported for several different growth conditions. Ag was deposited by electron beam evaporation in vacuum, in a molecular O 2 background, and in the presence of an electron cyclotron resonance (ECR) oxygen plasma. The presence of an oxygen background converts the random polycrystalline growth of Ag in vacuum to three dimensional epitaxial growth of Ag with a 〈110〉 surface normal. At sufficiently low deposition rates (0.1 nm/s), the presence of the ECR oxygen plasma leads to the growth of Ag 2O films with a one dimensional epitaxy having the 〈111〉 direction normal to the surface but random orientation about this normal. The effects of thermal decomposition of Ag 2O were examined by annealing the samples in vacuum above 625 K and characterizing the surfaces with X-ray photoelectron spectroscopy and atomic force microscopy to observe the segregation of silver into islands as the Ag 2O decomposes.

Growth and structure of silver and silver oxide thin films on sapphire

The growth and epitaxy of Ag and Ag2O films on r-cut sapphire surfaces is reported for several different growth conditions. Ag was deposited by electron beam evaporation in vacuum, in a molecular O2 background, and in the presence of an electron cyclotron resonance (ECR) oxygen plasma. The presence of an oxygen background converts the random polycrystalline growth of Ag in vacuum to three dimensional epitaxial growth of Ag with a 〈110〉 surface normal. At sufficiently low deposition rates (0.1 nm/s), the presence of the ECR oxygen plasma leads to the growth of Ag2O films with a one dimensional epitaxy having the 〈111〉 direction normal to the surface but random orientation about this normal. The effects of thermal decomposition of Ag2O were examined by annealing the samples in vacuum above 625 K and characterizing the surfaces with X-ray photoelectron spectroscopy and atomic force microscopy to observe the segregation of silver into islands as the Ag2O decomposes.

Nanopatterning of diamond films with composite oxide mask of metal octylates in electron beam lithography

The fabrication of diamond nanopatterns by electron cyclotron resonance (ECR) oxygen plasma with a composite metal octylate mask was investigated using electron beam lithography technology. A high etching selectivity of 14 was obtained with Bi4Ti3O12 octylate film as a mask under the plasma-etching conditions of microwave power of 300 W and oxygen gas flow rate of 3 sccm. The metal naphthenates and metal octylates exhibited negative exposure characteristics. The sensitivity of metal naphthenates (1.2×10−3 C cm−2) was ten times lower than that of polymethyl methacrylate (PMMA) resist, while that of octylates (8.0×10−5 C cm−2) was in good agreement with that of PMMA resist (6.0×10−5 C cm−2). The resulting minimum chemical vapor deposited (CVD) diamond line-width of 100 nm with a height of approximately 1 μm was fabricated with a Bi4Ti3O12 octylate mask.

Pulse-modulated plasma-enhanced chemical vapor deposition of SiO 2 coatings from octamethylcyclotetrasiloxane

Silicon dioxide coatings can be grown at low substrate temperatures in a pulse-modulated microwave electron cyclotron resonance (ECR) oxygen plasma with octamethylcyclotetrasiloxane (OMCTS) as the organosilicon precursor. The 2.45 GHz microwave power was pulse-modulated with repetition frequencies of 20 Hz–20 kHz, duty ratios (pulse on-time/pulse period) from 25 to 100%, and peak microwave power from 800 to 2400 W. The coatings are SiO 2-like with Si:O ratios of approximately 3:4 and carbon percentages of 20–25%. Pulsed plasma deposition significantly lowers the deposition substrate temperature as the peak power and duty ratio decrease. With 1600 W input continuous microwave power, substrate temperatures were 140–150 °C after 10 min of deposition, while with a 50% pulse duty cycle and 1600 W peak power the temperature decreased to 90 °C. The coating hardness decreased with pulsed operation compared to continuous operation, unless the average microwave power levels were made equivalent. Deposition growth rates depended only weakly on the pulse repetition frequency and duty ratio, but increased strongly as the pulse peak power was raised. Pulsed deposition at 800 W peak power and 50% duty ratio gave a growth rate of 0.5–0.6 μm/min for all frequencies between 20 Hz and 20 kHz, increasing to 0.8–0.9 μm/min at 1600 W peak power.

Low SiO 2/Si interface state density for low temperature oxides prepared by electron cyclotron resonance oxygen plasma

The interface state densities of SiO 2 films were investigated. Films of SiO 2, 250 Å thick were grown by electron cyclotron resonance diffusion method using O 2 plasma at a substrate temperature of 200 °C for 40 min and these films were annealed at 600 °C for 60 min in N 2 gas. The oxygen to Si ratio was 2.02–2.13 throughout the films, indicating uniform SiO 2 stoichiometry that was identical to high temperature thermal oxide. The range of interface state density value before annealing was 2 × 10 11–1 × 10 12 eV −1 cm −2. But the value after annealing was 2.2 × 10 9–1 × 10 10 eV −1 cm −2. It is assumed that the positive ions (O 2 + or O +) in the bulk of the oxide can neutralize the interface state density during annealing. The best interface state density value was 2.2 × 10 9 eV −1 cm −2. This represents the lowest interface state density value achieved to date.

Comparison of silicon dioxide layers grown from three polymethylsiloxane precursors in a high-density oxygen plasma

We have compared the elemental composition, growth rates, and hardness of silicon dioxide layers grown from hexamethyldisiloxane (HMDSO), octamethylcyclotetrasiloxane (OMCTS), and tetramethylcyclotetrasiloxane (TMCTS) in a high-density electron cyclotron resonance oxygen plasma. Hard colorless coatings could be grown from each precursor; coating composition, growth rates, and hardness depended strongly on the ratio of oxygen to precursor flow. At the highest O2/precursor flow ratios (4:1 for HMDSO and 8:1 for OMCTS and TMCTS), the coatings were SiO2-like with oxygen-to-silicon ratios close to 2:1 and carbon percentages as low as 12% for HMDSO, 3.4% for OMCTS, and 1.4% for TMCTS. Growth rates were 0.7–1.1 μm/min, initially increasing with the O2/precursor flow ratio; final coating thicknesses after 5 min were 3.5 μm to 5.5 μm. Coating hardness values generally increased with increasing O2/precursor flow ratio, attaining 6 GPa, 7.4 GPa, and 8.7 GPa for HMDSO, OMCTS, and TMCTS, respectively.

Electrical Characterization of GaN Metal Oxide Semiconductor Diodes Using MgO as the Gate Oxide

GaN metal oxide semiconductor diodes were demonstrated utilizing MgO as the gate oxide. MgO was grown at 100°C on metal oxide chemical vapor deposition grown n-GaN in a molecular beam epitaxy system using a Mg elemental source and an electron cyclotron resonance oxygen plasma. -based wet-chemical etchant was used to remove MgO to expose the underlying n-GaN for ohmic metal deposition. Electron deposited Ti/Al/Pt/Au and Pt/Au were utilized as ohmic and gate metallization, respectively. An interface trap density of low-to-mid- eV−1 cm−2 was obtained from temperature conductance-voltage measurements. Terman method was also used to estimate the interface trap density, and a slightly lower number was obtained as compared to the conductance method. Results from elevated temperature (up to 300°C) conductance measurements showed an interface state density roughly three times higher eV−1 cm−2) than at 25°C. © 2002 The Electrochemical Society. All rights reserved.

Low-orbit-environment protective coating for all-solid-state electrochromic surface heat radiation control devices

We suggest use of low-orbit space ambient protective surface coatings for our recently reported all-solid-state electrochromic surface-heat emissivity modulation device in order to (i) to improve the infrared emissivity modulation upon use of the protective layer's antireflection effect; and (ii) protect the layer stack within hazardous space environments. We study the optical properties of ZnSe as potential coating material before and after electron cyclotron resonance oxygen plasma treatment, which is a simulation of the low earth orbital environment. The influence on the device performance is evaluated.

Electrical Characterization of GaN Metal Oxide Semiconductor Diode Using Sc[sub 2]O[sub 3] as the Gate Oxide

GaN metal oxide semiconductor diodes were demonstrated utilizing Sc 2 O 3 as the gate oxide. Sc 2 O 3 was grown at 100°C on MOCVD grown n-GaN layers in a molecular beam epitaxy system, using a scandium elemental source and an electron cyclotron resonance oxygen plasma. Ar/Cl 2 based discharges were used to remove Sc 2 O 3 , to expose the underlying n-GaN for ohmic metal deposition in an inductively coupled plasma system. Electron beam deposited Ti/Al/Pt/Au and Pt/Au were utilized as ohmic and gate metallizations, respectively. An interface trap density of 5 X 10 1 1 eV - 1 cm - 2 was obtained with the Terman method. Conductance-voltage measurements were also used to estimate the interface trap density and a slightly higher value was obtained as compared to the Terman method. Results of capacitance measurements at elevated temperature (up to 300°C) indicated the presence of deep states near the interface.

Gadolinium Oxide and Scandium Oxide: Gate Dielectrics for GaN MOSFETs

Scandium oxide was deposited epitaxially on (0001) GaN via gas-source molecular beam epitaxy (GSMBE) using elemental Sc and an electron cyclotron resonance (ECR) oxygen plasma. HXRD indicated that the Sc2O3 has a lower defect density than similarly prepared films of Gd2O3. The scandium oxide was atomically smooth, with a rms roughness of 0.5–0.8 nm, and was uniform in stoichiometry as measured by Auger electron spectroscopy (AES) depth profiling. An interface state density of mid 1011 eV—1 cm—2 was determined from capacitance–voltage profiling using the Terman method. This interface state density was roughly a factor of five lower than that obtained from similar diodes made from SiO2 on GaN.

Gadolinium Oxide and Scandium Oxide: Gate Dielectrics for GaN MOSFETs

Scandium oxide was deposited epitaxially on (0001) GaN via gas-source molecular beam epitaxy (GSMBE) using elemental Sc and an electron cyclotron resonance (ECR) oxygen plasma. HXRD indicated that the Sc2O3 has a lower defect density than similarly prepared films of Gd2O3. The scandium oxide was atomically smooth, with a rms roughness of 0.5–0.8 nm, and was uniform in stoichiometry as measured by Auger electron spectroscopy (AES) depth profiling. An interface state density of mid 1011 eV—1 cm—2 was determined from capacitance–voltage profiling using the Terman method. This interface state density was roughly a factor of five lower than that obtained from similar diodes made from SiO2 on GaN.

Study of surface chemical changes and erosion rates for CV-1144-O silicone under electron cyclotron resonance oxygen plasma exposure

CV-1144-O silicone thin films were irradiated in an electron cyclotron resonance oxygen plasma, which is a simulation of the low earth orbital environment. A crude equivalence between this plasma system and the low earth orbital environment was determined by measuring Kapton weight loss in the plasma and comparing to Kapton weight loss in space experiments. Changes in optical properties and erosion rates under ultraviolet light and atomic oxygen radiation were studied using in situ spectroscopic ellipsometry (SE). The erosion rate at the beginning of the plasma exposure was significantly faster than that at later stages. Approximately one third of the total silicone thickness was etched away within 1 h, which according to the equivalence experiment, corresponds to about two months in low earth orbit. The refractive index of silicone in the visible range increased during the exposure, indicating that the film was being densified. Optical constants (both before and after plasma exposure) were determined by ex situ spectroscopic ellipsometry in the ultraviolet–visible–near-infrared (0.7–8.5 eV) and IR (200–7000 cm−1) ranges. Also, SE was used to map thickness and uniformity before and after radiation. Regression fits using Lorentzian and Gaussian oscillators as parametric models for the optical constants were excellent, and the major absorption peaks in the IR region were identified. The before- and after-radiation spectra showed significant decreases in CH3-associated peaks and increases in SiOx-associated peaks.

Electrical Characterization of GaN Metal Oxide Semiconductor Diodes Using MgO as the Gate Oxide

AbstractGaN metal oxide semiconductor diodes were demonstrated utilizing MgO as the gate oxide. MgO was grown at 100°C on MOCVD grown n-GaN in a molecular beam epitaxy system using a Mg elemental source and an electron cyclotron resonance oxygen plasma. H3PO4 based wet-chemical etchant was used to remove MgO to expose the underlying n-GaN for ohmic metal deposition. Electron deposited Ti/Al/Pt/Au and Pt/Au were utilized as ohmic and gate metallization, respectively. An interface trap density of low-to-mid 1011 eV-1cm-2was obtained from temperature conductance-voltage measurements. Terman method was also used to estimate the interface trap density and a slight lower number was obtained as compared to the conductance method. Results from elevated temperature (up to 300°C) conductance measurements showed an interface state density roughly three times higher(6x1011 eV–1 cm-2 ) than at 25°C.