bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of the cantilever beam technique for stress measurement during the physical vapor deposition process
Authors: Moulard G. , Contoux G. , Motyl G. , Gardet G. , Courbon M.
Published: July 2002

An improvement of an optical method for in situ measurement of the intrinsic stress in thin films is described. The method presented is based on the well-known beam bending technique using the deflection of a laser beam that reflects itself on a sample. The first new development lies in the evaluation of the bending plate equation. The second uses image processing to determine the deformation of the sample. The method has been applied to pure chromium films on glass substrates to validate the stress measurements. The reproducibility of stress measurement is of about 8%. Results show the great adaptability of the technique to any kind of stress evolution during the physical vapor deposition process and give additional information about the evolution of stress versus film thickness, in comparison with ex situ techniques. Finally, a correlation between stress measurement and microstructure has been carried out.
Effects of argon addition to a platinum dry etch process
Authors: Milkove K. R. , Coffin J. A. , Dziobkowski C.
Published: July 2002

The influence of Ar addition to a Cl2/CF4 dry etch gas mix on the etch character of patterned Pt films is evaluated. The incremental substitution of Ar for Cl2 is shown to be detrimental to the Pt etch process by enhancing the severity of redeposits that form on the sidewalls of the fully etched structures. In addition, the water solubility of this redeposited layer diminishes with increasing Ar concentration. Ultimately, the residue becomes insoluble when Cl2 is eliminated from the gas mix. This residue dependence on Ar concentration is accompanied by a decrease in the etch rate of the Pt film layer. In order to clarify that the Ar concentration directly contributed to this decrease, additional etch rate measurements were made on blanket Pt films. First, the etch conditions used for the patterned samples were repeated. Then, a second set of measurements were made with CF4 excluded from the gas mix. In both instances, the etch rate of Pt decreased as the percentage of Ar rose. Since the blanket film results were similar to those obtained from the patterned samples, we conclude that neither redeposition of photoresist from the mask or plasma deposition of CF4 cracking fragments strongly influence the observed Pt etch behavior.
Visualization of etching mechanisms of a vicinal Cu surface using scanning tunneling microscopy
Authors: Nakakura C. Y. , Altman E. I.
Published: July 2002

The reaction of Br2 with a Cu surface vicinal to (100) was studied by recording scanning tunneling microscopy (STM) movies during exposure to Br2. Initial exposure to Br2 resulted in the formation of a chemisorbed layer of Br atoms with a c(2×2) structure on the (100) terraces. The STM movies showed that, as the chemisorbed layer saturated, thermal fluctuations in the step positions slowed, and the steps aligned parallel to the [001] and [010] directions. Further exposure to Br2 resulted in the formation of CuBr; the STM movies showed that the Cu atoms were consumed from the steps with the reaction proceeding predominantly perpendicular to the step edges. Channels created in the step edges indicated that the reactivity of the steps was not uniform. The CuBr formed by the reaction did not accumulate at the sites where the Cu atoms were consumed; rather, large two-dimensional CuBr islands were observed at seemingly random locations. This indicated that CuBr formed at the step edges was mobile and that the CuBr islands formed by nucleation of diffusing CuBr species. The CuBr islands spanned many steps suggesting that the diffusing CuBr can cross step edges. Atomic-resolution images of the CuBr islands revealed hexagonal symmetry consistent with CuBr(111) parallel to the surface.
Platinum complex/Zn-porphyrin macrosystem assemblies: Electronic structure and conformational investigation by x-ray photoelectron spectroscopy
Authors: Polzonetti G. , Ferri A. , Russo M. V. , Iucci G. , Licoccia S. , Paolesse R.
Published: July 2002

In this study we used x-ray photoelectron spectroscopy (XPS) to characterize newly synthesized platinum/zinc-porphyrin assemblies. Our investigation provides information both on the electronic structure and on the composition and conformation of the linked systems. In particular, the N 1s and Pt 4f7/2,5/2 spectra reveal the presence of a charge transfer interaction between the two subunits in which the charge flows from the Zn-porphyrin towards the platinum unit. Analysis of the Cl 2p3/2 core level electrons has led to a greater understanding of the conformational structure of these systems, verifying the occurrence of cis-trans isomerization from the pristine platinum complex to the linked assemblies, or the persistence of the conformation of the precursor platinum complex. We used XPS quantitative evaluation of the atomic ratios to estimate the subunit ratio between the Zn-porphyrinato and the Pt complex and also identified a platinum linked tetramer. The XPS results are consistent with nuclear magnetic resonance, infrared and matrix assisted laser desorption ionization spectroscopy.
Study of the SiO2-to-Si3N4 etch selectivity mechanism in inductively coupled fluorocarbon plasmas and a comparison with the SiO2-to-Si mechanism
Authors: Schaepkens M. , Standaert T. E. F. M. , Rueger N. R. , Sebel P. G. M. , Oehrlein G. S. , Cook J. M.
Published: July 2002

The mechanisms underlying selective etching of a SiO2 layer over a Si or Si3N4 underlayer, a process of vital importance to modern integrated circuit fabrication technology, has been studied. Selective etching of SiO2-to-Si3N4 in various inductively coupled fluorocarbon plasmas (CHF3, C2F6/C3F6, and C3F6/H2) was performed, and the results compared to selective SiO2-to-Si etching. A fluorocarbon film is present on the surfaces of all investigated substrate materials during steady state etching conditions. A general trend is that the substrate etch rate is inversely proportional to the thickness of this fluorocarbon film. Oxide substrates are covered with a thin fluorocarbon film (<1.5 nm) during steady-state etching and at sufficiently high self-bias voltages, the oxide etch rates are found to be roughly independent of the feedgas chemistry. The fluorocarbon film thicknesses on silicon, on the other hand, are strongly dependent on the feedgas chemistry and range from ∼2 to ∼7 nm in the investigated process regime. The fluorocarbon film thickness on nitride is found to be intermediate between the oxide and silicon cases. The fluorocarbon film thicknesses on nitride range from ∼1 to ∼4 nm and the etch rates appear to be dependent on the feedgas chemistry only for specific conditions. The differences in etching behavior of SiO2, Si3N4, and Si are suggested to be related to a substrate-specific ability to consume carbon during etching reactions. Carbon consumption affects the balance between fluorocarbon deposition and fluorocarbon etching, which controls the fluorocarbon steady-state thickness and ultimately the substrate etching.
Gas source MBE of InP and GaxIn1−xPyAs1−y : Materials properties and heterostructure lasers
Authors: Panish M. B. , Temkin H. , Sumski S.
Published: July 2002

The growth of useful GaxIn1−xPyAs1−y by MBE is inhibited by the difficulty in maintaining precise control over the flux from condensed source As and P effusion ovens. The use of P2 and As2 beams generated from the cracking of PH3 and AsH3 as an alternative approach is reviewed and new data are presented. Accommodation coefficients were determined for P2 and As2 on heated InP and GaAs surfaces. The flux composition as a function of epitaxial layer composition was determined for the lattice-matching quaternary. Studies of doping were done and injection laser structures were grown. Although detailed studies of layer composition control were not done, the achievable control seems quite adequate for injection lasers. A variety of heterostructure lasers emitting at nominally 1.5 μm with broad area 300-K threshold-current densities from 1300 to 2400 A/cm2 were demonstrated. Ridge waveguide lasers fabricated from the same wafers had Ith of about 40 mA and differential efficiencies of 36%–45%. They lased cw to 50 °C.
Computer simulation of current density profiles in focused ion beams
Authors: Ward J. W. , Utlaut M. W. , Kubena R. L.
Published: July 2002

We have made a computer simulation of the target current density in our single-lens focused ion beam column. This column images at unity magnification the virtual source of a liquid metal ion source. We simulate the nonlaminar properties of the emitted ions with a two-dimensional function f (r,r′) that represents the phase space density distribution of the beam, where r and r′(dr/dz) are the radial position and slope, respectively, in the aperture plane. This analysis further shows how f (r,r′) can be described in terms of the experimentally measured target current density profile.
X-ray sources for microlithography created by laser radiation at λ=0.26 μm
Authors: Pépin H. , Alaterre P. , Chaker M. , Fabbro R. , Faral B. , Toubhans I. , Nagel D. J. , Peckerar M.
Published: July 2002

We discuss the conversion efficiency and spectral characteristics of x-ray sources produced by focusing 0.26 μm radiation on targets. We optimize the x-ray emission in given spectral ranges by choosing the appropriate target atomic number and irradiation conditions. We study the exposure of PBS photoresist with well characterized subkilovolt and kilovolt x-rays and find the sensitivity as well as the contrast of the resist increase with subkiloelectron volt radiation. The results confirm that the value of x-ray energy per unit volume absorbed at the resist surface is approximately independent of wavelength. A model for the development rate is also proposed to reproduce the experimental data.
Mass-spectrometric determination of antimony incorporation during III–V molecular beam epitaxy
Authors: Evans K. R. , Stutz C. E. , Yu P. W. , Wie C. R.
Published: July 2002

The antimony incorporation rate α(Sb) during molecular beam epitaxy (MBE) of GaAs1−ySby, AlAs1−ySby, and Al0.5Ga0.5As1−ySby is determined as a function of growth conditions via mass-spectrometric measurements of the nonincorporated fraction of the incident antimony flux. The observed trends of an increase in Sb incorporation rate with decreasing substrate temperature and increasing group III flux, and an increase in resulting Sb content with Sb flux, are found to be in agreement with previous studies using ex situ techniques only. Additionally, the process of GaAsSb on GaAs interface formation is shown to result in a time dependent α(Sb) and is understood on the basis of a surface Sb-content dependent Sb desorption rate. Similarly, the Sb desorption rate is found to be time dependent when an incoming Sb flux reacts with a growth interrupted GaAs surface to form a GaAsSb surface layer which is likely to be graded in composition.
Defects in alkylcyanobiphenyl molecular crystals studied by scanning tunneling microscopy
Authors: Smith D. P. E.
Published: July 2002

The ordering of alkylcyanobiphenyls liquid crystals grown on graphite and MoS2 is examined using scanning tunneling microscopy. The molecules are seen to form a rigid two-dimensional molecular lattice with properties similar to a crystalline solid. The molecular film is free of defects over distances of hundreds of nanometers. Monoatomic steps in the substrate and grain boundaries and screw dislocations in the adsorbate molecular lattice are observed. Both the ordering and the defects are successfully analyzed taking into account the registry of the molecules with the underlying substrate.
Morphology of initial growth stages and tunneling spectroscopy of electropolymerized polyaniline thin films
Authors: Jeon D. , Kim J. , Gallagher M. C. , Willis R. F. , Kim Y.-T.
Published: July 2002

The morphology of polyaniline electrochemically deposited onto a thermally evaporated gold electrode substrate has been investigated in the nucleation stages using scanning tunneling microscopy. The films are grown in the galvanostatic mode at 70 μA/cm2 current density for 25, 50 and 100 s durations and the topography is measured in air. The results show that for films deposited for 25 s, the coverage of nuclei on the electrode is sparse, but the nuclei of various shapes tend to connect in partial coalescence. For the 50 s deposition, the population of nuclei increases significantly resulting in high surface coverage, but nuclei still retain their original features. After 100 s deposition, a homogeneous film is obtained. The electronic properties of the fully protonated emeraldine salt form of polyaniline are also studied by tunneling spectroscopy. An 1100 Å thick film is prepared electrochemically and the I/V curves are measured at many different positions on the film. The preliminary results show that the π–π* gap is 4 eV which agrees with the results of optical absorption spectroscopy. The tunneling conductance at the Fermi level is finite and changes spatially, suggesting that the observed results are consistent with metallic behavior of a single polaron lattice model.
Scanning tunneling microscopy of various graphitic surfaces
Authors: Siperko L. M.
Published: July 2002

Scanning tunneling microscopy, on atomic scale and larger, was used to study the surface structure of highly oriented pyrolytic graphite (HOPG), pyrolytic graphite (PG), benzene-derived graphite (BDG), and triphenylene-derived graphite. Good registry of the (0001) surface of PG and BDG was determined by comparison with HOPG. Using a large-scale scan (1 μm), steps, crystallite sizes, and other large features were compared. Highly symmetric hexagonal etch pits a few hundred nm in width and tens of nm deep, representing the nm scale effects of oxidation, were observed on the surface of BDG.
Scanning force/tunneling microscopy of a graphite surface in air
Authors: Sugawara Y. , Ishizaka T. , Morita S.
Published: July 2002

We discuss atomic resolution imaging of a graphite surface in air by simultaneously measuring repulsive contact forces and surface conductance with the scanning force/tunneling microscope (AFM/STM) under two types of operating modes: the constant height mode and the constant current mode. We also discuss the coherence of the images during simultaneous imaging with the AFM/STM, and further clarify the measurement condition for simultaneous imaging.
A low magnification focused ion beam system with 8 nm spot size
Authors: Kubena R. L. , Ward J. W. , Stratton F. P. , Joyce R. J. , Atkinson G. M.
Published: July 2002

A 50 keV Ga+ beam has been focused to a spot diameter of 8 nm (full width at half-maximum) in our two-lens microprobe system by reducing the contributions of both chromatic aberration and the virtual ion source size to the final image size. Features as small as 6 to 8 nm were distinctly visible in scanning ion images. To our knowledge, this is the smallest focused beam of ions produced to date. The limiting resolution in 30-nm thick films of poly(methylmethacrylate) exposed with this beam was approximately 8 to 10 nm. Effects such as ion scattering, atomic recoil, and statistical dose fluctuations during exposure are believed to set inherent limits to the lithographic resolution.
Simulation of the microstructure of chemical vapor deposited refractory thin films
Authors: Dew S. K. , Smy T. , Brett M. J.
Published: July 2002

A ballistic deposition model (SIMBAD) has been extended to provide qualitative cross-sectional depictions of the microstructure present in chemical vapor deposited (CVD) films. The model qualitatively depicts the pronounced columnar structure typical of refractory metal, nitride, and silicide films−especially when deposited over integrated circuit topography. The important factors affecting thin film microstructure are seen to be flux shadowing, precursor surface diffusion, and a nonunity sticking coefficient. While the conformal step coverage typical of refractory CVD films is primarily due to a low sticking coefficient, the detailed columnar structure is the result of all three of these mechanisms. The angular distribution of the incident precursor flux is important to the shadowing mechanism, and a sticking coefficient-dependent angular distribution relevant to CVD is presented. Variations of the model to represent selective deposition (including selectivity loss) are also shown.
In situ core-level photoelectron spectroscopy study of indium segregation at GaInAs/GaAs heterojunctions grown by molecular-beam epitaxy
Authors: Larive M. , Nagle J. , Landesman J. P. , Marcadet X. , Mottet C. , Bois P.
Published: July 2002

In situ ultraviolet photoelectron spectroscopy (UPS) measurements have been performed at GaInAs/GaAs (100) interfaces. The high depth resolution of the UPS technique applied to the specific case of GaInAs/GaAs heterostructures [core-level photoelectron escape depth λ≊2.1 monolayers (MLs)] is shown, yielding quantitative informations on the Ga/In atomic profiles at the ML scale. A surface segregation model is developped and the phenomenological segregation energy is obtained by UPS. This energy is used to generate potential energy profiles in a calculation of the energy of photoluminescence (PL) lines in GaInAs/GaAs quantum wells; the quantitative agreement with measured PL lines is very good.
Junction locations by scanning tunneling microscopy: In-air-ambient investigation of passivated GaAs pn junctions
Authors: Tseng Wen F. , Dagata John A. , Silver Rick M. , Fu Joseph , Lowney Jeremiah R.
Published: July 2002

Scanning tunneling microscopy (STM) and atomic force microscopy operating in air have been used to investigate locations of molecular-beam epitaxially grown GaAs multiple pn junctions cleaved and passivated with P2S5. Symmetrically and asymmetrically doped junctions were prepared within topographically delineated AlAs/GaAs marker regions for this in-air study of electronic junction contrast. Our results indicate that the STM-delineated junction locations do not coincide with the electrical junction locations, but rather shift into the p-type regions.
Magnetic force microscopy on high-T
c superconductors
Authors: Moser A. , Hug H. J. , Fritz O. , Parashikov I. , Güntherodt H.-J. , Wolf T.
Published: July 2002

We demonstrate that magnetic force microscopy is able to detect the superconducting state and to distinguish between the Meissner and Shubnikov phase of a high temperature superconductor. In the Meissner phase we observe an increasing, repulsive force with decreasing tip-to-sample distance. The force depends on the screening current density and therefore on the London penetration depth. Indeed, we detect a decrease in the maximum force as the temperature increases. In the Shubnikov phase a different behavior is observed. If the tip is approached staircase-like to a superconductor the repulsive force first increases and then decays rapidly. The superconductor has reacted to the increased stray field of the tip by readjusting the vortex structure to lower the total energy. The experiments are discussed in relation to existing theoretical predictions. We point out that magnetic force microscopy might become an important tool to directly observe the vortex structure and its complex phase transitions.
Scaling of emission currents and of current fluctuations of gated silicon emitter ensembles
Authors: Busta H. H. , Pogemiller J. E. , Zimmerman B. J.
Published: July 2002

The scaling of emission currents and of their corresponding current fluctuations of ensembles of gated, monocrystalline silicon emitters ranging from n=1 to n=20 800 emitters have been investigated. For randomly selected ensembles, the current scales approximately with n and the fluctuation with n−0.16. For selected ensembles of identical emission behavior, the current scales with n and the fluctuations with n−0.5 as is expected from theory. The discrepancy in the exponent for the scaling of the current fluctuations is caused by the poor participation of the emitters within an ensemble. Only a few emitters per ensemble contribute to the total current. The scaling behavior can thus be used as a diagnostic tool to evaluate a given process. The measurements were performed at room temperature and at pressures of approximately 1×10−8 Torr.
Design of an atomic force microscope with interferometric position control
Authors: Schneir J. , McWaid T. H. , Alexander J. , Wilfley B. P.
Published: July 2002

Advances in the manufacture of integrated circuits, x-ray optics, magnetic read–write heads, optical data storage media, and razor blades require advances in ultraprecision metrology. Each of these industries is currently investigating the use of atomic force microscopy (AFM) to improve the precision and accuracy of their manufacturing process control. To facilitate the use of AFMs for manufacturing we have developed an AFM capable of making accurate dimensional measurements. We call this system the calibrated AFM (C-AFM). The C-AFM has been constructed as much as possible out of commercially available components. We use a flexure stage driven by piezoelectric transducers for scanning, a heterodyne interferometer to measure the X and Y displacements of the sample, a capacitance sensor to measure the Z displacement of the sample, and a commercially available AFM control system. The control system has two feedback loops which read from the X and Y interferometers, respectively, and adjust the piezoelectric voltages to keep the X-Y scan position accurate. The critical electromechanical and metrology issues involved in the construction and operation of such a system will be discussed in detail.
Investigation of electron source and ion flux uniformity in high plasma density inductively coupled etching tools using two-dimensional modeling
Authors: Ventzek Peter L. G. , Grapperhaus Michael , Kushner Mark J.
Published: July 2002

Inductively coupled plasma (ICP) sources are being developed as reactors for high plasma density (1011–1012 cm−3), low-pressure (<10–20 mTorr) etching of semiconductors and metals for microelectronics fabrication. Transformer coupled plasmas (TCPs) are one variant of ICP etching tools which use a flat spiral coil having a rectangular cross section powered at radio frequencies (rf) to produce a dense plasma in a cylindrical plasma chamber. Capacitive rf biasing of the substrate may also be used to independently control ion energies incident on the wafer. The uniformity of generating the plasma and the uniformity of the flux of reactants to the substrate are functions of the geometry and placement of the coil; and of the materials used in the construction of the chamber. In this article, we use results from a two-dimensional model to investigate design issues in TCPs for etching. We parametrize the number of turns and locations of the coil; and material properties of the reactor. We find that at low pressure, designs which produce ionization predominantly at larger radii near the edge of the wafer produce more uniform ion fluxes to the substrate. This results from a ‘‘converging’’ ion flux which compensates for losses to lateral surfaces. Careful attention must be paid to metal structures in the vicinity of the coils which restrict the azimuthal electrical field. This situation results in reduced power deposition at large radii, which can be compensated by over sizing the coil or by using auxiliary solenoidal coils. The plasma and neutral transport, dominated by diffusion, treats the advective flow from the gas inlets and pump port as local sources and sinks which are rapidly volume averaged.
Morphology of anodically etched Si(111) surfaces: A structural comparison of NH4F versus HF etching
Authors: Houbertz R. , Memmert U. , Behm R. J.
Published: July 2002

We present a comparative scanning tunneling microscopy (STM) study on the porous layer formation in two different fluoride containing solutions, HF/ethanol and concentrated NH4F solution. After etching in dilute HF solution the samples display a high density of micropores with typical diameters ranging from 5 to 25 nm, while NH4F treated surfaces display shallow macropores of several hundred nm in diameter. These structural differences are discussed by comparing the different activity of both solutions for chemical etching of Si in the absence of an external potential, which provides an additional reaction channel also under anodic conditions.
Optical properties of InAs/InP surface layers formed during the arsenic stabilization process
Authors: Tabata A. , Benyattou T. , Guillot G. , Gendry M. , Hollinger G. , Viktorovitch P.
Published: July 2002

Optical characterization has been performed on the InAs/InP surface layer in order to study the arsenic (As) stabilization process of InP. The InAs layers are formed by the simple exchange of phosphorus (P) from the InP surface substrate by arsenic. Samples prepared under arsenic overpressure in the temperature range 450–600 °C have been examined. Luminescence from the InAs layer which acts as a surface quantum well has been detected. We have compared this emission with theoretical calculations and reasonable agreement was observed. Moreover, we have determined that when the arsenic stabilization temperature increases the InAs thickness increases as a consequence of P–As exchange and that after the replacement of the five first top monolayers this exchange seems to stop. We explain this result in terms of the shield effect of the InAs overlayers which efficiently cap the InP substrate against further P evaporation and the restoration of surface structural order which limits any other phosphorus exodiffusion. Comparing our results with those of x-ray photoelectron spectroscopy measurements we have concluded that on samples treated at high temperatures, three-dimensional InAs islands are formed.
Characterizing wearout, breakdown, and trap generation in thin silicon oxide
Authors: Dumin D. J. , Maddux J. R. , Subramoniam R. , Scott R. S. , Vanchinathan S. , Dumin N. A. , Dickerson K. J. , Mopuri S. , Gladstone S. M. , Hughes T. W.
Published: July 2002

It has been shown that trap generation inside thin oxides during high voltage stressing can be coupled to time-dependent-dielectric-breakdown distributions through the statistics linking wearout to breakdown. Since the traps play a crucial role in the wearout/breakdown process, it is important to understand the properties of these traps. Oxides with thicknesses between 2.5 nm and 22 nm have been studied with emphasis on oxides in the 6 nm to 13 nm thickness range. The cross-section of the traps responsible for the scattering of electrons in the tunneling barrier, the thickness dependence of measured trap density, the spatial and energy distribution of the traps, and the charging/discharging properties of the traps have been measured.
Fabrication and characterization of quantum wire transistors with Schottky in-plane gates formed by an in situ electrochemical process
Authors: Hasegawa Hideki , Hashizume Tamotsu , Okada Hiroshi , Jinushi Keiichiro
Published: July 2002

Novel Schottky in-plane gate (IPG) quantum wire transistors were fabricated for the first time, and their transport properties were investigated. For fabrication of transistors, an AlGaAs/GaAs quantum well wire (QWW) was produced by etching, and platinum IPG electrodes were directly formed on both edges of the QWW by a new in situ electrochemical process. The current–voltage (I–V) characteristics of the fabricated long-channel and short-channel devices exhibited good field effect transistor operation at 3–300 K. Simple theoretical models assuming either a constant mobility or a constant velocity were developed. They provide a reasonably good phenomenological description of the observed I–V characteristics. Limitations of the models are also discussed. At low temperatures, the short-channel device exhibited sharp quantized conductance steps in the units of 2e2/h near pinch-off, indicating one-dimensional ballistic quantum transport. The first plateau of the conductance step remained visible up to 40 K, which is the highest reported so far for the AlGaAs/GaAs system.
Calculations for an experiment for determining the duration of quantum tunneling with a laser-illuminated field emitter
Authors: Hagmann Mark J.
Published: July 2002

Previous experiments with heterostructures and Josephson junctions suggest that quantum tunneling has a specific duration. We have used four different methods to simulate laser-illuminated field emission with the Fowler–Nordheim (one-dimensional) model for the static potential. The emitted current varies with the wavelength of the laser, having a small asymptotic increase at large wavelengths and a resonance that is centered at the wavelength for which the period of the laser equals twice the semiclassical time for barrier traversal. These results suggest that the laser-induced increase in the emitted current may be used as the basis for determining the duration of quantum tunneling. We will make pulsed measurements with lasers at several different wavelengths in order to examine these effects and to separate them from competing phenomena.
Cathodic arc ion implantation for semiconductor devices
Authors: Xia Z. , Chan C. , Meassick S. , Purser R.
Published: July 2002

Cathodic arc ion implantation was used to make n+–p junction diodes and n-channel metal–oxide–semiconductor (MOS) transistors. Antimony, with a dosage in the range of 6×1014 to 4×1015 ions/cm2, was implanted as the n-type dopant into p-type 〈100〉 oriented silicon with a resistivity in the range of 2–5 Ω cm. The implantation voltage applied to the substrate was approximately −20 kV. Regular thermal oxidation and photolithography techniques were used in making the devices. The I–V characteristics of both diodes and transistors and the reverse breakdown of the n+–p junction were found to be comparable to the devices made by diffusion under similar conditions. The standard deviation of the sheet resistance of the implanted layer across a 3 in. wafer was found to be less than 4% of the average value. The implantation dosage and distribution characteristics were estimated by secondary ion mass spectrometry (SIMS) and Rutherford backscattering spectrometry (RBS) measurements. The experimental results were found to agree with numerically calculated values. The ion charge state of the arc plasma was extracted by comparing the experimental results and numerical results.
Electron cyclotron resonance plasma etching of silicon dioxide for deep-submicron ultralarge scale integrations
Authors: Nojiri Kazuo , Iguchi Eri
Published: July 2002

Silicon dioxide etching technology for deep-submicron ultralarge scale integration has been developed using an electron cyclotron resonance (ECR) plasma etcher. The optimum conditions for silicon dioxide etching are obtained in terms of etch rate, geometrical controllability, and radiation damage by fully utilizing such advantages of the ECR plasma etcher as low-pressure operation, high plasma density, and independent control of ion energy and plasma discharge. High selectivity is also found at low pressures with C4F8/CH3F. The technology has been successfully applied to the formation of 0.35 μm contact holes with an aspect ratio of 4 without a decrease in etch rate.
Dry sequential process of photochemical etching and surface passivation of In0.52Al0.48As using HBr and H2S
Authors: Habibi Soheil , Totsuka Masahiro , Tanaka Jun , Matsumoto Satoru
Published: July 2002

In order to improve the Schottky diode characteristics of metal-In0.52Al0.48As, a new dry photochemical etching and sulfur passivation process has been developed. Excimer and deep UV lamps were used for photochemical etching and surface passivation, respectively. Auger electron spectroscopy measurement shows that this passivation process is as good as wet (NH4)2Sx and P2S5/(NH4)2S passivation in terms of sulfur coverage. Schottky diodes were fabricated on n-In0.52Al0.48As by electron beam evaporation of a multilayer metal contact of the form Mo/Ti/Pt/Au (2/30/300/200 nm). The leakage current has been reduced by three orders of magnitude after applying this passivation process. X-ray photoelectron spectroscopy measurements illustrate that these free S* radicals are capable of replacing As–O and In–O bonds to As–S and In–S bonds. The conclusion is that the As–O and In–O bonds are the primary causes of leakage current. These bonds are dissolved after this photochemical sulfur surface passivation.
Use of Ti in ohmic metal contacts to p-GaAs
Authors: Ren F. , Abernathy C. R. , Pearton S. J. , Lothian J. R.
Published: July 2002

A sacrificial Ti layer on electron-beam deposited AuBe ohmic metallization to p-type GaAs is shown to prevent oxidation of Be that segregates to the surface of the AuBe during its deposition. In the absence of this Ti layer, the oxidation of the surface Be upon removal from the vacuum chamber creates a current blocking layer on the overlayer contact. For nonalloyed ohmic contacts to p-GaAs, Ti/Pt/Au metallization is found to be superior to Ti/Ag/Au because of its thermal stability and the fact that Au–Ag alloys have higher resistivities than either of the pure component metals. For the sputtered refractory metals, surface displacement damage to GaAs during sputter deposition of W or WSix can be prevented by protecting the semiconductor with a thin (400 Å) Ti layer. This is particularly relevant for heterojunction bipolar transistors and other devices that cannot be annealed at the high temperatures (800 °C) needed to remove displacement damage.
Field emission characteristics of transition-metal nitrides
Authors: Endo Michiaki , Nakane Hideaki , Adachi Hiroshi
Published: July 2002

Transition-metal nitrides seem to have good field emission characteristics, but their field emission properties are not well known. NbN, Nb2N, TiN, and ZrN emitters were fabricated by nitriding elemental metal needles. These nitride field emitters gave step- and spikelike current fluctuations. The NbN emitters, which had been flash heated at 900 °C, showed the most stable field emission current among the nitride emitters examined.
Nickel doping of boron carbide grown by plasma enhanced chemical vapor deposition
Authors: Hwang Seong-Don , Remmes N. B. , Dowben P. A. , McIlroy D. N.
Published: July 2002

We have nickel doped boron carbide grown by plasma enhanced chemical vapor deposition. The source gas closo-1,2-dicarbadodecaborane (ortho-carborane) was used to grow the boron carbide, while nickelocene [Ni(C5H5)2] was used to introduce nickel into the growing film. The doping of nickel transformed a p-type, B5C material, relative to lightly doped n-type silicon, to an n-type material. Both n-n heterojunction diodes and n-p heterojunction diodes were constructed, using as substrates n- and p-type Si(111), respectively. With sufficient partial pressures of nickelocene in the plasma reactor, diodes with characteristic tunnel diode behavior can be successfully fabricated.
Sidewall deposition film in platinum etching with Ar/halogen mixed gas plasmas
Authors: Shibano Teruo , Oomori Tatsuo
Published: July 2002

Experimental studies of the deposition of films formed on the sidewalls of a photoresist pattern in the etching of platinum films with Ar and halogen mixed gas plasmas were performed. In platinum etching with Ar/halogen gas plasmas there is no enhancement of the etch rate by adding halogen gases, and deposition films are formed on the sidewall of a photoresist pattern. The thickness of the sidewall deposition film is minimized in etching with pure Ar plasma. The addition of halogens increases the thickness of the sidewall deposition film. These films were analyzed by x-ray photoelectron spectroscopy (XPS) to investigate their formation mechanism. Carbon was detected even in the deposition films formed during etching with gases that did not include carbon. From the results of XPS analysis it was found that the etching reaction products from the photoresist relate to the formation of these films, and that the reason for the increase in the film thickness is the increase in the etch rate of the photoresist by adding halogens. Therefore in the etching of platinum films it is important to suppress the etching of the photoresist to decrease the thickness of the sidewall deposition film.
Nanopotentiometry: Local potential measurements in complementary metal–oxide–semiconductor transistors using atomic force microscopy
Authors: Trenkler T. , De Wolf P. , Vandervorst W. , Hellemans L.
Published: July 2002

In nanopotentiometry a conductive atomic force microscope tip is used as a voltage probe in order to measure the distribution of the electrical potential on the cross section of an operating device. The information thus obtained is complementary to the carrier profiles and provides a method for calibration of device simulations. The experimental procedure is discussed in detail with emphasis on preparation techniques and contact force calibration. The present results are obtained on the cross section of a 0.25 μm complementary metal–oxide–semiconductor transistor cell which was designed such that even after sectioning, the device is still operational. I–V characteristics of the transistors before and after preparation indicate that the sectioned transistors show a higher leakage current, but are still functionally operational. Using nanopotentiometry, potential maps are measured under various bias conditions, showing the progressive creation of the channel. The present results demonstrate that nanopotentiometry provides insight into the actual working behavior of the transistors. The sensitivity and the spatial resolution are limited by the finite size of the conductive probe and by the quality of the surface preparation.
Investigation of ultrathin SiO2 film thickness variations by ballistic electron emission microscopy
Authors: Kaczer B. , Im H.-J. , Pelz J. P.
Published: July 2002

We investigate the feasibility of using ballistic electron emission microscopy (BEEM) to study possible thickness variations of ultrathin SiO2, which might exist at substrate defects, such as steps. We find that simple BEEM imaging of the oxide film sandwiched into a metal–oxide–semiconductor (MOS) structure does not reveal any features that could be related to the oxide film. We further present initial results suggesting that hot-electron resonance in the oxide conduction band could be observed by BEEM and could be sensitive to local film thickness. We also confirm the ability of oxide film to sustain injection of very high densities of hot electrons without any observable damage. In some cases we observe local damage of the MOS structure induced by BEEM measurements, but we conclude that it is most likely related to failure of the metal overlayer and probably not related to hot-electron breakdown of the oxide.
Interaction between gas rarefaction and metal ionization in ionized physical vapor deposition
Authors: Rossnagel S. M.
Published: July 2002

The process known as ionized physical vapor deposition, or I-PVD, consists of the physical sputtering of metal atoms into a dense, inert gas plasma, ionization of the sputtered metal atoms, and subsequent deposition of the films from these metal ions. Measurements have shown a decrease in electron temperature coupled with an unexpected decrease in plasma density as a function of increasing metal flux. Recent plasma modeling work has suggested gas rarefaction as the underlying factor in these declines. Measurements of neutral gas density in the plasma region reported here confirm this model and are consistent with earlier studies of sputtered atom induced gas heating and rarefaction.
Nitridation of GaAs(001) surface: Auger electron spectroscopy and reflection high-energy electron diffraction
Authors: Aksenov Igor , Iwai Hidekazu , Nakada Yoshinobu , Okumura Hajime
Published: July 2002

Auger electron spectroscopy (AES) and reflection high-energy electron diffraction (RHEED) have been used to investigate the processes taking place during the initial stages of nitridation of GaAs(001)–2×4 surface by active nitrogen species. The results of analysis of the spectral shapes and the spectral positions of the Auger electron signals from Ga, As, and N, as well as their dependencies on the nitrogen exposure combined with RHEED results show that the processes taking place during nitridation greatly differ depending on the nitridation temperature. On the one hand, at low temperatures (Ts⩽200 °C) nitridation is hindered by kinetic restrictions on the atomic migration, leading to island growth with formation of the disordered GaAsN phase in the subsurface region, which cannot be completely re-crystallized even after prolonged annealing. On the other hand, at high temperatures (Ts⩾500 °C) the process of nitridation takes place simultaneously with etching of the surface due to decomposition of the substrate, leading to growth of facets and resulting in a rough interface between the GaN and GaAs phases. However, for intermediate nitridation temperatures (300 °C⩽Ts⩽400 °C) it was found that the disordered GaAsN phase, formed at the initial stage of nitridation, partly crystallizes even without annealing. Moreover, AES results indicate that a monolayer of N atoms may well be formed on the substrate during the initial stage of nitridation. The postnitridation annealing of the samples nitrided at the intermediate temperatures results in the formation of a crystalline GaN layer. The line shape of the AES signals from this layer is identical to that for a thick GaN reference sample.
Comparative study of two-dimensional junction profiling using a dopant selective etching method and the scanning capacitance spectroscopy method
Authors: Mahaffy R. , Shih C. K. , Edwards H.
Published: July 2002

The importance to industry of a two-dimensional dopant profiling technique becomes more critical as the sizes of the devices shrink. As these techniques develop, their relative reliability comes into question and the only comparisons that exist are with accepted one-dimensional techniques such as secondary ion mass spectroscopy (SIMS) and spreading resistance profiling or with each other. In this article, we make one such comparison between a newly introduced technique of scanning capacitance spectroscopy and a somewhat older technique of selective etching. Based on vastly different principles, these two techniques provide an opportunity to learn about each through comparison. The results of the comparisons are shown to be consistent both in the qualitative shape similarities of the n-type metal-oxide semiconductor (NMOS) data from both methods and in the quantitative agreement of the lateral junction position under the gate to within 30 nm. The p-type metal-oxide semiconductor (PMOS) data from both techniques differ somewhat in the channel region due to the fact that under these etching conditions the channel region tends to etch out and at long times can etch out to a point comparable to the true junction. The vertical alignment with SIMS and thus with the etching data is within the 30 nm error margin. The general comparison between the two techniques indicates that the junction is determined at the same point in the lateral direction for the NMOS device, and there is some disagreement on the PMOS junction position under these conditions.
Properties of Ga2O3(Gd2O3)/GaN metal–insulator–semiconductor diodes
Authors: Hong M. , Anselm K. A. , Kwo J. , Ng H. M. , Baillargeon J. N. , Kortan A. R. , Mannaerts J. P. , Cho A. Y. , Lee C. M. , Chyi J. I. , Lay T. S.
Published: July 2002

Ga 2 O 3 ( Gd 2 O 3 ), electron beam evaporated from a single crystal Ga5Gd3O12 garnet, was ex situ deposited on molecular beam epitaxy grown GaN of Ga-polar surface. Using capacitance–voltage measurement, accumulation and depletion behavior was observed in the Ga2O3(Gd2O3)/GaN metal–oxide–semiconductor diodes, with an interfacial density of states less than 1011 cm−2 eV−1. The Ga2O3(Gd2O3)/GaN interface remains intact with the samples subject to rapid-thermal annealing up to 950 °C, as studied from x-ray reflectivity measurements.
Hydrogen diffusion through silicon/silicon dioxide interfaces
Authors: Nickel N. H.
Published: July 2002

In order to improve the electrical properties of semiconductor devices residual defects have to be passivated. In c-Si metal–oxide–semiconductor devices, these defects are located at the Si/SiO2 interface, while in polycrystalline silicon thin-film transistors, in addition to interface defects, grain-boundary defects have to be passivated. In both device structures, H has to diffuse through numerous layers of oxides, silicon, and possible surface barriers. To improve the H passivation efficiency, it is important to understand H transport through Si/SiO2 interfaces. H transport through the oxide was studied by measuring the changes of the flux through the oxide as a function of time, temperature, and oxide thickness. The oxide layer reduces the H flux into the underlying layers by more than four orders of magnitude. The temperature dependence of the H flux was found to be independent of the oxide thickness. This indicates that the striking decrease in H flux is not due to an increase in barrier height.
Molecular Rulers for Scaling Down Nanostructures
Authors: Hatzor A. , Weiss P. S.
Published: July 2002

A method of constructing <30-nanometer structures in close proximity with precise spacings is presented that uses the step-by-step application of organic molecules and metal ions as size-controlled resists on predetermined patterns, such as those formed by electron-beam lithography. The organic molecules serve as a ruler for scaling down a larger “parent” structure. After metal deposition and lift-off of the organic multilayer resist, an isolated smaller structure remains on the surface. This approach is used to form thin parallel wires (15 to 70 nanometers in width and 1 micrometer long) of controlled thickness and spacing. The structures obtained were imaged with field emission scanning electron microscopy. A variety of nanostructures could be scaled down, including structures with hollow patterns.
Observation of
d

x

2

-y
2

-Like Superconducting Gap in an Electron-Doped High-Temperature Superconductor
Authors: Sato T. , Kamiyama T. , Takahashi T. , Kurahashi K. , Yamada K.
Published: July 2002

High-resolution angle-resolved photoemission spectroscopy of the electron-doped high-temperature superconductor Nd
2-x
Ce
x
CuO
4
(x = 0.15, transition temperature
T
c
= 22 K) has found the quasiparticle signature as well as the anisotropic
d

x

2

-y
2

–like superconducting gap. The spectral line shape at the superconducting state shows a strong anisotropic nature of the many-body interaction. The result suggests that the electron-hole symmetry is present in the high-temperature superconductors.
Memory Extinction, Learning Anew, and Learning the New: Dissociations in the Molecular Machinery of Learning in Cortex
Authors: Berman Diego E. , Dudai Yadin
Published: July 2002

The rat insular cortex (IC) subserves the memory of conditioned taste aversion (CTA), in which a taste is associated with malaise. When the conditioned taste is unfamiliar, formation of long-term CTA memory depends on muscarinic and β-adrenergic receptors, mitogen-activated protein kinase (MAPK), and protein synthesis. We show that extinction of CTA memory is also dependent on protein synthesis and β-adrenergic receptors in the IC, but independent of muscarinic receptors and MAPK. This resembles the molecular signature of the formation of long-term memory of CTA to a familiar taste. Thus, memory extinction shares molecular mechanisms with learning, but the mechanisms of learning anew differ from those of learning the new.