bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of heavy particles in kinetics of low current discharges in argon at high electric field to gas number density ratio
Authors: Petrović Z. Lj. , Stojanović V. D.
Published: July 2002

We have developed a coupled system of Monte Carlo simulation codes for modeling of electron, ion, and fast neutral kinetics in low pressure, low current discharges. The procedure was tested for ion drift tube data by using different cross-section sets including the recent anisotropic set of Phelps [A. V. Phelps, J. Appl. Phys. 76, 747 (1994)]. The code was applied to modeling absolute emission profiles obtained at very high electric field to gas number density ratio, where heavy particle excitation dominates electron excitation by more than two orders of magnitude, and also to an inhomogeneous field experiment of Scott and Phelps [D. A. Scott and A. V. Phelps, Phys. Rev. A 43, 3043 (1991)]. The qualitative agreement between the Monte Carlo and experimental results is good, giving confidence in the available models and data for ion and fast neutral transport in gas discharges, and for their interaction with surfaces.
Characteristics of a mesh-bias-controlled electron cyclotron resonance plasma for the growth of gallium nitride epitaxial films
Authors: Yasui K. , Iizuka K. , Akahane T.
Published: July 2002

Characteristics of mesh-bias-controlled electron cyclotron resonance (ECR) plasma for the growth of gallium nitride (GaN) were investigated. Dependence on the mesh electrode bias of the plasma parameters such as electron temperature, electron density, and plasma space potential in the ECR plasma chamber and in the growth chamber was investigated using a Langmuir probe. The ion energy distribution function incident on the substrate surface was also investigated using a Faraday cup. Variation in the plasma parameters as a function of the position in the growth chamber was investigated. From the probe characteristics, the deactivation process of electrons in the growth chamber was clearly observed. From the crystal growth with the mesh electrode bias and substrate bias, it also became clear that the growth of zinc-blende GaN films was enhanced at the bias condition at which the number of electrons to the substrate surface was increased and the impinging ions were suppressed.
Hot filament chemical vapor deposition diamond growth kinetics on an epitaxial CoSi2 surface monitored by three electron spectroscopies
Authors: Arnault J. C. , Lang B. , Le Normand F.
Published: July 2002

Diamond deposition on an epitaxial CoSi2 layer over Si(111) is preceded by the formation of a 4 nm thick silicon carbide layer. The steps of carbide formation, diamond nucleation, and diamond growth are monitored in situ by three electron spectroscopies (x-ray photoelectron spectroscopy, Auger electron spectroscopy, and electron-loss spectroscopy). By comparison with our previous studies of diamond growth on clean Si(100) and Si(111), the time required to stabilize the SiC composition is much longer. This slow step is interpreted by a strong carbon diffusion into the bulk which goes together with silicon enrichment of the carbide phase. The lack of carbon saturation at the surface induces a large delay for the subsequent diamond nucleation process by a time scale factor of 10. In addition, the electron spectroscopy measurements reveal the appearance of C–C sp3 species before the diamond nucleation starts. These species probably correspond to carbon aggregates which act as precursors of the diamond phase.
Experiments on the plasma assisted chemical vapor deposition of copper
Authors: Lakshmanan Satish K. , Gill William N.
Published: July 2002

Low resistivity (≈2.2–3.0 μΩ cm), high purity copper films have been deposited by the hydrogen plasma assisted chemical vapor deposition of copper(II) hexafluoroacetylacetonate, Cu(Hfa)2, at pressures of 1.0–3.0 Torr, substrate temperatures of 160–240 °C, plasma powers of 3.0–15.0 W and precursor mole fractions of 0.25%–0.8%. The film purity and morphology have been analyzed by X-ray photoelectron spectroscopy, scanning electron microscopy and X-ray diffraction. Under the conditions investigated, the film growth rates were measured to be in the range of 40.0–200.0 Å/min. The experiments suggest that the deposition rate, precursor conversion, film purity and morphology can be tailored by adjusting the operating conditions appropriately. Our results have been used in conjunction with a reactor model of plasma assisted chemical vapor deposition to suggest operating conditions for high copper growth rates and high purity.
Use of 2H-heptafluoropropane, 1-iodoheptafluoropropane, and 2-iodoheptafluoropropane for a high aspect ratio via etch in a high density plasma etch tool
Authors: Karecki Simon , Pruette Laura , Reif Rafael , Beu Laurie , Sparks Terry , Vartanian Victor
Published: July 2002

An issue currently facing the semiconductor industry is the use and emission of perfluorocompounds (PFCs), gases which are believed to contribute to global warming, in a number of plasma processes used in integrated circuit manufacture, including wafer patterning. Several approaches to reducing emissions of these compounds are being considered, namely abatement, recapture/recovery, process optimization, as well as the development of alternative chemistries as PFC substitutes. The authors present here the results of an effort to test several alternatives in a silicon dioxide etch application (high aspect ratio via etch). 2H-heptafluoropropane, 1-iodoheptafluoropropane, and 2-iodoheptafluoropropane, were tested in an Applied Materials Centura 5300 high density plasma etch tool. Fourier transform infrared spectroscopy was used to analyze the process effluent. The process performance and emissions of the alternative etchants were compared to those of a standard chemistry on the Centura 5300 etch tool.
Pumping properties using an electrolytic polished stainless steel vacuum chamber
Authors: Watanabe S. , Kurokouchi S. , Aono M.
Published: July 2002

An electrolytic polished stainless steel chamber was fabricated in order to examine its pumping-down properties. The pumping-down properties depend on the heat history of the chamber and the performance of the pump. Pumping-down tests of the chamber using an oil diffusion pump and a titanium sublimation pump were demonstrated. The chamber was evacuated from atmospheric pressure to an extremely high vacuum in a short period of time.
Fabrication and characteristics of rugate filters deposited by the TSH reactive sputtering method
Authors: Tang Qi , Matsuda Hideaki , Kikuchi Kazuo , Ogura Shigetaro
Published: July 2002

Theoretical investigations on rugate filters have recently received much attention. For the most efficient use of the rugate filters, the deposition processes such as EB coevaporation, reactive ion beam assisted deposition and chemical vapor deposition methods, have been investigated as the most importance to achieve our objective. However, since periodic rugate filters manufactured in these manners require sophisticated and precise control of the process, they cannot sufficiently offer either the required stable deposition rate, wide variation of refractive index, or a particularly long-time constant deposition process. In this experiment, the two-stage high-rate reactive sputtering method, called TSH reactive sputtering, is used to fabricate such rugate filters. Their spectral performance, elemental composition ratio, and cross-section morphology have been investigated.
Deposition of high quality silicon dioxide on Hg1−xCdxTe by low-temperature liquid phase deposition method
Authors: Wang N. F. , Chang W. J. , Houng M. P. , Wang Y. H. , Huang C. J.
Published: July 2002

A low temperature (35–45 °C) process of liquid phase deposition (LPD) for the growth of silicon dioxide (SiO2) on Hg1−xCdxTe is proposed. To enhance the formation of SiO2, the HgCdTe surface has to be treated by ammonia solution before LPD. A thin native oxide which is formed by previous surface treatment involving OH− radicals greatly enhances the SiO2 deposition on HgCdTe. Thus, SiO2 films with a high refractive index (1.465) and a low p-etching rate (34 Å/s) were obtained. Auger electron spectroscopy depth profile shows less interdiffusion of constituent atoms between the SiO2 layer and the HgCdTe substrate. Electrical properties of the SiO2/p-HgCdTe interface are also characterized at 77 K. It is found that the p-HgCdTe surface is accumulated and the effective surface charge density is estimated to be −2.25×1010 cm−2. The leakage current and dielectric breakdown strength are also found to be 0.356 nA (at −5 V) and above 650 KV/cm, respectively. Furthermore, the growth mechanism of LPD-SiO2 on HgCdTe is proposed.
Effect of laser-induced dissociation of SiH3 radicals in SiH4 plasmas during atomic hydrogen measurements using laser-induced fluorescence by a two-photon excitation
Authors: Miyazaki K. , Mishiro Y. , Kajiwara T. , Uchino K. , Muraoka K. , Okada T. , Maeda M.
Published: July 2002

We investigated the influence of laser-induced dissociation of SiH3 radicals in SiH4 plasma during measurements of atomic hydrogen densities in the plasma. The measurements were made using two-photon excitation of hydrogen atoms from the ground state to the n=2 state at 243 nm and simultaneous excitation from the n=2 state to the n=3 state at 656 nm. We concluded that some hydrogen atoms were generated by laser-induced dissociation of SiH3 radicals. The ratio of atomic hydrogen density thus generated to the total density observed by the method was 20±20% for the following discharge conditions: gas flow rate of 5 sccm, gas pressure of 11 Pa, and radio frequency (13.56 MHz) power of 2 W, for electrode diameters of 100 mm and the separation of 40 mm. Taking this into account, we determined the atomic hydrogen density in the plasma for the condition to be (5±2)×1017 m−3.
Mass spectroscopy of recoiled ions, secondary ion mass spectroscopy, and Auger electron spectroscopy investigation of Y2O3-stabilized ZrO2(100) and (110)
Authors: Herman G. S. , Henderson M. A. , Starkweather K. A. , McDaniel E. P.
Published: July 2002

We have studied the (100) and (110) surfaces of yttria-stabilized cubic ZrO2 using Auger electron spectroscopy, low energy electron diffraction (LEED), direct recoil spectroscopy, mass spectroscopy of recoiled ions (MSRI), and secondary ion mass spectroscopy (SIMS). The concentration of yttrium at the surface was weakly influenced by the surface structure under the experimental conditions investigated. Both MSRI and SIMS indicated a more enhanced yttrium signal than zirconium signal at the surface compared to the respective bulk concentrations. The surfaces were not very well ordered as indicated by LEED. The yttria-stabilized cubic ZrO2 single crystal surfaces may not be a suitable model material for pure phase ZrO2 surfaces due to significant yttria concentrations at the surface.
Density measurement of thin glass layers for gas barrier films
Authors: Fukugami Norihito , Nishino Hideo , Yanaka Masa-aki , Tomiyama Kozue , Tsukahara Yusuke
Published: July 2002

In the food packaging industry, transparent gas barrier films consisting of a 10–100 nm thick glass layer deposited on a polymer substrate are being developed. The accurate density measurement of the thin glass layers with thickness ranging from 10 to 100 nm was important to characterize nanostructures, hence the gas permeation property of the films. First, densities of SiOx layers which were deposited by vacuum evaporation on silicon wafer surfaces(100) were measured with a weight-volumetric method. The densities were 2.15±0.01 and 2.16±0.03 g/cm3 for layers with slightly different deposition conditions. Next, a novel method was invented for the density measurement of thin SiOx layers deposited by vacuum evaporation on polymer substrates. The method made use of the fact that parallel multiple cracks were induced in the SiOx layer when the film was stretched. The thickness of the SiOx layer was estimated by measuring the depths of crack openings. The density was found to be larger: 2.32±0.09 g/cm3.
Two mechanisms of scanning tunneling microscopy assisted nanostructure formation using precursor molecules
Authors: Lyubinetsky I. , Mezhenny S. , Choyke W. J. , Yates J. T.
Published: July 2002

Scanning tunneling microscopy has been employed to create nanostructures at both polarities of the applied bias voltage, using the hexafluoroacetylacetonate Cu (I) vinyltrimethylsilane precursor molecule on the Si(111) surface at 300 K. Two distinctive mechanisms controlling the formation of nanostructures have been delineated. The first mechanism causes the dissociation of the molecule by an electron attachment process. The second process involves excitation of the molecule by the applied electric field; here field induced surface diffusion acts to supply molecules to the nanostructure growth region under the tip. Both mechanisms have a threshold in the range of 2.5–4.5 V, and while the electron current induced process operates only at positive sample bias, the field induced mechanism works at both bias polarities. Model calculations of the field assisted growth mechanism, which involves both the radial diffusion of the precursor species from outer surface regions and their activation underneath the tip, show a very reasonable quantitative agreement with the experimental data.
Ex situ growth of the c-axis preferred oriented SrBi2Ta2O9 thin films on Pt/Ti/SiO2/Si substrates
Authors: Bae Choelhwyi , Lee Jeon-Kook , Lee Si-Hyung , Jung Hyung-Jin
Published: July 2002

SrBi 2 Ta 2 O 9 (SBT) thin films were deposited on (111) oriented Pt bottom electrodes using the rf magnetron sputtering method and then postannealed at 650–800 °C for 30 min in different oxygen atmospheres. The effect of Bi content on the c-axis preferred oriented growth was confirmed by the control of the Bi2O3 loss during the postannealing. With increasing Bi content in SBT thin films, the degree of the c-axis preferred orientation was enhanced. In addition, a bimodal grain size distribution due to the Sr deficiency in the SBT film was observed. It is suggested that the c-axis preferred oriented growth on Pt(111) bottom electrodes can be attributed to growth controlled by surface energy minimization.
Atomic hydrogen temperature in silane plasmas used for the deposition of a-Si:H films
Authors: Miyazaki K. , Kajiwara T. , Uchino K. , Muraoka K. , Okada T. , Maeda M.
Published: July 2002

Atomic hydrogen temperature in a silane plasma used for the deposition of a-Si:H films was measured using a two-photon laser-induced fluorescence technique. The temperature was found to be 2200±600 K and higher than both the parent-gas temperature and the atomic hydrogen temperature in a hydrogen plasma. We considered the mechanism of atomic hydrogen temperature determination in the plasma as follows. Hydrogen atoms generated by the dissociation of gas molecules due to electron impact in the plasma have a kinetic energy of several eV, which they then lose through collisions with gas molecules. At the same time, they disappear from the plasma due to chemical reactions and diffusion before thermal equilibrium with gas molecules has been established. Thus, an atomic hydrogen temperature higher than that of gas molecules becomes the equilibrium value in the plasma. We show, in the new experiment, that this model provides a good estimation of atomic hydrogen temperature in the plasma under various conditions of silane-hydrogen mixtures.
Secondary ion emission from molecular overlayers: Thiols on gold
Authors: Rading D. , Kersting R. , Benninghoven A.
Published: July 2002

The secondary ion emission behavior of 10 different thiols (8 alkanethiols, with n=4–18 C atoms, TSA, and MCP) was investigated. In particular, we determined the generated negative secondary ion species Xi−, their yields Y, the corresponding damage cross section σ(Xi−), and the activation energy for desorption ED(Xi−) (from the temperature behavior) of these secondary ions. The results supply important information on the analytical capabilities of secondary ion mass spectrometry (e.g., sensitivity and ultimate lateral resolution), as well as on the capabilities and limits of ion beam induced modification of these molecular overlayers. By comparing spectra and yields for different thiols bonded in the same way to the same substrate, these results give some additional insight into the ion formation process. A comparison of the activation energy for desorption ED(Xi−) with the corresponding damage cross section σ(Xi−) supplies insight into the energy distribution within the impact cascade.
Study on nanosized TiO/ WO3 thin films achieved by radio frequency sputtering
Authors: Guidi V. , Comini E. , Ferroni M. , Martinelli G. , Sberveglieri G.
Published: July 2002

Production of nanosized oxides was reliably accomplished through magnetron radio frequency sputtering of a W/Ti composite target under oxidizing environment. Depending on the temperature at which annealing was carried out, the resulting thin films were either WO3/TiO or W-doped TiO and the semiconductor doping changed from n to p type, respectively. The films were structurally characterized through microscopy techniques. Electrical characterization was executed over the samples. In particular, it was observed that the films responded with high sensitivity to NO2, a gas of increasing importance in environmental monitoring. We describe the features of the sensing layers with particular focus on the role of TiO—this p-type material being a novelty for the field of gas sensing.
Review of pumping by thermal molecular pressure
Authors: Hobson J. P. , Salzman D. B.
Published: July 2002

Pumping energy is supplied by temperature changes alone. A general feature of such pumps is that the upper pressure limit is reached when the mean free path becomes small relative to the physical dimensions of the pump in the region of the temperature transition. Thus, the upper pressure limits of these pumps have been determined by the microfabrication limits of the day; they have operated at relatively low pressures, with low throughputs, and have not become main line pumps. In recent years, however, Micro-Electronic-Mechanical Systems (MEMS) has introduced a whole new level of miniaturization to devices in general, including vacuum devices, and hence has raised the upper pressure limits, and thus the throughputs of thermal molecular pumps to atmospheric levels. The purpose of this article is to isolate the various physical manifestations of thermal molecular pumps, which have been realized over the years. The general pumping phenomenon has had various names: Knudsen compressor; thermal transpiration; thermal creep; thermodynamic, thermolecular, thermal molecular, and accommodation pumping. This multiplicity of terminology can cause some confusion and it is one of the aims of the article to simplify the situation. We have chosen the title “Pumping by Thermal Molecular Pressure” following the terminology of Knudsen. Broadly speaking, it is found that these pumps divide into two classes: (a) those requiring no specially prepared surfaces, (b) those in which special surfaces are essential. The latter have no low pressure limit. A table is assembled comparing pumps which have been built and tested, rather than those calculated on paper. Scaling rules for multiple stage pumps in series, based on results obtained for single-stage pumps are presented. A Knudsen compressor in series with an accommodation pump already promises operation from atmosphere to indefinitely low pressures, whereas an accommodation pump alone may be able to cover this range in the future. A number of potential applications of the technology such as small gas chromatographs and small valves are noted. Despite this complexity, thermal molecular pressure devices all have the compelling advantage that there are no moving parts nor any fluids in the vacuum.
Similarities in chemical intermixing at the Cu/InP and Cu/Si interfaces
Authors: Kendelewicz T. , Rossi G. , Petro W. G. , Babalola I. A. , Lindau I. , Spicer W. E.
Published: July 2002

In this work we present a comparative study of the electronic and atomic structure of the interactive Cu/Si and Cu/InP interfaces. We use surface sensitive techniques, including soft x-ray photoemission and photon- and electron-induced Auger electron spectroscopy (AES), to show the strikingly similar chemical reactions and electronic properties at both interfaces. For both Cu/Si and Cu/InP, the valence band spectra and core level intensity profiles show intermixing of the metal with the substrate atoms. Moreover, for both semiconductors, the increase in Cu coverage induces an increase of the width of the Si L2,3VV (∼92 eV) and P L2,3VV (∼120 eV) Auger peaks at the earliest stage of barrier formation followed by a 4.4 eV splitting for higher coverages. These experimental observations lead to very similar models of the chemical reaction at the interface and the formation of the intermixed region and indicate bonding between Cu and P or Si for the InP and Si interfaces. In the case of the Cu/InP interface, we observe segregation of In to the surface and the formation of metallic islands.
A low-energy, ultrahigh vacuum, solid-metal ion source for accelerated-ion doping during molecular beam epitaxy
Authors: Rockett A. , Barnett S. A. , Greene J. E.
Published: July 2002

The design and operation of a compact single-grid, ultrahigh-vacuum-compatible, low-energy ion gun capable of utilizing gaseous, liquid, or solid source material are described. The gun can provide >100 μA/cm2 at ion energies ranging from 20 to 500 eV, and grid and filament lifetimes of several hundred hours have been obtained while operating with Zn and As. Current–voltage characteristics of the source as well as resulting ion beam profiles are reported. With appropriate grid design, uniform ion beam intensities were obtained over 4 cm diam wafers at a distance of 20 cm from a 1 cm diam ion source. In initial experiments using the ion source for accelerated-ion doping of (100)Si and (100)GaAs, several orders of magnitude increases in elemental As and Zn incorporation probabilities were observed.
Thermal nitridation of silicon: An XPS and LEED investigation
Authors: Maillot C. , Roulet H. , Dufour G.
Published: July 2002

Two thermal, low pressure nitridation processes are achieved on silicon(111), using two different nitridant gases, and studied in situ by x-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED). The results show two different growth rates but the same evolution of the electronic and surface crystallographic stucture. A correlation is established between XPS and LEED measurements, associating the characteristic ‘‘quadruplet’’ patterns with the presence of intermediate nitrides. On the contrary, such compounds are absent when the LEED displays ‘‘8×8’’ patterns. Complementary results by reflection high energy electron diffraction (RHEED) and scanning electron microscopy (SEM), permit us to conclude that our thickest films, up to 40 Å, are stoichiometric Si3N4, poorly crystallized in the β phase, presenting no surface rugosity.
Electronic transport properties of TiSi2 thin films
Authors: Malhotra V. , Martin T. L. , Mahan J. E.
Published: July 2002

High purity, single-phase TiSi2 thin films were prepared by deposition of titanium onto polycrystalline silicon layers followed by furnace annealing. Measurements of the temperature dependence of resistivity show that the material behaves as a classical metallic conductor, with an intrinsic resistivity proportional to temperature and having a room temperature value of ∼11μΩ cm. Geometrical magnetoresistance measurements on Corbino disk samples give a ‘‘representative’’mobility value (∼60 cm2/V-s at room temperature) that mirrors the temperature dependence of resistivity. The very small Hall effect, taken together with a sizeable physical magnetoresistance, indicates the material is predominantly an electron conductor with a spectrum of mobility values for carriers on the Fermi surface because an isotropic, two-band model cannot quantitatively account for the data.
Surface photochemical phenomena in laser chemical vapor deposition
Authors: Higashi G. S. , Rothberg L. J.
Published: July 2002

The role of surface adsorbate photochemistry in laser assisted Al film growth by photodecomposition of trimethylaluminum is investigated using a pulsed optoacoustic apparatus. The technique permits in situ measurements of the vibrational spectra of surface adsorbates on single crystal sapphire even under the ambient pressures typical of laser chemical vapor deposition. We characterize the initial sapphire surface and follow the nucleation and growth of photodeposited films to obtain a microscopic understanding of the growth mechanism. We show that high quantum yield nonthermal photodesorption of methyl groups from growth surfaces occurs with 193 nm irradiation and can be used to produce Al films of higher quality. Features of the vibrational spectra are shown to be correlated with macroscopic properties of metallic films grown under the same conditions and can be used to identify and evaluate the parameters important to high quality film growth.
Time-resolved vibrational energy relaxation of surface adsorbates
Authors: Heilweil E. J. , Casassa M. P. , Cavanagh R. R. , Stephenson J. C.
Published: July 2002

Time-resolved measurements of picosecond vibrational population decay of chemisorbed species (OH, OD, BOH, NH2, and OCH3) on high surface area colloidal silica at room temperature have been performed. The influence of solvents on OH relaxation and the variation in observed relaxation rates are discussed in terms of the vibrational level structure and surface coordination of each adsorbate.
Angular, velocity, rotational, and electronic distributions of vibrationally elastically scattered NO(v=1) from LiF(100)
Authors: Misewich J. , Zacharias H. , Loy M. M. T.
Published: July 2002

Infrared laser excitation has been utilized to excite part of a molecular beam of NO to a single well-defined quantum state, NO(v=1, J=3/2, Ω=1/2), which is scattered from a cleaved LiF(100) surface. Laser spectroscopic detection techniques then allow the determination of rotational and electronic distributions as well as state-specific angular and velocity distributions for scattering from a single initial vibrational-rotational state.
Studies on the mechanism of chemical sputtering of silicon by simultaneous exposure to Cl2 and low-energy Ar+ ions
Authors: Dieleman J. , Sanders F. H. M. , Kolfschoten A. W. , Zalm P. C. , de Vries A. E. , Haring A.
Published: July 2002

The sputtering yield of Si when bombarded with a flux φAr+ of low-energy Ar+ ions may be enhanced a few times when the Si surface is exposed simultaneously to Cl2 fluxes φCl2 about one order of magnitude larger than φAr+. The mechanism of this synergistic etching has been studied, using mass spectroscopy and time-of-flight techniques, for a φAr+ of about 5×1014 Ar+ cm−2 s−1 at Ar+ ion energies (Ep) from 0.25 to 5 keV, Cl2 fluxes between 1015 and 5×1016 Cl2 cm−2 s−1 and T in the range 300–625 K. As has been shown previously [J. Vac. Sci. Technol. A 2, 487 (1984)] the main products of the synergistic reaction are atomic Si and Cl and molecular SiCl and SiCl2; the kinetic energy distributions of the molecular products consist of two parts, a Maxwell–Boltzmann and a collision cascade-like distribution. The Maxwell–Boltzmann part decreases relative to the collision cascade-like part when T and/or Ep are increased and/or φCl2 is decreased. At the same time the collision cascade-like part shifts to higher kinetic energies. These observations and the dependence of the relative contributions of the various products on φCl2, T, and Ep can be understood from the Ar+ ion-induced amorphization and Ar+ ion-induced mixing of adsorbed Cl into the top atomic layers of the Si, in which the molecular products SiCl and SiCl2 are formed and also trapped, without further chemical binding to the surrounding bulk network; and for higher T also by the competition between the thermal reaction, yielding SiCl4 (and SiCl2), and synergistic etching. The yields of the molecular products SiCl and SiCl2 show an increase relative to atomic Si and their binding energies are reduced when φCl2 is enhanced and/or Ep and/or T are decreased. It is suggested that this is due to an increasing concentration of Cl ion mixed into the top atomic layers of the Si.

The experiments also suggest that the binding energy of atomic Si decreases systematically with increasing Cl concentration in the Si. The results show that the etching of Si with Cl2 under simultaneous Ar+ ion bombardment is not due to stimulation of the thermal reaction but to chemically enhanced physical sputtering.
An investigation of the lithographic properties of the poly (p-methylstyrene-co-chloromethylstyrene) resist system
Authors: Ledwith A. , Mills M. , Hendy P. , Brown A. , Clements S. , Moody R.
Published: July 2002

The lithographic performance of the resist system poly(p-methylstyrene-co-chloromethylstyrene) PMS–CMS has been assessed. Copolymerization of the monomers, PMS and CMS, produced resists with CMS increasing from 0% to 52%, molecular weights between 122 000 and 167 000, and dispersivities between 1.7 and 2.3. The sensitivity (D0.5n) and contrast of pure PMS for 20 kV electrons was 38 μC cm−2 and 2.8, respectively. Addition of 4.2% CMS increased the sensitivity to 2.1 μC cm−2 but only reduced the contrast to 2.3, a value sufficient for submicron resolution. Further increases in CMS content, to 52%, produced smooth variations in sensitivity and contrast to 1.2 μC cm−2 and 1.5, respectively. Exposure of 4.5% CMS resist with deep UV light (22 mJ cm−2) produced 1 μm lines and spaces with vertical profiles. The etch rate of this resist, during poly-Si definition in a chlorine plasma, was almost half that of the photoresist HPR206.
Nozzle beam deposition of SiO2 films
Authors: Wong J. , Lu T.-M. , Mehta S.
Published: July 2002

SiO2 films were deposited on 2 in. Si(100) wafers at an oxygen pressure of 10−2 Pa and substrate temperature of 300 °C using a nozzle beam deposition technique. High purity SiO2 grains were evaporated in a graphite crucible at a temperature of 1500 °C. The evaporated species were then ejected through a nozzle and were partially ionized by electron bombardment prior to deposition. The index of refraction and infrared absorption spectrum of the films were found to depend strongly on the ionization current and acceleration voltage applied to the beam. The thickness and refractive index of the film are uniform over the entire 2 in. wafer if the applied acceleration voltage is less than 1 kV.
The performance of a microwave ion source immersed in a multicusp static magnetic field
Authors: Dahimene M. , Asmussen J.
Published: July 2002

Many applications requiring high beam currents and operation with chemically active gases impose lifetime and operational requirements on the discharge electrodes in conventional ion sources. Despite the development of specially designed hot filaments and hollow cathodes, the presence of these electrodes in the discharge zone still limits the practical application of ion and plasma sources. Thus, the development of an efficient, simple, electrodeless discharge would result in an important improvement in ion beam and plasma processing technology. Recently, an electrodeless microwave ion source and plasma source have been developed. An improvement of this ion source is discussed. This is the redesign to surround the discharge zone with many closely spaced rare earth magnets producing a confining and cyclotron resonant multicusp static magnetic field. The experimental performance of this ‘‘modified’’ ion source using argon gas is presented. Experimental measurements of extracted ion beam current versus accelerating voltage and discharge electron and ion densities, etc. are presented over a range of gas flow rates and operating pressures.
A statistical analysis of ultraviolet, x-ray, and charged-particle lithographies
Authors: Smith Henry I.
Published: July 2002

We analyze photo, x-ray, e-beam, and ion-beam lithographies from a statistical point of view in order to relate linewidth control to the contrast provided by the exposure technique, the resist contrast, and the resist sensitivity. Assuming a linewidth control of 20% at a minimum linewidth of 0.5  μm, we compare UV and x-ray lithographies and find that the former is practical only with very high contrast resists (δN/N̄<0.16). We derive a simple expression for the minimum number of photons or charged particles required per pixel, and compare the pixel-transfer rates of various lithographies. We find that beyond UV photolithography, synchrotron and pulsed-plasma x-ray sources offer the highest pixel-transfer rates and appear most attractive for submicron lithography.
Acceptor-like electron traps control effective barrier for ultrahigh vacuum-cleaved and laser-annealed Al/InP
Authors: Slowik John H. , Brillson L. J. , Richter H.
Published: July 2002

We analyze the temperature dependence of the current and capacitance responses for Al contacts on UHV-cleaved (110) n-InP. We compare pulse-laser-annealed contacts to unannealed contacts formed concurrently on the opposite half of each freshly-cleaved InP surface. Acceptor-like electron traps lying 0.10 eV below the conduction band (a level sometimes ascribed to donors in the unified defect model) dominate electronic behavior. These traps occur in an interfacial layer whose thickness is reduced from ∼160 to ∼34 Å by laser annealing. Both laser-pulsed and unannealed contacts have a 0.22 eV barrier height. The fact that the 0.5 eV barrier of Al reported on treated InP also decreases to 0.22 eV upon heating suggests that the barrier stabilizes between two states with a stable, reproducible concentration ratio.
Total-energy calculations on the Takayanagi model for the Si(111) 7×7 surface
Authors: Qian Guo-Xin , Chadi D. J.
Published: July 2002

Total-energy calculations have been performed on a class of (2n+1)×(2n+1) reconstructed (111) surfaces based on the Si(111) 7×7 structure proposed by Takayanagi et al. The models feature dimers, adatoms, and stacking faults (DAS) in the first two layers at the surface. The energy changes resulting from the formation of adatoms, dimers, and stacking faults have been separately calculated. The presence of dimers is intimately related to that of stacking faults at the surface. A strain energy of 0.53 eV per dimer is calculated. The strain energy is compensated by a reduction in the dangling-bond density. This reduction is caused by a lowering of the number of surface layer atoms and by the introduction of adatoms. The results of the calculations show that among all the proposed Si(111) 7×7 models, the DAS model has the lowest surface energy.
Energy deposition at insulator surfaces below the ultraviolet photoablation threshold
Authors: Dreyfus R. W. , McDonald F. A. , von Gutfeld R. J.
Published: July 2002

A surface deformation technique measures the energy deposited in sapphire and other surfaces upon irradiation by focused excimer laser light. For sapphire, the thermal deformation indicates a linear dependence of absorbed energy on excimer fluence with about 3% of the incident light absorbed per surface at 193 nm. Just below etching threshold this absorbed energy should raise the surface temperature to about 430 K, an insufficient temperature for ablation of Al2O3 by thermal vaporization. In contrast the absorbed energy creates ≲3 electron–hole pairs/oxygen atom, consistent with a photochemical (electronic type) etching process.
Dependence of the condensation coefficient of Hg on the orientation and the stability of the Hg–Te bond for the growth of Hg1−xMxTe (M=Cd, Mn, Zn)
Authors: Sivananthan S. , Chu X. , Faurie J. P.
Published: July 2002

We investigate here the influence of the crystallographic orientation of the CdTe substrate and the stability of Hg–Te bond on the condensation of Hg during the growth of Hg1−xCdxTe. Our experiments show that the crystallographic orientation of the substrate indeed has a strong influence on the growth parameters, such as the Hg and Cd condensation coefficients, for the growth of Hg1−xCdxTe by molecular-beam epitaxy. The CdTe (111)B face required about one order of magnitude less mercury than a (111)A face when the growth temperature was 185 °C. Whereas for a CdTe (100) face, the Hg condensation coefficient falls in between. Orientation dependence of the Hg condensation coefficient can be explained in terms of the bonding of the surface atoms. For the same growth rate, and substrate temperature Mn needed the most mercury and Zn needed the least, while Cd falls in between. HgTe needed less Hg compared to that of Hg1−xCdxTe. This supports the theoretical prediction where, Cd destabilizes the Hg–Te bond while Zn does no harm to the Hg–Te bond. The orientation dependence of the condensation coefficient confirms that surface kinetics plays an important role in molecular beam epitaxial growth. The high mobilities, along with the fact that Zn is less harmful to the Hg–Te bond means that Hg1−xZnxTe may be the potential candidate to replace Hg1−xCdxTe, which is currently the most important material for infrared detectors.
The future costs of semiconductor lithography
Authors: Hill Robert W.
Published: July 2002

A method for comparing the costs for photoprocessing high volume semiconductor logic and memory wafers is presented. Industry lithographic trends and process structures are discussed and a cost model is applied. Some typical results obtained with optical tooling and x-ray synchrotron based lithography are discussed for 1/2 μ ground rules. The model consists of two sections; exposure costs and process costs per level. Both areas are addressed and discussed. Equivalent yield has been assumed for all processes. Normalized results done with the model are presented and discussed. Net conclusions are that photo process costs are as great or greater than the exposure costs, and that x-ray technology with a synchrotron source becomes competitive with optical technologies for large volume applications because of process simplicity. Optical technologies will continue to be used by many manufacturers because of their lower initial investment and evolutionary nature.
Control of compound semiconductor–insulator interfaces by an ultrathin molecular-beam epitaxy Si layer
Authors: Hasegawa Hideki , Akazawa Masamichi , Ishii Hirotatsu , Matsuzaki Ken-ichirou
Published: July 2002

Based on the disorder induced gap state (DIGS) model, an attempt is made to control the insulator–semiconductor (I–S) interfaces of GaAs and In0.53Ga0.47As by an ultrathin surface-oxidized silicon (Si) interface control layer (ICL). A Si ICL is grown on GaAs or InGaAs by molecular beam epitaxy (MBE), and is partially oxidized. Then, a thick SiO2 or Si3N4 layer is deposited by in situ photo-CVD processes. An in situ XPS analysis confirms formation of the intended structures. In the GaAs structure, the state density in the midgap region is remarkably reduced. However, the interface Fermi level is blocked by a high density of interface states near the conduction band minimum, contrary to the recent reports of ‘‘complete unpinning.’’ These states are Si-derived intrinsic states, judging from the band line-up. On the other hand, no such states exist in the InGaAs structure and completely ‘‘unpinned’’ behavior with a very small hysteresis is realized after annealing. The result is interpreted in terms of successful pseudomorphic matching of Si ICL to InGaAs combined with excellent I–S matching between Si ICL and SiO2.
Epitaxy of III–V diluted magnetic semiconductor materials
Authors: Munekata H. , Ohno H. , von Molnar S. , Harwit Alex , Segmüller Armin , Chang L. L.
Published: July 2002

A new class of III–V based diluted magnetic semiconductors, specifically In1−xMnxAs (x≲0.2) and InAs/InMnAs multilayer structures, has been prepared by molecular beam epitaxy. The x-ray diffraction measurements reveal that the incorporation of Mn can be predominantly either homogeneous (200 °C) or inhomogeneous (300 °C), depending on the growth temperature. Semiconducting properties of the films have been examined by optical absorption and Hall effect measurements, and it has been found the films of homogeneous alloy are n-type and have a band gap which decreases with increasing Mn composition. Magnetization measurements indicate that the homogeneous alloy exhibits paramagnetic behavior, whereas ferromagnetic behavior dominates for the inhomogeneous case. The growth of GaMnAs has also been examined.
Step structure and interface morphology: Arsenic on vicinal silicon surfaces
Authors: Ohno T. R. , Williams Ellen D.
Published: July 2002

Changes in the structure of the steps on vicinal Si(100) and Si(111) due to arsenic adsorption have been characterized using low-energy electron diffraction. Under equilibrium conditions all the surfaces studies show reversible step rearrangements as a function of arsenic coverage. On vicinal Si(111) double layer steps form at approximately 0.2 ML of As. On vicinal Si(100) arsenic adsorption causes the steps to group to form facets. If the surfaces are not equilibrated, the step structures formed depend sensitively on preparation procedure. Prior observations on the growth of GaAs on stepped Si(100) are discussed in terms of our observations of step rearrangements.
New surface atomic structures for column V overlayers on the (110) surfaces of III–V compound semiconductors
Authors: LaFemina John P. , Duke C. B. , Mailhiot Christian
Published: July 2002

Two new minimum-energy surface structures have been identified for p(1×1) overlayers of Sb on the (110) surface of III–V compound semiconductors using a tight-binding total-energy formalism previously developed for these systems. The first is the ‘‘epitaxical on top structure’’ (EOTS) in which Sb zig–zag chains are commensurate with, and on top of, the Ga–As unreconstructed surface zig–zag chains. This structure differs from the previously found ‘‘epitaxical continued layer structure’’ (ECLS) by virtue of the registry of the Sb chains ‘‘on top of ’’ rather than ‘‘in between’’ the substrate Ga–As chains. Like the ECLS, the EOTS is compatible with both scanning tunneling microscopy (STM) and photoemission data. The second new structure is the ‘‘epitaxical overlapping chain structure’’ (EOCS) in which the Sb chains are 180° out-of-phase with, and on top of, the Ga–As substrate chains. This structure is, however, incompatible with both low-energy electron diffraction and STM data for GaAs(110)–p(1×1)-Sb. Computations for GaP(110)–p(1×1)-Sb and InSb(110)–p(1×1)-Sb reveal that the energy difference between the EOTS and ECLS is approximately constant over this range of overlayer/substrate lattice mismatch.
Reactive ion etching of GaAs, AlGaAs, and GaSb in Cl2 and SiCl4
Authors: Pearton S. J. , Chakrabarti U. K. , Hobson W. S. , Kinsella A. P.
Published: July 2002

High rate (≤10 μm min−1 ) etching of GaAs, AlxGa1−x As, and GaSb in Cl2/Ar or SiCl4/Ar discharges is reported. The etching was investigated as a function of discharge pressure, power density and composition, and changes in the etching rate of AlxGa1−xAs when SF6 was added to the gas mixtures. Highly anisotropic etching was achieved with SiCl4 for all materials, whereas a greater degree of chemical etching was evident with Cl2. Provided self-biases were ≤50 V, excellent Schottky diode characteristics were exhibited by TiPtAu contacts on SiCl4 or Cl2 etched GaAs surfaces. Energetic-ion bombardment caused carrier compensation up to 2200 Å from the surface in n-type (1017 cm−3 ) GaAs, with this depth being less for lower self-biases. Photoluminescence decreases of 2–25 times were observed after reactive ion etching of GaAs for both types of discharge. Chlorine residues were typically present to a depth of <20 Å after etching, with cleaner surfaces obtained with SiCl4 than with Cl2.
Subhalf-micron patterning of negative working resist by using new phase-shifting masks
Authors: Jinbo Hideyuki , Yamashita Yoshio , Sadamura Masao
Published: July 2002

A lithographic technique using phase-shifting masks combined with i-line reduction projection printing in negative working results has been evaluated for subhalf-micron patterning. The combination of a ‘‘standard’’ phase-shifting mask and image reversal resist, AZ 5214E (from Hoechst), makes it possible to resolve 0.3-μm line and space patterns with practically enough focus latitude on a 0.42 numerical aperture i-line aligner (σ:0.5). New phase-shifting masks which are adapted to isolated spaces and holes for negative working resist have been developed. Of these new masks, a mask whose patterns consist of only shifter film gives excellent results. By using this mask and the i-line aligner, 0.3-μm hole patterns are clearly resolved in LMR-UV (low-molecular-weight resist for UV lithography resist) film.
Tailoring nanostructures with a scanning tunneling microscope
Authors: Staufer U. , Scandella L. , Rudin H. , Güntherodt H.-J. , Garçia N.
Published: July 2002

The use of a scanning tunneling microscope (STM) has become a powerful technique for getting information on the topography of a conducting or semiconducting surface as well as for performing local tunneling spectroscopy. But there is also an increasing interest to use this particular technique for the fabrication of nanostructures in a desired and well-controlled way. Such structures are valuable for the investigation of the physics in small dimensions as well as for the development of new devices that take advantage of quantum size effects. The analysis of the processes creating nanostructures can provide important information about different interactions between the tip, the sample and their surrounding. In this letter we present one of the mechanisms involved in the fabrication of such nanostructures on glassy metals. We investigated the response of different glassy metals to our fabrication process and compared it to the theoretical predictions derived from the solution of the thermal diffusion equation. Furthermore, we will show a method to analyze the fabrication process by measuring the current during the creation of the structures.
A positive, chemically amplified, aromatic methacrylate resist employing the tetrahydropyranyl protecting group
Authors: Taylor Gary N. , Stillwagon Larry E. , Houlihan Francis M. , Wolf Thomas M. , Sogah Dotsevi Y. , Hertler Walter R.
Published: July 2002

In this article we describe the synthesis, properties, and lithographic behavior of a new class of chemically-amplified, positive-tone, aromatic methacrylate resists incorporating the tetrahydropyranyl protecting group bound to base-solubilizing carboxylic acid moieties. Copolymers containing equimolar amounts of benzyl methacrylate and tetrahydropyranyl methacrylate were prepared by free radical and group transfer polymerization (GTP). Photogenerated sulfonic acids formed from covalent ester or ionic salt precursors were used to remove the acid labile tetrahydropyranyl (THP) group by heating after exposure. The resulting copolymers of benzyl methacrylate (BMA) and methacrylic acid (MAA) are extremely soluble in aqueous base solutions when the MAA concentration exceeds 38 mol %, thus affording positive tone patterns. We have studied these copolymer resists and find them to have high sensitivity (<30 mJ/cm2) when formulated with aromatic sulfonate or trifluoromethyl sulfonate sensitizers. Contrast is greater than 2 and submicrometer patterns in 1 μm thick films are resolved. Resolution is significantly influenced by the sensitizer, post exposure heating and development conditions. Molecular weight distribution appears to have little effect on the lithographic properties. Resolution presently is limited by resist adhesion which remains to be optimized. Plasma etching resistance to conditions used to etch Al is 1.8 times less than for hard-baked HPR-206 photoresist, but can be improved to a value of 1.5 by postexposure thermolysis. Improvements are needed before this type of chemically-amplified resist is able to meet all deep-UV lithographic requirements. However, it appears quite promising for other lower resolution (≫1 μm), thick-film-imaging applications which will be the subject of future papers.