bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport and phototransport properties of plasma-deposited hydrogenated amorphous silicon nitrogen alloys, a-Si,N:H
Authors: Williams M. J. , He S. S. , Cho S. M. , Lucovsky G.
Published: July 2002

There are two potential applications for a-Si,N:H alloys in photovoltaic (PV) tadem devices (i) as a wide band gap photoactive i-region material, and (ii) as a heavily doped p-type window material. This paper addresses the first of these, discussing transport and phototransport properties of thin films deposited by remote plasma-enhanced chemical-vapor deposition. Chemical and structural properties have been characterized by infrared spectroscopy, high resolution transmission electron microscopy, and secondary ion mass spectrometry. Other measurements include the photo- and dark-conductivities, the optical absorption edge, and the minority carrier transport by the steady state photocarrier grating technique. Comparisons of the properties of a-Si,N:H alloys deposited from two different N-atom source gases, N2 and NH3 are presented. Significant increases in the slope of the optical absorption edge, and the magnitude of the Staebler–Wronski light-induced-degradation are identified for the films deposited from the NH3 source gas relative to those deposited from the N2 source gas.
Reactive ion etching of copper with BCl3 and SiCl4: Plasma diagnostics and patterning
Authors: Howard B. J. , Steinbrüchel Ch.
Published: July 2002

The reactive etching of copper in BCl3 and SiCl4 based plasmas has been investigated and empirically modeled using statistically designed experimentation. Gas mixtures with N2 exhibit considerably higher etch rates than mixtures with Ar. In the temperature range of 225 to 275 °C, the copper etch rate in BC13/N2 can be as much as an order of magnitude larger than in BCl3/Ar. Plasma diagnostics [optical emission spectroscopy (OES) and Langmuir probe measurements] were used to study the effect of the diluent gas on the discharge characteristics and the resulting etch process. OES indicates that N2 does not act merely as a diluent but rather increases the concentration of Cl atoms. Langmuir probe data show very little difference in the ion densities between the various gas mixtures. These results suggest, in combination with the empirical model, that the etch rate is limited by the amount of available reactant rather than by product desorption in the temperature range investigated. High-resolution patterning is demonstrated, but the effectiveness of the etch is dependent on the processing conditions, especially on temperature and pressure.
Estimations and results of energetic condensation processes in relation to hard carbon deposition
Authors: Rother B.
Published: July 2002

A concept of basic relations for ion assisted film growth conditions is presented and applied to establish a relationship between the industrial requirements of coating techniques and processing. Additionally, deposition parameter ranges can be estimated from these relations which is applied to the deposition of hard carbon coatings from free atoms and ions. Thereby, the formation of sp3 bondings, is considered to be a sensitive probe of film forming processes. The selection of cathodic arc technique for the deposition of hard carbon coatings is justified for the industrial requirements. Results of the deposition experiments are presented.
Deposition of diamondlike carbon using a planar radio frequency induction plasma
Authors: Pappas D. L. , Hopwood J.
Published: July 2002

The use of a planar radio frequency inductively coupled plasma for the preparation of diamondlike carbon (DLC) thin films is investigated. This approach offers a number of advantages over conventional rf parallel plate plasma processes for studying the deposition of DLC. In the latter case, substrate ion bombardment energy is determined by the rf self-bias which is a function of discharge power. For the rf induction plasma, discharge power absorption and rf substrate bias are decoupled, allowing independent evaluation of the effects of each parameter. Along with these quantities, the influence of CH4 flow rate and Ar dilution are investigated. Film properties examined include hardness, stress, optical transmittance, and hydrogen concentration. In addition, plasma optical emission spectra have been collected under various conditions. Films deposited at room temperature are found to be typical of DLC prepared by conventional plasma enhanced chemical vapor deposition processes, with microhardness values up to 30 GPa, optical bandgaps between 1.3 and 1.8 eV, and hydrogen content ranging from 20% to 36%. The planar geometry and high degree of dissociation in the rf induction plasma permit the coating of large areas at high rates (≳1000 Å/min). Other observations include a maximum in the hardness versus substrate bias curve.
Production and characterization of multilayer KCl:LiF thin films on glass
Authors: Somma F. , Ercoli A. , Santucci S. , Lozzi L. , Passacantando M. , Picozzi P.
Published: July 2002

Alkali halide films containing color centers have important applications in information storage, lithography, radiation dosimetry, and solid state lasers. KCl:LiF multilayers have been grown by thermal evaporation on glass substrates at p<10−4 Pa under continuous monitoring of the substrate temperature (Ts=30–350 °C) and deposition rate (Vd=0.3–0.7 nm/s). Optically active point defects have been produced by low energy (3 keV) electron irradiation in these thin layers of dielectric materials. The characterization of the samples has been performed using depth profile x-ray photoelectron spectroscopy for the profile composition, x-ray diffraction and scanning electron microscopy for the structural analysis, and optical absorption for defect formation. At substrate temperatures ranging from 30 to 350 °C the LiF and KCl layers grow with (200) crystallite planes parallel to the substrate surface.
Thermal relaxation kinetics of strained Si/Si1−xGex heterostructures determined by direct measurement of mosaicity and lattice parameter variations
Authors: Sardela M. R. , Hansson G. V.
Published: July 2002

The thermal stability of strained Si1−xGex/Si heterostructures grown by molecular-beam epitaxy was investigated. Alloy structures with Ge fractions between 5% and 23% and thicknesses from 160 to 200 nm, corresponding to excess stress from 112 to 712 MPa, were grown at 450 °C. X-ray high-resolution reciprocal lattice mapping (HRRLM) was employed as the major analysis tool to investigate the status of the strain and the material quality of the structures prior to and after high-temperature furnace annealing between 700 and 1000 °C. By this technique, the variations of the alloy lattice parameters parallel and perpendicular to the growth direction were independently determined as functions of the annealing temperature (Ta) within an accuracy ≊10−5. In addition, the annealing-induced variations in the shape of the x-ray scattering distributions were used to investigate the material quality and the changes in the mosaic character of the structures. For 700≤Ta≤800 °C, a strong increase in the strain relaxation with an activation energy of (2.3±0.2) eV was observed. The relaxation dependence on the excess stress was determined to follow a power of (1.9±0.2) law. In addition, strong broadening of the diffraction peaks was observed in the direction orthogonal to the scattering vector, demonstrating that the formation of strain-relieving dislocations introduces significant mosaicity in the structures.

At Ta≳800 °C, the levels of strain relaxation and mosaicity were found to be high, but the rate of increase was clearly reduced. The contribution to this effect owing to the dislocation–dislocation interaction was evaluated and was shown to be an important mechanism in limiting the maximum attainable relaxation in the structures. Effects of Ge diffusion were estimated and were shown to be relevant at Ta=1000 °C. The relaxation was significantly higher for structures with a higher Ge fraction but, in a structure with 5.67% Ge, a low-intensity diffuse scattering probably related to local strain fields from the initial stages of relaxation and dislocation formation, was observed. The use of HRRLM in the characterization of this important heterostructure system appeared to be appropriate not only for providing an accurate determination of lattice parameter variations as a function of Ta but, in addition, for differentiating between the effects of strain character and those of defect-related contributions to Bragg reflections.
Waterjet cutting of cross-linked glass
Authors: Yuan Fang , Johnson John A. , Allred David D. , Todd Robert H.
Published: July 2002

The cutting of cross-linked glasses such as silica and Corning 7059 can be difficult. We conducted an experimental study to determine the feasibility of using a high-speed waterjet to cut thin Corning 7059 glass. Cutting using either pure de-ionized high pressure water at 380 MPa (55 000 psi) or de-ionized water with entrained garnet abrasive was studied. The roughness of the cut surfaces was measured and compared. Photomicrographs were taken of glass examples cut at different traversing rates with pure water and with the abrasive entrained waterjet. Comparative studies of cutting with and without the entrained abrasive material showed that a cutting rate of 127 mm/min with abrasive could achieve a smoothness of about 9 μm rms. The abrasive waterjet can cut Corning 7059 glass into any desired shape. The process is safe, inexpensive, fast, and amenable to computer operation.
Growth of ternary alloy Si1−x−yGexCy by rapid thermal chemical vapor deposition
Authors: Bodnar S. , Regolini J. L.
Published: July 2002

Epitaxial layers of the ternary alloy SiGeC were grown on 〈100〉 Si substrates. Using a rapid thermal chemical vapor deposition reactor working at low temperature and reduced pressure (550 °C and 1 Torr), we obtained SiGeC layers with a carbon concentration into substitutional sites of up to 1.5%. We used two methods to measure the substitutional C fraction in the SiGeC samples: Fourier transform infrared measurements at room temperature and x-ray diffraction of the d004 atomic distance in the alloys. Using methylsilane (SiH3CH3 or MS) as the carbon precursor, we measured an activation energy for Si0.845Ge0.15C0.005 growth of around 52 kcal/mol and showed that C incorporation into substitutional sites saturates at high MS flows. Finally, thermal annealing of these ternary alloys has been studied: a 800 °C annealing for 15 min leads to oxygen and carbon diffusion, whereas strain relaxation occurs by amorphous SiC precipitation with a 900 °C, 15 min annealing.
Measurements of reflected electron energy loss spectrometry and x-ray photoelectron spectroscopy spectra for derivations of the energy loss function and source function for Au 4f photoelectrons
Authors: Yoshikawa Hideki , Irokawa Yoshihiro , Shimizu Ryuichi
Published: July 2002

An energy loss function for keV electrons from Au has been derived from reflected electron energy loss spectrometry spectra using a Landau formula modified to account for elastic scattering. The influence of the latter was analyzed using Monte Carlo analysis. The energy loss function was verified by using it for background subtraction of the Au 4f x-ray photoelectron spectroscopy spectrum according to Tougaard’s method. This approach led to a more reasonable source function, characterized by two satellite peaks. Herman–Skillman atomic orbital calculation, based on the Xα approximation, suggests these might correspond to shake-up peaks associated with the Au 6s→7s transition.
Generation and behavior of particulates in a radio frequency excited CH4 plasma
Authors: Yeon Chung-Kyu , Whang Ki-Woong
Published: July 2002

The behavior of particulates in a capacitively coupled, 13.56 MHz radio frequency (rf) excited CH4 plasma was investigated by time-resolved laser light scattering (LLS). The ballistic motion of the large particulates causes the LLS signal to fluctuate with peaks at the plasma sheath boundary. In an Ar plasma with a substrate which had been coated by diamondlike carbon film in the CH4 plasma process, a quasistatic particulate cloud formed and the LLS signal, the self-bias voltage, and the optical emission oscillated slowly, all with the same period. Also, the shape of the particulate cloud changed periodically. The time variation of the particulate’s mean size in the cloud was obtained by the angular dissymmetry measurement of scattered light intensities. The behavior of the particulates seemed to depend on the particulate size. The time-resolved plasma potential obtained from the heated, fast scanning Langmuir probe indicates that the formation of particulates influences the plasma state. The optical microscope and scanning electron microscopy were used to observe the morphology and the size of the particulates. Transmission electron microscopy and electron probe x-ray microanalysis studies indicate that they have an armorphous structure. Together with the observation of the collected particulates, the results of LLS studies showed that two different groups of particulates are generated in CH4 plasma. The optical emission spectra of the particulate-contaminated Ar plasma and the normal clean Ar plasma were obtained and compared. The difference between the two spectra indicates that the mean energy of the secondary electrons which come out of the powered electrode changes as a result of the interaction with the particulate cloud formed around the plasma-sheath boundary. The distribution of the particulate cloud was highly dependant on the rf power. The ion drag force due to the ambipolar diffusion flux from the central high plasma density region to the wall is thought to play an important role in particulate cloud distribution. A modified turn-off process is suggested to prevent particulates from falling on the wafer surface.
Microstructure and characterization of electron-trapping stimulable phosphor SrS:(Eu,Sm) thin film on glass
Authors: Hsieh T. J. , Revay R. , Brower D. , Chi P. H. , Simons D. S. , Newbury D. E. , Robey S. W.
Published: July 2002

Strontium sulfide doped with europium and samarium is an infrared stimulable phosphor that is being investigated as the active thin film layer of a photonic data storage disk. Lithium and fluorine can be added to the SrS:(Eu,Sm) to fully activate the photonic properties of the material, and care must be taken to ensure sufficient crystallite size, minimize structural defects within crystal grains, and maintain a uniform chemistry throughout the film thickness. In this article we present the initial stages of a study of the relationship of these properties to film performance. A number of techniques are employed including x-ray diffraction, electron probe x-ray microanalysis, transmission electron microscopy, and secondary ion mass spectrometry. Initial findings provide information on the effect of structural defects on film performance, and the importance of the mismatch in thermal coefficient of expansion between film and substrate.
Optical multilayer films based on an amorphous fluoropolymer
Authors: Chow Robert , Loomis Gary E. , Ward Raymond L.
Published: July 2002

Multilayered coatings were made by physical vapor deposition (PVD) of a perfluorinated amorphous polymer, Teflon AF2400, and with other optical materials. A high reflector for 1064 nm light was made with ZnS and AF2400. An all-organic 1064 nm reflector was made from AF2400 and polyethylene. Oxide (HfO2 and SiO2) compatibility with AF2400 was also tested. The multilayer morphologies were influenced by coating stress and unintentional temperature rises from the PVD process. Analysis by liquid nuclear magnetic resonance of the thin films showed slight compositional variations between the coating and starting materials of perfluorinated amorphous polymers.
Simple, efficient technique for exposing surfaces to hydrogen atoms
Authors: Bermudez V. M.
Published: July 2002

A device is described for the efficient generation of H atoms by thermal dissociation of H2. Hydrogen molecules exit a small hole in the wall of a Mo tube (with a solid end cap) and strike a hot W foil held at ∼45° to the flux. The sample is positioned to intercept the H-atom flux leaving the foil. The technique is demonstrated by exposing a Si (100)-(2×1) surface to the H-atom flux and the efficiency for producing the H-induced (2×1)→(1×1) conversion compared with that of the conventional approach using a W filament and a random H2 flux.
Surface chemical reaction between polycarbonate and kilo-electron-volt energy Ar+ ion in oxygen environment
Authors: Choi Won-Kook , Koh Seok-Keun , Jung Hyung-Jin
Published: July 2002

In order to improve wettability of polycarbonate to triple distilled water, an Ar+ ion and an oxygen ion were irradiated on a polycarbonate (PC) surface under various oxygen flow rates. Doses of ions were changed from 5×1014 to 5×1016 ion/cm2 in a range from 500 eV to 1.5 keV energy by a broad ion beam source. Wetting angle of PC was not reduced much with only Ar+ irradiation, but the wetting angle was significantly decreased by Ar+ ion irradiation with flowing oxygen gas and had a minimum of 12° by 1 keV Ar+ ion irradiation at oxygen flow rate of 4 sccm. Change in wettability by O+2 ion irradiation shows the similar feature as compared with those of Ar+ ion irradiation. In atomic force microscopy study, root mean square of surface roughness was changed from 14 to 22–27 Å by Ar+ ion irradiation, to 26–30 Å by Ar+ ion irradiation with the oxygen flow, but did not depend on amounts of ion fluence which indicates that the wetting angle change was not influenced by surface morphology. Improved wettability of modified polymer surface is explained in terms of a two-step process. Formation of hydrophilic groups on the polymer was identified by Fourier transform infrared and by the increase of carbonyl oxygen peak in O 1s x-ray photoemission spectroscopy spectra of PC in the sample modified by Ar+ ion irradiation with the oxygen flow.
Residual macroscopic stress in highly preferentially oriented titanium nitride coatings deposited on various steel types
Authors: Quaeyhaegens C. , Knuyt G. , Stals L. M.
Published: July 2002

The residual macroscopic stresses present in 1.5-μm-thick TiN coatings on martensitic hot work tool steel and austenitic stainless steel are studied with a Θ−2Θ decoupled x-ray diffractometer using glancing angle x-ray diffraction optics. All coatings exhibit a preferential orientation which complicates the interpretation of the conventional sin2 Ψ method. To overcome this complication, a method is used, called the fixed crystal orientation (FCO) sin2 Ψ method, in order to determine the mechanical stress in the presence of a symmetrically distributed preferential orientation. It is shown that in contrast to the glancing angle sin2 Ψ method and the conventional sin2 Ψ method interpretational problems resulting from elastic incompatibility can be avoided using the FCO method. In the TiN coatings studied a biaxial stress state can be assumed and different stress values are measured depending on the preferential orientation and the substrate material. The stress values obtained with the FCO sin2 Ψ method for the different samples are compared with the stress values obtained using the glancing angle sin2 Ψ method and the conventional sin2 Ψ method.
Negative ion density in inductively coupled chlorine plasmas
Authors: Hebner G. A.
Published: July 2002

Laser photodetachment spectroscopy has been used to infer the density of chlorine negative ions in an inductively coupled chlorine plasma. Time dependent, excess electron density produced by photodetaching electrons from Cl− was detected by a microwave interferometer operating at 80 GHz. By focusing the microwave probe beam through the center of the discharge, negative ion density measurements could be performed in a small, 1.5 cm3, volume. As the rf power into the plasma increased from 155 to 340 W at 20 mTorr, the Cl− density in the center of the bulk plasma increased from 3.4 to 5.2×1011 cm−3. As the pressure was increased from 15 to 50 mTorr at 240 W, the Cl− density increased from 3.5 to 5×1011 cm3. Over this parameter space, the negative ion density equaled the electron density to within a factor of 2. The negative ion radial distribution was relatively constant, with a 20% decrease in the center of the plasma for some operating conditions. When the surface of the bias electrode was changed from stainless steel to silicon, the electron density remained constant but the Cl− density decreased by a factor of 2 to 3.
Noncontact minority carrier lifetime measurement of Si and SiGe epilayers prepared by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition
Authors: Hwang Seok-Hee , Eo Yun-Phil , Seo Jung-Hyun , Whang Ki-Woong , Yoon Euijoon , Tae Heung-Sik
Published: July 2002

A 70 MHz inductively coupled rf bridge probe is used to measure the minority carrier lifetime of the Si and SiGe epilayers grown by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition (UHV-ECRCVD) at temperatures below 560 °C. Proper surface treatments before HF immersion are required for the accurate measurement of the bulk minority carrier lifetime. The effects of the process parameters such as the substrate dc bias, the distance of the ECR layer from the substrate, and the substrate temperature, including in situ surface cleaning, on the minority carrier lifetime of the Si and SiGe epilayers are examined by the rf bridge probe. It is confirmed that the rf bridge probe can monitor the epitaxial quality of low temperature Si and SiGe epilayers, making it an indispensable tool for the high quality device fabrication with Si and SiGe epitaxial layers grown by low temperature UHV-ECRCVD.
The dust direct current self-bias potential in a time varying plasma sheath
Authors: Melandso/ Frank , Nitter Tore , Aslaksen Torsten , Havnes Ove
Published: July 2002

We introduce an important physical effect, namely, the response of the dust particle charge to an oscillating electric field in a plasma sheath. The ac field may lower the average dust potential well below the corresponding floating potential Uf in a dc sheath. The resulting dust potential will be called the dust dc self-bias potential Udc and is generally a sensitive function of the ac potential amplitude and of the ratio ωch/ω between the so-called dust charging frequency ωch and the ac frequency ω. The difference between Udc and Uf maximizes for ωch≪ω and approaches 0 for ωch≫ω. We propose that the dust dc self-bias effect is important in all plasmas having a rapid potential variation and always has to be taken into account when calculating the charge and the force on dust particles in such plasmas. Since levitation of dust particles above surfaces normally requires negative dust particles, the dust dc self-bias effect may explain why some experiments indicate that levitation of dust particles is easier in rf discharges than in dc discharges.
Structure and properties of diamondlike carbon films produced by pulsed laser deposition
Authors: Voevodin A. A. , Walck S. D. , Solomon J. S. , John P. J. , Ingram D. C. , Donley M. S. , Zabinski J. S.
Published: July 2002

Pulsed laser deposition was used to produce hydrogen-free amorphous diamondlike carbon (a-C) and hydrogenated amorphous diamondlike carbon (a-C:H) from graphite and polycarbonate targets, respectively. Films were grown under identical conditions in high vacuum at low temperatures onto steel and Si substrates. The a-C films were uniform, while a-C:H films contained a great number of particles ejected from the target surface. The a-C films have hydrogen contamination about 0.1 at. %, while a-C:H have about 25 at. % H and 10 at. % O. High percentages of sp3 bonding were found in both films. Film densities were estimated to be 3.0 g cm−3 for a-C films and 2.2 g cm−3 for a-C:H films. Chemical and structural characteristics of the films were correlated with their thermal stability and mechanical properties. Temperatures for starting graphitization were about 500 °C for a-C and 350 °C for a-C:H. The presence of hydrogen reduced film hardness from 60 GPa for a-C films to 14 GPa for a-C:H films. Hydrogen was also associated with dependence of a-C:H films friction coefficient on environment and with higher wear rates of a-C:H films in comparison to a-C films.
Silicon-based group IV heterostructures for optoelectronic applications
Authors: Soref Richard A.
Published: July 2002

This article presents an overview of trends and progress in group IV heterostructures for optoelectronics. The outlook is good in electronics because the commercialization of SiGe/Si heterotransitors is proceeding nicely. However, the pace of progress is slower in SiGe/Si photonics. This article covers five innovative topics in an effort to enhance the development of heterostructure photonics: (1) band-gap studies of SiGeC, an alloy that can be lattice matched to Si, (2) direct-band-gap, strained heterostructures of GeSn upon GeSi/Si, (3) silicon-based quantum-well intersubband lasers (ISBLs) including SiGe/Si quantum-cascade, Raman, and inversionless ISBLs, (4) 1.5 μm ISBLs based on Si quantum wells with high barriers, such as heterosystems of Si/ZnS, and Si with SiO2/Si strained superlattice barriers, and (5) low-cost substrates of 3C SiC upon SiO2/Si, a platform for SiC heterodevices and for InGaN/AlGaN heterodevices.
Optical fiber structures studied by a tapping-mode scanning near-field optical microscope
Authors: Tsai Din Ping , Li Wen Kai
Published: July 2002

A tapping-mode scanning near-field optical microscope system with a bent optical fiber probe has been successfully developed to study the near-field optics at fiber end faces. Topographic and near-field intensity images of fiber end faces were obtained simultaneously. A brief and gentle etching process on fiber end faces in a saturated solution of ammonium bifluoride was able to reveal the structures of fibers. The topographic features generated by different local chemistry is closely related to the local doping concentration and the distribution of refractive index. The correlation between fiber structures and their near-field intensity profiles of propagating modes can be acquired directly by this novel method. Fibers of step-index, graded-index, single-mode, multimode, and circular, or noncircular geometry were imaged with a near-field resolution.
Near-field optical recording on the cyanine dye layer of a commercial compact disk-recordable
Authors: Tsai Din Ping , Guo Wen Rei
Published: July 2002

A tapping-mode near-field scanning optical microscope system with a bent optical fiber probe has been successfully developed to deliver the optical energy to the surface of cyanine dye layer of a commercial compact disk-recordable. The interference and damage result from the force-sensing laser beam can be avoided by using a bent fiber probe. Results of our optical writing showed the size of writing bits can be <40 nm. The estimated writing density may be 400 times higher than available commercially. We have also found the heating of metal coating at the end of fiber probe can perform thermal writing. Atomic force microscope images showed the raised edge of writing bits caused by this thermal writing effect. For the pure optical writing, we found the depth of writing bits should be controlled in a range less than the probe height maintained by the feedback electronics.
Mechanism of efficient carbon monoxide oxidation at Ru(0001)
Authors: Stampfl C. , Scheffler M.
Published: July 2002

We performed density-functional theory calculations using the generalized gradient approximation for the exchange-correlation functional to investigate the unusual catalytic behavior of Ru under elevated gas pressure conditions for the carbon monoxide oxidation reaction, which includes a particularly high CO2 turnover. Our calculations indicate that a full monolayer of adsorbed oxygen actuates the high rate, enabling CO2 formation via both scattering of gas-phase CO molecules as well as by CO molecules adsorbed at oxygen vacancies in the adlayer, where the latter mechanism is expected to be very efficient due to the relatively weak adsorption energy of both CO and O, as well as the close proximity of these reactants. We analyze the bonding and electronic properties associated with the reaction pathway for CO2 production via the scattering reaction. We find that the identified “bent” transition state is due to electron transfer into the unoccupied 2π orbitals of the CO molecule which reduces the Pauli repulsion between the impinging CO and the O-covered surface. Bond formation to CO2 then proceeds by electron transfer back from the CO 2π orbitals into the bonding region between CO and the adsorbed O atom.
Ultrahigh vacuum chemically assisted ion beam etching system with a three grid ion source
Authors: Hryniewicz John V. , Chen Y. J. , Hsu Shih Hsiang , Lee Chau-Han D. , Porkolab Gyorgy A.
Published: July 2002

A chemically assisted ion beam etching system has been developed which performs high quality, highly anisotropic etching of AlGaAs/GaAs at relatively low ion energies (200 eV). The use of three grid ion optics in a Kaufman ion source allows etching at low energies with reasonable rates without loss of profile verticality. All ultrahigh vacuum etching chamber construction with a high throughput turbomolecular pump and high vacuum loadlock provide routine high quality etching of AlGaAs without the use of etch chamber cryo panels or cryo pumps. Low ion energy and a clean vacuum environment permit the use of a single level, non hard baked photoresist mask. Benefits include high pattern resolution and fidelity, low mask erosion rate, good dimensional control, and easy, complete mask stripping as well as reduced substrate damage.
Essential points for precise etching processes in pulse-time-modulated ultrahigh-frequency plasma
Authors: Samukawa Seiji , Tsukada Tsutomu
Published: July 2002

Since ultrahigh-frequency (UHF) plasma has a low electron temperature (less than 2 eV) and uniform density, the effects of electron confinement due to the sheath potential barrier or plasma potential distributions are less prominent than with electron cyclotron resonance plasma or inductive coupled plasma. Consequently, multiple cusp magnetic fields are needed to maintain pulsed UHF plasma even at pulse intervals of a few tens of μs and they can significantly improve the etching rate and etching selectivity. Moreover, the characteristics of pulse-time-modulated plasma strongly depend on the substrate position from the generation region to the downstream region. Near the plasma generation region, pulsed plasma can be used to produce a higher rate and higher selectivity for polycrystalline silicon etching, compared with a continuous discharge. By transporting the plasma from the generation region to the downstream region, however, improvements in the etching characteristics of the pulsed plasma are gradually reduced.
Physical and optical properties of an antireflective layer based on SiOxNy
Authors: Gaillard F. , Schiavone P. , Brault P.
Published: July 2002

SiO x N y based materials were deposited at low substrate temperature (300 °C) and low pressure (0.6 Torr) in a plasma enhanced chemical vapor deposition reactor. The precursor gases were nitrous oxide (N2O) and silane (SiH4); the ratio of the two-gas concentration N2O/SiH4=α was a critical determinant of film structure and composition. An extensive analysis of SiOxNy based materials was carried out using Fourier transform infrared, and Rutherford backscattering, and Auger and ellipsometric spectroscopies. The two-phase structure of this material was deduced. This structure favors a high silicon film concentration and provides a sufficiently absorbing layer at photolithographic wavelengths (365, 248, and 193 nm). Thanks to its optical and physical properties silicon oxynitride constitutes a good antireflective layer for photolithographic applications.
Simulations of BCl3/Cl2 plasma in an inductively coupled gaseous reference cell
Authors: Choi Seung J. , Veerasingam Ramana
Published: July 2002

A gas mixture of BCl3/Cl2 is widely used in the microelectronics industry to etch the Al metal layers on semiconductor wafers. An understanding of the plasma chemistry is necessary and crucial to improve the uniformity and etch rate of the metal etch on the wafers. To study the plasma characteristics of metal etch reactors a two-dimensional numerical plasma reactor model is used to simulate the processing etching chemistry. The predictive capability of the model depends sensitively on the accuracy of the plasma chemistry mechanisms, the database, and the surface chemistry that are included in the model. First, the model is validated over a wide range of power, pressure, and gas compositions with the available experimental data. For low-pressure (few to tens of mTorr) etching reactors used in the semiconductor industry, the boundary conditions for the model are very important because of the relatively large gas mean-free paths. The gas phase chemistry is strongly influenced by the surface chemical processes. Unfortunately, the correct boundary conditions for the surface chemistry in the model are extremely difficult to set since the chamber wall condition is determined by the wall temperature, surface type (wall material and the covered chemical species), and the process history (wall coverage) of the reactor. The sensitivity of the surface condition is demonstrated with the aluminum etching chemistry in an inductively coupled plasma gaseous reference cell reactor geometry by performing numerical simulations with different wall recombination coefficients.
Diffusion bonding of steel to Ti-6Al-4V to produce hard wearing surface layers
Authors: Church S. C. , Wild R. K.
Published: July 2002

Titanium is a light, strong alloy used extensively in applications where weight saving is important. However, the surface does not resist abrasion with the result that it cannot be used in applications where the component must resist wear, such as gear components. Attempts to harden the surface, such as nitriding, have met with limited success. To produce a light component with a hard wearing surface, steel has been diffusion bonded to titanium. This has been done using a bench top diffusion bonding rig, operating in vacuum at temperatures up to 1273 K, which has been designed and built in house. Computer control allows predetermined stresses and strains to be carefully controlled. The diffusion bond has been achieved both without interlayers and with up to three interlayers of elements such as copper, vanadium and nickel. The diffusion bonding of both flat and grooved surfaces has been investigated. Results are presented showing the effect of stress, strain, surface finish and interlayers on the strength of the diffusion bond. In many cases bond strengths approaching that of the bulk matrix have been achieved. The microstructure of the interfaces have been characterized using optical metallography and scanning electron microscopy.
Effect of atomic hydrogen on Er luminescence from AlN
Authors: Pearton S. J. , Abernathy C. R. , MacKenzie J. D. , Hömmerich U. , Zavada J. M. , Wilson R. G. , Schwartz R. N.
Published: July 2002

AlN(Er) doped with Er during metal organic molecular beam epitaxy has been plasma hydrogenated in situ at 200–250 °C using an electron cyclotron resonance source. By isotopic substitution of H2 for H1, we have found from secondary ion mass spectrometry profiling that a 30 min hydrogenation treatment can incorporate ∼2×1019 cm−3 deuterium atoms to depths ⩾1 μm. The intensity of the 1.54 μm Er3+ luminescence is increased by a factor of ∼5 by the 200 °C hydrogenation, and this effect is thermally stable to 300 °C, indicating a binding energy of >1.5 eV for hydrogen at defects in the AlN. These defects would normally either be recombination centers or provide an alternative de-excitation path for the Er. We have previously found that AlN provides the best resistance to thermal quenching of Er luminescence of any semiconductor due to its wide bandgap. Together, these results suggest that AlN(Er) may be a promising material for optical control of devices such as light-triggered SiC or GaN thyristors for power switching applications, where a fiber-transmitted signal from temperature-tolerant material is necessary in controlling power distribution grids. Hydrogen does not leave the AlN until ∼800 °C and presumably forms an intermediate state such as H2 or larger clusters prior to evolution from the surface, and again this stability is among the best for any semiconductor.
Cell-based sensor microelectrode array characterized by imaging x-ray photoelectron spectroscopy, scanning electron microscopy, impedance measurements, and extracellular recordings
Authors: Jung D. R. , Cuttino D. S. , Pancrazio J. J. , Manos P. , Cluster T. , Sathanoori R. S. , Aloi L. E. , Coulombe M. G. , Czarnaski M. A. , Borkholder D. A. , Kovacs G. T. A. , Bey P. , Stenger D. A. , Hickman J. J.
Published: July 2002

We are developing a cell-based biosensor consisting of a planar microelectrode array that allows detection of extracellular potentials and their modulation in the presence of toxins or other active agents. To improve cell–electrode coupling, the microelectrodes were electroplated with platinum black. We report on the use of imaging x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), impedance measurements, and extracellular recordings to assess the effectiveness of this procedure. SEM provided highly detailed images of the shape and structure of well-formed deposits of thickness on the order of 1 μm or more. Because of its inherent high surface sensitivity, imaging XPS could reveal the presence of platinum deposits that were too thin to be detected by SEM. For typical, well-plated microelectrodes, impedance measurements showed reductions in the electrical resistance at 100 Hz from roughly 60 MΩ or more 1 MΩ. The overall electronic coupling of biopotentials to the microelectrodes was demonstrated by recordings obtained from beating rat myocytes and from rat spinal cord cells.
Large magnetoresistance effect in as-grown epitaxial LaxCa1−xMnO3 films prepared by a molecular beam epitaxy coevaporation technique
Authors: Miniotas A. , Karlsson U. O. , Brazdeikis A. , Chu C. W.
Published: July 2002

Thin films of LaxCa1−xMnO3 (0.64⩽x⩽0.68) have been grown by NO2-assisted molecular beam epitaxy on single crystal SrTiO3(100) and LaAlO3(100) substrates. As-grown films are found to be grown epitaxially, b-axis oriented on both SrTiO3 and LaAlO3 substrates, and exhibit a large magnetoresistance effect {[R(0)−R(H)]/R(H)×100} of about 1500% at 214 K. The magnetoresistance effect values obtained are similar to those reported for as-grown LaxCa1−xMnO3 (0.60⩽x⩽0.7) films synthesized either by so-called “block-by-block” or “layer-by-layer” molecular beam epitaxy techniques, but the effect appears at significantly higher temperatures. For epitaxial La0.68Ca0.32MnO3 films grown on SrTiO3 a relatively large resistance suppression of 200% at 1.0 T is observed.
In situ growth of evaporated TiO2 thin films using oxygen radicals: Effect of deposition temperature
Authors: Grahn J. V. , Linder M. , Fredriksson E.
Published: July 2002

The growth and characterization of TiO2 thin films deposited by electron-beam evaporation of TiO2 have been studied. The growing film was exposed to a flux of atomic oxygen supplied from an oxygen radical beam source at a total deposition pressure of 1×10−5 mbar. The properties of as-deposited 1000 Å thick films on silicon substrates have been studied in the growth temperature interval 100–680 °C. X-ray diffractometry demonstrated a phase evolution as a function of growth temperature, from amorphous (100 °C) to anatase (300 °C) and eventually rutile (680 °C). While the amorphous film surface had a smooth film surface as evidenced by atomic force microscopy, the anatase and rutile specimens exhibited a grain-like morphology. No apparent difference in surface roughness was observed between the anatase and rutile phase. Secondary ion mass spectrometry indicated that silicon diffused into the rutile film grown at the highest temperature. Ellipsometry measurements revealed that the crystallized films exhibited significantly larger refractive index and absorption than the amorphous film. Current–voltage (C–V) measurements demonstrated that the leakage was very high in the amorphous and anatase films (3–5 A/cm2 at 0.3 MV/cm). With increasing amount of rutile phase, the leakage current decreased resulting in a leakage current density of 70 nA/cm2 at an electrical field of 0.3 MV/cm for rutile films grown at 680 °C. High-frequency C–V measurements on rutile films resulted in typical metal-insulator- semiconductor behavior with a measured static dielectric constant of 39.
Improved formation of silicon dioxide films in liquid phase deposition
Authors: Huang C. J. , Houng M. P. , Wang Y. H. , Wang N. F. , Chen Jiann-Ruey
Published: July 2002

This work is to reveal the novel technique of liquid phase deposition silicon dioxide (SiO2) films which will increase the deposition rate and also improve the film quality. It is well known that deposition at a lower temperature without residual OH− on the substrate is difficult to achieve. Therefore, it is important to treat the substrate wafer before deposition. The substrate surface dipped into hydrofluoric acid (HF) is usually terminated with hydrogen (H) and has hydrides (Si–H) which react with water so that hydroxyls (Si–OH) can be obtained. No silicon dioxide can be grown on a clean Si substrate without native oxide. Therefore, a model is proposed to show that native oxide growth with chemical pretreatment of HF and ultrapure deionized water has rich hydroxyl (OH) molecules on surface in order to grow silicon dioxide. Another constant parameter, the growth rate of SiO2 is found to increase linearly with the time of reaction with ultrapure deionized water. At the same concentration of boric acid and hydrofluosilicic acid, the corresponding deposition rate of SiO2 is found to be about 70 Å/h larger than the films which are grown without reacting with chemical pretreatment of HF and ultrapure deionized water. In this study, the refractive index and deposition rate are found to be as high as 1.47 and 1400 Å/h, respectively. Good and reliable quality SiO2 film grown in this work was supported by various analytical techniques, such as Fourier transform infrared, Auger electron spectroscopy, refractive index measurement, etching rate measurement, and leakage current measurement.
Thermal desorption spectroscopy study of native and electron irradiated glycine overlayers on graphite(0001)
Authors: Löfgren P. , Krozer A. , Chakarov D. V. , Kasemo B.
Published: July 2002

The adsorption of glycine deposited at 95 K on the graphite basal (0001) plane was studied from submonolayer to multilayer coverages by thermal desorption spectroscopy (TDS) and high- resolution electron loss spectroscopy (HREELS). At all coverages glycine adsorbs in three-dimensional (3D) clusters (no distinct monolayer formation was observed). Glycine molecules desorb around 300 K in a single desorption peak (α peak) with a binding energy of 0.85 eV, representing the cohesive energy of glycine. HREELS analysis of these overlayers is severely hampered by charging of the 3D clusters; only one vibrational feature at 26 meV was observed reproducibly. The glycine adlayers are very sensitive to electron irradiation. This effect was studied in some detail by TDS. Electrons of ∼50 eV energy cause: (i) conversion of glycine molecules from the α state to (surprisingly) a more weakly bound β state (desorption temperature ∼250 K), interpreted as 2D adsorbates, and (ii) dissociation of glycine into fragments that either desorb spontaneously or adsorb on the bare graphite surface, and desorb upon heating (γ peak) at 170 K, i.e., earlier than both the α and β peaks. The cracking pattern of the γ peak suggests that the electrons break the C–C bond in glycine, into COOH and H2N–CH2 fragments.
Nanoindentation hardness, abrasive wear, and microstructure of TiN/NbN polycrystalline nanostructured multilayer films grown by reactive magnetron sputtering
Authors: Ljungcrantz H. , Engström C. , Hultman L. , Olsson M. , Chu X. , Wong M. S. , Sproul W. D.
Published: July 2002

TiN, NbN, and TiN/NbN polycrystalline nanostructured multilayer films were deposited on high-speed steel substrates by unbalanced reactive magnetron sputtering of Ti and Nb targets in Ar–N2 discharges. Two techniques were used for obtaining a series of multilayers with compositional modulation period, Λ, in the range 3.8–100 nm; rotation of a cylindrical substrate holder between two opposing cathodes or by positioning inclined cathodes above the substrate and using shutters. For the two setups, ions were accelerated from the discharge by a negative substrate bias Vs=120–150 V and Vs=100 V, respectively, with an ion-to-metal arrival rate ratio of ∼1. The nanoindentation hardness and abrasive wear resistance by dimple grinding test of the coatings were compared between the sample series and related to the microstructure, phase composition, and residual stress σres obtained by transmission electron microscopy, x-ray diffraction, and substrate curvature technique, respectively. All films exhibited a dense and columnar microstructure with 20–90 nm grain sizes. Nanoindentation test of the high-Vs series showed similar hardness for TiN/NbN nanostructured multilayers and homogeneous films in the range of 32–34 GPa. For the low-Vs series, mixed-phase hexagonal β-Nb2N/cubic δ-NbN films exhibited the highest hardness of 39 GPa, TiN had the lowest hardness with 26 GPa, and TiN/NbN multilayers had values in between. The absence of superlattice hardening in the polycrystalline TiN/NbN nanostructured multilayer is suggested to be due to microcracking at grain boundaries under the indentor tip. For both series, σres was lower for the multilayers than the corresponding homogeneous films. The low-Vs multilayers exhibited σres⩽1.6 GPa for Λ⩽16.6 nm, more than a factor of 2 smaller than for homogeneous TiN, NbN, and TiNbN-alloy films. High-Vs multilayers had σres∼4 GPa. The abrasive wear resistance of films between sample series showed a negative correlation with grain size. Films of the high-Vs series exhibited higher wear resistance compared to the corresponding films of the low-Vs series. Wear constants of high-Vs β-Nb2N films and TiN/NbN multilayers were as low as 28 and 40 μm3 mm−1 N−1, respectively.
Ion energy distribution functions in inductively coupled radio-frequency discharges—Mixtures of Cl2/BCl3/Ar
Authors: Nichols C. A. , Woodworth J. R. , Hamilton T. W.
Published: July 2002

We have used a gridded energy analyzer to measure positive ion energy distributions and fluxes at the grounded electrode of a high-density rf discharge. We present details of ion energies and fluxes in discharges containing mixtures of chlorine, boron trichloride and argon. These feedstock mixtures have been used extensively in the patterning of metal films for semiconductor interconnects. Our experiments were carried out in a Gaseous Electronics Conference Reference Cell which had been modified to produce inductively coupled discharges. The 15-cm-diam bottom electrode was grounded for these experiments. Stainless steel, anodized aluminum, and silicon were used as bottom electrode materials to understand the effects of various chamber boundary conditions on the ion energy parameters. In most cases, the ion energy distributions had a single peak, well separated from zero energy with a 1.0–3.0 eV full width at half maximum. These peaks were typically centered at 12–16 eV, with ion energy increasing as pressure decreased. Addition of BCl3 to a Cl2 discharge resulted in a reduction of total ion flux of more than a factor of 2, e.g., from 5 to 2.5 mA/cm2 (20 mTorr, 200 W). The ion fluxes decreased with increasing pressures in BCl3/Cl2 mixtures, while increasing with pressure in pure Cl2 discharges. Addition of Ar to several mixtures of BCl3/Cl2 changed the ion fluxes and mean ion energies by less than 15%. At high pressures or low inductive rf powers, the distributions can split into two overlapping peaks separated by as much as 8 eV. This splitting is indicative of capacitive coupling between the rf coil and the discharge. Insertion of a Faraday shield between the coil and the discharge removed most of the splitting.