bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of nitric-phosphoric acid etches on material properties and back-contact formation of CdTe-based solar cells
Authors: Li Xiaonan , Niles David W. , Hasoon Falah S. , Matson Richard J. , Sheldon Peter
Published: July 2002

Forming a low-resistance contact to p-type CdTe is a critical issue for successful commercialization of CdTe-based photovoltaic devices. One solution to this problem has been to incorporate surface pretreatments to facilitate contact formation. In this article, the effects of a nitric–phosphoric (NP) acid pretreatment on material properties and device performance are investigated for polycrystalline CdTe-based devices. We demonstrate that the NP acid pretreatment, when applied to CdTe thin films, forms a thick, highly conductive Te layer on the back surface of the film and on exposed grain boundaries. When etched under optimal conditions, this results in CdS/CdTe devices with reduced series resistance and enhanced performance. On the other hand, we find that the NP etch preferentially etches grain boundaries. Overetching can result in complete device failure by forming shunt paths that extend to the heterointerface. Therefore, carefully controlling the etch concentration and duration is critical to optimizing device performance.
Microwave plasma nitriding of pure iron
Authors: Camps Enrique , Muhl Stephen , Alvarez-Fregoso O. , Juarez-Islas J. A. , Olea Oscar , Romero Saúl
Published: July 2002

This article presents the results of a study of the plasma characteristics of an electron cyclotron resonance plasma source used for nitriding pure Fe. Diagnostic measurements, using optical emission spectroscopy, Langmuir probes, and an ion analyzer, were recorded as functions of the working pressure (2–8×10−4Torr) and the external magnetic field near the substrate (from the extremes of highly compressed and divergent plasma fluxes). It was observed that the plasma source is capable of producing high density discharges, about 5×1011 cm−3 and ion energies about 15–48 eV. The ion energy was highest for the case of a divergent plasma (∼45 eV). The most abundant excited radicals produced in the N/H discharges were the NH, N2 and N2+ species. Experiments for nitriding of Fe showed the formation of distinct material structures dependent on the plasma conditions. Conditions were found for which it was possible to form almost single phases of Fe3N and Fe16N2 in the sample surface.
Thermal stability and sealing performance of perfluoroelastomer seals as a function of crosslinking chemistry
Authors: Heller Mark , Legare John , Wang Shuhong , Fukuhara Shu
Published: July 2002

Perfluoroelastomer (e.g., Kalrez®, Chemraz®, etc.), fluoroelastomer (e.g., Viton®, etc.), and silicone parts are widely used in sealing applications for semiconductor wafer processing equipment. More specifically, they are often used as o-ring seals in dry chemical process equipment (e.g., plasma etchers, ashers, diffusion furnaces, chemical vapor deposition, low pressure chemical vapor deposition, rapid thermal processing, and lamp anneal, etc.). Many of these seals are required to function at process temperatures ranging from 200–300 °C and in some cases higher. The ability of an elastomer to resist thermal degradation has a significant impact on its ability to function effectively as a seal over time. This article evaluates and compares the relative long term sealing performance of perfluoroelastomers having different crosslinking chemistries and other typically specified high performance elastomers. Long-term compression set and seal force retention data are presented, including a discussion of the different test methods and their relative value in predicting seal performance at elevated temperatures. In addition, air heat aging data for other typically measured physical properties (i.e., shore A hardness, 100% modulus, tensile strength at break, elongation at break, percent weight loss) are also presented and discussed. Results indicate perfluoroelastomers seals have the best long-term compression set characteristics and retain the highest percentage of their original sealing force over time. In addition, data shows perfluoroelastomers having an organometallic cross-linking system are the most thermally stable and exhibit the best long term seal performance at elevated temperatures versus those having an organic-peroxide cross-linking system. Finally, because the test conditions best reflect static o-ring seal service conditions, analysis of seal force retention test results provide a more realistic comparison of thermal stability and its relative impact on sealing performance.
Roughness at Si/SiO2 interfaces and silicon oxidation
Authors: Chen Xidong , Gibson J. M.
Published: July 2002

With a plan-view transmission electron microscopy technique of directly imaging buried Si/SiO2 interfaces, we studied the interface roughness resulting from the oxidation process. Our results show that thermal annealing in nitrogen at 900 °C can dramatically remove the interface roughness for Si(100)/SiO2 interfaces [X. Chen and J. M. Gibson, Appl. Phys. Lett. 70, 1462 (1997)]. In contrast, Si(111)/SiO2 interfaces, which tend to be smoother than Si(100)/SiO2 interfaces, are not affected by annealing. A model to link interface roughness and silicon oxidation kinetics was developed. This model not only qualitatively explains the difference between Si(111) and Si(100) interfaces that we saw but also shows that oxidation dynamics is the origin of the interface roughness. Hence, it might be a new approach to understand oxidation dynamics through studying interface roughness.
Design of a 300 mm chemical vapor deposition tungsten reactor using computational fluid dynamics
Authors: McInerney E. J. , Pratt T. M. , Taheri A.
Published: July 2002

Computer simulation is used to optimize the design of a 300 mm chemical vapor deposition tungsten reactor, in order to improve its concurrency of operations, relative to 200 mm designs. Typically, in tungsten sequential batch systems, some deposition stations sit idle while a newly loaded wafer is heated up and exposed to a protective silane flow. This idling is necessary to prevent the device attack and gas phase nucleation that can result from early introduction of WF6 to the chamber. In the 300 mm chamber design presented here, this problem is addressed by altering the chamber geometry to greatly improve the isolation of individual deposition stations. This allows incompatible processes to take place simultaneously on adjacent stations with minimal cross talk, providing a substantial improvement to the throughput of the system.
Formation and characterization of metal atom nanostructures on Si(112) facet surfaces
Authors: Prokes S. M. , Glembocki O. J.
Published: July 2002

Auger electron spectroscopy (AES) and reflectance anisotropy (RA) have been used to study the formation of Ga or Al chains and nanowires on the Si(112) surface. The Ga or Al chains form on the step ledges by a self-limiting process at higher temperatures (>350 °C), while at lower temperatures, Ga or Al nanowires form on the terraces in addition to the chains on the ledges. The process has been tracked in real time from the rapid change of the (2×1) Si(112) reconstruction under subcritical coverage to chain formation leading to a 5×1 reconstruction followed by a 6×1 reconstruction. During sequential deposition of Ga and Al, we observe (in RA and AES) that Ga atoms forming the chains can be replaced by Al. This indicates that the Al–Si bond is stronger than the Ga–Si bond and confirms the chemical sensitivity of the light scattering in RA. Low temperature depositions (in the 300 °C range) are shown to lead to the formation of Ga or Al metallic wires on the Si(111) terraces. Continued deposition of less than 10 monolayers at T below 250 °C leads to a very anisotropic but patterned Al or Ga structure in registry with the substrate which retains an unexpectedly large polarizability for coverages as thick as 40 monolayers.
Nickelocene adsorption on single-crystal surfaces
Authors: Pugmire D. L. , Woodbridge C. M. , Root S. , Langell M. A.
Published: July 2002

Nickelocene adsorption onto Ag(100), Ni(100), and NiO(100)/Ni(100) surfaces was studied with x-ray photoelectron spectroscopy and high-resolution electron energy loss spectroscopy at 135 K for monolayer and multilayer coverages of NiCp2. On the relatively inert Ag(100) surface, nickelocene physisorbs molecularly, with its molecular axis perpendicular to the surface plane. Exposure to the reactive Ni(100) surface results in the decomposition of nickelocene into acetylene and acetylene-like fragments and, when this surface is warmed to 273 K, carbide contamination is observed. There is evidence for double-bond carbon on nickelocene-exposed NiO(100), and vinyl and propenyl fragments are the most likely decomposition products on this surface. At very large exposures, adsorbed nickelocene is molecularly condensed and, therefore, produces similar thin films on all three surfaces.
Photoelectron diffraction intensity calculation by using tensor low-energy electron diffraction theory
Authors: Omori Shinji , Nihei Yoshimasa
Published: July 2002

We applied the tensor low-energy electron diffraction (LEED) approximation to photoelectron diffraction (PED) for efficient structural searches of complex surfaces including multiple parameters to be optimized. It turned out that the tensor LEED scheme can be included into the multiple-scattering cluster model usually utilized for PED intensity calculation with slight modification concerning the treatment of the atomic displacements of photoelectron emitters. The results of numerical calculation for a simple system show that the approximation is applicable to PED over almost the same range of displacements as in tensor LEED.
Structure and electronic states of single-crystal Fe1−xNixOy (0⩽x⩽1) thin films
Authors: Chern G. , Chang C. L. , Chen C. L. , Dong C. L.
Published: July 2002

In a previous report, we showed that a series of single-crystalline iron–nickel oxide alloy thin films, with various Fe–Ni concentration ratios, could be fabricated by a molecular beam epitaxy technique. With x-ray diffraction and adsorption studies, the distribution of Fe and Ni in these compounds are found different from a bulk Fe2NiO4 ferrite phase. We extend the study to a more detailed x-ray adsorption on oxygen K edge from these films. The new results again support the model of the unique ionic distribution in these ferrite alloy films. It further reveals a detailed hybridized feature with transition metal d and sp bands, which is sensitive to the local structure and near neighbors of Fe and Ni. This precisely characterized ionic structure can be directly compared to a local magnetic moment theory. A preliminary result of the magnetic response from these films is discussed.
Interface morphology of CdS thin films grown on cadmium stannate and glass substrates studied by grazing incidence x-ray scattering
Authors: Huang S. , Soo Y. L. , Bechmann M. , Kao Y. H. , Wu X. , Coutts T. J. , Dhere R. , Moutinho H. R.
Published: July 2002

The semiconductor CdS is widely used as a window material in many photovoltaic applications. The interface between CdS and the front collector transparent conducting material plays a pivotal role in the solar cells; a physical understanding and control of the interface morphology are needed in order to improve the device performance. Cadmium stannate has recently been recognized as an important transparent conducting material in light of its superior physical properties over the conventional transparent conducting oxides. Physical understanding of the interface between CdS and cadmium stannate is therefore of great practical interest. For this study, the grazing incidence x-ray scattering (GIXS) technique has been demonstrated very useful for the nondestructive characterization of the interface morphology in a variety of layered structures, thus, it is well suited for this task. In the present work, various thin films of CdS deposited on cadmium stannate are investigated by the GIXS technique using synchrotron radiation. Also, similar measurements were made with CdS films deposited on glass substrates for comparison. Variations of surface and interfacial roughness as well as lateral correlation lengths of interface height fluctuations as functions of film thickness and processing conditions are investigated.
Preferred orientation in carbon and boron nitride: Does a thermodynamic theory of elastic strain energy get it right?
Authors: McCarty K. F.
Published: July 2002

We address whether the elastic strain-energy theory (minimizing the Gibbs energy of a stressed crystal) of McKenzie and co-workers [D. R. McKenzie and M. M. M. Bilek, J. Vac. Sci. Technol. A 16, 2733 (1998)] adequately explains the preferred orientation observed in carbon and BN films. In the formalism, the Gibbs energy of the cubic materials diamond and cubic boron includes the strain that occurs when the phases form, through specific structural transformations, from graphitic precursors. This treatment violates the requirement of thermodynamics that the Gibbs energy be a path-independent, state function. If the cubic phases are treated using the same (path-independent) formalism applied to the graphitic materials, the crystallographic orientation of lowest Gibbs energy is not that observed experimentally. For graphitic (hexagonal) carbon and BN, an elastic strain approach seems inappropriate because the compressive stresses in energetically deposited films are orders of magnitude higher than the elastic limit of the materials. Furthermore, using the known elastic constants of either ordered or disordered graphitic materials, the theory does not predict the orientation observed by experiment.
Residual stress in GaN films grown by metalorganic chemical vapor deposition
Authors: Chen Ying , Gulino Daniel A. , Higgins Ryan
Published: July 2002

We have studied the growth of gallium nitride (GaN) on (0001) sapphire substrates in a commercial (CVD Equipment Corp.) metalorganic chemical vapor deposition reactor. High quality epitaxial GaN films were obtained by deposition at 1000 °C from trimethylgallium and ammonia precursors (1.5 slpm total flow rate with V/III molar flow ratio of 5800) on a 24-nm-thick GaN buffer layer grown at 500 °C. X-ray rocking-curve measurements of films grown under these conditions showed a full width at half maximum of 0.28°. The x-ray lattice parameter method was used to determine the residual stress in GaN films by measuring the c-axis and a-axis strains separately. The results indicate that residual stress in GaN film grown on sapphire is compressive and is reduced as the buffer layer thickness increases.
Analytical modeling of silicon etch process in high density plasma
Authors: Abdollahi-Alibeik Shahram , McVittie James P. , Saraswat Krishna C. , Sukharev Valeriy , Schoenborn Philippe
Published: July 2002

Plasma etching of silicon is one of the important etching processes used in modern integrated circuit manufacturing and micro-electro-mechanical systems fabrication. A good understanding of this process leads to better models which are the key to easier and less costly plasma etching process design. The main focus of this paper is on the simulation of the ion reflection from feature sidewalls and the resulting microtrenches. Pure Cl2 plasma was used for experiments because of the simple chemistry. SPEEDIE (Stanford etching and deposition profile simulator) was used in this work. Langmuir adsorption model was used for etching kinetics. Self-consistent calculations were done for fluxes using surface coverage dependent sticking probabilities. For ion reflection, it was assumed that the reflected ions come off with a distribution about the specular reflection angle. This distribution is modeled as cosnθ (θ is the deviation from the specular angle) and is important in getting the correct shape for microtrenches in simulations. A three-dimensional (3D) calculation of the reflection flux was done taking into account the 3D angular distribution of the incoming ions. The ion reflection efficiency was deducted from the silicon ion enhanced etching yield versus ion angle of incidence data. The simulation results match the experimental profiles fairly well.
Investigations of different dry etching methods on LaAlO3
Authors: Dienelt J. , Zimmer K. , Bigl F. , Höhne R.
Published: July 2002

Different dry etching methods were used to structure single crystal LaAlO3 (100). Utilization of reactive ion beam etching with CHF3 caused enhancement of the etch rate, the selectivity and the step angles compared to conventionally applied Ar ion milling. The influence of the etch parameters on the surface damage was investigated by Rutherford backscattering spectroscopy/channeling studies and x-ray spectroscopy. The chemically assisted ion beam etching with chlorine gas examined causes the lowest degree of surface damage but also the lowest etch rate.
Video-game controller joystick
Authors: Kurtz Richard L. , Subramanian Krishnan , Mankey Gary J.
Published: July 2002

A method is described to use an inexpensive commercial video-game controller as a joystick for operating stepper-motor controlled manipulators.
Plasma chemistry in fluorocarbon film deposition from pentafluoroethane/argon mixtures
Authors: Agraharam Sairam , Hess Dennis W. , Kohl Paul A. , Bidstrup Allen Sue A.
Published: July 2002

Plasma-enhanced deposition of fluorocarbon films was performed at 120 °C from a mixture of pentafluoroethane (CF3CHF2) and argon in a parallel plate plasma reactor. Mass spectrometry of the reactor effluent was used to gain an understanding of the plasma chemistry of this monomer. The monomer primarily dissociated into CF3• and CHF2• in the plasma. The results from mass spectrometry indicated that CHF2* was the primary precursor for deposition and that the fluorine radicals in the plasma were primarily scavenged as CF4 and HF. Monomer conversion (fraction of monomer fragmented) in the plasma was determined based on mass spectrometer partial pressure analysis of CH3CHF+ fragments (parent molecule: CF3CHF2) before and after plasma ignition. The conversion correlated directly with both the applied power and the deposition rate. The overall gas phase reactions did not change significantly with rf power within our range of operation, indicating a common reaction mechanism at all powers. No significant change in the composition of the deposited films was found, as measured by x-ray photoelectron spectroscopy (XPS), supporting the common mechanism conclusion. Further, XPS studies showed a fluorine-to-carbon ratio between 1.05 and 1.15 suggesting extensive crosslinking of the polymer. Infrared spectra of the deposited films showed negligible CHx concentration despite the presence of hydrogen in the monomer.
Laser-induced particle formation and coalescence in a methane discharge
Authors: Stoffels W. W. , Stoffels E. , Ceccone G. , Rossi F.
Published: July 2002

Laser-induced formation of submicrometer dust particles and the subsequent coalescence phenomena in a low-pressure methane radio-frequency plasma have been analyzed. Six distinct phases can be distinguished: (a) nanoparticle synthesis by laser interaction with the plasma species, (b) particle conglomeration and the formation of ordered Coulomb lattices at the plasma–sheath region above the powered electrode, (c) coalescence of grains within the Coulomb lattice and formation of submillimeter strings, (d) condensation of the strings in the discharge and the formation of V-shaped structures, (e) condensation of the V structures into a single network of several centimeters in diameter suspended in the plasma, (f) deposition of the network on the electrode and its subsequent growth on the surface. Large carbon structures as well as nanoparticles have been analyzed in situ by He–Ne laser light scattering and laser ablation and ex situ by an optical and a scanning electron microscope, and by micro-Raman spectroscopy.
Development of an all-metal vacuum bellows following twist motion
Authors: Suetsugu Yusuke , Shiraishi Masamitsu , Mishiba Takashi , Ohno Yuici
Published: July 2002

A novel all-metal vacuum bellows that can follow a twist motion around the axis was designed and developed. The bellows, called here a “twist bellows,” consists of two normal bellows sections and one special bellows section whose corrugation is oblique to the axis. A trial model with a total length of 400 mm and an inner diameter of 100 mm is able to absorb the twist up to about ±22° (44° total) within a twist torque of about 12 N m (120 kg cm) while keeping the total length constant. The twist bellows can also follow the usual bending, shifting, expanding and contracting motion easily like a conventional bellows. The twist bellows allows an unobstructed direct view along the axis and is especially useful for vacuum system of accelerators or synchrotron light beam lines.
Low-cost alternative to motorized linear and rotary motion feedthroughs
Authors: McCabe P. R. , Utz A. L.
Published: July 2002

A simple adapter converts a manual motion feedthrough device into its motorized equivalent.
Improvement on lithography pattern profile by plasma treatment
Authors: Soo C. P. , Bourdillon A. J. , Valiyaveettil S. , Huan A. , Wee A. , Fan M. H. , Ang T. C. , Chan L. H.
Published: July 2002

New chemical information has been obtained which explains “footing” and “bottom pinching” effects in chemically amplified (CA) resists on a silicon nitride surface. X-ray photoelectron spectroscopy measurements indicate that the residual alkaline molecules on the nitride surface play a major role in the formation of nitride footing. It appears that the organic contaminants are not responsible for nitride footing. O2 and N2O/SiH4 plasma treatment are used to modify the silicon nitride surface. Less severe footing is observed if the nitride surface is treated with N2O/SiH4 plasma. This is attributed to the deposition of a thin oxide cap on the nitride substrate, which suppresses the surface basicity. However, extended N2O plasma treatment causes resist bottom pinching. This is ascribed to the surface acidity of a newly formed oxide cap which enhances the CA resist development process. Results show that the N (1s) peak, after extended N2O/SiH4 plasma treatment, has shifted to a higher binding state which suggests that the nitride surface becomes acidic, causing bottom pinching.
Study of interdiffusion between thin Y–Ba–Cu–O films and MgO substrates by applying Rutherford backscattering spectrometry combined with scanning tunneling microscopy
Authors: Fujino Y. , Igarashi Y. , Yamaura S. , Suzuki N. , Iimura K.
Published: July 2002

Interdiffusion between sputter-deposited thin Y–Ba–Cu–O films and MgO (100) substrates has been reinvestigated by applying 3.2 Mev 4He+ Rutherford backscattering spectrometry (RBS) combined with scanning tunneling microscopy. The effects on the RBS spectra from large morphology variation up to “lake-like” structure of the films during annealing have been quantitatively evaluated and excluded. The obtained value of the interdiffusion coefficient of Cu in MgO is 1.2×10−21 m2 s−1, which is smaller by three orders of magnitude than the value reported by other workers.
Low-temperature deposition of Si thin layer by gas-source molecular beam epitaxy
Authors: Ohtsuka K. , Murai A. , Oizumi T. , Yoshida T. , Kurabayashi T. , Suto K. , Nishizawa J.
Published: July 2002

Low-temperature gas-source molecular beam epitaxy using hydride sources for the fabrication of Si thin layers was investigated. In the case of a Si2H6 source, the temperature dependence of the growth rate is relatively small in the desorption- and/or decomposition-dominated region at temperatures of 300–500 °C, which is useful for atomic- and molecular-level controlled growth. Simultaneous and alternate supply of oxygen prevented the deposition of SiO2 and resulted in the deposition of Si. Supplying oxygen brought about a decrease of the deposition rate of Si.
Feature evolution during plasma etching. II. Polycrystalline silicon etching
Authors: Lane J. M. , Klemens F. P. , Bogart K. H. A. , Malyshev M. V. , Lee J. T. C.
Published: July 2002

The effect of source power, bias power, chamber pressure, flow rate, and feed gas composition on profile evolution during polycrystalline silicon etching with an oxide hardmask has been studied in a transformer-coupled plasma system. The large resultant data set provides a comprehensive look at feature evolution as plasma parameters are varied. This data set is valuable for evaluating the importance of several proposed mechanisms for feature evolution and for validating computational models. Microtrench formation was found to be a strong function of the plasma condition. A correlation between sidewall shape and microtrench development was observed. Profile development was found to be highly sensitive to feed gas composition. Results are consistent with a previous study on the etching of crystalline silicon under identical plasma conditions.
X-ray photoelectron spectroscopy studies of novel Π-conjugated ethynyl thiophene containing Pd(II) complexes and of their interaction with chromium
Authors: Iucci G. , Polzonetti G. , Altamura P. , Paolucci G. , Goldoni A. , Russo M. V.
Published: July 2002

The structure of some novel oligomeric thiophene-containing π-conjugated Pd(II) complexes, recently prepared in our laboratory, Cl–Pd(PBu3)2-C≡C–C4H2S-C≡C–C4H2S–C≡C–C4H2S–C≡C-Pd(PBu3)2Cl or Pd–TRI and Cl[–Pd(PBu3)2–C≡C–C4H2S–C≡C–]3–Pd(PBu3)2Cl or Pd–DET, were studied by means of x-ray photoelectron spectroscopy. The interface formation between chromium and the organometallic π-conjugated polymer films was also investigated. Chromium was evaporated stepwise in situ onto the surface of the polymer films and the XPS core-level spectra of the polymer and of the metal overlayer were studied as a function of Cr coverage. A charge-transfer reaction from the deposited metal atoms to the substrate material was evidenced by the modifications taking place in the polymer spectra upon Cr deposition. A comparison with the surface reactivity towards chromium of [–Pd(PBu3)2–C≡C–C6H4–C6H4–C≡C–]n, Pd–DEBP, a related polymer where benzene groups replace thiophene in the organic conjugated moiety, will be discussed.
Annealing studies on monocrystalline CuInSe2 used as substrates in photovoltaic cells
Authors: Champness C. H. , Ahmad G. I.
Published: July 2002

Partial conductivity-type conversion has been observed in monocrystalline p-type CuInSe2 samples after heat treatment in argon at atmospheric pressure at a temperature of 500 °C. The hole concentration in the samples at room temperature was about 1017 cm−3. The depth of the outer converted n layer in the original p-type material, as determined by hot probing and etching, increased approximately as the square root of the annealing time. This variation suggested an outdiffusing acceptor with a diffusion coefficient at 500 °C of about 7.3×10−7 cm2 s−1 and a compensation donor/acceptor concentration ratio in the original p-type material of less than 10%. Auger profiles recorded on similar stoichiometrically prepared monocrystals, after annealing at 350 °C for 2 h, indicated a 2%–4% loss of Se, thus identifying this element as the main outdiffusing agent.
Ultrathin oxynitride formation by low energy ion implantation
Authors: Khoueir A. , Lu Z. H. , Ng W. T. , Ma Y.
Published: July 2002

Oxynitride films have been formed by rapid thermal processing of N-implanted wafers. The formation mechanism, the chemical composition, and the physical thickness of the oxynitride films were studied by x-ray photoelectron spectroscopy (XPS). Segregation of nitrogen to the surface was performed on nitrogen ion-implant wafers under nitrogen gas. The outcome of the segregation is the formation of an ultrathin oxynitride layer ranging in thickness from 4 to 8.5 Å . Oxidation of nitrogen ion-implanted wafers, where the nitrogen is segregated beforehand and nitrogen ion-implanted wafers with no segregation prior to oxidation, is the focus of this study. XPS results showed that simultaneous segregation and oxidation forms an oxynitride film consisting of two layers where the interface is rich in nitrogen and the surface in oxygen. In the case of nitrogen segregation prior to oxidation, the nitrogen atoms in the oxynitride film, formed at oxidation temperatures less than 1000 °C, are uniformly distributed throughout the film in the form of SiOxNy. At high temperatures (∼1100 °C), the composition of the oxynitride formed by simultaneous segregation and oxidation becomes similar to that where N-segregation is performed prior to oxidation. The presence of nitrogen atoms retards significantly the diffusion of oxygen to the substrate surface thus producing uniform ultrathin films ranging in thickness from 13 to 40 Å.
Direct extraction of the channel thermal noise in metal-oxide-semiconductor field effect transistor from measurements of their rf noise parameters
Authors: Chen Chih-Hung , Deen M. Jamal
Published: July 2002

This article presents an extraction method to obtain the channel thermal noise in metal-oxide-semiconductor field effect transistor (MOSFETs) directly from the dc, scattering parameter and rf noise measurements. In this extraction method, the transconductance (gm), output resistance (RDS), and source and drain resistances (RS and RD) are obtained from dc measurements. The gate resistance (RG) is extracted from scattering-parameter measurements, and the equivalent noise resistance (Rn) is obtained from rf noise measurements. This method has been verified by using the measured data of a 0.36 μm n-type MOSFET up to 18 GHz. Comparisons between simulated and measured characteristics of noise parameters versus frequency are also presented.
Scaling the SiGe channel pmetal–oxide–semiconductor field effect transistor: The case for p+SiGe gates
Authors: Wong D. M. , Tarr N. G.
Published: July 2002

A theoretical study of the scalability of the SiGe channel pmetal–oxide–semiconductor field effect transistor to the 0.1 μm generation is presented. Devices with n+ polysilicon gates, p+ polysilicon gates, and intermediate workfunction p+ SiGe gates were considered. It was found that short channel effects became severe in the n+ gated device for channel lengths below 0.15 μm. The p+ gated device provided excellent short channel behavior, but suffered from a very poor crossover voltage. The best compromise between short channel effects and crossover voltage was obtained with the p+ SiGe gate, which gave −VCROSS close to VDD and VDIBL≈98 mV in the 0.1 μm generation.
Two-dimensional simulation of the transient electrothermal effects during the gate turn-off thyristor turn-off
Authors: Mezroua F. Z. , Abid R.
Published: July 2002

The electrothermal behavior of a 1200V-30A gate turn-off (GTO) thyristor operating in its electrical circuit has been studied using two-dimensional (2D) simulation tools. The program realized for this purpose uses a combination of Silvaco tools and takes into account the thermal environment of the GTO. It was validated by direct experimental measurements. The studied GTO is a silicon device with a symmetrical doping profile (N+PN−P+). It operates in a dc-dc converter at a 400 Hz commutation frequency, its conduction time is in the range of 0.05–0.25 ms. The thermal environment of the device is reproduced by including its thermal parameters and those of its package in the calculation, the simulation accounts, then, for all the thermal generation and conduction in the device. The simulation program was validated by comparing the electrical parameters (anode and gate currents, anode–cathode voltage, and dissipated power) of the GTO, obtained in the same operating conditions, by both simulation and direct measurements. The transient behavior of the GTO during its turn-off at a nanosecond scale was then obtained. We first obtained the 2D time-dependent distribution of most of the internal electrical parameters (carriers, current density, …); then we obtained the 2-D time-dependent distribution of temperature inside the GTO.
Application of direct bias control in high-density inductively coupled plasma etching equipment
Authors: Patrick Roger , Baldwin Scott , Williams Norman
Published: July 2002

The use of a novel method of power delivery control at the wafer chuck in a high-density inductively coupled plasma reactor has been investigated. This method involves using a peak voltage sensor mounted immediately below the chuck in a feedback loop to the rf generator such that the rf peak voltage can be set as a recipe parameter. By controlling the power delivery in this manner, it is demonstrated that the effects of power losses in the rf circuit between the generator and the chuck, especially in the match network, can be compensated for. In addition, the effect of interactions among source power, bias power and other process parameters on sheath voltage can also be eliminated. In this manner a more complete decoupling of plasma density and ion energy can be achieved than more conventional methods of power delivery allow.
Study of the ignition behavior of a pulsed dc discharge used for plasma-assisted chemical-vapor deposition
Authors: Beer Thomas A. , Laimer Johann , Störi Herbert
Published: July 2002

An investigation of a pulsed dc discharge used for plasma-assisted chemical-vapor deposition of titanium nitride has been performed in order to understand the nonuniformity of quality and thickness of the deposited films. The experiments have been performed using a gateable image intensifier to study the temporal and spatial light intensity of the discharge. Additionally, a single Langmuir probe has been used to study the temporal evolution of the plasma potential and the charged particle density. The influence of varying parameters like geometry, gas composition, voltage, pressure, duration of the pulses, etc., on the spreading of the plasma has been investigated. Our experiments reveal that in the presence of electronegative species like TiCl4, which is a source gas for the production of titanium nitride, the spreading of the discharge along the substrates is slow, reaching some parts of the reactor with substantial delay. The result is a nonuniform plasma power density in front of the cathode as well as a spatially varying exposure time of the surface to the plasma. These effects are the reason for the inhomogeneity of the deposited films. The experiments revealed that the slow spreading of the discharge is accompanied with low local cathode fall voltages. The problems with the slow spreading of the discharge can be solved by measures which increase the conductivity of the plasma at the beginning of the pulses. The effectiveness of such measures has been studied.
Optical breakdown of InGaAsP/InP based multiquantum well optical attenuators
Authors: Boudreau M. , Yan J. , Hobbs L.
Published: July 2002

This work describes a technique for halting the optical breakdown process in reverse biased p-i-n structures under high optical stress before significant damage to the material can occur. The devices investigated are waveguide based InGaAsP/InP multiquantum well structures used as optical attenuators or modulators. Analysis of the devices using focused ion beam milling and scanning electron microscopy can identify the point within the device where the optical breakdown is initiated, and demonstrates that optical damage is greatly limited by this technique. The degree of damage is controlled, and is correlated to the increase in dark current measured in the device. The technique can allow for a clear understanding of how the breakdown process begins, as well as its dependence on device design. In addition, comparisons between the site where breakdown is initiated and the predicted site calculated from a finite element thermal model of the device are made.
Widely tunable self-assembled quantum dot lasers
Authors: Hinzer K. , Allen C. Nı́. , Lapointe J. , Picard D. , Wasilewski Z. R. , Fafard S. , SpringThorpe A. J.
Published: July 2002

Quantum dot laser diodes with up to five well-defined electronic shells are fabricated using self-assembled quantum dots (QDs) grown by molecular beam epitaxy. At 77 K, we tune the lasers from the first to the fourth excited state of the QDs by varying the cavity length, this covers a wavelength range from 869 to 963 nm. At room temperature, we obtain lasing from the second to the fourth excited state covering the 938 to 984 nm wavelength range. For high injection currents, a large part of the QD ensemble contributes at once to the stimulated emission yielding a lasing emission linewidth having a full width at half maximum of 25 nm. By increasing the energy spacing between the QD energy level contributing to the lasing and the wetting layer energy levels, improved thresholds at higher temperatures are observed, leading to lasing below 100 A/cm2 at room temperature.
Two-dimensional gain profiles of InP/InGaAs separate absorption, grading, charge, and multiplication avalanche photodiodes modeled by a simplified stochastic approach
Authors: Xiao Yegao G. , Deen M. Jamal
Published: July 2002

The two-dimensional (2D) gain profiles of InP/InGaAs separate absorption, grading, charge, and multiplication (SAGCM) avalanche photodiodes (APDs) have been modeled by using a simplified stochastic approach. The influence of the curved diffusion edge on the electric field in the periphery has been considered and electric field equations have been derived from the cylindrical Poisson’s equation. The electric field in the multiplication layer is significantly reduced when a partial charge sheet is incorporated in the device’s periphery. The modeled 2D gain profile for such a device agrees with experiment and demonstrates an effective suppression of the premature edge breakdown. These results and the uniformity issue of the 2D gain profiles are further discussed. From our analyses, we find that controlling the diffusion process within the p+ InP top layer and patterning the charge sheet mesa structure are most likely to affect the uniformity and symmetry of the 2D gain profiles for the InP/InGaAs SAGCM APDs.
Photoconductor selection for digital flat panel x-ray image detectors based on the dark current
Authors: Kasap S. O. , Rowlands J. A.
Published: July 2002

We consider a flat panel direct conversion x-ray image detector in which a photoconductor is used to directly convert absorbed x-ray photons to collectable electron hole pairs. The storage capacitor at each pixel stores a quantity of charge proportional to the incident radiation. The charge stored at each pixel is read out every Δt seconds. Based on a condition for a minimal dynamic constraint, we have examined the corresponding range of constraints on the material properties to establish approximate x-ray photoconductor selection criteria. We consider requirements for radiology and fluoroscopy in which Δt=1 and 1/30 s, respectively. When the electrical contacts are totally blocking, the dark current is limited by bulk thermal generation. Minimum band gap Eg requirements depend on the concentration of defects Nd around the Fermi level and their recombination cross section Sr. For single crystal photoconductors with a neutral-defect concentration of the order of ∼1014 cm−3, we need Eg>1.5 eV for fluoroscopy and Eg>1.7 eV for radiology. For high purity single crystals, these band gap values can be lower, for example, Eg≈1.42 eV (GaAs) requires Nd<1012 cm−3. In the case of amorphous semiconductors, the dark current is due to the emission of carriers from a distribution of localized states in the energy gap. For a maximum integrated concentration of ∼1016 cm−3 of localized states around the Fermi level, calculations suggest Eg>1.75 eV for fluoroscopy and Eg>1.9 eV for radiology; amorphous selenium readily satisfies these conditions. When the dark current is controlled to thermal emission from the metal electrode into the semiconductor over a potential barrier φB (i.e., bulk thermal generation of carriers is negligible) then we find that the required Schottky barrier φB can be expressed in terms of the band gap Eg. For Schottky barriers φB∼0.6Eg, Eg>1.8 eV for fluoroscopy and >2.0 eV for radiology.
Secondary ion mass spectrometry and x-ray photoelectron spectroscopy correlation study of nitrided gate oxide
Authors: Bradbury C. A. , Blackmer C.
Published: July 2002

Reliability of dielectric films such as silicon dioxide in the metal–oxide semiconductor gate insulator has become a key issue as devices shrink in size. Many of the problems associated with reduction in both the width and thickness of the gate oxide can be controlled with the addition of nitrogen. Nitrogen incorporation into the oxide has been shown to have significantly better charge trapping properties, less interface state generation, and more resistance to continued oxidation and incorporation of impurities. The nitrogen also acts as a barrier to diffusion of dopants from the silicon substrate. The amount of nitrogen present and its location in the oxide control the extent to which each of these properties is exhibited. The concentration and distribution of nitrogen in gate oxides was studied using secondary ion mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS). The SIMS analysis used Cs ion bombardment and detection of the CsN+ cluster to reduce the matrix effects associated with profiling from silicon oxide into silicon. A procedure was developed for XPS to provide the necessary signal to noise required for these low nitrogen concentrations. In addition to comparing the concentrations and spatial resolution of the nitrogen in the gate oxide, repeatability studies were also performed for each technique.
Effects of ultraviolet illumination on dry etch rates of NiFe-based magnetic multilayers
Authors: Cho H. , Lee K. P. , Hahn Y. B. , Lambers E. S. , Pearton S. J.
Published: July 2002

NiFe and NiFeCo were dry etched in inductively coupled plasma Cl2/Ar and CO/NH3 discharges, either with or without concurrent UV illumination from a Hg arc lamp. No enhancement was observed for CO/NH3 etching of the two materials, or for Cl2/Ar etching of NiFe. However, enhancements in etch rate of up to a factor of three were observed for Cl2/Ar etching of NiFeCo when ultraviolet (uv) illumination was employed. The etched surface morphologies were similar both with and without the UV irradiation. The etch rates in Cl2/Ar discharges were strongly correlated with the amount of chlorinated residues detected on the surface by Auger electron spectroscopy, indicating that the desorption of the metal chloride reaction products was the rate-limiting step in the etching.
Decomposition of 1,3-butadiene on Ru(001): Evidence for a (CH)4 metallacycle
Authors: Weiss Michael J. , Hagedorn Christopher J. , Weinberg W. Henry
Published: July 2002

The adsorption and thermal decomposition of 1,3-butadiene has been studied on Ru(001). Starting with a condensed multilayer at 80 K, the decomposition of 1,3-butadiene was monitored as a function of temperature using temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). Annealing the multilayer-covered surface to 800 K results in the decomposition of some of the adsorbed 1,3-butadiene, leaving a surface carbon coverage corresponding to 0.67±0.03 carbon adatoms per surface ruthenium atom, as determined by titration with oxygen. As the butadiene decomposes between 230 and 700 K, hydrogen desorbs in an amount corresponding to 1.01±0.05 adatoms per surface ruthenium atom. A HREEL spectrum taken after annealing to 260 K for 10 s provides spectroscopic evidence for the presence of a (CH)4 metallacycle decomposition product. This assignment is consistent with and supported by the determination of a surface stoichiometry of CH1.04±0.11 using TPD spectra. The formation of the catalytically important (CH)4 metallacycle has been predicted theoretically, but this work represents the first experimental evidence for the formation of this intermediate from the decomposition of 1,3-butadiene.
Reaction between NO and CO on rhodium (100): How lateral interactions lead to auto-accelerating kinetics
Authors: Hopstaken M. J. P. , Niemantsverdriet J. W.
Published: July 2002

The reactions between NO and CO adsorbed on Rh(100) were studied with temperature programmed reaction spectrometry and static secondary ion mass spectrometry and compared with similar reactions on Rh(111). Elementary steps in the overall reactions, such as dissociation of NO, and reaction between CO and O atoms were studied as well. Dissociation of NO is faster on the more open Rh(100) surface, while formation of N2 is slower. Desorption of either CO or NO occurs at comparable rates on Rh(100) and Rh(111). The oxidation of CO to CO2 proceeds much faster on Rh(100) than on Rh(111). When the Rh(100) surface is saturated with NO and CO, explosive formation of CO2 is observed, which can be explained by an autocatalytic mechanism, in which the availability of empty sites plays a crucial role.
Preparation of Co and CoNx thin films by unbalanced radio frequency magnetron sputtering
Authors: Tanaka T. , Kawabata K. , Kitabatake A.
Published: July 2002

We have developed a modified process based on an unbalanced magnetron sputtering of a magnetic Co target (100 mm φ, 5 mm thick) to deposit Co and CoNx films. The plasma confinement can be controlled by the shape of the magnetic field in the sputter deposition device with a multipolar magnetic-field plasma confinement. Cobalt films were prepared by this sputtering system at the radio frequency powers of 100–200 W and argon pressure down to 8.0×10−2 Pa. It is shown that the deposition rate of Co films significantly increases from 8.7 to 25 nm/min whose values are two times that of a conventional magnetron sputtering. A Co film with the orientation of (111) plane is formed and the value of the grain size estimated from the plane is about 30 nm. Cobalt nitride (CoNx) films were also prepared by unbalanced magnetron sputtering in a plasma of an argon and nitrogen gas mixture. It is also found from the results of electron probe microanalysis that the content of nitrogen in CoNx films increases with the increasing gas flow ratio of N2. The electrical resistivity for reactively sputtered films is less than 80 μΩ cm, which makes this compound a relatively good conductor.
Electrical properties and surface morphology of heteroepitaxial-grown tin-doped indium oxide thin films deposited by molecular-beam epitaxy
Authors: Taga Naoaki , Shigesato Yuzo , Kamei Masayuki
Published: July 2002

Heteroepitaxial growth of nondoped indium oxide (IO) and Sn-doped indium oxide (ITO) thin films was carried out on optically polished single-crystalline yttria-stabilized zirconia (YSZ) substrates by molecular-beam epitaxy. The surface morphology of the epitaxial films was analyzed by field-emission-type scanning electron microscopy. The IO and ITO films showed quite different surface morphology, implying that the crystal-growth mechanisms were strongly affected by the Sn doping. The surface migration of In on the (111) plane should be suppressed with increasing Sn concentration, resulting in the relatively large growth rate along the 〈111〉 direction. The epitaxial IO film deposited on YSZ(001) substrate showed very high mobility (μ=86 cm2/V s) and low carrier density (n=3.5×1018 cm−3). Sn doping by 2.6 at. % increased the carrier density by 6.5×1020 cm−3, where doping efficiencies were about 81%.
Application of porcelain enamel as an ultra-high-vacuum-compatible electrical insulator
Authors: Biscardi C. , Hseuh H. , Mapes M.
Published: July 2002

Many accelerator vacuum system components require electrical insulation internal to the vacuum system. Some accelerator components at Brookhaven National Laboratory are installed in ultra-high-vacuum systems which require the insulation to have excellent vacuum characteristics, be radiation resistant, and be able to withstand high temperatures when used on baked systems. Porcelain enamel satisfies all these requirements. This article describes the process and application of coating metal parts with porcelain enamel to provide electrical insulation. The mechanical and vacuum testing of Marman flanges coated with porcelain and using metal Helicoflex seals to form a zero-length electrical break are detailed. The use of porcelain enameled parts is attractive since it can be done quickly, is inexpensive and environmentally safe, and most of all satisfies stringent vacuum system requirements.