bluuebunny/crossref_metadata_2025 huggingface dataset:
Alkali metal adsorption on the Si(111)7×7 surface
Authors: Hashizume Tomi , Motai K. , Hasegawa Y. , Sumita I. , Tanaka H. , Amano S. , Hyodo S. , Sakurai T.
Published: July 2002

Alkali metal (K,Cs) adsorption on the Si(111)7×7 surface has been investigated with the field ion-scanning tunneling microscope. At the initial coverage, K(Cs) atoms adsorb mainly at the on-top site of the center adatoms and are ionized. Some of the adsorbed alkali metal atoms form clusters (often trimers), which have more covalent character with back-donation of the charge distribution, and those clusters become the dominant species on the surface with increasing coverage. When the Si(111)-K surface is heated at 300 °C, a new 1×3 phase grows as islands which are made of incommensurate linear chains with misfit defects.
Experimental study on the influence of liquid metal ion source energy distribution on focused ion beam induced deposition
Authors: Yasaka A. , Yamaoka T. , Kaito T. , Adachi T.
Published: July 2002

We investigated the halo around the carbon film deposited by a focused ion beam (FIB) for photomask repair. The halo size depends significantly on the operating condition of the liquid metal ion source (LMIS). The LMIS operation with high temperature and/or high emission current produces the large halo around the deposited film. It seems that the halo production is mainly due to the deposition by the broad tail of the FIB. We also measured the energy distributions of the ions emitted from the LMIS. According to our measurement, the tendency of the energy spread agrees qualitatively with the halo size.
Thermal stability improvement in novolak based resist by synchrotron radiation hardening process
Authors: Kumar Rakesh , Fujii Kiyoshi
Published: July 2002

This report describes the synchrotron radiation (SR) flood exposure hardening process to improve the thermal stability in negative working x-ray resist, based on Novolak resin, an acid generator and a crosslinker. This simple SR flood exposure hardening process renders sub-half-micron size images in novolak resist, which are resistant to flow at a higher temperature. Our investigation shows that resist images in SAL601-ER7 resist remain thermally stable at 300 °C after SR flood exposure treatment. Study with infrared spectroscopy suggests that the activator (triazine) which produces strong acid to induced acid catalyzed condensation reaction in the resist film during lithographic exposure, is further decomposed as a result of the SR flood exposure treatment to catalyze further crosslinking of the melamine crosslinker with the novolak resin, during hardbaking to enhance the resist image thermal stability.
Energy distribution measurement of a gallium liquid metal ion source modulated at high frequency by a focused laser beam
Authors: Zhou Li , Holmes Fred , Orloff Jon
Published: July 2002

The emission current of a gallium liquid metal ion source (LMIS) was modulated at 500 KHz by focusing a modulated laser beam to 20 μm diam on the tip of LMIS. The peak-to-peak amplitude of the modulated ion current was 300 nA when the average laser power was 15 mW with 83% modulation depth, when the ion source was operated at 1–10-μA dc emission current range. Total energy distributions of ions emitted by the LMIS were measured with and without modulation. We found minimal difference between the energy distributions spread with and without modulation, to within the experimental error.
Selective reactive ion etching of GaAs/AlGaAs metal-semiconductor field effect transistors
Authors: Cameron N. I. , Hopkins G. , Thayne I. G. , Beaumont S. P. , Wilkinson C. D. W. , Holland M. , Kean A. H. , Stanley C. R.
Published: July 2002

The high selectivity between the etch rates of GaAs and AlxGa1−xAs or AlAs obtained in plasmas containing both chlorine and fluorine is widely used to obtain accurate and uniform etching of molecular beam epitaxy grown high electron mobility transistor and (less commonly) metal-semiconductor field-effect transistor (MESFET) layers. The influence of gas residence time on the selectivity of GaAs to Al0.3Ga0.7As in CCl2F2 reactive ion etching (RIE) at 50 V dc bias is investigated, finding that maximum selectivity (>4000 to 1) and maximum GaAs etch rate (1.75 μm/min) are achieved with a residence time for CCl2F2 of between two and four seconds. No evidence of any significant damage to MESFET layers when overetching a 50 Å Al0.3Ga0.7As etch stop was observed at these RIE conditions by either Hall measurements or by CV and IV characterization of Schottky diodes. MESFETs with 0.2 μm gates recessed in CCl2F2 show good dc and microwave performance.
Relaxed GexSi1−x structures for III–V integration with Si and high mobility two-dimensional electron gases in Si
Authors: Fitzgerald E. A. , Xie Y.-H. , Monroe D. , Silverman P. J. , Kuo J. M. , Kortan A. R. , Thiel F. A. , Weir B. E.
Published: July 2002

To obtain a large lattice constant on Si, we have grown compositionally graded GexSi1−x on Si. These buffer layers have been characterized with electron-beam-induced current, transmission electron microscopy, scanning electron microscopy, x-ray diffraction, and photoluminescence to determine the extent of relaxation, the threading dislocation density, the surface morphology, and the optical properties. We have observed that it is possible to obtain completely relaxed GexSi1−x layers with 0.1<x<1, threading dislocation densities of 105–5 × 106 cm−2, and with bulk GexSi1−x optical properties. Calculations show that gradually graded layers grown at relatively high temperatures can remain in equilibrium throughout growth, thereby avoiding strain buildup and the introduction of more threading dislocations through dislocation nucleation. It is also shown that the degree of surface crosshatch is related to inhomogeneous strain fields in the epilayer and to the thickness at which dislocations are introduced. These relaxed buffers have been used for the fabrication of very high mobility two-dimensional electron gases in Si and also as templates for lattice-matched III–V growth. We have obtained electron gases in Si with mobilities as high as 170 000 cm2/V s and red-emitting InGaP light emitting diodes on Si with less than 20 μA reverse current at −6 V bias.
Long wavelength HgMnTe avalanche photodiodes
Authors: Becla P. , Motakef S. , Koehler T.
Published: July 2002

Long wavelength avalanche photodiodes have been fabricated using bulk Hg1−xMnxTe (0.10<x<0.12) single crystals, grown by the traveling heater method. Avalanche multiplication gains (M) greater than 40 and 10 were obtained at wavelengths of 7 and 10.6 μm, respectively. The ionization coefficient ratio of electrons to holes was determined experimentally from the measurements of the excess noise versus the avalanche multiplication factor. At both wavelengths, the ionization coefficient ratio was found to be approximately 12.
Three-dimensional analysis for contrast enhancement lithography by a three-dimensional photolithography simulator
Authors: Ito Tetsuo , Takahashi Shigeru , Okano Sadao , Sugimoto Aritoshi , Kobayashi Masamichi
Published: July 2002

Photoactive parameters of contrast enhancement material CEM 420 for Dill’s model were measured to analyze the contrast enhancement lithography (CEL) process. Then using the three-dimensional photolithography simulator RESPROT, photoresist images in the CEL process were analyzed and compared with images got in a conventional process. The nature of the photosensitizer concentration distribution in contrast enhancement material (CEM) differs from that in conventional photoresist. The former has a higher contrast distribution. In the CEL process, the sidewall of the photoresist image has a steeper slope than that in the conventional one, and the depth of focus is improved 25% for the former. When defocus is 2.0 μm in the conventional process, the photoresist holes do not open but in the CEL process they do. The contrast of an aerial image in the photomask pattern is improved in the CEL process. For a three-line pattern in the conventional process, the center photoresist line is narrow and low, but in the CEL process, all three lines have the same height and width. For a double elbow pattern in the conventional process, photoresist thicknesses differ inside and outside of the two elbow photoresist lines after development, however, they are the same in the CEL process.
The interaction of synchrotron light with water adsorbed on a Ag-field emitter in the presence of a high electric field
Authors: Dirks J. , Drachsel W. , Block J. H.
Published: July 2002

Synchrotron radiation in the energy range between 6 and 30 eV was used to study the photon-stimulated field desorption (PSFD) from a water covered Ag-field emitter. Above a threshold energy of 7.4 eV (extrapolated for zero electric field) a variety of protonated water clusters (H2O)n⋅H+, n=1,...,15, are observed. The influence of the surface temperature, electric field, photon energy, and photon flux on the PSFD spectra are measured. Under certain experimental conditions the predominance of the magic cluster ion (H2O)4⋅H+ is observed.
Practical implementation of metal oxide semiconductor capacitor majority carrier corrected dopant profiling
Authors: Anders B.
Published: July 2002

Application of the majority carrier corrected (MCC) dopant profiling technique described by Ziegler can be complicated by instrumentation, programming, and numeric analysis problems. A practical implementation of the MCC method is described which addresses these problems. The method has been implemented in a system based on the Keithley Package 82 C–V measurement system and was coded using HP-BASIC 5.13. An automatic method for locating the region of valid C–V data for doping profile analysis by using a limiting solution of Ziegler’s equations is described. Accurate, low-noise differentiation of the 1/C2 data (required for profile calculation) by use of Savitsky–Golay convolution is presented. Averaging, dose integration, and doping extrema are all calculated with the aid of a mouse-driven plot interface. The software was written in a modular form which allows easy modification and reduced code development overhead.
Applications of sawtooth doping superlattice for negative-differential-resistance devices fabrication
Authors: Liu Wen-Chau , Sun Chung-Yih , Lour Wen-Shiung , Guo Der-Feng
Published: July 2002

A negative-differential-resistance (NDR) device with a sawtooth-doping-superlattice (SDS) structure, prepared by molecular-beam epitaxy, has been fabricated and demonstrated. The SDS structure contains two different δ-doping superlattices. Multiple-state NDR performance is observed due to the strong field effect and avalanche multiplication. Theoretical analysis for a single δ-doping structure and a SDS structure is carried out to study the two-dimensional electronic properties of quantized states and minibands. An S-shaped NDR device with the SDS structure is fabricated and studied. The δ-doping density profile provides a barrier height variation in the superlattice which influences the transport properties. With adequate design of device parameters, e.g., superlattice periods and doping density, the proposed structure may provide good potential for multiple-state logic circuit applications.
Low-energy etching of GaAs using a single-grid ion beam
Authors: Uenishi Yuji , Yanagisawa Keiichi
Published: July 2002

When microfabricating semiconductor materials, it is necessary to reduce etching damage and to apply a high-selectivity mask. A single-grid ion beam etching system can generate much larger ion currents at low accelerator voltages than a dual grid system. In this experiment, a tenfold ion current as that from a dual grid system is extracted at accelerator voltages below 1000 eV. Here, GaAs samples are etched with an Ar ion beam in order to evaluate the physical etching damage, as measured from the I–V curves of a Schottky diode. The normalized n factor, which indicates the amount of etching damage, is less than 1.2 for an accelerator voltage less than 100 eV. The ion current density can be increased without increasing the etching damage. Additionally, several mask materials for GaAs etching are examined. Ion beam sputtered carbon has the highest selectivity, about 15–20 at Va below 150 eV, among the materials examined. The selectivities of Ti for a metal mask and Al2O3 for a transparent mask are more than 10 at Va below 100 eV, whereas the selectivity of SiO2 is 2.6.
Investigation by scanning tunneling microscopy of the effect of preparative variables on the degree of aggregation of platinum on highly oriented pyrolytic graphite
Authors: Lee Sangho , Permana Haryani , Ng K. Y. Simon
Published: July 2002

The scanning tunnel microscope (STM) technique was used to investigate the effect of preparative variables on the degree of aggregation of platinum clusters on a highly oriented pyrolytic graphite (HOPG). Two methods of depositing Pt were investigated: impregnation and vapor deposition. The diameters of the Pt clusters formed on an oxidized HOPG sample prepared by impregnation range from 50 to 500 Å. The clusters were apparently concentrated along the steps and rough patches on the surface. The sizes of the Pt clusters formed by vapor deposition range from 20 to 50 Å. However, the heights of the Pt clusters formed by these two methods are similar and range from about 10 to 40 Å. Distribution of Pt cluster size was formed to be depended on impregnated platinum loading on an oxidized HOPG surface prepared by impregnation. The platinum clusters observed were not mobile on an oxidized HOPG surface during scanning, and STM images were very reproducible.
Vacuum integrated fabrication of vertical-cavity surface emitting lasers
Authors: Choquette Kent D. , Hong M. , Freund R. S. , Chu S. N. G. , Wetzel R. C. , Mannaerts J. P. , Leibenguth R. E.
Published: July 2002

The novel fabrication of buried active region index-guided GaAs/AlGaAs vertical-cavity surface emitting lasers (VCSELs) using vacuum integrated fabrication is reported. Electron cyclotron resonance plasma etching and molecular beam epitaxial (MBE) regrowth are linked by an ultrahigh vacuum transfer tunnel to avoid air exposure of reactive AlGaAs surfaces. MBE regrowth on etched AlGaAs/AlAs heterostructures shows good quality epitaxial overgrowth exhibiting microtwin plates but few dislocation defects. Applying this regrowth technology to VCSEL fabrication, devices are obtained which exhibit laser emission over a wider current range and higher output power than etched air-post VCSELs. The room-temperature continuous wave characteristics demonstrate efficient current confinement and low thermal impedance for the etched/regrown lasers. Vacuum integrated fabrication promises further performance and functionality enhancements for VCSELs and other optoelectronic devices.
Properties of thin copper films, condensed from a copper plasma with ion energies between 2 and 150 eV
Authors: Mausbach Michael , Ehrich Horst , Müller K. G.
Published: July 2002

A steady vacuum arc with a consumable anode, the anodic vacuum arc, was used to produce thin copper films of 1 μm thickness. This type of discharge is ignited in vacuum (10−3 Pa) and is characterized by a cold copper cathode operating in the spot mode and by copper vapor produced at a hot anode. This discharge generates a gas- and droplet-free copper vapor plasma which expands into the ambient vacuum and produces thin copper films at the surface of substrates. The degree of flux ionization (1%–30%) and the ion energy (2–150 eV) was manipulated by changing the geometric parameters of the arc discharge and by biasing the substrate relative to the vacuum vessel. The produced films are homogeneous and show bulk density. Their purity is ∼99.995%. The films show a strong [111] texture. The films exhibit a metastable state, which recrystallizes at room temperature within a few days. As a characteristic parameter describing the metastability the product of ion energy and degree of flux ionization, the mean ion energy per atom can be introduced. The final grain size decreases with increasing ion flux and ion energy and is determined by this recrystallization process. The surface topology is smoothed with increasing flux ionization. The surface roughness increases with higher ion energy due to an increase of the substrate temperature. The electrical resistivity of the copper films is ∼1.8 μΩ cm for ion energies below 25 eV (bulk value 1.67 μΩ cm). Towards higher ion energies the resistivity increases due to a higher dislocation density, lower grain size, and lower average distance of twin boundaries.
Metal–oxide–semiconductor characterization of silicon surfaces thermally oxidized after reactive ion etching and magnetically enhanced reactive ion etching
Authors: Settlemyer Kenneth T. , Ruzyllo Jerzy , Hwang David K. , Leary Herbert J.
Published: July 2002

In this study the performance of reactive ion etching (RIE) and magnetically enhanced reactive ion etching (MERIE) processes in pregate oxidation etching of the field oxide are compared. The comparison is carried out through metal–oxide–semiconductor (MOS) characterization of oxides and interfaces formed on etched silicon surfaces. The results revealed differences in the outcome of RIE and MERIE processes with the latter displaying overall superior characteristics. MERIE induced surface damage is shallower, and is mostly removed during oxide growth. RIE damage propagates deeper into the Si bulk and still influences the MOS devices even after the top Si layers are converted into the oxide. The results obtained emphasize the importance of adequate cleaning of silicon surfaces following RIE/MERIE processes.
Comment on the imaging of immunoglobulin G by scanning tunneling microscopy
Authors: Müller A. , Diemann E. , Branding A. , Richter M. , Frey J. , Engelhardt W.
Published: July 2002

Scanning tunneling microscopy has been used to image the shape of individual IgG molecules deposited onto a graphite surface. Images of these noncrystalline biological specimens free of the contradictions reported earlier could be obtained under atmospheric conditions. The results are reported including some comments on problems associated with the assignment of the visible features.
Characteristics of gas-assisted focused ion beam etching
Authors: Young R. J. , Cleaver J. R. A. , Ahmed H.
Published: July 2002

Gas-assisted etching with a finely focused ion beam has been studied. The presence of a reactive gas, in this case Cl2, results in an enhanced etch rate compared to the rate for sputtering for many materials, including Si, Al, and GaAs. Other advantages over sputtering are the absence of redeposited material and the high etch selectivity possible with some material combinations, which has been exploited in the etching of microstructures. In some applications of this technique, a protective layer of low etch rate material is used over the substrate to improve the quality of the etched structure. The characteristics of the etching process have been studied with variation in the scan speed, gas flux, and current density into the scanned area. In general, a high scan speed, high gas flux, and low current density were found to give the maximum enhancement in the etch rate over sputtering. The application of these results to etching over a wide range of experimental conditions is discussed, to give a basis for estimating the etching results that would occur under other conditions.
Two-dimensional modeling of high plasma density inductively coupled sources for materials processing
Authors: Ventzek Peter L. G. , Hoekstra Robert J. , Kushner Mark J.
Published: July 2002

Inductively coupled plasma sources are being developed to address the need for high plasma density (1011–1012 cm−3), low pressure (a few to 10–20 mTorr) etching of semiconductor materials. One such device uses a flat spiral coil of rectangular cross section to generate radio-frequency (rf) electric fields in a cylindrical plasma chamber, and capacitive rf biasing on the substrate to independently control ion energies incident on the wafer. To investigate these devices we have developed a two-dimensional hybrid model consisting of electromagnetic, electron Monte Carlo, and hydrodynamic modules; and an off line plasma chemistry Monte Carlo simulation. The results from the model for plasma densities, plasma potentials, and ion fluxes for Ar, O2, Ar/CF4/O2 gas mixtures will be presented.
Relationship between void formation and electromigration performance in Al/TiW multilayered interconnections
Authors: Fukada Shin-ichi , Kudo Kazue , Suzuki Masayasu
Published: July 2002

The effects of the grain size in the Al layer and the passivation structure on the electromigration performance in the two level Al interconnections, the bottom (M1) and the top (M2) interconnections, each of which had a TiW/Al/TiW multilayered structure, were studied regarding void and extrusion formation in the Al layers. In M2, the resistance increase of the interconnection having a larger grain size in the Al layer formed with a reflow treatment, was smaller than that without any reflow treatment. Larger numbers of Al extrusions were, however, observed in the M2 interconnection with the reflow treatment than without it. In M1 which was buried under a thick insulation layer, enlargement of the Al grains by the reflow treatment was more effective to suppress the resistance increase than in the M2 interconnections. This result meant that the combination effect occurred when both treatments, enlargement of the Al grains in the interconnection and strengthening the passivation layer surrounding it, were applied simultaneously.
New chemically amplified positive resist for electron beam lithography
Authors: Hashimoto Kazuhiko , Katsuyama Akiko , Endo Masayuki , Sasago Masaru
Published: July 2002

A novel chemically amplified positive resist with high sensitivity for electron beam (EB) direct-writing lithography has been developed for deep submicron pattern fabrication. This positive EB resist consists of a tert-butoxycarbonyl group-protected poly (p-vinylphenol) type matrix polymer installing cyano group and a metal-free photoacid generator (PAG). The matrix polymer is insoluble in aqueous alkaline solutions. The acid-catalyzed deprotection of matrix polymer results in poly (p-vinylphenol), which can be easily dissolved in an aqueous alkaline solution. Three types of monomers, which can generate an acid by EB irradiation, are investigated as PAG in this resist system. Resist pattern profile is dependent on PAG characteristics, and the profile could be tapered in spite of the high contrast. It is found that ketosulfone-type PAG is one of the most effective catalysts for this resist system. High resist sensitivity below 1.5 μC/cm2 at 20 keV is obtained after postexposure bake at 90 °C. Reverse tapered profile in a 0.5 μm thick resist can be achieved in a 0.2 μm line and space resist pattern by using a conventional alkaline developer. This new positive EB resist can be used to delineate 0.35 μm device patterns in a trilayer resist process. Furthermore, 0.2 and 0.3 μm line and space patterns in 0.5 and 1.0 μm film thickness, respectively, can also be fabricated below 2.0 μC/cm2 at 50 keV.
Electrical and structural characterization of boron-doped Si1−xGex strained layers
Authors: Moriya N. , Feldman L. C. , Luftman H. S. , King C. A.
Published: July 2002

The electrical activity and structural properties of rapid thermal chemical vapor deposition grown, boron-doped, strained Si1−xGex layers were investigated for different Ge content and doping levels. Strain measurements were obtained by Rutherford backscattering experiments and show good correlation between the mismatch strain and Ge content. Differential Hall effect profiling, secondary ion mass spectroscopy, and spreading resistance profiling were used to study the electrical doping activity of boron in the strained alloy and were directly compared in this investigation for the first time. It is shown that high electrical efficiency can be achieved in the grown material with boron concentration in the range of 1019–1020 cm−3. Nuclear reaction channeling experiments performed on the doped material were used to correlate the electrical behavior of the layers with structural incorporation of the dopants in the strained film. It was found that most of the dopant atoms occupy lattice sites in the strained alloy. Lower limits on the dopant solubility for the growth conditions are also reported.
Anomalous low-temperature dopant diffusion from in situ doped polycrystalline and epitaxial Si layers into the monocrystalline Si substrate
Authors: Caymax M. , Baert K. , Poortmans J. , Vandervorst W.
Published: July 2002

In situ phosphorous-doped Si layers have been deposited in three different ways: (i) by low-pressure chemical vapor deposition (CVD) at 615 °C resulting in polycrystalline Si; (ii) by radio-frequency plasma-enhanced CVD at 250–300 °C resulting in either epitaxial Si, or (iii) in amorphous Si which is subsequently crystallized at 600 °C, resulting in epitaxially regrown Si. From secondary ion mass spectrometry and spreading resistance profile measurements, the P appears in cases (i) and (iii) to be diffused into the underlying substrate across several hundreds of nanometers, much further than normal diffusivities would forecast. An explanation of this anomalous behavior, based on precipitation of P causing supersaturated self-interstitial concentrations is proposed.
Size-scalable, 2.45-GHz electron cyclotron resonance plasma source using permanent magnets and waveguide coupling
Authors: Getty Ward D. , Geddes Joseph B.
Published: July 2002

A plasma is produced in 1–10 mTorr Ar using 200–700 W of power at 2.45 GHz in a 20-cm-diam vessel. Electron cyclotron resonance (ECR) conditions are produced with an array of permanent magnets arranged over the surface of the dielectric waveguide window. No electromagnet coils are used. The microwave circuit is nonresonant and can be easily matched to the power source using an E–H waveguide tuner. The 20-cm-diam plasma is 16 cm long, and is surrounded mainly by grounded metal walls. The plasma expands from the ECR source region at the window and completely fills the chamber. Measurements of the electron density, electron temperature, and plasma space potential have been made as functions of spatial position using Langmuir probes. The density ranges up to 6×1011 cm−3 and the electron temperature is in the 2 eV range. The density axial and radial profiles are described by an ambipolar diffusion model which accounts for ionization in the bulk plasma. By applying the same permanent magnet arrangement to a rectangular waveguide, rectangular modules can be made which can be arranged in an array to produce a large-area plasma source with independent power control for each waveguide channel.
Ultra-shallow depth profiling with time-of-flight secondary ion mass spectrometry
Authors: Bennett J. , Dagata J. A.
Published: July 2002

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is an efficient, sensitive method for characterizing semiconductor surfaces. In addition, TOF-SIMS can be applied in a depth profiling mode allowing qualitative characterization of the top 20 nm of material. The utility of TOF-SIMS ultra-shallow depth profiling is demonstrated on GaAs substrates that were passivated with P2S5 solutions and oxidized by exposure to an UV/ozone treatment.
Comparison between computer simulation and direct secondary ion mass spectrometry measurement of lateral dopant distributions
Authors: Cooke G. A. , Dowsett M. G. , Hill C. , Pearson P. J. , Walton A. J.
Published: July 2002

A two-dimensional secondary ion mass spectrometry dopant profiling technique, using a specially prepared sample, has been used to provide high spatial resolution, high sensitivity, dopant maps of boron and arsenic. These have been compared with TSUPREM(IV) simulations. However, investigation of the disagreements between the modeled and experimental data cannot be made, as a major problem has been accurately determining the position of the mask edge on the reconstructed profile. Previous methods have introduced errors of up to 0.2 μm. This has been overcome by using a low energy, low dose, germanium implant as a marker of the mask window. The effect of this marker implant on the dopant distribution to be measured has been investigated and estimates of the accuracy of locating the mask edge have been made using the TSUPREM(IV) code. It is expected that the mask edge in later profiles will be located to better than 15 nm.
Two-dimensional doping profiles from experimentally measured one-dimensional secondary ion mass spectroscopy data
Authors: Goodwin-Johansson Scott , Liu Xuefeng , Ray Mark
Published: July 2002

Two-dimensional doping profiles can be determined from multiple one-dimensional secondary ion mass spectroscopy (SIMS) profiles using computed tomography techniques. The chemical nature of SIMS enables the measurement of both as-implanted and annealed profiles with this technique. Mechanical lapping was done of multiple samples to expose different faces of the substrates followed by one-dimensional SIMS measurements. Measurements have been done with a Perkin Elmer Model 6300 SIMS and a Cameca IMS-3f SIMS. Refinements have been made in the numerical alignment of the separate one-dimensional SIMS data sets, which lead to more accurate reconstructions of the two-dimensional profiles.
Profiling of silicide–silicon structures using a combination of the spreading resistance and point contact current–voltage methods
Authors: Heddleson J. M. , Weinzierl S. R. , Hillard R. J. , Rai-Choudhury P. , Mazur R. G.
Published: July 2002

Silicides are increasingly being used as diffusion sources to form the ultra-shallow, low resistance source-drain junctions, which will be needed in the next generation of ultra-large-scale integration technology. The silicide thickness and impurity profile in the silicon must be determined accurately as they are critical parameters in determining the performance of the resulting devices. In order to analyze the spreading resistance data measured on silicide structures, the interface between the silicide and silicon must be precisely located. In this article, the use of point-contact current–voltage (PC I–V) measurements for accurately determining the thickness of ultrathin cobalt silicide–monocrystalline silicon layers is demonstrated. This method is based on the potential barrier, which exists at the probe/silicon interface, but which does not exist at the probe–silicide interface. By monitoring this potential barrier, PC I–V can locate the silicide–silicon interface with a resolution of 10 Å.
Doping profiles characterization in GaAs semi-insulating substrates using capacitance–voltage, conductance–voltage, and current–voltage measurements
Authors: Iniewski K. , Liu M. , Salama C. A. T.
Published: July 2002

An accurate doping profile extraction in devices fabricated in semi-insulating GaAs substrates is difficult. The conventional Schottky barrier diode C–V technique is prone to large errors caused by bias dependent series resistance, gate current conduction, deep-level traps, and breakdown of the depletion approximation. It is shown that using both ac admittance (G–V and C–V) and dc (I–V) measurements of Schottky barrier diode the doping profile can be extracted more accurately and the range of accurate measurements can be clearly established. The characterization procedure has been verified experimentally using devices fabricated in a commercial 1 μm GaAs process.
Plasma deposited SiO2 for planar self-aligned gate metal–insulator–semiconductor field effect transistors on semi-insulating InP
Authors: Tabory Charles N. , Young Paul G. , Smith Edwyn D. , Alterovitz Samuel A.
Published: July 2002

Metal–insulator–semiconductor (MIS) field effect transistors were fabricated on InP substrates using a planar self-aligned gate process. A 700–1000 Å gate insulator of SiO2 doped with phosphorus was deposited by a direct plasma enhanced chemical vapor deposition at 400 mTorr, 275 °C, 5 W, and power density of 8.5 mW/cm2. High frequency capacitance–voltage measurements were taken on MIS capacitors which have been subjected to a 700 °C anneal and an interface state density of 1×1011/eV cm2 was found. Current–voltage measurements of the capacitors show a breakdown voltage of 107 V/cm and a insulator resistivity of 1014 Ω cm. Transistors were fabricated on semi-insulating InP using a standard planar self-aligned gate process in which the gate insulator was subjected to an ion implantation activation anneal of 700 °C. MIS field effect transistors gave a maximum extrinsic transconductance of 23 mS/mm for a gate length of 3 μm. The drain current drift saturated at 87.5% of the initial current, while reaching to within 1% of the saturated value after only 1×103. This is the first reported viable planar InP self-aligned gate transistor process reported to date.
Friction force microscopy of heavy-ion irradiated mica
Authors: Hagen T. , Grafström S. , Ackermann J. , Neumann R. , Trautmann C. , Vetter J. , Angert N.
Published: July 2002

The effects of energetic heavy ions passing through a solid are reflected in the size, shape, and structure of individual latent tracks. Their detailed study thus provides information on the primary processes of energy deposition, which results in bond breaking, lattice disruption, and increased chemical reactivity. Furthermore, ion track cross sections, being objects very limited in size, are well suited for studies of material properties such as friction on a nanometer scale. The present work displays results of scanning force microscopy of mica, irradiated with 11.4 MeV/u Pb28+ and Xe21+ ions at the UNILAC heavy-ion accelerator of the Gesellschaft für Schwerionenforschung. Their track diameters were determined to be 10.6 and 7.5 nm, respectively. Recording topographical and lateral force data simultaneously allows one to quantify the contribution of friction to topographic images. In this way the kinetic friction coefficient of the sensor (Si3N4) on the sample (mica) was measured. It was found that the value obtained from the latent track area and from the intact mica lattice differ by a factor of 2.
Effects of Cl incorporation during Si oxidation
Authors: Stepniak F. , Weaver J. H.
Published: July 2002

High-resolution synchrotron radiation photoemission has been used to examine the oxidation states of Si atoms near the Si/SiO2 interface. The quality of the starting Si surfaces was intentionally varied and oxidation was done with pure O2 and with a mixture of O2 plus Cl2. The distribution of intermediate oxidation states and the interface thickness was unaffected by Cl2 exposure for atomically flat, well-ordered Si(100) or (111) surfaces. However, for disordered Si surfaces the presence of Cl2 in the oxidizing gas reduced the concentration of Si1+ and Si2+ species by a factor of 2, indicating a tendency to produce better interfaces. In all cases, Cl was present near the SiO2/Si interface, bonded to Si, and in solution with SiO2 as Cl2.
Repair of phase-shifting mask defects using a novel planarization technique with conventional blanks
Authors: Pierrat C. , DeMarco J. , Vella R. M. , Vaidya S. , Rolfson B. , Johnson J. C.
Published: July 2002

A new phase defect repair technique of phase-shifting masks made using conventional chrome-on-quartz blanks is proposed. This technique is based on the planarization of defects and dry etching of the defective area under conditions where the planarization layer etch rate is made equal to the quartz etch rate. The process consists of defining an opening on top of the defective area of the mask in a photoresist layer covering the planarization layer using UV exposure. Phase defects can, therefore, be etched away independent of their three-dimensional profile. An additional advantage of this technique is that the lithography for defect repair and therefore the repair itself is automatically self-aligned to the chrome edge. The feasibility of this process defect repair has been demonstrated using a test mask with programmed phase defects. Wafer printability results show that the defects were effectively removed. This technique has been used to successfully fabricate a phase-shifting mask contact level for a 4 Mbit DRAM product.
Fabrication and transport measurements of atomic force microscope modified silicon metal–oxide–semiconductor field-effect transistors
Authors: Fayfield T. , Higman T. K.
Published: July 2002

The channel areas of n-channel silicon metal–oxide–semiconductor (MOS) field-effect transistor devices have been patterned with a modified atomic force microscope operated in air. Grating nanostructures were fabricated both parallel and perpendicular to the direction of electron travel using a direct write process. The gratings were transferred into both the gate oxide as a thickness modulation and directly into the silicon substrate. Subsequent MOS processing steps were completed and the devices were electrically tested. Measurements made on devices with gate oxide thickness modulations operated near threshold indicated different mobilities corresponding to the different grating orientations. This is likely due to local threshold shifting resulting from the grating induced surface potential modulation in the silicon channel.
Scanning probe lithography of novel Langmuir–Schaefer films: Electrochemical applications
Authors: Demir U. , Balasubramanian K. K. , Cammarata V. , Shannon C.
Published: July 2002

Novel Langmuir–Schaefer (LS) films composed of all aromatic molecules have been studied as resist materials for use in scanning probe lithography. These materials are ideally suited for electrochemical applications for two reasons: First, the mass transport and electron transfer blocking ability of the films can be easily controlled by the number of layers transferred to the substrate; second, the fidelity of the tip induced features is high due to the mechanical properties of the film. We have used the tungsten tip of a scanning tunneling microscope to define square features with lateral dimensions of 1×1 μm into LS films transferred to Au(111) substrates. The dependence of feature depth and morphology on tunneling conditions was also investigated: Well-defined features can be produced only over a narrow range of tip-to-sample distances. Direct electrodeposition of Cu from aqueous solution has been used to metallize the lithographically defined domains.
A comparative study of Cl2 and HCl gases for the chemically assisted ion beam etching of InP
Authors: Youtsey C. , Adesida I.
Published: July 2002

Chemically assisted ion beam etching using an Ar ion beam and Cl2 and HCl gases was investigated for the etching of high quality facets in InP. The etch rate, anisotropy, and surface morphology for the Cl2 and HCl processes are compared for different conditions of substrate temperature and reactive gas flow rate. Elevated substrate temperatures above 150 °C were required due to the low volatility of InClx reaction products below this temperature. At higher substrate temperatures, etch rates in the range of 1–5 μm/min using Cl2 and 200–500 nm/min using HCl were obtained. Vertical etch profiles were obtained above 200 °C for Cl2 and above 300 °C using HCl. The HCl process provided very smooth etched surfaces under most conditions investigated. Surface analysis using Auger electron spectroscopy and secondary ion mass spectroscopy techniques was conducted. Auger electron spectroscopy indicated surface depletion of In using Cl2, HCl resulted in increased depletion of P. Secondary ion mass spectroscopy depth profiles carried out using deuterium gas indicated diffusion of deuterium greater than 10 μm at a process temperature of 325 °C, while a postetch anneal at 325 °C/10 min was demonstrated to reduce the level of deuterium near the surface.
Tungsten plug etchback and substrate damage measured by atomic force microscopy
Authors: Allen Lynn R. , Grant John M.
Published: July 2002

Filling contact and vias holes with chemical vapor deposited (CVD) tungsten (W) eliminates the problems encountered with poor metal step coverage when using sputtered metals. Because of this advantage CVD W plugs have become widely used. The most common method of forming W plugs is to etchback a blanket layer of W leaving only the plugs intact. One major problem to overcome in this processing is the need for selectivity to the underlying barrier metal. This is especially true if the intent is to leave the barrier metal intact using it as the basis for the aluminum (Al) metallization. If this approach is taken, the effect of the W etchback process on the barrier metal and on any subsequent Al deposition is important. A blanket etchback process using a transformer coupled plasma (TCP) etcher was developed taking into account not only etch rate, selectivity, and plug loss, but also the effect of the structure of the barrier metal on the subsequent Al deposition. Surface damage of the underlying barrier metal during the W etch was examined by atomic force microscopy. The process flow used in our interconnect scheme leaves the barrier in place. Since the structure of the underlying barrier metal has been shown to affect the subsequent sputtered metal crystal structure [Hikoshi et al., VLSI Multilevel Interconnection Conference, June 1993 (unpublished)], knowing how the structure of the titanium nitride (TiN) surface affects the Al deposition is important. The roughness of the TiN was studied as a function of the TCP coil power, wafer bias power, and gas flows. The parameters used to quantify the roughness of the surface were the area Ra and rms roughness and the fractal dimension of the surface. In addition, both the roughness of the deposited Al surface and the grain size of the Al were measured.
Nanometer-size surface features produced by single, low energy, highly charged ions
Authors: Parks D. C. , Bastasz R. , Schmieder R. W. , Stöckli M.
Published: July 2002

We have studied the interaction of ions with solid surfaces in the limit of slow, highly charged ions (Xe44+ 0.1–20 keV/q). Using atomic force microscopy we are able to see individual ion impact sites on mica, approximately one site per incident ion. Such features are typically circular with ∼20 nm diameter. This damage may be caused by local charge depletion and conversion of the 50 keV Coulomb potential energy of the ions. Contact mode microscopy shows the features to be either pits or blisters depending on scanning direction and force between tip and substrate. By using lateral force microscopy we see the features to be regions of increased friction. The observed surface damage is independent of the ion kinetic energy. Repeated scanning over the same region causes erasure of the observed features.
Photovoltaic effect for a single-barrier structure
Authors: Sumetskii M.
Published: July 2002

The theory of the photovoltaic effect for a single-barrier structure under the zero bias is presented. We find general expression for the induced current in the case when the quantum energy of the applied radiation is smaller than the electron Fermi energy and the height of the barrier. We distinguish between the cases when inelastic transitions take place mostly outside and, alternatively, inside the barrier. It is shown that the photocurrent, as a function of the radiation frequency ω has a maximum for ωτ0∼1, where τ0 is the time it takes for an electron to cross the region of interaction with radiation. In specific cases, the photocurrent may change its direction with increasing frequency. As a function of the barrier width d this current has a maximum for dγ∼1, where γ−1 is the decay length of the electron wave function in the barrier region.
Atomic force microscope as a tool for metal surface modifications
Authors: Göbel H. , von Blanckenhagen P.
Published: July 2002

Atomic force microscopy has been used for direct surface modification and imaging of bulk polycrystalline Au, thin Au films, and a microstructure. Single surface scratches and periodic profiles as well as more complicated structures have been produced. The underlying process is discussed in terms of abrasive wear such as microploughing and microcutting as well as of the temperature rise during modification. In the case of plastic deformation and slow sliding one can estimate a temperature increase of about 0.6 μK for typical structurization parameters. The method described here is promising as regards the structurization of various materials and fundamental studies in tribology.
Improved properties of ‘‘pure’’ Langmuir films of tetra(cumylphenoxy) phthalocyanines
Authors: Xu L. , Krishnaswamy L. , Burrows V. A. , George R. D.
Published: July 2002

Langmuir–Blodgett films of pure peripherally substituted metal tetra(cumylphenoxy) phthalocyanines [MPc(CP)s] have been formed on substrates of silicon (Si) and interdigital electrode arrays. Films were obtained by deposition of MPc together with octadecanol as a transfer promoter. Films were then purified by extracting the transfer promoter with 1-pentanol. The resulting films have been chemically and structurally characterized using multiple internal reflection infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. The removal of the promoter shows results in improved thermal stability and a smoother, and more uniform film structure.
Atomic species identification in scanning tunneling microscopy by time-of-flight spectroscopy
Authors: Spence J. C. H. , Weierstall U. , Lo W.
Published: July 2002

We report the first chemical identification of a cluster of atoms from identifiable sites on an extended crystal surface. The instrument used combines the functions of a scanning tunneling microscope (STM) with a time-of-flight (TOF) atom probe. Atoms are transferred from regions of interest identified in STM images to the tip, from which they are ejected into a TOF spectrometer. Preliminary results are shown in which a cluster of silicon atoms taken from the Si(111) 7×7 surface is identified by TOF spectra. Applications of these ‘‘atomic tweezers’’ for microanalysis are discussed.
Surface morphologies associated with thermal desorption: Scanning tunneling microscopy studies of Br–GaAs(110)
Authors: Cha C. Y. , Brake J. , Han B. Y. , Owens D. W. , Weaver J. H.
Published: July 2002

Scanning tunneling microscopy was used to characterize the developing surface morphology found during typical temperature programmed desorption experiments for halogen–GaAs. Surfaces exposed to Br2 at 300 K were heated to temperatures between 450 and 675 K, followed by scanning at room temperature. This made it possible to relate the temperature-dependent gas phase etch product distribution to the surface structure and thereby examine atomic-level surface processes associated with the evolution of volatile products. We associate the desorption of GaBr3 around 500 K with the initiation of single-layer-deep terrace pits. Desorption of GaBr and As2 above 600 K accounts for the lateral enlargement of the pits.
Development of a low permittivity fluorinated copolymer for interlevel dielectric applications
Authors: Buckley Leonard J. , Snow Arthur W. , Hu Henry S. , Griffith James , Ray Mark
Published: July 2002

Technology for future integrated circuits will require advances in all facets of materials and processing. Low dielectric constant materials will require advances in electrical, thermal, and mechanical behavior before process integration can occur. The dielectric constant must be lower than that of amorphous silicon dioxide and possess the right properties for integration with future metallurgies such as copper. Several organic thermoset resins that were predicted to possess the necessary characteristics have been synthesized and studied. A thermoset copolymer of 1,3,5-tris(2-allyloxy-hexafluoro-2-propyl) benzene with polymethylhydrosiloxane oligomers was identified as a material worthy of further development. Thermal gravimetric analysis indicates relative stability up to 350 °C for short periods of time (30–60 min). The complex permittivity was measured up to 40 GHz and was found to be 2.40 with a loss tangent of 0.008. Compatibility with copper multilevel processing was determined by a secondary ion mass spectroscopy analysis. Copper ion migration did not occur. The processability of the dielectric resins was investigated to address the integration issues associated with the fabrication process.