bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical sulfur passivation of visible (∼670 nm) AlGaInP lasers
Authors: Howard A. J. , Ashby C. I. H. , Lott J. A. , Schneider R. P. , Corless R. F.
Published: July 2002

III–V based devices such as field effect transistors, heterojunction bipolar transistors, and lasers often have surface leakage and thermal degradation problems due to surface states which pin the Fermi level to the midgap. Sulfur based passivation processes are known to improve device performance by altering surface-state densities. We have developed a voltage-controlled anodic sulfur passivation scheme using Na2S dissolved in ethylene glycol. Our process has repeatedly produced a ∼25% improvement in peak output power near the catastrophic damage limit in visible (λ=670 nm) AlGaInP edge-emitting lasers. The threshold current density before and after passivation, and the I–V characteristics before and after catastrophic failure, were essentially unchanged indicating that passivation raises the threshold for facet damage.
Thermal and electron-stimulated chemistry of Fomblin–Zdol lubricant on a magnetic disk
Authors: Lin Jong-Liang , Bhatia C. Singh , Yates John T.
Published: July 2002

The thermal and electron-induced decomposition of Fomblin–Zdol lubricant on a rigid magnetic disk with a hard carbon overcoat are studied by temperature-programmed reaction/desorption spectroscopy and electron stimulated desorption. The thermal spectroscopy shows two desorption features peaked at 640 and 700 K resulting from decomposition of the Fomblin–Zdol molecules. The threshold temperature for dissociation of the Fomblin–Zdol molecule is at 500–550 K in accordance with the known thermal stability of the free molecule. HF originating from thermal reactions with either surface OH or surface CH groups is a prominent desorption product. Electron impact also causes Fomblin–Zdol dissociation. Two efficient mechanisms for electron impact dissociation have been resolved separately above and below the ionization threshold of ∼14 eV. The low-energy process is likely due to the formation of negative ions followed by dissociation (dissociative electron attachment) and has a cross section of ∼2×10−16 cm2. These results show that Fomblin–Zdol as a lubricant on a magnetic disk is inherently unstable thermally and in the presence of triboelectrons.
Adsorption and decomposition of trichlorosilane and trichlorogermane on porous silicon and Si(100)2×1 surfaces
Authors: Dillon A. C. , Wise M. L. , Robinson M. B. , George S. M.
Published: July 2002

The adsorption and decomposition of trichlorosilane (SiHCl3) and trichlorogermane (GeHCl3) on silicon surfaces were studied using Fourier transform infrared (FTIR) spectroscopy and temperature programmed desorption investigations. The FTIR transmission spectroscopy experiments were performed in situ in an ultrahigh vacuum chamber on high surface area porous silicon samples. The FTIR spectra revealed that SiHCl3 dissociatively adsorbed at 200 K and formed SiH, SiClx, ClSiH, and Cl2SiH surface species. The presence of ClxSiH species indicated incomplete decomposition of SiHCl3 upon adsorption at 200 K. GeHCl3 also dissociatively adsorbed at 200 K and formed SiH and SiClx species. The absence of an infrared absorption in the Ge–H stretching region suggests complete transfer of hydrogen from Ge to surface Si atoms at 200 K.

The thermal stabilities of the surface species were then studied with annealing experiments. The ClxSiH species deposited by SiHCl3 exposure at 200 K decomposed between 200 and 590 K and formed additional SiH and SiCl species. The SiClx (x=2 or 3) species deposited by either GeHCl3 or SiHCl3 dissociative adsorption converted to silicon monochloride species between 200 and 600 K. The SiH surface species subsequently decreased at temperatures between 680 and 780 K as H2 desorbed from the silicon surface. FTIR spectroscopy was also utilized to monitor the adsorption of SiHCl3 and GeHCl3 on porous silicon at different surface temperatures. These adsorption studies were in agreement with the thermal annealing experiments. Temperature programmed desorption (TPD) studies were performed following saturation SiHCl3 and GeHCl3 exposures on Si(100)2×1. After SiHCl3 adsorption, the only desorption species were H2, HCl, and SiCl2, and they were observed at 810, 850, and 970 K, respectively. Following GeHCl3 adsorption, the TPD experiments monitored H2, HCl, SiCl2, and Ge at 810, 850, 950, and 1200 K, respectively. The adsorption kinetics of SiHCl3 and GeHCl3 were also measured on Si(100)2×1 and initial reactive sticking coefficients of S0≊.019 for SiHCl3 and S0≊1 for GeHCl3 were determined at 500 K. These experiments provide insight into the surface chemistry of chlorosilanes and chlorogermanes during Si, Ge, and Si1−xGex chemical vapor deposition on silicon surfaces.
Adsorption and decomposition of dichlorosilane on porous silicon surfaces
Authors: Robinson M. B. , Dillon A. C. , George S. M.
Published: July 2002

The adsorption and decomposition of dichlorosilane (SiH2Cl2) on silicon surfaces were studied using Fourier transform infrared (FTIR) transmission spectroscopy. These FTIR studies were conducted in situ in an ultrahigh vacuum chamber using high surface area, porous silicon samples. The FTIR spectra of porous silicon following saturation SiH2Cl2 exposures at 200 K revealed the presence of primarily dihydride (SiH2) and monochloride (SiCl) surface species. These surfaces species are consistent with an adsorption mechanism involving Si–Cl bond breakage, i.e., SiH2Cl2 (g)+2Si*→Si*–SiH2Cl+Si*–Cl. The stability of these surface species was then examined as a function of annealing temperature. The infrared absorbance for the SiH2 scissors mode decreased as the temperature was raised from 300 to 660 K. Concurrently, the absorbance increased for the SiH monohydride stretch. These spectral changes indicated that the dihydride (SiH2) species were converted to monohydride (SiH) species. Above 660 K, the SiH species disappeared concurrently with H2 desorption from the silicon surface. The uptake of dichlorosilane on porous silicon was also monitored as a function of substrate temperature. These experiments confirmed that SiH2 is the major surface hydride species following SiH2Cl2 adsorption at low temperatures. These studies of dichlorosilane adsorption and decomposition on silicon surfaces should help to clarify the mechanism of silicon chemical vapor deposition and atomic layer epitaxy with dichloro- silane.
Thermal annealing of the epitaxial Al/Si(111)7×7 interface: Al clustering, interfacial reaction, and Al-induced p+ doping
Authors: Wen H. J. , Dähne-Prietsch M. , Bauer A. , Cuberes M. T. , Manke I. , Kaindl G.
Published: July 2002

The structural and electronic properties of the epitaxial Al/Si(111)7×7 interface and their modifications upon thermal annealing were investigated by scanning tunneling microscopy, high-resolution photoelectron spectroscopy, and low-energy electron diffraction. Room-temperature deposition of 40 Å Al on Si(111)7×7 is mainly characterized by epitaxial growth and a decrease of the Fermi-level position by 0.32 eV. Annealing at temperatures around 500 °C results in the formation of large Al clusters with a thin reacted film in between. Subsequent annealing up to 900 °C results in complete desorption of Al and a recovery of the original 7×7 surface structure, while a potential variation underneath the Si surface, completely different from that of the starting surface, is observed in the Si 2p photoemission spectra. These results strongly indicate the formation of a p+-Si layer induced by Al diffusion.
Thermal desorption studies of high-coverage hydrogen overlayers on Ru(001) created with gas-phase atomic hydrogen
Authors: Jachimowski T. A. , Meng B. , Johnson D. F. , Weinberg W. H.
Published: July 2002

The adsorption of gas-phase atomic hydrogen on the Ru(001) surface results in a saturation coverage of 1.42 hydrogen adatoms per primitive surface unit cell, which is significantly greater than the saturation coverage of one hydrogen adatom per primitive unit cell in the case of dissociative chemisorption of molecular hydrogen. Thermal desorption spectra of these high-coverage hydrogen overlayers are characterized by a peak temperature of ∼320 K which shifts downward slightly with increasing coverage beyond one monolayer. An isosteric analysis of the thermal desorption spectra yields a desorption energy that decreases from 29.5 kcal/mol at zero coverage to 22 kcal/mol at a coverage of 1.42.
Physical properties of thin carbon nitride films deposited by electron cyclotron resonance assisted vapor deposition
Authors: Bousetta A. , Lu M. , Bensaoula A.
Published: July 2002

Electron cyclotron resonance (ECR) plasma-assisted vapor deposition has been used to grow thin carbon nitride films on Si(100) and sapphire substrates. The composition, structure, and optical properties of the films were investigated by x-ray photoelectron spectroscopy (XPS), Rutherford backscattering (RBS), Raman, and optical absorption spectroscopies. The effect of varying the nitrogen gas flow, at constant substrate temperature and carbon deposition rate, on the C/N composition ratio and the CxNy crystal structure was investigated. From both RBS and XPS, the nitrogen concentration in the film was found to be in the range of 20%–48% and varied directly with the nitrogen partial pressure in the ECR source. In CN films with low nitrogen content, the Raman spectra showed no evidence of CN bonding and were characteristic of graphitic carbon. In contrast, the Raman spectra of high nitrogen content thin films show a wide peak at 1291 cm−1, suggesting the formation of a CxNy phase with predominately sp3 bonding. The optical band gap of CN films deposited on sapphire was found to be about 1.95 eV, which is below that reported for amorphous CN films, suggesting a higher structural order.
High density, low temperature dry etching in GaAs and InP device technology
Authors: Pearton S. J. , Abernathy C. R. , Ren F.
Published: July 2002

Electron cyclotron resonance (ECR) plasma etching of GaAs, AlGaAs, and GaSb in Cl2/Ar or BCl3/Ar, and of InP in CH4/H2/Ar discharges is performed down to −30 °C substrate temperature and characterized in terms of rate, anisotropy, damage introduction and near-surface stoichiometry. Below −10 °C the vertical etch rates of all these semiconductors decrease due to reduced volatility of the products, and there is suppression of lateral etching with chlorine-based mixtures, but no change in anisotropy of CH4/H2/Ar etched features. Etching of typical dielectrics (SiNx,SiO2) and metals (W) used in bipolar or field effect transistors in SF6/Ar discharges was also characterized, and for substrate temperatures below −20 °C increased concentrations of fluorine-containing residues are found on the exposed semiconductor surface after removal of the dielectric or metal. These can be removed by a 500 W microwave ECR H2 plasma with low additional (−25 V) dc bias on the sample. The effect of an additional lower collimating magnet on the etch anisotropy was also examined and found to have a significant improvement at low ion energies. The uniformity of etching was improved when the lower collimating magnet was operational.
Energy correction by evaporated gold in x-ray photoelectron spectroscopy
Authors: Ogama T.
Published: July 2002

This work reports measurements of the binding-energy shift of gold evaporated on several insulating materials including polymers such as polytetrafluoroethylene and polyethylene and inorganic materials such as silicon oxide. The Au binding energy showed higher values than that for bulk gold in the initial stage of deposition even after correction for charging effects. The energy shifts seen for the polymer substrates were smaller to those for inorganic materials such as silicon oxide and silicon nitride. The thickness of gold necessary to obtain the bulk Au binding energy was small for substrates whose Au binding-energy shifts were small. Thus, it was confirmed that it is very important to deposit an appropriate amount of gold to obtain the correct binding energies. These results can be explained by extra-atomic relaxation, because a larger extra-atomic relaxation energy is expected for substrates on which gold atoms or clusters can migrate easily and form larger clusters. These clusters cause smaller binding-energy shifts and require smaller amounts of evaporated gold.
Thermal stability of rapidly annealed CoSi2/n-GaAs and CoSi2/p-InP Schottky contacts
Authors: Eftekhari G.
Published: July 2002

Thermal stability of rapidly annealed CoSi2/n-GaAs and CoSi2/p-InP contacts was studied. Annealing time was 10 s and the proximity method was used during annealing. Annealing at 700 and 800 °C made contacts more reliable, which is related to the removal of sputter created defects. Annealing at temperature higher than 900 °C caused significant degradation, which is attributed to the diffusion and reaction of elements at the interface.
Strengthening of Al2O3-based ceramics by metalorganic chemical vapor deposition
Authors: Konyashin I. Yu.
Published: July 2002

Results on exploring the possibility of improvement in physical, mechanical, and performance properties of Al2O3 based ceramics by use of chromium based thin coatings obtained with the aid of metalorganic chemical vapor deposition are presented. The coatings are assumed to heal various surface defects of the ceramic specimens, which leads to strengthening and toughening of the near-surface layer of the Al2O3 substrate. This results in retardation of initiation and propagation of Palmquist cracks during Vickers indentation and allows enhancement in microhardness of the near-surface layer. As a result, considerable improvement in tool lifetime in turning and milling carbon steel and gray cast iron is achieved when employing the coated ceramic indexable inserts.
Numerical ellipsometry: Applications of a new algorithm for real-time, in situ film growth monitoring
Authors: Urban Frank K. , Comfort John Craig
Published: July 2002

The equations associated with the popular models of film deposition of a material on a substrate tend not to be invertible in practical situations. Thus development of numerical techniques for obtaining approximate solutions to these equations has become necessary. At present, real-time, in situ thin film growth ellipsometry data are limited to a single angle of incidence due to the deposition system windows. The 2C algorithm, developed by the authors, represents a new approach to solve this problem. This algorithm is fast enough for reliable real-time solutions without requiring either accurate initial estimates or any off-line processing. Algorithm 2C employs the techniques of dynamic step adjustment, overrelaxation, and reduction in dimension, as well as curve following and curve intersection location techniques developed by the authors. The algorithm was originally developed for nickel deposited on BK7 glass, and in this article it is applied to silver, silicon, and gold depositions on BK7 glass. Gold films could be solved readily with no changes, while problems with convergence were encountered with some silver measurements and silicon data required changes in the ‘‘standard’’ initial estimate.
Recoil spectrometry of thin film reactions in the Pd/InP system
Authors: Persson Leif , El Bouanani Mohamed , Hult Mikael , Jönsson Patrik , Whitlow Harry J. , Andersson Margaretha , Georgsson Kristina , Bubb Ian F. , Johnston Peter N. , Walker Scott R. , Cohen David D. , Dytlewski Nick , Zaring Carina , Östling Mikael
Published: July 2002

Interfacial reactions between (100) InP and Pd were investigated as part of a systematic study aimed at investigating the stability of planar nonalloyed metallizations to InP. A 50-nm-thick Pd film was deposited on an InP substrate, and parts of it were subsequently thermally treated for 30 min at temperatures varying from 100 to 500 °C in steps of 50 °C. Separate characterizations of the Pd, In, and P depth distributions were obtained using mass and energy dispersive recoil spectrometry. The different phases were determined using x-ray diffraction, and scanning electron microscopy was used to study the surface topography. It is assumed that the interaction starts in the as-deposited sample, and definite formation of a ternary phase with the suggested composition Pd5In2P2 starts at an annealing temperature of 100 °C. At 250 °C all Pd is chemically reacted. Preferential outdiffusion of P leads to a loss of P from the surface at 500 °C, and the only phase observed in the x-ray diffraction spectrum from the surface is PdIn.
Focusing glass capillary array molecular beam inlet for a high sensitivity mass spectrometer system
Authors: Ma Y. , Liu B. Y. H. , Lee H. S. , Mauersberger K. , Morton J.
Published: July 2002

A molecular beam is formed using a focusing glass capillary array to serve as the gas inlet of a mass spectrometer beam system. The glass disk has a diameter of 13 mm. The number of pores in the capillary array is about a half-million. The pore diameter is 10 μm and the pore length is 0.5 mm. The focal length of the glass capillary array is 9.5 cm. Results show that within the 0–30 mTorr input range, the molecular beam intensity is proportional to the inlet pressure. High sample transmission is obtained for low pressure gas input. Beyond this range, the beam intensity levels off rapidly. As opposed to the orifice beam formation, a relatively narrow operational window exists which limited the ability of the capillary array to obtain high sample transmission efficiency for high pressure gas input applications.
Production and destruction of CFx radicals in radio-frequency fluorocarbon plasmas
Authors: Haverlag M. , Stoffels W. W. , Stoffels E. , Kroesen G. M. W. , de Hoog F. J.
Published: July 2002

Spacially resolved densities of CF, CF2, and CF3  radicals in capacitively coupled 13.56 MHz radio-frequency (rf) discharges in CF4 and CHF3 were determined by means of infrared absorption spectroscopy employing a tunable diode laser spectrometer. It was established that the stationary CF2 density and density profile in a CF4 plasma depend strongly on the electrode material. This is attributed to different sticking coefficients of CF2 on different surfaces. Furthermore, it was found that the densities of all CFx radicals increase near the electrodes at high gas pressures and rf powers in a CHF3 plasma. This leads to the conclusion that production of CFx radicals takes place in the sheath region close to the electrodes. It is proposed that collisions between ions and source gas molecules are responsible for this production of CFx radicals. In the presence of a destruction process in the plasma glow (e.g., by three-body recombination with other radicals) and the absence of a fast surface loss process this results in the observed increase of CFx densities near the electrodes. In order to study the radical kinetics time dependent measurements were performed during power modulation of the plasma. It was found that the decay time of the CF2 density in the afterglow of a CF4 plasma is much shorter than the corresponding decay time in a CHF3 discharge. This suggests that the surface loss is relatively less important in the latter case, in agreement with measurements of spatial density distributions. This is explained by the presence of a (CFx)n layer, which is readily deposited on the electrodes in a CHF3 discharge, and by low sticking probabilities of CF and CF2 radicals on such a layer.
Simulation and dry etching of field emitter tips in Si
Authors: Rakhshandehroo M. R. , Sukardi F. , Pang S. W.
Published: July 2002

To increase the efficiency of field emission devices, the design of the emitters should be optimized. A simulation program using the finite element method was developed to investigate the effects of emitter geometry on the emission current and voltage for ungated emitters. It was found that the tip-anode spacing and tip radius have the most significant effects on the emitted current. The simulation predicted that a field emitter consisting of a vertical base and a cone shaped tip on the top has a higher enhancement factor and therefore a lower operating voltage. Emitters were fabricated in Si based on the optimized design. Dry etching in CF4 was used to control the slope of the SiO2 mask. The SiO2 sidewall angle decreased from 80° to 51° as pressure was increased from 40 to 300 mTorr. The SiO2 mask profile was also changed substantially by adding CHF3 or O2 to CF4 during etching. An electron cyclotron resonance source was used to generate a Cl2 plasma to etch Si field emitters. SiO2 mask was eroded during etching to control the Si emitter profile. The slope of the Si etch profile increased from 52° to 78° as the SiO2 slope increased from 17° to 45°. Radio frequency and microwave power had little influence on the Si etch profile, but they were adjusted to achieve the desired etch rate. The lateral etch rate of SiO2 decreased at higher pressure, resulting in more vertical Si profiles. Oxygen was also added to the Cl2 plasma and the Si sidewall angle was changed between 47° and 80°. Using the above results, the Si etch profile was controlled and field emitter tips and arrays with different geometries were etched in Si. To comply with the optimum design, emitter tips with two different sidewall angles of 85° and 70° were fabricated by changing the pressure from 5 to 0.5 mTorr during the etch. Arrays of emitter tips with sidewall angle of 80°, 11 μm height, and 2.2 μm basewidth were also fabricated at 10 mTorr with a packing density of 4×106 tip/cm2.
Generation of intense, hexapole-selected, supersonic beams of fluorocarbon radicals: CF, CF2, and CF3
Authors: Weibel Michael A. , Hain Toby D. , Curtiss Thomas J.
Published: July 2002

Intense molecular beams of fluorocarbon radicals were generated with a corona discharge passing through a supersonic jet expansion of 15% C2F6 in Ar. An electrostatic hexapole separated the polar neutrals entrained in the beam by selectively focusing them through a small aperture. Molecules were separated according to the ratio of their mass to permanent electric dipole moment (m/μ) and according to their rotational state. Our most dramatic success was in isolating CF radicals in a single rotational state: |JΩMJ〉=|1/21/21/2〉. The pure, state-selected CF radical beam was characterized by a narrow velocity distribution (Δv/v∼14%) and high flux density (J=8×1011 radicals cm−2 s−1). Adjustments in the hexapole voltage and discharge conditions produced variations in the beam composition of 100% CF, 0% CF2, 0% CF3 to 20% CF, 0% CF2, 80% CF3, and 60% CF, 15 CF2, 25% CF3 with no other detectable components (e.g., F and C atoms, C2F6).
Nanofabrication using selective thermal desorption of SiO2/Si induced by electron beams
Authors: Fujita S. , Maruno S. , Watanabe H. , Ichikawa M.
Published: July 2002

It has been found that selective thermal desorption of extremely thin oxide films on Si(111) and Si(001) substrates is induced by electron beam irradiation. By using focused electron beams and this selective thermal desorption, a new nanofabrication technique has been demonstrated on oxide films. Open windows about 10 nm or less in width have been fabricated in oxide films by this technique. By pattern transfer from the open windows to Si and Ge films using surface chemical reaction, Si and Ge nanowires 10–20 nm in width have been fabricated.
Engineered sculptured nematic thin films
Authors: Messier R. , Gehrke T. , Frankel C. , Venugopal V. C. , Otaño W. , Lakhtakia A.
Published: July 2002

By controlling the angular relation of the substrate surface with respect to the incoming vapor direction in an evaporation deposition system, it is possible to engineer the morphology of thin films. Sculptured nematic thin films result under low adatom mobility conditions when the substrates are rotated about an axis perpendicular to the vapor direction. Thin films of MgF2 were deposited onto room temperature substrates to produce columnar morphologies ranging from chevron structures to continuously varied structures resembling S shapes and C shapes. The specific morphologies are virtually unlimited within the restriction that the minimum angle χM of the local columnar direction with respect to the substrate plane is about 30°.
Crystallinity and texture promotion in WS2 thin films
Authors: Regula M. , Ballif C. , Remškar M. , Lévy F.
Published: July 2002

A systematic study of the promoting effect of various elements on crystallization and texture of tungsten sulfide (WS2) thin films is presented. Best crystallization at relatively low annealing temperatures Ta=650–750 °C is achieved by adding sodium sulfide or nickel to the film, while the strongest texture is achieved with cobalt. An improvement of crystallization and texture is equally achieved with iron, manganese, or cesium. The promoting effect is mostly independent of the way the promoter is added. The promoting element can be added as a thin layer on the substrate or on the top of the WS2 film or it can be codeposited with the WS2 film. Since rheotaxy models cannot satisfactorily explain these results, the possibility of a catalytic growth mechanism is discussed.
Study of distributed ion pumps in the Cornell Electron Storage Ring
Authors: Li Yulin , Kersevan Roberto , Mistry Nariman
Published: July 2002

It is desirable to reduce anode voltage of distributed ion pumps (DIPs) in the Cornell Electron Storage Ring (CESR) in order to suppress beam instability caused by the leakage of electric field from the DIPs and to extend the lifetime of the DIPs and DIP power supplies. The DIP pumping speed is measured as a function of anode voltage with and without the stored beam in order to determine whether the anode voltage can be reduced without sacrificing the DIP pumping speed. It is found that the DIP pumping speed remains relatively unchanged when the anode voltage changes from a “normal” operating voltage of 7.6 kV to as low as 1.8 kV when there is a stored beam in the CESR. On the other hand, the pumping speed drops rapidly as the anode voltage is decreased below 5 kV and there is no stored beam in the CESR. A simple model is used to explain the operation of DIPs under the influence of the stored beam.
Cyclization and related reactions of iodoethanol on Ag(110)
Authors: Jones G. Scott , Barteau Mark A.
Published: July 2002

The adsorption and reaction of 2-iodoethanol (IEtOH) on a clean Ag(110) surface were studied under ultrahigh vacuum conditions using temperature programmed deposition (TPD). Under these conditions alcohols are typically unreactive on the clean Ag(110) surface. Replacement of one of the β hydrogens with a weakly bound (53 kcal/mol) iodine atom, however, opens a channel for IEtOH decomposition by initial carbon–iodine scission. TPD results indicate that there are two major reaction channels at 263 and 340 K for IEtOH decomposition on the clean Ag(110) surface. The reaction intermediates that give rise to these two pathways were deduced based upon the products observed, the overall product stoichiometry, and the desorption temperatures of the products. The 263 K reaction channel has an overall stoichiometry of C2H5O, corresponding to a hydroxyethyl intermediate. The hydroxyethyl intermediate undergoes a β-hydride elimination and C-O scission, ultimately yielding volatile acetaldehyde, ethylene, water, ethanol, and another surface intermediate that decomposes at 340 K. Unlike unsubstituted alkyl groups on clean Ag(111) and Ag(110) which couple to form alkanes, there is no evidence for hydroxyethyl coupling to give butanediol. Thus, the hydroxyethyl cannot be treated simply as a substituted alkyl group; that is probably due to interactions between oxygen and the surface. The stoichiometry of the products released at 340 K, C2H4O, is suggestive of an oxametallacycle intermediate. The products of this reaction channel are the same as the 263 K channel with the addition of a cyclic ester product, γ-butyrolactone. This species has not previously been synthesized from a C2 precursor in ultrahigh vacuum, and its observation suggests that surface oxametallacycle chemistry may be richer than previously recognized.
Electron transport to a substrate in a radio frequency capacitively coupled plasma by the Boltzmann equation
Authors: Matsui Jun , Shibata Mari , Nakano Nobuhiko , Makabe Toshiaki
Published: July 2002

Anomalous etching, caused by the local charging of a patterned wafer surface immersed in a plasma, is one of the obstacles which must be overcome in plasma processing. We have developed a quantitative argument for the potential control of both the fluxes and the velocity components of charged particles on the wafer in a pulsed radio frequency plasma with a short off-cycle in SF6. We have then used relaxation continuum/Boltzmann equation model to create a phase-space model.
Halogen uptake by thin SiO2 layers on exposure to HBr/O2 and Cl2 plasmas, investigated by vacuum transfer x-ray photoelectron spectroscopy
Authors: Donnelly V. M. , Layadi N.
Published: July 2002

Thin SiO2 layers were subjected to short exposures (10–40 s) to HBr/O2  and Cl2 high-density plasmas, simulating the over-etching process encountered when polycrystalline Si gate electrodes are etched down to the gate oxide layer. Following this treatment, the samples were transferred under vacuum to an x-ray photoelectron spectrometer and spectra were recorded as a function of the take-off angle between the sample surface plane and the photoelectron collection lens. These angle-resolved measurements were inverted, using a maximum entropy approach, to obtain depth profiles. After etching in Cl2 or HBr plasmas at an ion energy of ∼40 eV (obtained with a grounded stage and a plasma potential of 40 V), surface layers were formed with halogen areal densities of ∼2×1015 cm−2, distributed over a half-depth of 10–20 Å. These results (both absolute areal densities and depth distributions) are similar to those found previously for etching of Si under the same conditions. For SiO2, buildup of Cl or Br near the surface is accompanied by a depletion of O. Addition of 10% O2 to HBr plasmas decreases the Br content in the film by nearly a factor of 2 (with the stage grounded), and dramatically slows the etching rate from ∼30 to <2 Å/min. Increasing the mean ion energy to ∼150 eV by applying an rf bias (resulting in a dc bias of −110 V) increases the etching rate in the 10% O2/HBr plasma to about 10 Å/min, and increases the Br areal density by 50. Implications for etching of polycrystalline-Si gate electrodes and selectivity to SiO2 are discussed.
Localized degradation studies of ultrathin gate oxides
Authors: Wen H. J. , Ludeke R.
Published: July 2002

We present studies on the limits of oxide reliability on a local, microscopic scale, using scanning tunneling microscope (STM)-based ballistic electron emission microscopy/spectroscopy (BEEM/S). In these studies, electrons are injected from the STM tip into the conduction band of a SiO2 layer that is imbedded in a metal–oxide–semiconductor (MOS) structure. The electron energy is determined both by the tip bias that can be set up to −13 V and by the applied oxide bias. Combining the two biases can heat electrons to energies that are unreachable in thin oxides by conventional Fowler–Nordheim injection methods. Our studies indicate that breakdowns are difficult to achieve for 7.1 nm oxides. A local breakdown was not observed even for an injected charge dosage of 1.8×103 C/cm2 at equivalent Fowler–Nordheim stress fields of ∼25 MV/cm, although defect densities in the oxide were as high as ∼5×1013/cm2. Evidence of anode hole injection is also observed under high oxide biases ∼8 MV/cm. Therefore we conclude that trap creation and hole injection processes are not sufficient to cause breakdowns at arbitrary locations on the 7.1 nm oxides. Whereas electron trapping is dominant during electron injection for 7.1 nm oxides, only a positive charge buildup was observed in the 2.8 nm oxides while stressing with only 1 eV electrons. For 2.8 nm oxides, a local breakdown did not occur for dosages of 3.1×103 C/cm2 at equivalent fields >43 MV/cm. The observed breakdowns were accompanied by gate metal failure and are hence believed to occur at weak spots in MOS capacitors. We conclude that an intrinsic breakdown limit of SiO2 has not yet been reached.
Hydrogen in silicon: Fundamental properties and consequences for devices
Authors: Van de Walle Chris G.
Published: July 2002

The interactions between hydrogen and silicon are investigated based on first-principles calculations. After a comprehensive overview of various configurations attention is focused on the energetics and dissociation of Si–H bonds. An examination of the dissociation mechanism of Si–H bonds suggests an explanation for the observed difference in stability between hydrogen and deuterium at dangling bonds. Connections between the phenomena at surfaces, interfaces, and in amorphous materials will be pointed out.
Improved optical scheme for nonintrusive vapor density monitoring by atomic absorption spectroscopy
Authors: Ray A. , Majumdar A.
Published: July 2002

A real-time atomic absorption sensor based on a hollow cathode lamp with the element as the resonant radiation source has been developed to improve the accuracy and long-term stability of monitoring the vapor deposition rate. The present experimental methodology utilizes a common optical path for the signal and reference hollow cathode emission lines, which originate from a suitable common upper level of the element. This optical scheme is capable of measuring the atomic absorption independent of changes in optical transmission due to those caused by hollow cathode output drift, viewport coatings, minor optical alignment shifts and the presence of molecular species during the process in progress. This technique allows unambiguous determination of the concentration of atoms in the vapor flux in real time. It has been used to monitor barium vapor density.
Observation of adsorption and reaction of NH3 on crystalline Al2O3 under steady-state conditions using external-reflection infrared spectroscopy
Authors: Bermudez V. M.
Published: July 2002

Thin crystalline films of Al2O3 have been grown by reaction of a NiAl(111) surface with chemisorbed O at elevated temperature. The resulting Al2O3/NiAl buried metal layer structure has then been used as a substrate for studies of NH3 adsorption under steady-state conditions at ∼300 K and up to ∼200 Torr. The technique used is polarization-modulated infrared reflection absorption spectroscopy, the application of which to in situ studies of surface chemistry is described in detail. Evidence is seen that suggests incorporation of N into the Al2O3, and adsorbed NH3 is detected under high (⩾25 Torr) static pressures.
Depth dependence of hydrogenation using electron cyclotron plasma in GaAs-on-Si solar cell structures
Authors: Kakinuma H. , Ueda T. , Gotoh S. , Akiyama M.
Published: July 2002

We have studied the effect of hydrogen-plasma exposure on GaAs-on-Si solar cell structures using electron cyclotron resonance (ECR). An increase in photoluminescence (PL) intensity near the GaAs/Si interface is found after the H-plasma exposure and 400 °C annealing, indicating passivation of threading dislocations by diffused hydrogen atoms. Secondary ion mass spectroscopy depth profiles of hydrogen concentration [H] for the ECR-plasma exposed solar cell structures have shown that the [H] near the GaAs/Si interface increases after the 400 °C annealing, which is in good agreement with the PL result. On the other hand, it is found that the [H] near the surface simply decreases with prolonged annealing time while the [H] near the GaAs/Si interface remains unchanged, which is favorable to the improvement of the conversion efficiency.
Reactive ion etching of Si by Cl and Cl2 ions: Molecular dynamics simulations with comparisons to experiment
Authors: Hanson D. E. , Kress J. D. , Voter A. F.
Published: July 2002

We present results of molecular dynamics simulations of reactive ion etching (RIE) of a reconstructed Si(100)(2×1) surface. The existing Stillinger–Weber interatomic potential for Si/Cl of Feil et al. has been modified by correcting the Si–Si bond strength for a SiCln moiety bound to a Si surface and the Si–Cl bond strength in SiClm molecules. This potential has been used to study RIE of Si by Cl and Cl2 ions. The calculated properties such as the Si yield, product stoichiometry, stoichiometry of the chlorosilyl surface, and Cl content of the chlorosilyl layer are in reasonable agreement with experiment. The dissociative chemisorption probability of Cl2 on Si(100)(2×1) as a function of energy has been simulated and the results are in reasonable agreement with experiment.
Control of atomic step arrangements on a patterned Si(111) substrate by using molecular beam epitaxy
Authors: Omi H. , Ogino T.
Published: July 2002

We present a new approach for designing atomic step arrangements on the Si(111) surface on a wafer scale. Steps on the surfaces patterned with mesas and trenches are rearranged during step-flow growth in molecular beam epitaxy. The step-flow growth produces straight arrays of [1̄1̄2]-type steps along the mesa tops. On the bottom of the trenches, however, resulting atomic steps curve toward the [1̄1̄2] direction, and are randomly distributed. These results show that step-flow growth on Si(111) mesa tops is promising for large-scale control of step arrangement and that the steps can be used as templates for step-initiated nanofabrication.
Characterizing metal-masked silica etch process in a CHF3/CF4 inductively coupled plasma
Authors: Kim Byungwhan , Kwon Kwang-Ho , Park Sang-Ho
Published: July 2002

A silica etch process conducted using a CHF3/CF4 inductively coupled plasma is characterized. This was accomplished by employing a statistical experimental design in conjunction with neural network process models. As a mask layer, patterned AlSi (1%) metal was used. Parameters varied in the design includes source power, bias power, and gas ratio. Besides those conventional etch responses including etch rate, selectivity, and profile, sidewall roughness of the etched pattern is first modeled. Etch rate and sidewall roughness were found to be predominantly influenced by source power with a trade-off between them. Bias power significantly affected selectivity while controlling a trade-off against etch rate. A decrease in profile angle with increasing bias power was attributed to AlSi (1%) film expansion induced by ion bombardment effects. As gas ratio was varied, profile angle remained almost constant due to nearly same chemical reaction of its plasma on the silica surface. The roughness was little affected by bias power at its low levels, thereby providing an increased degree of freedom to optimizing the process. The gas ratio exerted no noticeable impact on the etch responses.
Stoichiometry dependency of the firing and sustain voltage properties of MgO thin films for alternating current plasma display panels
Authors: Son Choongyong , Cho Jinhui , Park Jong-Wan
Published: July 2002

MgO thin films were prepared on soda-lime glass substrates by the radio frequency magnetron sputtering using a MgO target at various oxygen gas flow ratios [O2/(Ar+O2)] in order to understand the relationship between MgO film properties and discharge characteristics. The gas discharge property of alternating current plasma display panels (ac PDP) was found to strongly depend on the crystallinity, surface morphology, and contamination with hydroxyl groups, as well as film stoichiometry. The MgO films had a tendency to form structures with a preferred growth orientation of (200) planes with an increasing oxygen gas flow ratio [O2/(Ar+O2)] to 0.1. The MgO films were also observed to be fully stoichiometric at an oxygen gas flow ratio [O2/(Ar+O2)] of 0.1. The fully stoichiometric MgO films were found to have a minimum in surface roughness and amount of hydroxyl groups and a maximum in grain size. The ac PDP with fully stoichiometric MgO films also showed lower firing and sustaining voltages than those with either magnesium-rich or oxygen-rich MgO films. This was largely attributed to the larger grain size and the reduced hydroxyl groups in the films.
Optical constants of crystalline WO3 deposited by magnetron sputtering
Authors: DeVries Michael J. , Trimble Chris , Tiwald Thomas E. , Thompson Daniel W. , Woollam John A. , Hale Jeffrey S.
Published: July 2002

Crystalline WO3−x is an infrared (IR) electrochromic material having possible applications in satellite thermal control and IR switches. Optical constants of electrochromic materials change upon ion intercalation, usually with H+ or Li+. Of primary concern for device design are the optical constants in both the intercalated and deintercalated states. In situ and ex situ ellipsometric data are used to characterize both the deposition process and the optical constants of the films. Ex situ data from a UV-Vis-NIR ellipsometer are combined with data from a mid-infrared Fourier-transform-infrared-based ellipsometer to provide optical constants over a spectral range of 0.031–6.1 eV.
Electrical control of the spatial uniformity of reactive species in plasmas
Authors: Sobolewski Mark A. , Steffens Kristen L.
Published: July 2002

We report a new method for controlling the spatial distribution of reactive chemical species in a parallel-plate plasma reactor, by means of a variable-impedance load placed between the unpowered electrode and ground. The technique was demonstrated in 89% CF4/11% O2 and 51% C2F6/49% O2 chamber-cleaning plasmas at 13.3–133 Pa (0.1–1.0 Torr) in a Gaseous Electronics Conference Reference Cell. The rf current and voltage at both electrodes were measured, and plasma spatial characteristics were observed using two-dimensional (2D) planar laser-induced fluorescence of the CF2 radical and 2D broadband optical emission measurements. By adjusting the load impedance to cancel the impedance of stray capacitances in parallel with the load, or the sheath capacitance in series with the load, the rf current at the load electrode could be made higher or lower than the current received when the electrode is grounded. When the rf current at the load electrode was minimized, regions of intense optical emission and high CF2 density were shifted radially outward from the center of the reactor. When the rf current at the load electrode was maximized, regions of intense optical emission and high CF2 density shifted radially inward, and the distribution of CF2 across the electrode surfaces became more uniform. These results suggest that variable loads could be used to direct reactive species in chamber-cleaning plasmas to the surfaces most in need of cleaning, or to increase the radial uniformity of reactive species in etching plasmas.
Study of CN films synthesized by facing target sputtering
Authors: Wang Yi , Jiang E. Y. , Bai H. L. , Wu P.
Published: July 2002

CN films were made by a facing target sputtering system. X-ray diffraction, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy spectra were measured to investigate the structure and the binding state of the film. The films are amorphous and the N/C increases as the N2 partial pressure increases and it reaches 0.46 when the N2 pressure is 100%. The N incorporated C forms N-sp2 C and N-sp3 C mainly and there is a small amount of C≡N. The incorporated N causes structural disorder of the C films and a reduction in the friction coefficient of the films.
Role of the surface roughness in laser induced crystallization of nanostructured silicon films
Authors: Hadjadj A. , Boufendi L. , Huet S. , Schelz S. , Roca i Cabarrocas P. , Estrade-Szwarckopf H. , Rousseau B.
Published: July 2002

The crystallization of hydrogenated nanostructured silicon (ns-Si:H) films deposited from Ar-silane mixture in a low-pressure pulsed radio-frequency glow discharge has been studied in relation with their structural and morphological properties. Different techniques of characterization converge to the fact that both the porosity and the surface roughness of the film increase with the plasma duration (Ton) used for the deposition. The correlation between the film structure and the crystallization threshold has been investigated. The modifications of the bulk structure of the film with Ton partly explain the decrease of the crystallization threshold (Ecryst). The role of the surface roughness in the lowering of the crystallization threshold is emphasized. Its contribution is interpreted by the enhancement of the electromagnetic field at the ns-Si:H film surface.
Atomic hydrogen-cleaned GaAs(100) negative electron affinity photocathode: Surface studies with reflection high-energy electron diffraction and quantum efficiency
Authors: Elamrawi K. A. , Hafez M. A. , Elsayed-Ali H. E.
Published: July 2002

The quantum efficiency of a vicinal GaAs(100) negative electron affinity (NEA) photocathode is studied and correlated to the surface morphology. Cleaning of a GaAs(100) vicinal surface by atomic hydrogen and by heating are investigated using reflection high-energy electron diffraction (RHEED). After atomic hydrogen cleaning at 500 °C, the GaAs surface exhibits a streaky (2×4)-reconstructed RHEED pattern. When the GaAs(100) surface is activated to NEA by the alternate deposition of cesium and oxygen, a quantum efficiency of ∼9% is measured. The photocathode quantum efficiency correlates with the out-of-phase RHEED intensity measured before activation. After the quantum efficiency decreases with operating time, further atomic hydrogen exposure also produces a (2×4) pattern. Surfaces prepared or revived by atomic hydrogen produce brighter out-of-phase electron diffraction patterns and, when activated to NEA, higher quantum efficiency compared to those that are heat cleaned.
Characterization of zirconia coatings deposited by inductively coupled plasma assisted chemical vapor deposition
Authors: Colpo P. , Ceccone G. , Sauvageot P. , Baker M. , Rossi F.
Published: July 2002

Thin films of zirconia have been deposited by an inductively coupled plasma assisted chemical vapor deposition reactor from a tetra (tert-butoxy)–zircon precursor diluted in Ar and O2 gas mixture. An independent rf generator is used to carefully control the substrate negative bias voltage during the deposition. Zirconia thin films, with thickness up to 10 μm were deposited on Si(100) polished wafers under different plasma conditions. Correlation between deposition parameters and microstructure has been established showing that the ion bombardment has a large influence on the coating characteristics. In particular, the possibility of tailoring mechanical properties of the films by controlling the applied dc bias voltage is discussed.
Reactions of substituted aromatic hydrocarbons with the Si(001) surface
Authors: Coulter Sarah K. , Hovis Jennifer S. , Ellison Mark D. , Hamers Robert J.
Published: July 2002

The interactions of toluene, para-xylene, meta-xylene and ortho-xylene with the (001) surface of silicon have been investigated using Fourier-transform infrared spectroscopy. Infrared spectra show that these methyl-substituted aromatic hydrocarbons are chemisorbed and oriented on the Si(001) surface at both 110 and 300 K. Peaks in the Si–H stretching region indicate that some dissociation occurs upon adsorption. Comparisons of infrared spectra of these molecules with deuterated and nondeuterated methyl groups reveal that the major source of decomposition is likely from C–H cleavage of the substituent groups, leaving the ring intact. Additionally, the striking similarity of the infrared spectra of benzene, toluene and the xylene isomers suggests that the methyl-substituted aromatic rings interact with the Si(001) surface in much the same way as benzene. Differences in relative peak intensity point to the possibility that the methyl substituent groups may steer the ring into different ratios of specific bonding geometries.