bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidation-enhanced roughening of thin Co films during sputtering by O+2 ions
Authors: Mohadjeri B. , Petravić M. , Svensson B. G.
Published: July 2002

Substantial variations in the erosion rate during low energy (5.5–10.5 keV) O+2 sputtering of polycrystalline Co thin films are demonstrated by crater depth measurements as a function of sputtering time. At normal incidence the erosion rate is constant, while for oblique angles (≤55°, with respect to surface normal) the rate is between ∼30% and 75% higher at the surface compared to that in the ‘‘bulk.’’ A clear relationship between the width of the preequilibrium region and the sputtering-induced roughness is shown, as revealed by surface stylus profilometry and atomic force microscopy measurements. Sputtering by Ar+ ions, where no chemical compounds form, results in significantly smoother craters and the erosion rate is constant. The development of the preequilibrium region during O+2 sputtering of Co is attributed to oxidation-induced roughening of Co. A model is proposed for the oxidation-enhanced roughening, which is further supported by results obtained from Rutherford backscattering spectrometry measurements of oxygen incorporation during O+2 bombardment and Ar+ sputtering combined with oxygen flooding.
Compact-heating stage for use in sputtering in active oxygen gas environments
Authors: Igarashi Y. , Fujino Y. , Takahashi T.
Published: July 2002

An easily movable compact heating stage for heating substrates in an oxidizing atmosphere up to a temperature of about 700 °C is described. A resistive heating element of Kanthal (72.5Fe-22Cr-5.5A1 wt %) wire is used. The heating element is mounted inside a stainless steel vessel to isolate it from active oxygen gas environments. The vessel is assembled in air of one atmospheric pressure at room temperature. Substrates are contacted for heating on the top plane of the vessel with a stainless steel substrate holder. In order to show the performance of the heating stage, the resistive transition property of a single crystal YBa2Cu3O7–x thin film formed by rf magnetron sputtering on a MgO (100) substrate heated by this stage is demonstrated.
YBa2Cu3O7−x thin film over 3 in. substrate using off-axis excimer laser deposition
Authors: Nagaishi T. , Itozaki H.
Published: July 2002

A large area c-axis oriented YBa2Cu3O7−x thin film was grown on a 3-in. LaAlO3 substrate using off-axis excimer laser deposition. Substrate rotation and laser beam scan on a target enabled thickness variations less than ±4% over the 3-in. film. The superconducting transition temperature was 88.4–90.8 K and the critical current density was in excess of 106 A/cm2 at 77 K under the zero magnetic field. The surface was smooth with few outgrowths, and the density of particles was 104/cm2, which is 1/100 less than that yielded on-axis laser deposition.
Particle beam mass spectrometer measurements of particle formation during low pressure chemical vapor deposition of polysilicon and SiO2 films
Authors: McMurry Peter H. , Nijhawan Sandeep , Rao Nagaraja , Ziemann Paul , Kittelson David B. , Campbell Stephen
Published: July 2002

We have recently built a particle beam mass spectrometer (PBMS) for measuring ultrafine particle size distributions (0.005–0.25 μm) at low pressures (≳100 mTorr). The PBMS is being used to study nucleation and growth in low pressure chemical vapor deposition processes relevant to the production of semiconductor devices. In this article, the function and performance of the PBMS is summarized, and results of measurements made while depositing polysilicon and silicon dioxide films in tube furnaces are discussed. Measurements made during deposition of polysilicon films showed that there was a critical reactor pressure below which particles were not present; this critical pressure varied in proportion to the residence time in the reactor, and was insensitive to reactor temperature. Above the critical pressure, however, the concentration of particles produced was sensitive to reactor temperature. The average particle size was in the 0.003–0.03-μm-diam range, with concentrations of ∼104 cm−3. In contrast, particles produced during the deposition of oxide films in a low-temperature oxide (LTO) furnace were considerably larger (0.1–0.3 μm) and were present at lower concentrations (∼103 cm−3). These differences suggest that the chemical mechanisms of particle formation and growth in the two systems are quite different. Simultaneous measurements of particle accumulation on witness wafers during the LTO experiments showed a reasonable correlation with PBMS data, thereby illustrating the relevance of PBMS measurements to device fabrication.
Scanning force microscopic studies of surface structure and protein adsorption behavior of organosilane monolayers
Authors: Takahara Atsushi , Kojio Ken , Ge Shou-Ren , Kajiyama Tisato
Published: July 2002

Alkyltrichlorosilanes, [2-(perfluorooctyl)ethyl]trichlorosilane (FOETS) and their mixed monolayers were polymerized on the water subphase and were subsequently immobilized onto the silicon wafer surface by covalent bonding. Atomic force microscopic (AFM) observation of the [n-octadecyltrichlorosilane(OTS)/FOETS] mixed monolayer revealed that the crystalline OTS formed circular domains of ∼1–2 μm in diameter that were surrounded by an amorphous FOETS matrix. Lateral force microscopic (LFM) and scanning viscoelasticity microscopic (SVM) observations of the (OTS/FOETS) mixed monolayer could also distinguish the difference in the physical and mechanical properties between domain and matrix. The (alkylsilane/FOETS) mixed monolayers with a shorter alkyl chain such as n-dodecyltrichlorosilane (DDTS) did not show the phase-separated structure maybe due to the lack in crystallinity of DDTS component. AFM observation of the [crystalline fatty acid (nonreactive)/FOETS (reactive)] mixed monolayer also revealed the phase-separated structure. The crystalline fatty acid domains in the mixed monolayer were extracted by solvent and then, the monolayer of FOETS with the holes of ∼1–2 μm in diameter, that is, the (Si/FOETS) monolayer was finally obtained. The Si phase of (Si/FOETS) was backfilled with the another organosilane by chemisorption. Then, the [(3-mercaptopropyl) trimethoxysilane (MTS)/FOETS] mixed monolayer was newly obtained by the chemisorption of MTS. The absorption of bovine serum albumin (BSA) onto mixed monolayers was studied by exposure of the mixed monolayers to a BSA solution. BSA was preferentially adsorbed onto the MTS part due to a specific reaction between disulfide bond (–S–S–) in BSA and SH groups in MTS. On the other hand, in the case of (OTS/FOETS) mixed monolayer, BSA adsorbed preferentially onto the FOETS matrix in order to minimize the interfacial free energy in the aqueous environment.
In situ high-resolution atomic force microscope imaging of biological surfaces
Authors: Sokolov I. Yu. , Firtel M. , Henderson G. S.
Published: July 2002

In situ high-resolution atomic force microscope imaging of biological surfaces was performed on cells with relatively rigid surfaces (e.g., bacteria). The surface of Lactobacillus helveticus (a rod-shaped bacterium) was investigated before and after exposure to LiCl, a denaturant. Image details were stable both at variant force loads and under different scan directions. From images of the oblique lattice structure (i.e., S layer of L. helveticus), it was estimated that the lateral resolution of the images was up to 2 nm. This resolution can be explained by assuming that there is an apex with a curvature of radius of ∼10 nm near the end of the tip. Modelling of this geometry indicates that such a tip configuration is particularly suitable for in situ high-resolution imaging of relatively soft objects covered by a rigid shell (membrane).
Characterization of carbon and carbon nitride thin films using time-of-flight secondary-ion-mass spectrometry
Authors: Huang L. J. , Hung Y. , Chang S. , Massoumi G. R. , Lennard W. N. , Mitchell I. V.
Published: July 2002

A methodology for quantitative measurement of nitrogen and hydrogen atomic composition of thin carbon nitride film using time-of-flight secondary-ion-mass spectrometry is demonstrated. The nitrogen and hydrogen compositions of the film are determined by the selected ion fragment intensity ratios ICN−/IC2− and IC2H−/IC2− measured in the negative-ion-mass spectrum of the film, respectively. Absolute values for hydrogen and nitrogen atomic compositions are extracted by calibration with nuclear reaction analysis and hydrogen forward scattering methods. The measured ion fragment mass intensities were also used to characterize the structure of the carbon nitride films. The results are compared with those measured from x-ray photoemission spectroscopy.
Understanding gas-surface interactions from direct force measurements using a specialized torsion balance
Authors: Cook Steven R. , Hoffbauer Mark A.
Published: July 2002

Measurements of the magnitude and direction of the forces exerted on surfaces by molecular beams are used to obtain information about the microscopic properties of gas-surface interactions. The reduced force coefficients are introduced as a new set of parameters that completely describe the macroscopic average momentum transferred to a surface by incident molecules and can be used to obtain the flux-weighted average velocity and translational energy of the scattered molecules. This approach avoids the complications associated with obtaining macroscopic average quantities from averages of microscopic measurements and can be used to determine microscopic details concerning gas-surface interactions. Using a specialized torsion balance, the reduced force coefficients were determined from measurements of the forces exerted on surfaces of a solar panel array material, Kapton, SiO2-coated Kapton, and Z-93-coated Al by molecular beams of H2, N2, CO, and CO2 as a function of the angle of incidence.
CF
X
(X=1–3)
radical densities during Si, SiO2, and Si3N4 etching employing electron cyclotron resonance CHF3 plasma
Authors: Miyata K. , Hori M. , Goto T.
Published: July 2002

The roles of CFX(X=1–3) radicals in etching reactions of Si, SiO2, and Si3N4 in an electron cyclotron resonance (ECR) CHF3 plasma have been investigated using infrared diode laser absorption spectroscopy (IRLAS). CFX radical densities in the plasma were measured as functions of Si, SiO2, and Si3N4 etch rates. The radical densities decreased with increasing etch rates of Si3N4, SiO2, and Si. Influences of byproducts from the etched substrates and substrate biases on CFX radicals were also investigated. Moreover, the FCN molecular density was measured using IRLAS in the ECRCHF3 plasma in the presence and absence of Si3N4 film. It was found that the FCN molecule was abundantly formed in the plasma during etching of Si3N4. The IRLAS measurement of the FCN molecule is considered to be suitable for detecting the FCN molecule and in situ monitoring of Si3N4 etching.
Optimization of an electron cyclotron resonance etch process using full wafer charge coupled device interferometry
Authors: Pendharkar S. V. , Resnick D. J. , Dauksher W. J. , Cummings K. D. , Tepermeister I. , Conner W. T.
Published: July 2002

Full wafer charge coupled device interferometry is a new technique that can be used for in situ monitoring of plasma etching. The use of this technique to optimize an electron cyclotron resonance etch process for TaSiN and its application to x-ray mask fabrication are presented. Fine tuning of the etch process was performed by optimizing the microwave power and the collimating magnet current. Under optimized conditions, etch rate uniformity (3σ) across a 4 in. substrate was as low as 2%. The full wafer interferometer enables in situ uniformity measurements, thus minimizing process development time. The etch process has been used to successfully fabricate sub-0.25 μm x-ray masks.
Tests of an environmental and personnel safe cleaning process for Brookhaven National Laboratory accelerator and storage ring components
Authors: Foerster C. L. , Lanni C. , Lee R. , Mitchell G. , Quade W.
Published: July 2002

A large measure of the successful operation of the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory (BNL) for over a decade can be attributed to the cleaning of its ultrahigh vacuum (UHV) components during and after construction. A new UHV cleaning process, which has to be environmentally and personnel safe, is needed to replace the harsh, unfriendly process which is still in use. Dow Advanced Cleaning Systems was contracted to develop a replacement process without the use of harsh chemicals and which must clean vacuum surfaces as well as the existing process. Acceptance of the replacement process was primarily based on photon stimulated desorption (PSD) measurements of beam tube samples run on NSLS beam line U10B. One meter long beam tube samples were fabricated from aluminum, 304 stainless steel, and oxygen-free copper. Initially, coupon samples were cleaned and passed preliminary testing for the proposed process. Next, beam tube samples of each material were cleaned, and the PSD measured on beam line U10B using white light with a critical energy of 487 eV. Prior to cleaning, the samples were contaminated with a mixture of cutting oils, lubricants, vacuum oils, and vacuum grease. The contaminated samples were then baked. Samples of each material were also cleaned with the existing process after the same preparation. Beam tube samples were exposed to between 1022 and 1023 photons per meter for a PSD measurement. Desorption yields for H2, CO, CO2, CH4, and H2O are reported for both the existing cleaning and for the replacement cleaning process. Preliminary data, residual gas scans, and PSD results are given and discussed. The new process is also compared with new cleaning methods developed in other laboratories. After modification, the new UHV cleaning process was accepted by BNL.
Hot-carrier effects on the scattering parameters of lightly doped drain n-type metal-oxide-semiconductor field effect transistor
Authors: Kwan W. S. , Deen M. J.
Published: July 2002

The latest evolution in complementary metal-oxide-semiconductor technology has made the metal-oxide-semiconductor field effect transistor (MOSFET) a viable choice for rf applications, especially for frequencies in the low GHz region. However, hot-carrier effects should also be considered carefully when the devices are operating in the GHz regime. Here, we studied the effects of dc hot-carrier stress on lightly doped drain (LDD) n-type MOSFET (NMOSFET) high-frequency performance by measuring and simulating its s parameters. This is the first time, to the authors’ best knowledge, that such experiments are reported. We demonstrated clearly the effects of hot-carrier stressing on LDD NMOSFETs by giving representative s-parameter and noise measurement results from a 0.8 μm long device. We showed that hot-carrier stress can significantly degrade both s parameters and noise of NMOSFETs, and thus can have considerable consequences for circuit designers. Therefore, these effects should be carefully considered when using MOSFETs in high-frequency analog circuits. Unfortunately, both MEDICI® and SPICE simulation could not satisfactorily model the LDD MOS structure after hot-carrier stress. Various results indicated that the current MEDICI platform is not very consistent for ac simulation, although dc simulation is very good. SPICE simulation showed very promising results when modeling the changes in S12 and S21 due to hot-carrier stress, yet the results for S11 and S22 were not very good. This deficiency implies that a better small-signal model for LDD MOS structures would be necessary for SPICE to be useful in modeling hot-carrier effects on MOSFET high-frequency performance.
Heterostructure Si1−xGex channel pMOSFETs with high Ge concentration
Authors: Pawlowicz C. , Tarr N. G. , Berndt L. P. , Williams R. L. , Landheer D. , Xu D.-X. , Abid R. , McAlister S. P.
Published: July 2002

Simultaneous numerical solution of Schrödinger’s and Poisson’s equations is used to show that a narrow triangular Ge composition profile graded to a peak value of 100% with rise and fall lengths of just 2 nm can provide very effective subsurface hole confinement in a heterostructure Si1−xGex channel p metal-oxide-semiconductor field effect transistor (pMOSFET). This result is confirmed by analysis of MOS capacitor C-V curves for experimental devices fabricated using a very low thermal budget process on substrates grown by ultrahigh vacuum chemical vapor deposition. Unfortunately, transconductance measurements on experimental long-channel MOSFETs indicate that the peak low-field mobility of holes in the buried channel is just 132 cm2 V−1 s−1, slightly lower than that for a typical surface channel Si MOSFET. Buried channel hole mobilities up to 262 cm2 V−1 s−1 were obtained for reference devices fabricated using the same process with more conventional wide triangular composition profiles graded to a peak Ge content of 40%.
Spatially resolved optical emission study of sputtering in reactive plasmas
Authors: Moshkalyov S. A. , Machida M. , Campos D. O. , Dulkin A.
Published: July 2002

The study of material sputtering under low-pressure reactive ion etching conditions in various gases (Cl2, SiCl4, O2) was performed using optical emission spectroscopy with high spatial resolution. Sputtering-induced secondary photon emission (atomic and molecular) from the processed materials (Si, Al2O3, GaAs) was found to be strongly localized near the target surface. A spatial distribution of atomic line emission intensity was shown to be essentially nonmonotonical with distance from the surface. This effect was explained by a cascade feeding from the upper lying atomic levels, which is enhanced in plasma (collisional) environment. A simplified model accounting for the cascading has been developed, and velocities of sputtered excited atoms (in the range of 2–7×106 cm/s) and molecules (about 2–5×105 cm/s) have been evaluated from the emission spatial decay parameters. The excited sputtered atoms and molecules are produced in different types of collisions. Fast excited atoms can be produced only in the first few collisions of the incident ion in the surface top layers, whereas excited molecules are knocked off by secondary (slow) atoms originated from a collision cascade inside the solid. Based on this concept of the process, simple expressions for atomic and molecular excitation yields as functions of the incident ion flux and surface coverage were deduced. The technique can be used for in situ surface probing during plasma processing.
Quantum well states in high-quality Cu films deposited on Co (100): A high resolution photoemission study
Authors: Segovia P. , Michel E. G. , Ortega J. E.
Published: July 2002

Quantum well (QW) states of thin Cu films deposited on Co (100) are studied using high resolution photoemission. In order to obtain a smooth Co–Cu interface, Cu films were prepared by evaporating the interfacial layer at 100 K. This allows us to obtain better defined QW features at the valence band. Furthermore, following this preparation method we are able to observe for the first time QW states at the neck of the Cu Fermi surface, which are not observable when the interfacial layer is deposited at 300 K. Using these high-quality films we also study final-state-related oscillations in the intensity of the photoemission spectra as well as the lifetime broadening of the QW states.
Doping scheme of semiconducting atomic chains
Authors: Yamada Toshishige
Published: July 2002

Atomic chains, precise structures of atomic scale created on an atomically regulated substrate surface, are candidates for future electronics. A doping scheme for intrinsic semiconducting Mg chains is considered. In order to suppress the unwanted Anderson localization and minimize the deformation of the original band shape, atomic modulation doping is considered, which is to place dopant atoms beside the chain periodically. Group I atoms are donors, and group VI or VII atoms are acceptors. As long as the lattice constant is long so that the s-p band crossing has not occurred, whether dopant atoms behave as donors or acceptors is closely related to the energy level alignment of isolated atomic levels. Band structures are calculated for Br (p-type) and Cs-doped (n type) Mg chains using the tight-binding theory with universal parameters, and it is shown that the band deformation is minimized and only the Fermi energy position is modified.
Comparison of plasma chemistries for inductively coupled plasma etching of InGaAlP alloys
Authors: Hong J. , Lee J. W. , Abernathy C. R. , Lambers E. S. , Pearton S. J. , Shul R. J. , Hobson W. S.
Published: July 2002

Two plasma chemistries, i.e., CH4/H2/Ar and Cl2/Ar, were compared for the etching of InGaP, AlInP, and AlGaP under inductively coupled plasma (ICP) conditions. While the etching with CH4/H2/Ar discharges appears to be ion driven, Cl2/Ar discharges showed an additional strong chemical enhancement. The highest etch rate (∼1 μm/min) for InGaP was achieved at high ICP source power (⩾750 W) with the Cl2/Ar chemistry. Cl2/Ar discharges provided very smooth surfaces in all three materials with root-mean-square roughness measured by atomic force microscopy around 2 nm. This result may be due to the efficient ion-assisted product desorption in this chemistry. The etched near-surface region of InGaP (∼100 Å) with Cl2/Ar maintained almost the same stoichiometry as that of the unetched control. By contrast, the CH4/H2/Ar plasma chemistry produced somewhat rougher surfaces and depletion of phosphorous (P) from the surface of InGaP.
Lateral manipulation of single Cu atoms on flat and stepped copper surfaces
Authors: Bartels L. , Meyer G. , Rieder K.-H.
Published: July 2002

We demonstrate that single Cu atoms can be pulled in single hops across stepped and flat Cu surfaces at low temperatures using a scanning tunneling microscope. By recording the tip height at constant current during manipulation the hopping length and the position of the tip apex relative to the substrate lattice, at which a hop is induced, can be measured. By this way it is possible to resolve that a Cu atom moves during manipulation on Cu(111) along [11̄0]—depending on the chosen gap resistance—either by long hops from one fcc adsite to the next or by short hops while intermediately occupying hcp sites. On the “stepped” Cu(211)-surface hops between adjacent fivefold adsites can be observed during manipulation along [01̄1].
Stable cancellation of x-ray errors in Bayard–Alpert gauges
Authors: Kendall B. R. F. , Drubetsky E.
Published: July 2002

X-ray induced emission of electrons from the ion collectors of Bayard–Alpert gauges has long been recognized as a cause of falsely high readings at low pressures. Less well known is the existence of a reverse x-ray effect leading to a superimposed, but usually smaller, error signal in the opposite direction. First explained by Redhead and others in the 1960s as being caused by photoemission from the gauge envelope, this phenomenon was immediately recognized as potentially useful in cancelling the forward x-ray effect. Although promising experimental results were obtained with special gauge tubes, these early researchers concluded that the cancellation process was too unstable to be of any practical use. We report the results of an attempt to stabilize the cancellation process by the use of identical materials at the two photoemission sites. Experimental Bayard–Alpert gauge tubes were built with gold coatings on the insides of the gauge envelopes and on the surfaces of the ion collectors. The envelope coatings were operated at approximately 15–25 V below the potential of the ion collector. Stable reduction of the x-ray errors by a factor of more than 20 has been demonstrated. Short-term improvements by a factor of 100 have been achieved. Useful improvements have also been observed in sensitivity and in stability at high pressures. Results of long-term stability tests at pressures in the 10−10 Torr range are described.
Texture and surface morphology improvement of Al by two-stage chemical vapor deposition and its integration in an Al plug-interconnect scheme for sub 0.25 μm metallization
Authors: Naik Mehul , Guo Ted , Chen Liang , Mosely Rod , Beinglass Israel
Published: July 2002

A two-stage deposition with successive seed and bulk deposition steps was developed to improve the morphology and texture of chemical vapor deposited (CVD) aluminum on titanium. Dimethylaluminumhydride (DMAH) was used as the precursor. Typically, CVD Al deposited using a single deposition stage showed highly granular structure with surface “defects” resulting in films that become rough with increase in thickness creating integration problems with photolithography and etch. Here, a two-stage deposition process for CVD Al is described that significantly improves the morphology and texture of Al on titanium. In this process, the wafer surface is preconditioned with a short burst of DMAH before stabilizing gas flows or pressure. Such a treatment in the very first step results in a seed layer upon which proceeds the bulk film deposition in a subsequent step after stabilizing pressure, gas flows and equilibrating temperature. The two-stage deposition resulted in reflectivity improvement of CVD Al on Ti from ⩽ 160% to >210% (%Si, 480 nm) for a 3.5 kÅ thick film with complete elimination of surface defects. X-ray rocking curves show a decrease in the full width at half maximum of the Al(111) peak from 5.1° to 2.6°, indicating significantly improved texture. Secondary ion mass spectroscopy analysis of the CVD Al shows a decrease in carbon content using the two-stage deposition. The two-stage deposition for CVD Al was integrated with AlCu sputter process at temperatures below 380 °C, without a vacuum break between the CVD Al and PVD AlCu, to develop sub-0.25 μm technology via fill capability.
Carbon overcoat composition and structure analysis by secondary ion mass spectrometry
Authors: Erickson J. W. , Sheng J. , Gao Y. , Pham H. , Singer I. L.
Published: July 2002

The composition and structure of carbon overcoat layers on hard discs were studied systematically using secondary ion mass spectrometry (SIMS). The amounts of H, C, N, and O in the carbon overcoat were measured along with Co and Cr outdiffusion from the underlying magnetic layer. Two SIMS techniques were used, the “MCs+” technique in which the secondary ion intensity is linearly proportional to the concentration [M], and the “M2M3” technique in which the secondary ion intensities show quadratic and cubic dependence on [M]. The MCs+ technique was used to measure stoichiometry and thus characterize diamond-like carbon, hydrogenated carbon, and carbon nitride overcoat layers or sublayers. The M2M3 technique was used to provide structural information on the physical uniformity of the overcoat. The SIMS results are compared to those from other techniques, emphasizing the relative value and cost of information. The tribological issues affecting hard disc durability and wear are discussed.
Thermal relaxation of hot filaments
Authors: Durakiewicz Tomasz , Halas Stanislaw
Published: July 2002

A stretched exponential function is used to fit the cooling curve of a tungsten filament. Fitting parameters are given for a set of tungsten filaments varying from 10 to 100 mm in length and from 0.05 to 1 mm in diameter. The instantaneous time constant of cooling and its dependence on temperature and position along the filament are discussed.
Assessment of as-deposited microcrystalline silicon films on polymer substrates using electron cyclotron resonance-plasma enhanced chemical vapor deposition
Authors: Bae Sanghoon , Fonash Stephen J.
Published: July 2002

We have been successful in fabricating as-deposited microcrystalline silicon (μc-Si) on polyethersulfone and polyethylene terephthalate substrates and have assessed the characteristics of the Si films. We note that 13.5 MHz radio-frequency (rf) substrate bias during electron cyclotron resonance plasma deposition can be used to tailor the characteristics of these as-deposited μc-Si microcrystalline silicon films on the polymer substrates. As the rf substrate bias is applied and increased, as-deposited Si films loose their degree of crystallinity. At the same time, the activation energy of the Si film tends to be decreased and the intensity of the film photoluminescence (PL) is enhanced. Part of this increased PL intensity that is found with the addition of rf substrate bias occurs in a PL band at about 0.9 eV. This PL band in Si films may be attributed to the amorphous silicon (a-Si) materials.
Atomic flux measurement by diode-laser-based atomic absorption spectroscopy
Authors: Wang Weizhi , Hammond R. H. , Fejer M. M. , Beasley M. R.
Published: July 2002

Diode-laser-based atomic absorption (AA) sensors have been developed for direct measurement of atomic flux, based on both atomic density and velocity information, which is important for in situ monitoring and control of physical vapor deposition processes. Laser beam schemes based on the Doppler shift measurement have been designed for measuring the velocity component normal to the surface of a substrate. Experimental results on electron-beam evaporated barium and yttrium, which are components in YBCO superconductor, demonstrate measurements of true flux instead of simple density in the deposition processes. The flux measurement was confirmed at different pressures showing true flux measurement independent of background pressure. A model-independent flux measurement was achieved by using a cross-beam scheme. In addition, the AA sensor was also used for diagnosing and helping better understand the deposition physics such as sticking coefficient, velocity of the evaporated atoms, and the oxidation of the elements on the substrate. Discussion on practical issues of the AA sensor application is also presented.
Influence of surface material on the boron chloride density in inductively coupled discharges
Authors: Hebner G. A. , Blain M. G. , Hamilton T. W.
Published: July 2002

The relative density of BCl radicals has been measured in a modified Applied Materials decoupled plasma source commercial metal etch chamber using laser-induced fluorescence. In plasmas containing mixtures of BCl3 with Cl2, Ar, and/or N2, the relative BCl density was measured as a function of source and bias power, pressure, flow rate, BCl3/Cl2 ratio, and argon addition. To determine the influence of surface materials on the bulk plasma properties, the relative BCl density was measured using four different substrate types; aluminum, alumina, photoresist, and photoresist-patterned aluminum. In most cases, the relative BCl density was highest above photoresist-coated wafers and lowest above blanket aluminum wafers. The BCl density increased with increasing source power and the ratio of BCl3 to Cl2, while the addition of N2 to a BCl3/Cl2 plasma resulted in a decrease in BCl density. The BCl density was relatively insensitive to changes in the other plasma parameters.
Deposition and 1.54 μm Er3+ luminescent properties of erbium-doped hydrogenated amorphous silicon thin films by electron cyclotron resonance plasma enhanced chemical vapor deposition of SiH4 with concurrent sputtering of erbium
Authors: Shin Jung H. , Kim Mun-Jun
Published: July 2002

Erbium-doped hydrogenated amorphous silicon (a-Si:H) thin films were deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition of SiH4 with concurrent sputtering of erbium. The oxygen and carbon contamination levels in all films were 1×1019 and 3×1019 cm−3, respectively, and the erbium concentrations could be controlled from 0.13 to 1.1 at. % by adjusting the erbium bias voltage. The half width Γ/2 of the Raman transverse-optic peak of the deposited films ranged from 32±1 to 36±1 cm−1, increasing with the increasing Er concentration. Strong 1.54 μm Er3+ luminescence with little temperature quenching was observed from all samples. The most intense Er3+ luminescence was observed from the as-deposited film with a deposition temperature of 380 °C and an erbium concentration of 0.13 at. %, showing that using the present method, erbium-doped a-Si:H films with good erbium optical activity and low structural disorder can be deposited directly while avoiding excessive contamination.
Effects of deposition conditions on the fluorine and hydrogen concentration in tantalum pentoxide (Ta2O5) thin films prepared by plasma enhanced chemical vapor deposition using a tantalum pentafluoride (TaF5) source
Authors: Luo E. Z. , Sundaravel B. , Guo H. Y. , Wilson I. H. , Four S. , Devine R. A. B.
Published: July 2002

Using Rutherford backscattering spectrometry, nuclear reaction analysis, and elastic recoil detection analysis, we have analyzed the fluorine (F) and hydrogen (H) incorporated in thin tantalum pentoxide (Ta2O5) films on Si substrates prepared by plasma enhanced chemical vapor deposition using a tantalum pentafluoride (TaF5) source. It is shown that both F and H contents depend strongly on the deposition conditions, especially on the microwave power. Narrow resonant reaction F19(α,p)22Ne analysis shows that there is considerable diffusion of F into the Si substrate.
Hardmask charging during Cl2 plasma etching of silicon
Authors: Vyvoda M. A. , Li M. , Graves D. B.
Published: July 2002

Feature profile evolution simulations of plasma etching rely to first order on the accurate prediction of ion fluxes to all points on the evolving surface. Previous experimental and theoretical work strongly suggests that dielectric charging effects play a key role in a type of anomolous feature evolution known as “notchings.” This involves charging of newly exposed gate dielectric material, subsequent ion trajectory bending, and notch formation due to localized ion flux enhancement. Few researchers, however, have considered charging of masking dielectrics (e.g., SiO2 hardmasks) and its associated effects on feature evolution, even though such charging is likely to occur in modern high-density plasma etching systems. In this article, we develop a combined reactor- and feature-scale model of Cl2 plasma etching of crystalline silicon, allowing for the possibility of hardmask charging and ion trajectory deflection. We show via comparison of simulation results to cross-sectional scanning electron micrographs of silicon trenches that these charging effects can explain the formation of wide, “triangular,” microtrenches seen when etching silicon at 2 mTorr pressure and low rf-bias power. Furthermore, the model correctly predicts the disappearance of these microtrenches when the rf-bias power is raised.
Separation of electron-stimulated-desorption neutrals from outgassing originating from the grid surface of emission-controlled gauges: Studies with a heated-grid gauge
Authors: Watanabe Fumio , Suemitsu Maki
Published: July 2002

With the construction of a heated-grid gauge, whose grid temperature can be varied independent of the electron emission, the two major barriers against precise pressure measurements in the extremely high vacuum (XHV) region, i.e., electron-stimulated-desorption neutrals and outgassing, have been successfully separated. In XHV, these two processes are both dominated by hydrogen molecules, while their strengths depend strongly on the grid temperature and the grid material. At elevated temperatures, outgassing caused by the out-diffusion of hydrogen atoms dissolved in the grid begin to dominate. This suggests use of a metal with low hydrogen solubility for XHV-compatible grid material.
Tau–Charm factory vacuum chamber design
Authors: Antropov V. , Perelstein E. , Sazonov M. , Garke B. , Schindler N. , Edelmann C.
Published: July 2002

The present article gives a description of the vacuum chamber required for a high luminosity electron e+−e− collider Tau–Charm factory. The beam lifetime, which is limited by the single particle collisions with molecules of the residual gas, is estimated. The synchrotron radiation gas loading is studied for the Tau–Charm factory vacuum chamber. The effect of various cleaning procedures on the outgassing behavior of samples of the chamber wall is studied. It is shown that a cleaning procedure by a suitable NaOH etching gives the best results of the tested techniques for minimizing of contaminations and outgassing rates.
Direct low-temperature chemical vapor deposition of fully crystalline micro- and polycrystalline silicon thin films on SiO2 using plasma immersion ion implantation
Authors: Shin Jung H. , Huh Hwang
Published: July 2002

Polycrystalline silicon films on SiO2 were deposited without external heating by plasma immersion ion implantation using bias voltages ranging from −5 to −15 kV and electron cyclotron resonance plasma of SiH4. Compared with films deposited without ion irradiation, ion implanted films have larger grains and lower grain density even when their deposition temperature was lower. Furthermore, ion irradiated films are fully dense and large-grained starting from the initial Si/SiO2 interface without the initial amorphous/microcrystalline seed layer often thought to be necessary to produce polycrystalline silicon films at low temperatures. Using plasma immersion ion implantation, deposition of fully polycrystalline Si films with thicknesses less than 30 nm was demonstrated at temperatures as low as 410 °C.
Preparation and stability of low temperature cobalt and nickel silicides on thin polysilicon films
Authors: Howell R. S. , Sarcona G. , Saha S. K. , Hatalis M. K.
Published: July 2002

Silicides of cobalt and nickel are formed on thin (18–100 nm) polycrystalline silicon films by in situ vacuum annealing. The dependence of silicide sheet resistance on silicon film thickness and crystallinity, surface preparation, integrity of vacuum during metal deposition, and anneal temperature is shown. Cobalt and nickel silicides with sheet resistances as low as 30 and 20 Ω/□ were formed on 18-nm-thick polysilicon films. A surface preparation method to produce a passivated silicon surface compatible with large area glass substrates is demonstrated. The resistance of nickel and cobalt silicide to chemical reagents used in semiconductor processing is studied, as is the thermal stability of these films.
Structure, hardness, and tribological properties of reactive magnetron sputtered chromium nitride films
Authors: He Xiao-Ming , Baker N. , Kehler B. A. , Walter K. C. , Nastasi M. , Nakamura Y.
Published: July 2002

Chromium nitride (CrN) films with Cr/N atomic ratios of 0.73–1.46 were prepared by reactive dc- magnetron sputtering with Ar as the sputtering gas and N2 as the reactive gas. The application of a negative bias voltage to the substrates and the decrement of the gas flow ratio of N2 to Ar (or FN2/FAr) promoted the growth of CrN films with preferred orientations of (200)+(220), high Cr/N ratios, and high densities. The functional hardness and compressive stress were highly dependent on the magnitude of the bias voltage and the Cr/N ratio that was adjusted by the FN2/FAr ratio during film deposition. The optimal energy conditions for ion impingement on growing CrN films with compact columnar crystal structure, high hardness, and enhanced tribological properties were studied with respect to the modulations of the bias voltages and the Cr/N ratios. The CrN films with high hardness and high wear resistance were synthesized in this study at low bias voltages of −(100–300) V and FN2/FAr ratios of 1–3.
Secondary defects engineering in c-Si: Influence of implantation dose, temperature, and oxygen concentration
Authors: Poirier R. , Schiettekatte F. , Roorda S. , Fortin M. O.
Published: July 2002

The influence of implantation temperature, dose, and oxygen concentration was investigated for 230 keV phosphorus implantation in crystalline silicon. It was found that oxygen impurities act as nucleation centers for extended defects, which increases their density in O-rich samples compared to conventional c-Si. For doses below 2×1014 P/cm2, the density of extended defects varies rapidly with dose and depends weakly on implantation temperature while for higher doses, the extended defect density varies linearly with dose and depends strongly on implantation temperature. Using a simple criterion for extended defect formation, the dose at which temperature control of extended defects becomes efficient is evaluated for several ion species and energies.
Temperature distribution over a GaAs heterojunction bipolar transistor measured by fluorescent microthermal imaging
Authors: Boyer N. , Oliver B. , Hagley A. , Masson D. P. , Simard-Normandin Martine , Meunier Michel
Published: July 2002

Fluorescent microthermal imaging (FMI) is used to measure the temperature at the surface of a 2×2 μm2 heterojunction bipolar transistor. The presence of an artifact at the emitter post indicates that accurate temperature measurements are limited to flat surfaces. The FMI measurements obtained for various power dissipations are compared with electrical measurements of the junction temperature. The good agreement between the two techniques suggests that the temperature drop along the emitter post of the device is within a few degrees.
Application of the traditional compact expressions for estimating the regional signal-delay times of heterojunction bipolar transistors
Authors: Pulfrey D. L. , Fathpour S. , St. Denis A. , Vaidyanathan M. , Hagley W. A. , Surridge R. K.
Published: July 2002

The applicability of the traditional compact expressions for estimating the regional signal-delay times of heterojunction bipolar transistors is examined by means of a comparison with numerical device simulation. Regional partitioning in the numerical simulations is achieved by means of a simple phenomenological scheme. It is shown that the traditional expression for the emitter delay is inadequate due to a neglect of both the stored free charge within the emitter-base, space-charge region, and the stored charge in the quasi-neutral emitter. The importance of properly choosing the effective collection velocity when estimating the base delay is demonstrated by considering the effects of band-gap narrowing, quasi-ballistic transport, and hot-electron injection. It is pointed out that the effects of finite charge in the collector-base, space-charge region cannot be neglected when computing the collector delay.
Three-dimensional flow analysis of spiral-grooved turbo booster pump in slip and continuum flow
Authors: Cheng H.-P. , Jou R.-Y. , Chen F.-Z. , Chang Y.-W. , Iwane Matsumi , Hanaoka Takashi
Published: July 2002

Computational fluid dynamics (CFD) methodology is successfully applied to investigate the flow field of a turbo booster pump (TBP) in slip and continuum flow. This pump was developed through cooperation between Kashiyama Industries Ltd. and the Precision Instrument Development Center with the goal of replacing the mechanical booster pump. The rotor of the TBP is equipped with five spiral blades that are hybrids of Becker’s turbo blade, Holweck’s helical-grooved element, and a connection area with a transition spiral-grooved segment. To simplify the computational model and to shorten the calculation time, only one single flow channel is calculated. The full computational domain is linked by five regions including a clearance area between the blade tip and the casing, a vacuum chamber upstream of the inlet of the pump, and an exhaust region of the pump. The experimental measurement is made according to Japan’s JVIS-005 standard. The flowmeter method is adopted here to calculate the pumping speed. Comparisons of measured and calculated inlet pressure show that the calculation is quite accurate when the pumping fluid is in slip and continuum flow. But, in transition flow, the continuum model of CFD proves to be unsuitable for calculating such rarefied gas. Because of variation of the averaged pressure, the tendency of pressure to increase is quite linear in the regions of the turbo blade and the connection design area. In the helical-grooved design area, the trend is similar to an exponential curve. According to the results of the velocity field, in lower pressure the velocity field of the flow channel is quite smooth, flowing from the pump inlet to the outlet. But in higher pressure, the velocity field is complex. There are vortices within the flow channel. And the backflow from the pump to the vacuum chamber is more serious, and will harm the pumping efficiency of the TBP.
Optical properties of semiconductor heterostructures for active photonic device modeling
Authors: Tolstikhin Valery I.
Published: July 2002

This article describes a newly developed physics-based approach to calculating the optical properties of III–V semiconductor heterostructures for active photonic device modeling. The consistent microscopic formulation of the complex permittivity in bulk and quantum well layers, in combination with the rigorous solution of the light propagation in absorbing multilayer structure with uniaxial anisotropy, provides a powerful tool for the design and simulation of the real life devices. As modeling examples, InP-based edge-emitting and vertical cavity laser structures are analyzed regarding free carrier effects on their optical properties.
Fabrication of parallel quantum point contacts with submicron airbridges
Authors: Feng Y. , Sachrajda A. S. , Zawadzki P. , Kolind S. , Buchanan M. , Smet J. H. , Lapointe J. , Marshall P. A.
Published: July 2002

An airbridge technique was developed and subsequently employed to fabricate mesoscopic devices, such as parallel quantum point contacts. The airbridge technique mainly involves two different electron sensitive polymers, polymethylglutarimide and polymethyl methacrylate. The airbridge was patterned by electron beam lithography and metal lift-off with bilayer resist. Conductance measurements were performed on the devices at low magnetic fields. The results confirmed both the presence of the elliptical antidot as a negative voltage was applied to the center gate, as well as the nonintrusive nature of the airbridge technique.
Surface morphology analysis in correlation with crystallinity of CeO2(110) layers on Si(100) substrates
Authors: Inoue T. , Nakamura T. , Nihei S. , Kamata S. , Sakamoto N. , Yamamoto Y.
Published: July 2002

CeO 2 layers having various crystallinity are prepared in the vicinity of the critical condition for epitaxial growth, using conventional evaporation and electron beam assisted evaporation. Surface morphology of CeO2 layers is studied using atomic force microscopy in correlation with crystallinity of the layer determined by reflection high energy electron diffraction. It is clearly observed that surface morphology changes with crystallinity of the CeO2 layers. Single crystal CeO2(110) layers have a nanometer-scale-periodically corrugated surface structure, which consists of (111) facets. As the crystalline quality of samples becomes worse, the number of irregular shaped hillocks and tetrahedral hillocks increases, which correspond to distorted (110) grains and (111)-oriented polycrystalline grains, respectively. It is found that crystalline quality is not uniform but various crystallinity regions are distributed from place to place and their population ratio changes according to the degree of crystalline quality. The surface of polycrystalline layers with a tendency of (111) orientation consists of tetrahedral hillocks with irregular in-plane rotational orientations within the horizontal plane. These features are discussed in terms of the surface properties of the substrates at the early stage of growth.
Registration mark detection in electron beam proximity printing
Authors: Nehmiz P. , Behringer U. , Bohlen H. , Kallmeyer M.
Published: July 2002

Electron beam proximity printing is a lithography method for high throughput exposure of repetitive patterns with submicron structures. An electron beam shadow projects the pattern contained in a transmission mask onto the wafer. Pattern registration in this projection printer is achieved by using the electron beam current absorbed in the wafer. Two registration steps are employed: one for wafer (or global) align, the other for chip (or local) align. The achieved registration accuracy is better than 0.1 μm using 10 keV electrons and 1.1 μm thick PMMA on the wafer registration marks.