bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactive ion etching of crystalline silicon using NF3 diluted with H2
Authors: Sidhwa A. J. , Goh F. C. , Naseem H. A. , Brown W. D.
Published: July 2002

Experimental and modeling work was performed to examine the etch rates and etch profiles during the reactive ion etching of crystalline silicon using NF3 diluted with H2 as a function of reactor pressure, etchant gas flow, rf power, and external dc voltage. All experiments were carried out at a frequency of 13.56 MHz. A regression model for the etch rate was developed using a statistical analysis program and the effects of the variables were studied using the e−chip computer program. In the early work on plasma etching of silicon using NF3 diluted with H2, a deposited layer was detected at high H2 dilutions. After a thorough study, it was determined by infrared spectroscopy that the deposit was ammonium hexafluorosilicate, (NH4)2SiF6. Utilizing the ammonium hexafluorosilicate as a side wall passivation layer and by a judicious choice of etching parameters, anisotropic etching of silicon was obtained. The gas phase concentration of NF3 was varied from 10% to 90%. No etching of silicon was obtained for 10%–40% NF3. By increasing the rf power, the self-bias increases but the deposit formation decreases. Low rf power was used to assist the formation of the deposit which acts as a side wall passivation layer during the etching process. A high external dc voltage (−500 V) promotes anisotropic etching at high etch rates.
Pumping of helium and hydrogen by sputter-ion pumps. I. Helium pumping
Authors: Welch K. M. , Pate D. J. , Todd R. J.
Published: July 2002

This article is divided into two parts. Part I deals with the pumping of helium by sputter-ion pumps, where Part II, to follow in a subsequent publication in this journal, deals exclusively with the pumping of hydrogen. In Part I, quantitative data are given for the He speeds and capacities of both noble and conventional diode and triode pumps. The effectiveness of various pump regeneration procedures, subsequent to the pumping of He, is reported. These included bakeout and N2 glow discharge cleaning. The comparative desorption of He with the subsequent pumping of N2 is reported on. The N2 speeds of these pumps were used as the benchmarks for defining the size of the pumps versus their respective He speeds.
Quick acquisition of clean ultrahigh vacuum by chemical process technology
Authors: Tatenuma K. , Momose T. , Ishimaru H.
Published: July 2002

Baking of vacuum system for removing adsorbed water is essential and important treatment to shorten pumping time and obtain clean UHV. Removing adsorbed water by chemical treatment, based on the decomposition and dissociation of O–H bond of the adsorbed water, was examined as an alternative method of rapidly attaining UHV conditions. Several experiments have been done using typical water decomposing gases, which are organic silane compounds, dichloro-propane and halogen gases, introduced and exposed to the vacuum chamber made of an aluminum alloy. In these gases, dichloro-propane gas exposed in vacuum chamber at a temperature of 50–100 °C and pressure (0.01–40 Torr) particularly shortens the pumping time to 1/4–1/500 of the time required without dichloro-propane treatment to obtain less than 10−8 Torr. For the exposure conditions of dichloro-propane gas at 70 °C and 0.1 Torr, a quadrupole mass spectrometer showed no remaining dichloro-propane gas and reaction products within 0.5 h after pumping started. This technology is available to obtain clean UHV in a short time and has a possibility to be used as a UHV technique instead of an ordinary baking.
First-principles electronic properties of model silicon-based quantum wires
Authors: Mintmire J. W.
Published: July 2002

Porous silicon materials created by etching with hydrofluoric acid solutions exhibit an anomalous photoluminescence intensity. One proposed origin of this behavior has been quantum size effects in silicon fibers with nanometer-scale diameter in the porous silicon material. We present first-principles results for the electronic structure and selected electronic properties—in particular for the optical absorption—of silicon fibers chosen as chemically realistic models of quantum wires.
X-ray and vacuum ultraviolet imaging for electron cyclotron resonance processing plasmas
Authors: Chew K. H. , Shohet J. L. , Castagna T. J. , Seaward K. L. , Mertz F. F.
Published: July 2002

Electron cyclotron resonance (ECR) plasma systems are currently being investigated for plasma etching and plasma enhanced chemical vapor deposition. ECR generates high charged-particle densities at lower operating pressures which permits a higher degree of directionality for plasma etching, but produces low-energy x rays and vacuum ultraviolet radiation (VUV). Both types of radiation may cause damage to the wafer being processed. To reduce or shield the radiation damage, one would need to determine the spectrum and locations where the radiation is produced. The regions of radiation production can be determined by the image obtained from a pinhole camera placed along and across the center line of the dc magnetic field. The location of x-ray production could be changed by altering the shape of the dc magnetic field. The results verify that x rays are produced whenever hot electrons that travel along magnetic field lines strike the chamber walls. Similar methods were used to image the VUV radiation. The images show that the VUV is produced over the entire bulk plasma in addition to locations of wall bremsstrahlung where the x rays were produced.
Growth of thin Ti films on Al(110) surfaces
Authors: Saleh Adli A. , Shutthanandan V. , Smith R. J.
Published: July 2002

High-energy ion scattering, x-ray photoemission spectroscopy, and low-energy electron diffraction (LEED) were used to study the interfacial reaction of very thin Ti films on Al(110) surfaces. The Al surface peak areas in the backscattering spectra of 0.96 MeV He+ ions incident along the [1̄1̄0] direction decreased sharply during the deposition of the first four monolayers of Ti. This suggests a growth model in which an ordered Ti overlayer shadows the Al surface atoms. This model is supported by electron diffraction measurements where sharp diffraction spots persisted with the rectangular symmetry of the substrate. Throughout this coverage regime, photopeak intensities due to Al were attenuated strongly with Ti coverage. With additional Ti deposition the Al surface peak intensities increase while the Al photopeak intensities remain unchanged, indicating a reaction at the Ti/Al interface that exposes additional Al surface atoms to the incident ion beam. Ion scattering spectra taken with the He+ ion beam incident along a random direction with respect to the Al substrate exhibit increased Ti peak areas indicating Ti shadowing. A LEED pattern was observed throughout the experiment suggesting the formation of an ordered overlayer. We present a growth model to explain these observations.
Reactive coevaporation of DyBaCuO superconducting films: The segregation of bulk impurities on annealed MgO(100) substrates
Authors: Smilgys Russell V. , Robey Steven W. , Chiang C. K. , Hsieh T. J.
Published: July 2002

This article reports results from a study on the effect bulk impurities in MgO substrates may have when substrates are annealed to improve film microstructure and transport properties. DyBaCuO thin films are prepared by molecular beam reactive coevaporation on both annealed and unannealed MgO(100). While predeposition annealing has led to improved film quality for some groups, under our conditions just the opposite occurs. We point out the existence of Ca segregation to the MgO surface as a factor that needs investigation because Ca is a common contaminant in commercially supplied MgO. Atomic force microscope images show decoration of annealed substrates with submicron size particles that may be composed of the segregated Ca. These particles seem to underlie the distinct differences seen in the surface microstructure of films on annealed and unannealed substrates. In the case of annealed substrates a more random microstructure is promoted. Under identical growth conditions, outgrowths present in films on unannealed (mechanically polished) substrates are oriented in an ordered pattern. These findings suggest that the expected benefits from predeposition annealing can be negated when significant surface segregation of bulk contaminants occurs.
Properties of ferroelectric PbTiO3 films grown in an ionized cluster beam system
Authors: Huffman Maria , Kalkur T. S. , Kammerdiner L. , Kwor R. , Levenson L. L. , Reeder M.
Published: July 2002

Two ionized cluster beam (ICB) sources were used to deposit PbTiO3 films 300 nm thick onto Pt-metallized, oxidized Si wafers 100 mm in diameter. Pb was deposited from one ICB source and Ti from the other. The deposition was carried out in a mixture of O2 and 6% O3 at a total pressure of 5×10−5 Torr. No substrate heating was used during deposition. However, thermal radiation from the ICB sources caused the substrate temperature to reach approximately 100 °C soon after the start of deposition. The as-deposited films were amorphous according to x-ray diffraction patterns. Annealing the films at 550 °C in 1 atm pressure O2 for 1 h led to the formation of a mixture of a perovskite-type phase and possibly some pyrochlore- and PbO-type structures. However, an anneal at 750 °C for 1 h in 1 atm pressure O2 produced the perovskite phase PbTiO3 with no other detectable phases. It was found that a slightly Pb-rich or stoichiometric Pb/Ti ratio in as-deposited films gave the best ferroelectric film properties. A Pb/Ti ratio much higher than stoichiometric (Pb/Ti ratio≳2) led to the formation of pits and pinholes in the films after annealing at 750 °C, whereas a Pb/Ti ratio lower than stoichiometric did not produce the perovskite phase after annealing at 750 °C. The pits and pinholes associated with Pb/Ti ratio larger than stoichiometric were probably caused by the evaporation of excess PbO during annealing. Films were deposited with and without the use of ionization and acceleration to 2 keV. In both cases, the as-deposited films were amorphous. There were no substantial differences between annealed films deposited with or without ionization and acceleration of the Pb and Ti beams. Ferroelectric domains in the annealed films have been observed by transmission electron microscopy. Ferroelectric switching (hysteresis loops) was recorded in annealed PbTiO3 films with stoichiometric Pb/Ti ratios after the films were capped with Pt to form small capacitors.
Oxidation behavior of annealed CoCr thin films
Authors: Demczyk B. G.
Published: July 2002

CoCr alloy thin films have solicited interest as potential perpendicular recording media. Enhancement of magnetic properties has been observed upon annealing. In this work, elemental redistribution and subsequent oxidation in annealed magnetron-sputtered Co-25%Cr alloy thin films of thicknesses 10 and 50 nm have been investigated by X-ray photoelectron spectroscopy. Results indicate that chromium redistribution to the surface occurs upon extended annealing (360 °C, 10−6 Torr). Furthermore, it was found to be the most extensive in films exhibiting a columnar (high angle boundary) microstructure. This chromium is preferentially oxidized, thus preserving the desired magnetic properties of the cobalt-based thin film.
Effects of chlorine based gettering on the electrical properties of rapid thermal oxidation/nitridation dielectric films
Authors: Kim Youn Tae , Jun Chi Hoon , Chung Sang-Koo
Published: July 2002

Dielectric films have been grown on single-crystalline silicon substrates with the thickness ranging from 100 to 180 Å at various gas and temperature conditions by using a rapid thermal processing that included an independent nitridation step. The film characteristics and their dependence on the additive contents of the hydrogen chloride gas and the processing time have been studied. The additive concentration of the hydrogen chloride gas in the oxidizing atmosphere were changed from 0% to 8%. By the addition of the hydrogen chloride gas, the oxidation rates and the initial oxide thickness were significantly increased, but after sequential nitridation processes the thickness of the films was nevertheless a little bit varied within 10 Å. The effective refractive index of the dielectric films were slightly changed with the additive contents of hydrogen chloride gas, and increased rapidly after nitridation process. All the samples of the dielectric films show the increased breakdown voltages and decreased average breakdown strength in proportion to the additive contents of the hydrogen chloride gas, as a result of the increment of the initial oxide thickness. In the nitridation of silicon dioxide films, the dielectric constant was increased by the addition of the hydrogen chloride gas. The accumulation capacitance was increased after nitridation of silicon oxide film which formed in the hydrogen chloride gas free atmosphere, due to the increased dielectric constants of the rapid thermal nitridation films as well as the actual change in the film thickness. But, after nitridation of hydrogen chloride gas processed oxide, the flatband voltages shift monotonically toward negative voltages, however the maximum capacitance value was decreased with the increase of additive concentration of the hydrochloric gas.
Preparation of amorphous BaTiO3 thin films on indium tin oxide-coated soda lime glass by metalorganic chemical vapor deposition
Authors: Yoon Y. S. , Lee D. H. , Kim T. S. , Oh M. H. , Yom S. S.
Published: July 2002

Metalorganic chemical vapor deposition of BaTiO3 thin films on indium tin oxide–coated soda lime glass substrate in the temperature range between 400 and 550 °C was investigated to produce an insulating layer with high breakdown voltage and a smooth surface for electroluminescence display. In order to prevent the diffusion of sodium ions toward the indium tin oxide layer and BaTiO3 insulating layer, the deposition temperature should not be higher than 500 °C. X-ray diffraction patterns showed that the BaTiO3 thin film deposited at 400 °C was amorphous. The stoichiometry of the films was identified by Auger electron spectroscopy. Scanning electron microscopy results suggested that BaTiO3 thin films deposited at 400 °C had smooth surfaces without defects such as pinholes and clusters, but surface flatness decreased at the deposition temperature of 550 °C. The dielectric constant was 12.9. The breakdown voltage determined from current–voltage measurements was as large as 2×106 V/cm.
Characterization by Auger spectroscopy of niobium–aluminum oxide–niobium sandwiches for Josephson junctions
Authors: Lacquaniti V. , Bergoglio M. , Steni R.
Published: July 2002

Auger electron spectroscopy (AES) combined with ion sputtering was used to study the chemical composition of Nb–Al2O3–Nb thin film sandwiches. Attention was focused on the interfaces between the aluminum oxide and the two niobium films, because they are responsible for the electrical quality of the Josephson junctions based on these sandwiches. The real composition of the analyzed interfaces as a function of thickness was reconstructed from the AES signal intensities versus time data through an approximate conversion method. The obtained results show that the niobium layers adjacent to these interfaces are less pure than the rest of the films, due to aluminum and oxygen diffusion: a gradual aluminum diffusion up to 10–20 nm in the base niobium film was found.
Depth profile optimization
Authors: Naumkin A. V. , Vasilyev L. A.
Published: July 2002

The method for determination of the interface proximity during depth profiling carried out using x-ray photoelectron spectroscopy and Auger electron spectroscopy in combination with ion etching is described. The optimization procedure is based on the additional registration of the true secondary electron peak (TSEP) taking into account that the true secondary electrons have greater escape depth and the peak energy position considerably depends on the work function alterations. The proposed method uses TSEP spectral characteristics that are capable of predicting the approach of the interface in advance compared to the traditional methods. Since the intensity of TSEP is much greater compared to that of Auger and photoelectron lines, then the time to register it is sufficiently less than the characteristic spectral acquisition time. On the other hand, the TSEP may be registered during ion etching as a result of ion-induced electron emission. The obtained results show that ion electron emission is very convenient for monitoring sputtering.
Combined instrument for the on-line investigation of plasma deposited or etched surfaces by monochromatized x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry
Authors: Jahn P. W. , Petrat F. M. , Wolany D. , Deimel M. , Gantenfort T. , Schmerling C. , Wensing H. , Wiedmann L. , Benninghoven A.
Published: July 2002

A combined instrument has been developed for the investigation of plasma deposited or etched surfaces which couples a versatile chemical reaction chamber on-line with a surface analytical system. The plasma can be generated either by microwave (2.45 GHz) or radio frequency (13.56 MHz) excitation, with and without magnetic field assistance. The surface analytical part of the instrument is equipped with monochromatized x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Auxiliary energy or mass spectroscopic techniques can be applied where necessary. All spectroscopies can be performed while the sample is heated or cooled. We report on the general design and the performance of the instrument, as well as first applications in the fields of polymer analysis and bioengineering.
Compact metalorganic molecular-beam epitaxy growth system
Authors: Hamm R. A. , Ritter D. , Temkin H.
Published: July 2002

This article describes a compact growth system specifically designed for metalorganic molecular-beam epitaxy (MOMBE) of InP-based materials. The system is designed to take full advantage of the MOMBE method, in particular the premixing of the group III and V precursors, respectively, and the elimination of large solid effusion cells. The system uses a fixed sample heating stage which is designed for indium wafer mounting, up to a 2 in. diameter, on molybdenum blocks. Temperature control during growth is done with a thermocouple inserted directly into the sample block with a small charge of indium to provide intimate thermal contact. Sample loading is done vertically from above in order to load the sample in the growth position. The system is controlled by a personal computer, which also replaces all of the analog temperature and pressure controllers. Initial results on 2-in. diameter wafers indicate excellent uniformity of the composition, Δa/a=±2×10−4 for InGaAs, and photoluminescence, ±4.5 nm for InGaAsP, respectively. In addition, high-speed InGaAs/InP heterostructure bipolar transistors and charge injection transistors grown in this system have demonstrated fT’s of 125 and 73 GHz, respectively.
Development of a primary standard ultrahigh vacuum calibration station
Authors: Levine P. D. , Sweda J. R.
Published: July 2002

The Metrology Laboratories at Lockheed Missiles & Space Company (LMSC) are required to calibrate a variety of vacuum gages in support of research programs and manufacturing processes. Currently, primary standards for this purpose are obtained through calibration at the National Institute of Standards and Technology (NIST), which is a costly and time-consuming process. In an effort to reduce the reliance on external sources of calibration, this laboratory has developed an ultrahigh vacuum primary standard. A constant-volume, pressure drop flow meter designed at LMSC is used to generate a known flow rate of gas in a vacuum chamber partitioned by an orifice of calculated conductance. The pressure drop across the orifice at constant flow uniquely defines chamber pressure as a function of flow rate while in molecular flow. This constitutes a vacuum standard relying on dimensional, volumetric ratio, and differential pressure measurements only. The system was designed for use in realizing absolute pressures in the range from 10−9 to 10−3 Torr. Calculated pressures in the range from 10−6 to 10−3 Torr are compared to those measured by a NIST-calibrated spinning rotor gage. The overall viability of the system as an intrinsic standard is assessed and plans for future development towards that end discussed.
Structure and properties of titanium nitride thin films deposited at low temperatures using direct current magnetron sputtering
Authors: Elstner F. , Ehrlich A. , Giegengack H. , Kupfer H. , Richter F.
Published: July 2002

Titanium nitride layers on silicon substrates have been deposited by magnetron sputtering at a constant temperature of 200 °C using nitrogen partial pressures (pN2) from 0.001 to 0.36 Pa. Distinct dependences between pN2 in the reactive gas and the mechanical and structural properties of the layers could be found by x-ray diffraction and other methods. The general absence of the Ti2N phase in layers deposited at low temperatures can be explained by the high energy impact of energetic particles during the deposition process as well as by the limited mobility of adatoms due to the low substrate temperature. Two different cases of lattice distortions were detected for low and high pN2, respectively. In the higher pressure range the lattice parameters a1110 are greater than the a2000. For this the variable density of interstitial sites in different planes together with the macroscopic film stress was found to be responsible. At lower pN2 the a1110 was smaller than the a2000. This effect could be explained by the presence of a high number of vacancies in the lattice influencing the chemical bonding and thus leading to an anisotropy of the stability of the interplanar spacings. From that macroscopic stresses results in an anisotropic deformation of the film crystallites. Both explanations could be supported by annealing experiments.
In situ infrared spectroscopic study on the role of surface hydrides and fluorides in the silicon chemical vapor deposition process
Authors: Chung Chan-Hwa , Moon Sang Heup , Rhee Shi-Woo
Published: July 2002

The role of surface hydrides and fluorides in the Si chemical vapor deposition (CVD) process was studied by in situ Fourier transform infrared spectroscopy using a porous silicon film as the substrate. Hydrides protect the silicon surface from oxidation until they are desorbed at 350–400 °C. However, the hydrides are replaced almost completely by surface fluorides when SiH2F2 is used as a reactant in the CVD process at temperatures above 400 °C. The surface is then etched due to a reaction between the fluorides and the surface silicon. When the process temperature is lowered to 250 °C, the surface is covered by both hydrides and fluorides, and a silicon film is deposited.
Pressure effect on YBa2Cu3O7 thin film growth in off-axis radio frequency magnetron sputtering
Authors: Wu S. C. , Tsai W. C. , Huang C. K. , Hsu H. T. , Huang C. J. , Tseng T. Y.
Published: July 2002

YBa2Cu3O7−x (123) thin films were fabricated on (100) MgO substrates by off-axis single target radio frequency (rf) magnetron sputtering. Our study focused on the effect of chamber pressure on the composition, microstructure, and superconductive properties on transition behavior and Tc of the grown film studied. An empirical formula was derived to explain the dependence of the deposition rate of various components on the pressure. Next, we compared the transport mechanism of the sputtered particles between the off-axis rf and the on-axis direct current sputtering and determined the processing conditions that result in superconducting films of better quality. According to our findings, growth at higher pressures (≳100 mTorr) produces more homogeneous and higher Tc superconducting films.
Deposition and properties of Mo–N films
Authors: Lin Kwang-Lung , Ho Yu-Jin
Published: July 2002

Mo–N films were deposited on glass or silicon wafers by reactive sputtering. The growth rate, composition, microstructure, and sheet resistance of the films were analyzed and determined to be controlled by deposition power as well as by N2 partial pressure. Grain refining, which increases the sheet resistivity of Mo–N films, was observed at higher N2 partial pressure as well as at lower deposition power input. τ-Mo2N was achieved at suitable conditions. We propose that the films formed by the reaction of nitrogen and Mo atoms on the substrate surface.
Multicomponent vapor transport model for viscous, transitional, and molecular flow
Authors: Ernst Michael J. , Hemond Harold F.
Published: July 2002

A multicomponent vacuum flow and vapor transport model for a long outgassing tube has been developed and verified experimentally. The model includes advective and diffusive vapor transport processes for a wide range of gas flow, from viscous to molecular. Existing single component approaches to the separation of vacuum flow into molecular and viscous fractions have been extended to include multicomponent transport with partial advection and interdiffusion. A set of nonlinear partial differential equations describing vacuum flow and transport in a tube are derived and solved with an iterative numerical scheme. Comparison of model simulations with laboratory measurements of vapor transport in a long vacuum sampling tube showed that the model accurately represents the process of interdiffusion in all flow regimes. Advection was accurately simulated by the model for all vapor components in fully viscous flow. Partial advection and tube limited diffusion in the transition flow range were also well simulated by the model for an argon–air mixture, while benzene–air and 1,1,1-trichloroethane–air mixtures showed slightly less than predicted partial advection. Reduced advection with these latter compounds may be due to the many energy storage modes available to the multiatomic molecules, which result in less momentum transfer than would be predicted by methods that assume fully elastic collisions between molecules.
GaN patterned film synthesis: Carbon depletion by hydrogen atoms produced from NH3 activated by electron impact
Authors: Hübner A. , Lucas S. R. , Partlow W. D. , Choyke W. J. , Schaefer J. A. , Yates J. T.
Published: July 2002

The electron-induced reaction of NH3 with a surface layer produced by adsorption of trimethylgallium on SiO2 at 108 K has been investigated by Auger electron spectroscopy. It is shown that atomic hydrogen, produced by electron-induced dissociation of NH3, to form NHX and H, extracts the methyl groups from the layer leading to carbon removal from the GaN film which is formed. This process is nonthermal. A procedure for the synthesis of GaN is demonstrated and the layer-by-layer growth of a GaN film is shown. The method permits GaN to be deposited in a localized region which has been bombarded by the electron beam.
Structural investigation of monolayer Sb on Si(100)-2×1 utilizing a Monte Carlo simulation of channeling and channeled ion energy loss
Authors: Boshart M. A. , Bailes A. A. , Dygo A. , Seiberling L. E.
Published: July 2002

The preferred bonding site of Sb on Si(100) is investigated using transmission ion channeling. A Monte Carlo simulation that includes a model for channeled ion energy loss has been used to calculate scattering yields and energy distributions for trial adatom sites. A method of data collection and analysis was developed to use the calculated scattering yields and energy distributions for quantitative site determination. The Sb site thus found agrees well with previous experiments on this system, namely, the Sb is in a modified bridge site with a bond length of 2.80±0.10 Å and a distance above the bulk-extrapolated silicon surface of 1.63±0.10 Å. However, the vibrational amplitude necessary for the simulated energy distributions to match experiment is anisotropic, apparently in contradiction with other results. A possible resolution is proposed.
Determination of the lateral spread of Xe ions in silicon nitride and hydrated silicon nitride films by oblique incidence Rutherford backscattering
Authors: Wang Ke-Ming , Qu Bao-Dong , Shi Bo-Rong , Lu Fei , Meng Ming-Qi , Wang Zhong-Lie , Wang Wei , Ding Pei-Jun
Published: July 2002

Both 100 and 200 keV Xe ions were implanted into silicon nitride (Si3N4) films and 600, 800, and 1000 keV Xe ions were implanted into hydrated silicon nitride (Si1N1.375H0.603) films at different angles. In order to determine the lateral spread of Xe ions implanted in Si3N4 and Si1N1.375H0.635 at room temperature, both normal and oblique incidence Rutherford backscattering were used. The results show that marked improvements in the measurement sensitivity to lateral spread is obtained by oblique incidence Rutherford backscattering. The lateral spread obtained agrees with the TRIM’92 prediction within experimental error for the 100–200 keV Xe+ implanted into the Si3N4 films, but a significant deviation of the lateral spread from the calculated value is observed for 600, 800, and 1000 keV Xe+ implanted into Si1N1.375H0.603 film.
Influence of adding transition metal elements to an aluminum target on electrical resistivity and hillock resistance in sputter-deposited aluminum alloy thin films
Authors: Onishi Takashi , Iwamura Eiji , Takagi Katsutoshi , Yoshikawa Kazuo
Published: July 2002

Effects of adding group VIII transition metals (Fe, Co, and Ni) to an aluminum target on electrical resistivity and hillock suppression of sputter-deposited Al alloy films were studied. It was found that the group VIII transition metals and Al formed a complete series of metastable solid solutions in the as-deposited state. The solid solutions were decomposed into intermetallic compounds, and the microstructures of the Al alloy films changed during annealing up to 300 °C. The electrical resistivities of Al–Fe, Al–Co, and Al–Ni alloy films changed corresponding to the change in their microstructures, and markedly decreased to 5.0 μΩ cm at the precipitation points. The film stresses also changed corresponding to the change in the microstructure of the Al alloy films, and were abruptly relieved by precipitation of intermetallic compounds and grain growth. Since Al–Fe, Al–Co, and Al–Ni alloy films did not yield, they are highly resistant to hillock formation. The low electrical resistivity and the excellent resistance to hillock formation of Al–group VIII transition metal alloy films were explained on the basis of microstructural changes before and after annealing.
Effects of Nd content in Al thin films on hillock formation
Authors: Onishi Takashi , Iwamura Eiji , Takagi Katsutoshi , Watanabe Takashi
Published: July 2002

The effect of Nd content in Al films on hillock formation was investigated for applications of interconnections for thin film transistor liquid crystal displays. It was found that the hillock density of Al–Nd alloy films was strongly dependent on the Nd content, and the hillocks were completely suppressed in Al–2.0–6.0 at. % Nd alloy films. X-ray diffractometry, x-ray absorption fine-structure spectroscopy, and transmission electron microscopy indicated that the microstructures of Al–Nd alloy films strongly depend on the Nd content, and Al–2.0–6.0 at. % Nd alloy films form a stable solid solution with a polycrystalline α-Al-like structure. The results obtained from microstructural analysis were largely in agreement with hillock formation behavior. In this study, it was found that the excellent hillock resistance of Al–2.0–6.0 at. % Nd alloy films originates from solid-solution hardening by the strongly distorted α-Al-like structure.
In situ monitoring and characterization of SiC interface formed in carbon films grown by pulsed laser deposition
Authors: Samano E. C. , Soto G. , Valenzuela J. , Cota L.
Published: July 2002

Very thin, smooth, and uniform carbon films have been produced by ablating a pyrolytic graphite target using an ultraviolet pulsed excimer laser at fixed energy in an ultrahigh vacuum system. The films were deposited on a Si (111) surface at room temperature. The deposition process is investigated in situ by analyzing the time evolution of spectra obtained by Auger electron, x-ray photoelectron, and electron energy loss spectroscopies at different stages of the film growth. A relationship of the atomic concentration of Si and C with the number of laser pulses and film thickness is obtained from the spectra. A SiC interface with a thickness between one and two monolayers is observed to be formed during the very first deposition pulses. The study of this SiC buffer layer is particularly relevant when a carbon film is used as a hard coating, where strong adhesion of the film to the substrate is required.
Octadecyltrichlorosilane self-assembled-monolayer islands as a self-patterned-mask for HF etching of SiO2 on Si
Authors: Komeda T. , Namba K. , Nishioka Y.
Published: July 2002

Octadecyltrichlorosilane (OTS), self-assembled-monolayer (SAM) grown on SiO2 in the submonolayer region is investigated by atomic force microscope (AFM), which is further applied to SiO2 characterizations technique. OTS-SAM forms characteristic dendrite-shaped islands in its submonolayer region, whose shape and size significantly depend on the surface roughness of SiO2 formed at different temperatures in the range of 700–1100 °C. Moreover, OTS-SAM islands have practical usefulness as a self-patterned-mask for HF etching. When an oxidized Si wafer covered by OTS-SAM islands is dipped into HF, SiO2 in the area uncovered by the islands is selectively removed. This technique is successfully applied for the precise SiO2 thickness measurement in ultrathin (<50 Å) regions by AFM. In addition, this technique enables a simultaneous observation of the morphologies of SiO2 surface and SiO2/Si interface. The result shows, for the first time, the continuity of the steps on SiO2 surface and SiO2/Si interface, indicating no lateral step motion of Si (111) surface during oxidation.
Hardness enhancement by compositionally modulated structure of Ti/TiN multilayer films
Authors: Kusano E. , Kitagawa M. , Nanto H. , Kinbara A.
Published: July 2002

In this article results of an investigation into effects of multilayer structures of compositionally modulated Ti/TiN films on their hardness is presented. Compositionally modulated Ti/TiN multilayer films were deposited onto borosilicate glass substrates by a reactive gas flow rate modulation magnetron sputtering method using a combination of a Ti metal target and an Ar–N2 mixture discharge gas. In this method, a N2 gas flow rate was changed by a computer-controlled mass flow controller to produce films with a varying composition distribution. The film hardness was measured by nanoindentation. The film composition depth profiles were estimated by Auger electron spectroscopy and x-ray photoelectron spectroscopy. A TiN single layer film was also deposited to compare its hardness with those of the Ti/TiN multilayer films. Modulation periods examined in this study were 10, 15, 20, and 40 nm. It was found that the film with a modulation period of 20 nm showed a maximum hardness of 29 GPa and that the films with modulation periods of 15 and 40 nm yielded a higher hardness value than that of the single layer TiN film of 15 GPa. The results obtained in this study indicate that the hardness of compositionally modulated Ti/TiN multilayer films strongly depend on modulation frequency.
Electronic structure and mechanical properties of resistant coatings: The chromium molybdenum nitride system
Authors: Hones P. , Sanjinés R. , Lévy F. , Shojaei O.
Published: July 2002

Cr 1−x Mo x N y thin films were deposited on silicon by radio-frequency reactive magnetron sputtering. The phase, texture, and residual stress were determined by x-ray diffraction analysis. All the films crystallize in the face-centered-cubic phase. The chemical composition was measured by electron probe microanalysis. Scanning tunneling microscopy revealed a finely grained surface morphology. Scanning electron microscopy showed a columnar crystal arrangement in every film of this study. The binary compounds Mo2N and CrN exhibit grain sizes of about 5 nm, whereas the ternary compounds show grain sizes up to 23 nm. The electronic structure was analyzed using x-ray photoelectron spectroscopy (XPS). The valence band N 2s and metal d peak separations show a minimum for films with about equal content of chromium and molybdenum. Hardness values, obtained by nanoindentation, exhibit also a pronounced minimum for x=0.4. The similarity between the trends of the XPS peak separation and hardness suggests that the differences in the mechanical properties of the films are mainly due to changes in the bonding character, caused by a different charge distribution between Cr and N.
High rate deposition of diamond-like carbon films by sheet-like plasma chemical vapor deposition
Authors: Nonogaki Ryozo , Yamada Suzuya , Araki Tsutomu , Wada Tetsuya
Published: July 2002

A high deposition rate of 0.69 μm/min was achieved in the formation of diamond-like carbon (DLC) film with sufficient hardness and flatness under a high density, widely spread sheet-like plasma at room temperature. The argon plasma was generated by a dc arc plasma gun under a magnetic field and it decomposed the toluene gas which was fed into the deposition chamber. During the deposition, the substrate was negatively biased by radio frequency (rf) in order to improve the hardness of the films. The DLC films were characterized by Raman and infrared absorption spectrometers. An optical emission spectrometer and a quadrupole mass spectrometer were used to identify the radicals in the plasma. The influence of the discharge current on the film properties is discussed.
In situ substrate temperature measurements during radio frequency sputtering of ZnO thin film using fiber Bragg grating
Authors: Zayer N. K. , Henderson P. J. , Grellier A. J. C. , Pannell C. N.
Published: July 2002

Several research groups throughout the world are currently working on fiber acousto-optic components, principally phase modulators, made by depositing a film of piezoelectric materials such as zinc oxide (ZnO) directly onto the optical fiber. It is well known that the quality of the resulting film is highly dependent on the temperature of the substrate (i.e., the fiber), but this has not been directly measured in situ. We present for the first time in situ measurements of the fiber temperature during the deposition process using a fiber Bragg grating temperature sensor. We show that the fiber temperature may rise substantially above that of its immediate surroundings. We also present a simple model for the heat flow for the fiber and the holder based on the heat gain from the plasma and the radiation loss between the various components in the sputtering chamber.
Determination of atomic oxygen density with a nickel catalytic probe
Authors: Šorli Iztok , Ročak Rudolf
Published: July 2002

A nickel catalytic probe was used to determine the density of neutral oxygen atoms in a glass tube. The O source was a low pressure weakly ionized inductively coupled rf oxygen plasma. The recombination coefficient for polycrystalline nickel (purity 99.8 at. %) was determined experimentally by use of a nickel tube with a well activated surface, recombining almost all the atoms entering the experimental chamber. The recombination coefficient was found to be constant over the temperature range of 500–1100 K with a value of 0.27±0.04. The catalytic probe was a disk with a diameter of 2 mm and thickness of 0.2 mm made of the same material. The O density was measured along a glass tube (Schott 8250) with an inner diameter of 3.6 cm and length of 40 cm. The density depended on the pressure in the experimental chamber and was found to decrease exponentially along the glass tube. The characteristic penetration depth depended slightly on pressure and was 60±16 cm. Comparison of the experimental data with theoretical predictions allowed estimation of the recombination coefficient for O atoms on a Schott 8250 glass surface: γ=(1.9±0.5)10−4.
Deposition of polycrystalline Si and SiGe by ultra-high vacuum chemical molecular epitaxy
Authors: Chen K. M. , Huang H. J. , Chang C. Y. , Chen L. P. , Huang G. W.
Published: July 2002

The polycrystalline Si1−xGex (poly-Si1−xGex) films have better properties than poly-Si for device fabrications, such as lower proceeding temperature and process thermal budget. For these reasons, the poly-Si1−xGex films have been utilized for low-temperature thin film transistor fabrications and gate electrodes of metal–oxide–semiconductor transistors. In this work, disilane and germane were used to grow poly-Si1−xGex films at low temperature (<600 °C) by the cold-wall type ultrahigh vacuum chemical molecular epitaxy system. The poly-Si1−xGex films were deposited on oxide and nitride surfaces. The Ge fraction x was evaluated from x-ray diffraction and Auger electron spectroscopy. It is observed that the Ge fraction increases with the increase of the GeH4 flow rate. The result is only slightly related to the substrate type. The growth rate increases with the Ge fraction at lower values and then decreases with the Ge fraction in the higher composition range. This implies that the growth mechanism of poly-Si1−xGex films is different from that of epitaxial Si1−xGex on Si. The uniformity of poly-Si1−xGex films depends on the Ge fraction, and it is improved by the addition of germanium. The result can be explained by the lower activation energy (<0.25 eV) of poly-Si1−xGex deposition as compared to that of poly-Si (∼2.1 eV). From the x-ray diffraction and atomic force microscopy analyses, the crystallinity and surface roughness of films are suitable for device fabrications.
A technique for the determination of stress in thin films
Authors: Bromley E. I. , Randall J. N. , Flanders D. C. , Mountain R. W.
Published: July 2002

Intrinsic stress, elastic bulk modulus, and yield strength of thin films has been determined by measuring the deformation versus pressure of circular membranes of the materials. Low pressure chemical vapor deposited (LPCVD) silicon-rich silicon nitride (SiNx) has been extensively characterized and found to have an intrinsic stress of ∼1×109 dyn/cm2 and a bulk modulus of ∼1.9×1012 dyn/cm2. A SiNx membrane 1.0 cm in diameter and 1.0 μm thick has been found to survive a differential pressure of 470 Torr with no measurable plastic deformation. Experimental data for several different types of silicon nitride membranes is given. It is shown that the stress measurement technique can be extended to measure accurately the intrinsic stress of thin films deposited onto SiNx membranes.
Selective reactive ion etching in SiCl4/SiF4 plasmas for gate recess in GaAs/AlGaAs modulation-doped field effect transistors
Authors: Ballegeer D. G. , Agarwala S. , Tong M. , Nummila K. , Ketterson A. A. , Adesida I. , Griffin J. , Spencer M.
Published: July 2002

Various issues concerning the utilization of SiCl4/SiF4 selective reactive ion etching (SRIE) for gate recess in the fabrication of GaAs/AlGaAs modulation-doped field effect transistors (MODFETs) have been studied. Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy, and Schottky diode measurements were performed to determine the effects of SRIE and post-SRIE processing on the surface conditions of GaAs and AlGaAs layers. Hall measurements were conducted at 300 and 77 K to characterize the degradation of the two-dimensional electron gas properties of GaAs/Al0.3Ga0.7As heterostructures due to ion bombardment during SRIE. Finally, direct-current and high-frequency measurements were performed on dry-etched GaAs/Al0.3Ga0.7As MODFETs to determine the effects of SRIE on device performance. It is shown that extensive overetching at low plasma voltages (<90 V) during gate recessing results in an increase in the device threshold voltage, but has little effect on the gate-to-drain breakdown voltage, maximum transconductance, and unity current gain frequency of the devices.
Effect of matrix stopping power on sputter depth profile broadening
Authors: Ronsheim P. A. , Tejwani M.
Published: July 2002

Collision cascade mixing in the sputter depth profiling process broadens the measured width of abrupt dopant structures by displacing the target atoms, predominantly through collisions with the disturbed matrix atoms prior to sputter removal. Sputtering theory predicts a profile broadening dependence on the nuclear stopping power of the projectile in the target matrix, but this is not supported by experimental data. In this experiment, abrupt boron profiles were measured in a matrix of silicon or germanium, at a range of energies from 2.5 to 10.5 keV. The higher mass matrix gives access to high stopping powers, particularly for Xe+ projectiles. As with the projectile mass experiments, this work does not support the predicted change in decay length with the range of the projectile. The data indicate the decay length dependence on projectile energy alone is due to dopant displacements by primary recoils as well as the collision cascade mixing.
Spatial-phase-locked electron-beam lithography and x-ray lithography for fabricating first-order gratings on rib waveguides
Authors: Wong Vincent V. , Ferrera Juan , Damask J. N. , Carter J. M. , Moon Euclid E. , Haus H. A. , Smith Henry I. , Rishton Stephen
Published: July 2002

The two basic structural elements of the integrated resonant channel-dropping filter are the rib waveguides and the first-order Bragg gratings. Spatial-phase-locked electron-beam lithography is used to write the Bragg grating patterns with a coherence better than λ0/150, and x-ray nanolithography is used to transfer the gratings onto optically patterned rib waveguides. These technologies are successfully combined to demonstrate a process by which channel-dropping filters and related devices can be fabricated.
Adsorption of Bi on Si(001) surface: An atomic view
Authors: Noh H. P. , Park Ch. , Jeon D. , Cho K. , Hashizume T. , Kuk Y. , Sakurai T.
Published: July 2002

Coverage dependent adsorption of Bi on Si(001) has been studied using scanning tunneling microscope and low-energy electron diffraction. At low coverages, Bi atom adsorbs without breaking the Si(001)-(2×1) structure. At the coverage of ∼0.5 ML, Bi atoms begin to sit on the troughs between the Si dimer row and form a Bi (1×2) structure with broken Si dimers. Strain due to the large misfit is relieved by the formation of antiphase boundaries and Bi missing line defects.
Real-time process and product diagnostics in rapid thermal chemical vapor deposition using in situ mass spectrometric sampling
Authors: Tedder L. L. , Rubloff G. W. , Shareef I. , Anderle M. , Kim D.-H. , Parsons G. N.
Published: July 2002

Mass spectrometry has been exploited for rapid real-time sensing of both reactant and product species in single-wafer rapid thermal chemical vapor deposition (RTCVD) of polycrystalline Si from SiH4. Active mass spectrometric sampling at pressures to 5 Torr is achieved using two-stage differential pumping of a sampling aperture in the exhaust stream, leading to response times as short as ∼3 sec to concentration and pressure changes in the reactor during a process carried out in ∼30 sec. In addition to reactant species, gaseous reaction byproducts have been identified and differentiated from cracking fragments of the reactant through relative intensities of mass fragments as a function of wafer temperature (i.e., reaction rate). For RTCVD of poly-Si from SiH4, carried out in the range 450–800 °C at 5 Torr in 10% SiH4/Ar, mass spectra reveal not only the time dependence of reactant (monitored by SiH2+, 30 amu), but also—at higher temperatures—reactant depletion and product generation (from H2+, 2 amu). These results demonstrate a basis for using mass spectrometry in real-time process diagnostics and control.