bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactive ion etching of RuO2 thin films using the gas mixture O2/CF3CFH2
Authors: Pan Wei , Desu Seshu B.
Published: July 2002

RuO2 thin films were successfully patterned by the reactive ion etching technique in O2/CF3CFH2 using SiO2 films as etch masks. The processing parameters have been optimized. The highest etch rate (1600 Å/min) was obtained by introducing a small amount (2.5%) of CF3CFH2 gas in O2. The etched surfaces were clean and shiny; the etched profiles were anisotropic and smooth. The etch rate ratios of RuO2 to SiO2, Si, and lead zirconate titanate (PZT) were studied as a function of CF3CFH2 gas concentration and the optimized ratios were obtained as 4:1 for RuO2 to SiO2, 14:1 for RuO2 to PZT, and 5:1 for RuO2 to Si. The surface chemistry of RuO2 films etched with different gas compositions was studied by x-ray photoelectron spectroscopy. Based on these experimental data, an etching mechanism is proposed.
Micromechanical structures for electron- and ion-beam irradiation phenomena
Authors: Ogo I. , MacDonald N. C.
Published: July 2002

Micromechanical structures are used to investigate the effects of electron- and ion-beam irradiation on silicon dioxide. The devices are simple cantilever beams (50 μm long) fabricated from different types of silicon dioxide and integrated with two parallel driving electrodes. The electrically floating silicon dioxide beams oscillate only under electron-beam irradiation with an ac voltage applied to the driving electrodes at resonance. Accumulated charge produced by electron-beam irradiation in a scanning electron microscope (SEM) produces a driving force between the cantilever beam and the driving electrode. A time-resolved SEM technique is used to determine the resonant frequencies of these micro-cantilever beams. Electron- and ion-beam damage is measured by detecting the shift in the resonant frequency as a function of the irradiation time (electron-beam dose or sputtering time). Experimental results show that the resonant frequency of the silicon dioxide cantilever beam increases under electron-beam irradiation; this frequency rise indicates that material hardening or mass loss or both occur when the cantilever is subjected to electron-beam irradiation. We also observed differences in the rate of change of the frequency shift between thermally grown silicon dioxide films and plasma enhanced chemical vapor deposition silicon dioxide films. Under argon sputtering, the resonant frequency of the silicon dioxide cantilever beam decreases due to the change in the dimensions and mass of the cantilever beam caused by sputtering.
Discontinuous gold island films on mica
Authors: Zheng Xiang-Yang , Ding Youzhen , Bottomley Lawrence A. , Allison David P. , Warmack Robert J.
Published: July 2002

Epitaxial Au films have been deposited on mica substrates at high temperatures (≳500 °C) and characterized by scanning tunneling microscopy, atomic force microscopy, and scanning electron microscopy. A critical growth temperature between 540 and 580 °C has been identified. Above this critical temperature, discontinuous films of micron-sized Au island are obtained. The islands have the appearance of microcrystals with interisland spacings ranging from 0.2 to 1.5 μm and atomically flat surfaces similar to continuous Au films.
Directional deposition of Cu into semiconductor trench structures using ionized magnetron sputtering
Authors: Cheng Peter F. , Rossnagel S. M. , Ruzic David N.
Published: July 2002

The primary metallization technique in the semiconductor industry for the past decade has been magnetron sputtering. The general industry trend towards damascene processing requires the capability to fill trenches and vias with sub-one-half micron widths and aspect ratios (AR) as high as 3:1. At these dimensions and geometries, the angular distribution of magnetron sputtered atoms results in the production of voids during deposition. A new approach to this problem is directional sputter deposition, where neutrals generated from magnetron sputtering are ionized through an inductively coupled rf plasma and accelerated towards the substrate via a small dc bias on the substrate, causing a significant portion of the flux to arrive at normal incidence. The experimental parameters of this process have been explored by depositing Cu on patterned Si wafers. The parameters have varying effects on the morphology of the deposited layer, which indicate relationships between the parameters and the ion-to-neutral ratio, the total flux, and the average ion energy. The ionized magnetron sputter deposition process has been used successfully to fill trenches of 600 nm width and 1.1 AR with Cu near room temperature, and appears to be extendable to more aggressive dimensions.
Nanostructure of thin metal films on silicon(111) investigated by x-ray photoelectron spectroscopy: Inelastic peak shape analysis
Authors: Schleberger M. , Fujita D. , Scharfschwerdt C. , Tougaard S.
Published: July 2002

We have investigated by x-ray photoelectron spectroscopy (XPS) the nanostructure of thin metal films on Si(111) at room temperature and during annealing. We studied the growth and in-depth distribution of Cu, Ag, Pt, and Au. These aspects are very difficult to determine by conventional surface analysis. Hence, we applied the Tougaard method for quantitative analysis of surface nanostructures by XPS. At room temperature we find island formation for Cu, Pt, and Au. For Ag, the analysis indicates either island formation or a Stranski–Krastanov growth mode. For temperatures ≂120 °C we find for Cu and Au strong diffusion deep into the bulk silicon, whereas for Ag and Pt, we find that the metal atoms agglomerate, i.e., the islands grow higher, while the coverage decreases. At higher annealing temperatures there are strong variations in the redistribution of the metal atoms for the different systems, but some silicon remains at the surfaces of all four systems.
Spectral and structural features of porous silicon prepared by chemical and electrochemical etching processes
Authors: Campbell S. D. , Jones L. A. , Nakamichi E. , Wei F.-X. , Zajchowski L. D. , Thomas D. F.
Published: July 2002

The surface morphology of porous silicon, produced by both chemical and electrochemical means, is studied by scanning force microscopy. Observed surface features in the macroscopic range (larger than 30 μm) include etch pits as well as rings and plateaus which are associated with hydrostatic forces during the etching process. In the microscopic regime (several hundred nanometers to a few microns) small hillocks, around 1 μm in diameter and approximately 100 nm high, dominate the surface structure. Missing hillocks are associated with nascent etch pits and etch pit growth is suggested to occur in steps by the rapid corrosive attack on a destabilized hillock. The presence and shape of the hillocks are attributed to surface strain which collapses the etched material. The strain can become so large as to lift the porous silicon from the surface, damaging the sample. The fluorescent properties of these materials is also discussed.
Achromatic interferometric lithography for 100-nm-period gratings and grids
Authors: Savas T. A. , Shah Satyen N. , Schattenburg M. L. , Carter J. M. , Smith Henry I.
Published: July 2002

For the fabrication of periodic structures with spatial periods of 100 nm or less, achromatic interferometric lithography is preferred over other lithographic techniques. We report on processes we have developed, using achromatic interferometric lithography, to fabricate large-area coherent gratings and grids with spatial periods of 100 nm.
Stencil mask temperature measurement and control during ion irradiation
Authors: Riordon James , Didenko Lidia , Melngailis John
Published: July 2002

In ion projection lithography a stencil mask consisting of a thin membrane of silicon is irradiated by a broad, uniform beam of ions. The resulting image is demagnified and projected on a resist-covered substrate. Energy deposited in the stencil mask by the ion beam can lead to temperature distributions resulting in nonuniform stress and unacceptably large feature displacement. Numerical simulations have shown that the presence of a cooled cylinder near the mask during irradiation is an effective means of temperature control. We have experimentally determined the temperature distribution in a thin glass disk which is chosen to be thermally equivalent to a Si stencil mask. We have found temperature distributions that approximately agree with the numerical computations, and have confirmed the effectiveness of a cooled cylinder in reducing the temperature variation over the disk. For example, a graphite coated (ε=0.85) glass disk, when irradiated by a 3.3 mW/cm2 ion beam, develops temperature differences of more than 5 °C between the center and edge of the disk. Introduction of a cylinder cooled 35 °C below room temperature reduces the temperature difference to 1.2°C, resulting in thermally induced feature displacement of less than 10 nm.
Surface passivation of In0.53Ga0.47As ridge quantum wires using silicon interface control layers
Authors: Fujikura Hajime , Kodama Satoshi , Hashizume Tamotsu , Hasegawa Hideki
Published: July 2002

Surface state effects in In0.53Ga0.47As one-dimensional quantum wires and the effectiveness of the Si interface control layer (Si ICL)-based passivation technique are investigated using photoluminescence (PL) as the probe. Scanning electron microscope and x-ray photoelectron spectroscopy measurements were made to characterize the structure and the interface properties. The In0.53Ga0.47As quantum wires embedded in In0.52Al0.48As barrier material were fabricated by selective molecular beam epitaxy growth on patterned InP substrates. Unpassivated near-surface quantum wires showed an exponential decrease of PL intensity with reduction of surface-to-well distance, tws, similarly to the near-surface quantum wells. By applying the Si ICL-based passivation, a nearly complete recovery of PL intensity was achieved with an observed maximum recovery factor of 250 for the InGaAs quantum wire directly passivated with SiO2/Si ICL (tws=0). The mechanism for the PL recovery is explained in terms of suppression of surface states by passivation.
High-resolution depth profiling of InxGa1−xAs/GaAs multiple quantum well structures by combination of secondary ion mass spectrometry and x-ray diffraction techniques
Authors: Gerardi C. , Giannini C. , Passaseo A. , Tapfer L.
Published: July 2002

In this work we investigate multiple quantum well semiconductor structures by secondary ion mass spectrometry (SIMS) and high-resolution x-ray diffraction measurements. The combined use of these techniques turns out to be a very powerful tool for an accurate investigation of both structural and chemical characteristics of complex structures consisting of thin alternating layers. We show that the x-ray data allow us to increase the accuracy of the SIMS analyses providing internal standards, for both depth scale and concentration calibration. This procedure allows us: (i) to determine accurate quantitative SIMS concentration profiles which lead to the determination of the elemental concentration in the quantum wells, (ii) the mole fraction and layer thickness of embedded layers, and (iii) also to investigate eventual segregation and diffusion phenomena occurring at the interfaces. Our procedure is demonstrated on a set of InxGa1−xAs/GaAs multiple quantum well structures grown by metalorganic chemical vapor phase epitaxy. The experiments, performed by secondary ion mass spectrometry and high-resolution x-ray diffraction measurements, as well as the methodology of the data analyses are discussed in detail. As the main result of our investigation we obtained the precise indium distribution in each of the investigated samples with an accuracy below 5% and the individual barrier and well layer thickness.
Physical properties and microelectronic applications of low permittivity fluoromethylene cyanate ester resins
Authors: Buckley Leonard J. , Snow Arthur W.
Published: July 2002

A series of fluoromethylene cyanate ester resins have been synthesized and studied as potential low dielectric resins for microelectronics. Physical properties were observed to change with the fluoromethylene segment length in the monomer. The polymer can be formed from a stable oligomer that is thermally converted in a single step to a crosslinked thermoset. The complex permittivity decreases with the number of fluoromethylenes in the monomer. The dielectric constant changes significantly with the n=6 monomer and appears to show very little change for the n=8, 10 compounds. The loss tangent appears to have a downward trend with increasing fluoromethylene chain length. Complex permittivities of select systems were studied up to frequencies as high as 40 GHz. Differential scanning calorimetry was used to determine melting points of the monomer series and show them increasing with the fluoromethylene chain length. With a broad exothermic curing reaction between 200 and 300 °C, the process window is sequentially shortened as the number of fluoromethylenes increases. This makes the processing of the larger monomers (i.e., n=8, 10) very difficult. A comparison of physical properties and ease of processing shows the n=6 compound to be an optimum compromise. A prepolymer of the n=6 system (F6Cy) was made for spin coat processing with a conversion of 30%–40% determined by F19 NMR. A 2 h cure at 175 °C was found to crosslink the material sufficiently for potential microelectronic applications. Excellent gap fill was observed via SEM of spin coated test wafers. Contact angle measurements and ASTM tape tests indicate good surface wetting and adhesion.
Phosphor challenge for field-emission flat-panel displays
Authors: Hunt Charles E. , Chakhovskoi Andrei G.
Published: July 2002

The requirements of low-energy excitation combined with practical constraints of commercial supply and other issues, mandate the use of readily available commercial CRT phosphors, such as ZnS and Y2O3-based P22, for first-generation field-emission flat-panel displays. The use of these phosphors at low (e.g., ⩽2–4 kV) excitation energies places considerable problems with brightness, efficacy, spectral response, long-term reliability, screen manufacture and materials synthesis, surface conditioning and outgassing protection, and low-cost manufacturing. The tradeoffs imposed by using phosphors designed for optimum performance in the 15–30 kV range at the low voltages employed by field-emission displays are presented and discussed.
Electrical evaluation of process-damaged layers using p-n junctions
Authors: Yuda M. , Kozen A.
Published: July 2002

Current–voltage characteristics of process-damaged p-n junction diodes are investigated for the purpose of damage evaluation. In this technique, damage is assessed by examining its effect on the diode characteristics of the peripheral portion of Zn-diffused p-n junctions. The depth information for the current–voltage measurements is obtained by wet etching. This technique is applied to determine the extent of damage caused by Ar bombardment during Ar-ion beam etching and film deposition of sputtered SiO2. The forward-bias current–voltage characteristics are found to be more effective for damage-depth evaluation than the reverse-bias ones. The depth of the damaged layer is determined from the behavior of the ideality factor (n) of the forward-bias current–voltage characteristics. This technique was used to probe a damaged layer to a depth of up to 350 nm in Ar-ion beam etching, which is much deeper than the 60 nm that is typically evaluated by the current–voltage characteristics of Schottky diodes. This thickness is equivalent to that evaluated by the photoluminescence intensity and cathodoluminescence properties of multiquantum well structures. In addition, the damage depth profile can be represented quantitatively by considering the n≃2 recombination current deduced from the diameter dependence of the diode current–voltage characteristics. Three damaged regions with different recombination current densities are revealed in both Ar-ion beam etching and film deposition of sputtered SiO2.
Highly anisotropic silicon reactive ion etching for nanofabrication using mixtures of SF6/CHF3 gases
Authors: Grigoropoulos S. , Gogolides E. , Tserepi A. D. , Nassiopoulos A. G.
Published: July 2002

A novel highly anisotropic room-temperature process for silicon etching, using mixtures of SF6 and CHF3 gases is presented. The etch rate, selectivity, dc bias voltage and anisotropy as a function of the reactive ion etching conditions (mixture composition, pressure and rf power) are discussed. Excellent anisotropy combined with clean, damage-free surfaces and etching uniformity and reproducibility have been achieved. It was thus possible to fabricate free standing silicon wires with diameter less than 50 nm and with aspect ratios up to 50:1. Optical emission spectroscopy, ex situ x-ray photoelectron spectroscopy and atomic force microscopy were employed as plasma gas phase and surface diagnostics.
Defects, surface roughening, and anisotropy on the tensile InxGa1−xAs/InP(001) system
Authors: Diéguez A. , Vilà A. , Cornet A. , Clark S. A. , Westwood D. I. , Morante J. R.
Published: July 2002

The structural analysis of thin InxGa1−xAs layers grown by molecular beam epitaxy on (001) oriented InP substrates in the range of tensile deformation (x<0.53) was performed by means of atomic force and transmission electron microscopies. The evolution of the surface from planar to faceted is described, together with a complete characterization of the defects nucleated during growth. The observed anisotropy on defect formation is proposed as being directly related to the anisotropy on the rough surface morphology.
Visible photoluminescence of Ge nanocrystallites embedded in SiO2 thin films
Authors: Yue Lanping , He Yizhen
Published: July 2002

A strong photoluminescence (PL) with a peak position of ∼420 nm (2.95 eV) under exciting radiation of λ=300 nm, and two new luminescence peaks at ∼420 and 470 nm, under λ=633 nm excitation at room temperature are observed, evidently for Ge nanocrystallites embedded in SiO2 thin films (Ge–SiO2) prepared by the ion-beam sputtering technique. The studies reveal that the nanometer-size crystalline Ge have a type of face-centered-cubic structure and characteristics of direct optical transition. It is suggested that the visible PL of Ge–SiO2 thin films is not only related to the quantum size effect due to three-dimensional confinement of electrons and holes, but also closely associated with the particular microstructure of the Ge nanocrystallites.
Anodic bonding technique under low temperature and low voltage using evaporated glass
Authors: Choi Woo-Beom , Ju Byeong-Kwon , Lee Yun-Hi , Haskard M. R. , Sung Man-Young , Oh Myung-Hwan
Published: July 2002

A silicon-to-silicon anodic bonding process using a glass layer deposited by electron beam evaporation will be described. Wafers are bonded at a temperature as low as 135 °C with an applied voltage as small as 35 Vdc, enabling this technique to be applied to vacuum packaging of microelectronic devices. Experimental results reveal that an evaporated glass layer of more than 1 μm thick is suitable for anodic bonding. Finally, the role of sodium ions in anodic bonding was also studied by investigating the theoretical bonding mechanism and examining the results of secondary ion mass spectroscopy analysis.
Performance of Zr/O/W Schottky emitters at reduced temperatures
Authors: Kim H. S. , Yu M. L. , Thomson M. G. R. , Kratschmer E. , Chang T. H. P.
Published: July 2002

Experimental measurements of emission stability and energy distributions from a Schottky emitter have been conducted at a tip temperature range from 1330 to 1800 K. The changes of emission properties have been observed at reduced tip temperatures. Noise fluctuations of the probe current increase with decrease of the tip temperature at a constant extraction voltage. The work function of the Schottky emitter increases with decrease of tip temperature. The energy distribution measurements show that the energy width at a given temperature increases with increasing angular emission current density. The energy width also increases with decreasing tip temperature at a given angular emission current density. The results indicate that the energy broadening is mainly contributed by electron tunneling. A comparison of the measured energy width with the theoretical predictions is discussed.
Chemically amplified deep ultraviolet resist for positive tone ion exposure
Authors: Bruenger W. H. , Torkler M. , Buchmann L.-M. , Finkelstein W.
Published: July 2002

The positive tone deep ultraviolet resist UV II HS-0.6 (Shipley) has been evaluated for ion exposure in the ion projector at the Fraunhofer Institute in Berlin. The chemically amplified resist showed extremely high sensitivity of 1×1012 H+ ions/cm2 at an ion energy of 75 keV. The contrast number was 11. Smallest lines with 65 nm linewidth could be delineated in 140-nm-high resist. At higher resist thickness of 370 nm, lines down to 70 nm were stable showing aspect ratios of >4. The exposure latitude at 100 nm nominal linewidth was ±10% dose variation for a ±10% linewidth change.
Preliminary empirical results suggesting the mapping of dynamicin situprocess signals to real-time wafer attributes in a plasma etch process
Authors: Rietman Edward A. , Ibbotson Dale E. , Tseng-Chung Lee J.
Published: July 2002

In many chemical engineering processes the input control parameters and the product output quality are monitored dynamically in real-time. Almost all the processing steps associated with semiconductor manufacturing are chemical processes in which the surface of crystals or thin films are being chemically modified. In situ monitoring of the wafer attributes in real-time is essentially nonexistent in modern semiconductor manufacturing. For plasma etching processes several new diagnostic techniques (e.g., full-wafer imaging interferometry and ellipsometry) provide improved endpoint observation and some provide metrics for the state of the wafer at a given time. However, the methods that do provide metrics are usually quite expensive for a manufacturing environment. We propose a method whereby simple and economic endpoint methods can indicate in real-time the state of the wafer. Our method consists of finding the algorithm to map in situ wafer-state signatures (e.g., interferometry, ellipsometry) to wafer attributes and then mapping the process signatures (e.g., reflected rf power, pressure, flow rate, OES) to wafer-state signatures. From these we then have an abstract mapping from the process signatures to the wafer attributes in real-time. In this article we suggest that a learning machine can perform the mapping between process signatures, as a function of time and wafer state signatures, as a function of time.
Sources of error in quantitative depth profiling of shallow doping distributions by secondary-ion-mass spectrometry in combination with oxygen flooding
Authors: Wittmaack K. , Corcoran S. F.
Published: July 2002

Using a magnetic sector field instrument we have performed a detailed study on profile artifacts produced when measuring very shallow boron doping distributions (0.5 keV 11B) in silicon by oblique oxygen bombardment (1.9 keV O2+ at 56°) in combination with oxygen flooding. The raw profiles were calibrated by standard procedures, i.e., by assuming a constant erosion rate and a constant B-to-Si sensitivity ratio. The 11B profiles derived from measurements at high oxygen pressures (rapid “saturation” of the Si+ reference signal) turned out to be shifted towards the surface by up to 4.5 nm compared to profiles recorded at base pressure. This shift is larger by a factor of 2 than the value previously reported for normally incident O2+ beams of the same energy without oxygen flooding. A particularly large artifact (7 nm shift) has been observed with profiles implanted into Si covered with a 6 nm surface oxide film. The profile shifts appear to be related to a significant (up to 40%) decrease of the matrix reference signals observed under high-pressure flooding conditions at (apparent) depths between about 10 and 50 nm. The ion yield reduction may be indicative of a rapid development of bombardment induced surface roughening, accelerated by oxygen flooding. An additional contribution to the profile shift may originate from the large change in erosion rate of the sample brought about by high-pressure oxygen flooding (reduction in erosion rate by up to a factor of 3.5). Last, but not least, evidence is presented that the concept of stable B-to-Si sensitivity ratios breaks down in the transient region. These findings imply that the oxygen flooding technique in combination with oblique oxygen bombardment is not suited for quantitative depth profiling of shallow doping distributions.
Scanning tunneling microscopy studies of Ge/Si films on Si(111): From layer by layer to quantum dots
Authors: Motta N. , Sgarlata A. , Calarco R. , Castro Cal J. , Nguyen Q. , Prosposito P. , Balzarotti A. , De Crescenzi M.
Published: July 2002

We have followed by scanning tunneling microscopy (STM) the growth of thin Ge films obtained by reactive deposition epitaxy on the Si(111) surface kept at 500 °C. For Ge thickness smaller than 0.45 monolayers (ML), STM images show large 7×7 flat regions without protrusions while at higher coverages flat, triangular 5×5 islands start nucleating. We have followed the evolution of this wetting layer up to its completion and investigated its surface composition at 3 ML by current imaging tunneling spectroscopy measurements. At larger coverages thick Ge islands (quantum dots) start to nucleate according to the Stranski-Krastanov mechanism. We analyze the evolution of the lattice strain both on the wetting layer and on the islands up to 15 ML coverage. A clear expansion of the lattice parameter as a function of the coverage is evidenced both on the islands’ top and on the wetting layer. The luminescence yield measured at 10 K on samples covered by 40 Å of Ge and capped with 10 Å of Si evidences a structure that could be assigned to Ge quantum dots.
Growth and characterization of defect-free GaAs/AlAs distributed Bragg reflector mirrors on patterned InP-based heterostructures
Authors: Gebretsadik H. , Kamath K. , Linder K. K. , Bhattacharya P. , Caneau C. , Bhat R.
Published: July 2002

The growth of defect-free GaAs/AlAs λ/4 distributed Bragg reflector (DBR) mirrors on patterned InP-based heterostructures is demonstrated. The optical quality of the regrown mirror was evaluated using reflectivity and photoluminescence measurements and cross-sectional transmission electron microscopy. It was found that defects did not form or propagate during regrowth of the thick DBR mirror in the mesa structures. In addition, the postregrowth luminescence from the active region remained unchanged. This technique was applied to the fabrication of an InP-based vertical cavity surface-emitting laser designed for 1.55 μm emission. This mirror technology enabled the simultaneous formation of a short-stack AlxOy/GaAs DBR mirror and an InAlAs current aperture by the selective wet-oxidation technique.
Metallization of Cu on polytetrafluoroethylene modified by keV Ar+ ion irradiation
Authors: Cho Jun-Sik , Choi Won-Kook , Koh Seok-Keun , Yoon Ki Hyun
Published: July 2002

A surface of polytetrafluoroethylene (PTFE) was modified with changing ion doses by 1 keV Ar+ ion irradiation and Cu films with a 5000 Å were deposited on the modified PTFE. The scanning electron microscopy study showed that the surface texture of modified PTFE was in the form of filaments whose height increased depending on ion doses. Through x-ray photoelectron spectroscopy spectra, it was found that the intensity of F 1s peaks decreased with ion doses by preferential sputtering of F atoms and the C–C and/or C–F chains were formed by the crosslinking in the newly unstable chains. Cu films were deposited uniformly along the filaments formed on the modified PTFE. In x-ray diffraction spectra of deposited Cu films on modified PTFE, a preferred orientation along (111) and (200) planes was found and a relative intensity of (111)/(200) orientation increased as surface roughness of modified PTFE increased. The resistivity of Cu films was changed from 2.7 μΩ cm of unmodified PTFE to 4.3 μΩ cm of modified PTFE at an ion dose of 1×1016/cm2 and the abrupt increase of resistivity in the modified PTFE at an ion dose of 1×1017/cm2 was due to being cut off the film which resulted from the increased surface roughness.
Low frequency noise in heavily doped polysilicon thin film resistors
Authors: Deen M. J. , Rumyantsev S. , Orchard-Webb J.
Published: July 2002

Low frequency noise and current–voltage measurements in several heavily doped polysilicon resistors of varying geometry and both p and n type, and over a limited range of temperatures from −60 to 50 °C were conducted for the first time. We found that the noise in p-type polysilicon was independent of temperature, but not the n-type polysilicon. For the p-type resistors, linear current–voltage characteristics were observed, and the relative noise spectral density was independent of bias and inversely proportional to frequency. For the n-type resistors, linear current–voltage characteristics were observed, and the relative noise spectral density was independent of bias. Finally, the normalized noise level in the linear n-type resistors was almost an order of magnitude lower than for the p-type resistors. We believe that this difference is because n-type dopants segregate to the grain boundaries, thus passivating some of the traps there. Boron (p-type dopant), on the other hand, does not segregate to the grain boundaries, leaving more unpassivated grain-boundary traps which capture and emit more carriers, resulting in more low frequency noise.
Reflection high-energy electron diffraction/scanning tunneling microscopy study of InAs growth on the three low index orientations of GaAs: Two-dimensional versus three-dimensional growth and strain relaxation
Authors: Joyce B. A. , Jones T. S. , Belk J. G.
Published: July 2002

It is generally believed that strain relaxation in semiconductor heterostructures having a significant misfit (>2%) occurs by the formation of coherent three-dimensional islands, following the growth of one or two continuous two-dimensional monolayers in a manifestation of the Stranski–Krastanov (SK) growth mode. For the InAs–GaAs system, for which the misfit is ≈7.2%, we have shown that this is a very special case, at least during growth by molecular beam epitaxy, as it occurs on only one of the low index orientations, the (001), and then only under As-rich growth conditions. On (110) and (111) surfaces, growth is always two-dimensional layer by layer and strain is relieved by the formation of misfit dislocations. Even when three-dimensional islands are formed on (001) substrates, the process is much more complex than the conventional SK mechanism would imply. We have used a combination of in situ reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM) and ex situ transmission electron microscopy to follow the initial growth processes and strain relaxation mechanisms of InAs on GaAs (001), (110), and (111)A surfaces. RHEED enables us to establish the symmetry of the wetting layer, whether growth is two- or three-dimensional and the external crystallography of any three-dimensional islands. STM images obtained by rapid quenching from the growth temperature show how growth is initiated, provide quantitative data on island formation (number density and volume), and indicate dislocation formation via strain field morphology effects. Detailed results for all three low index surfaces are presented, together with possible reasons for the major differences between them.
Field emitter array development for high frequency applications
Authors: Jensen K. L. , Abrams R. H. , Parker R. K.
Published: July 2002

Radio frequency vacuum microelectronics combines the advantages of electron transport in vacuum with gated electron emission structures derived from solid-state microfabrication. The advent of practical gated vacuum emitters of micron size will have a strong impact on rf source technology. Next-generation rf amplifiers incorporating microfabricated emitters will allow amplifier designs that minimize the need for high-voltage power supplies, complex modulating circuitry, and the heavy magnets common with linear beam tubes. One attractive application for such efficient compact amplifiers is as the vacuum power booster of a microwave power module, a device that combines a solid-state preamplifier with a low-gain vacuum amplifier for efficiency. Program goals are to create a 50 W 10 GHz amplifier with 10 dB gain and efficiency exceeding 50%. We will survey the requirements placed on field emitter arrays for performance in a microwave amplifier as determined by various analyses, describe the present status of the performance of ring cathodes designed for inductive output amplifiers, i.e., the narrow-band, cavity-based klystrode under development at Varian/CPI and the wide-band, helix-based twystrode under development at NRL, and identify the challenges that remain before this new rf source technology is realized.
Combined method of focused ion beam milling and ion implantation techniques for the fabrication of high temperature superconductor Josephson junctions
Authors: Chen C.-H. , Jin I. , Pai S. P. , Dong Z. W. , Sharma R. P. , Lobb C. J. , Venkatesan T. , Edinger K. , Orloff J. , Melngailis J. , Zhang Z. , Chu W. K.
Published: July 2002

We have studied the Tc degradation of epitaxial YB2Cu3O7−x (YBCO) films on (100) LaAlO3 substrates implanted with 100 keV O+ ions at different conditions. The influence of Au mask thickness and the implantation doses on the film characteristics have been investigated systematically. YBCO bridges have been modified by local oxygen ion implantation at optimal condition through a narrow trench in an Au/photoresist mask, which was fabricated formed by focused ion beam milling and reactive ion etching. The critical current and normal resistance of the modified bridges were found to be characteristic of superconductor/normal/superconductor Josephson junction behavior. Microwave irradiation of the junctions resulted in Shapiro steps in the I–V characteristics.
Electron beam and scanning probe lithography: A comparison
Authors: Wilder Kathryn , Quate Calvin F. , Singh Bhanwar , Kyser David F.
Published: July 2002

Electron beam lithography (EBL) and scanning probe lithography (SPL) are electron exposure techniques capable of high resolution patterning of organic resists. This article compares the exposure properties of these two systems. We consider the resist sensitivity to EBL and SPL electrons, exposure tolerances, patterning linearity, and proximity effects. It is possible to print sub-50 nm features using both systems, but SPL has a wider exposure latitude at these small feature sizes. SPL requires a significantly higher incident electron dose for exposure than does EBL. In EBL, lithography control is most limited by proximity effects which arise from backscattered electrons whose range is considerably larger than the forward scattering range in the resist film. As a result, the exposed feature dimension depends strongly on the local feature density and size, leading to unacceptable linewidth variations across a wafer. These limitations are alleviated in the case of SPL exposures. We demonstrate improved linearity and reduced proximity effects with SPL. We have patterned 200 nm pitch grids with SPL where all individual features are resolved. The linewidth of features in these grids is the same as the width of an isolated line at the same dose. Finally, we suggest that the SPL exposure mechanism may be different than that for EBL.
Recent developments in deep x-ray lithography
Authors: Ehrfeld Wolfgang , Schmidt Andreas
Published: July 2002

Deep x-ray lithography (DXRL) with synchrotron radiation represents the technological core of the Lithographie, Galvanoformung, Abformung (LIGA) microfabrication process, thus defining the lateral shape and the accuracy of the final product. High aspect ratio microcomponents with a height of some micrometers up to several millimeters can be manufactured with submicron precision. We report on recently performed theoretical investigations on the structure transfer accuracy in the shadow printing process. Model calculations revealed the importance of photoelectron emission compared to Fresnel diffraction and beam divergence for typical DXRL conditions. The parameters used to model the effects correspond to the spectral distribution of the BESSY I wavelength shifter, Berlin (0.8 GeV, 5 T) equipped with several vacuum windows and a mask membrane made of beryllium with a thickness of 500 μm. A poly(methylmethacrylate) resist layer of 300 μm thickness with a bottom dose of 5 kJ cm−3 is assumed. The calculated dose profiles are supplemented by a detailed experimental analysis confirming the calculation results which indicate a microstructure precision of less than 0.05 μm per 100 μm resist height. Additionally, advanced irradiation techniques like multiple tilted exposures and aligned double exposures are discussed with respect to their technological capacity. Resist side walls exposed under an inclination angle of 45° turned out to follow an accuracy of approximately 1 μm over a height of up to 500 μm, where overlay accuracy for multiple aligned irradiations can be achieved within submicron scale using an internal alignment system in the DEX2 JENOPTIK scanner. Both specially treated beryllium masks and optically transparent LIGA masks made of thin silicon nitride membranes have been utilized. Finally, novel applications of microproducts using DXRL as a prerequisite for mass production will be given.
Use of polymethylmethacrylate as an initial pattern transfer layer in fluorine- and chlorine-based reactive-ion etching
Authors: Smith Christopher J. M. , Murad Saad K. , Krauss Thomas F. , De La Rue Richard M. , Wilkinson Christopher D. W.
Published: July 2002

The properties of polymethylmethacrylate (PMMA) as a pattern transfer mask in commonly used fluorine- and chlorine-based reactive-ion etching processes have been studied. A reduction in the PMMA etch rate in CHF3 and SiCl4 has been observed for a machine with a lower oxygen background level and an optimum selectivity of silicon nitride to PMMA in CHF3 reactive-ion etching (RIE) was obtained also. The machine with the lower base pressure does not exhibit high RIE lag and this allows better transfer of submicron patterns from PMMA to dielectric layers. This improved selectivity has led to a better intermediate mask for the fabrication of photonic band gap structures in AlGaAs.
Long-wavelength luminescence from In0.5Ga0.5As/GaAs quantum dots grown by migration enhanced epitaxy
Authors: Baklenov O. , Nie H. , Campbell J. C. , Streetman B. G. , Holmes A. L.
Published: July 2002

We report on a systematic study of In0.5Ga0.5As quantum dots grown by the migration enhanced epitaxy technique. A maximum room-temperature luminescence wavelength of 1.37 μm has been achieved. We observe the presence of two emission maxima, which we attribute to the formation and interaction of two different dot-size distributions. Photoluminescence data analysis shows the formation of large quantum dots with good size uniformity that emit at 1.3 μm and longer due to the enhanced atomic migration lengths.
High temperature reaction of nitric oxide with Si surfaces: Formation of Si nanopillars through nitride masking and oxygen etching
Authors: Prabhakaran K. , Ogino T.
Published: July 2002

In this article, we report the fabrication of Si nanopillars by surface reaction with nitric oxide (NO) at high temperature. NO was leaked onto clean Si surfaces, at a temperature of ∼850 °C, in ultrahigh vacuum chamber and examined in situ by x-ray and ultraviolet photoelectron spectroscopy, Auger electron spectroscopy, low energy electron diffraction, and ex situ by atomic force microscopy. NO molecules dissociate on the surface and nitrogen atoms thus produced form nitride islands. These islands act as protective masks for the etching of Si by the oxygen atoms, through the desorption of SiO species. Occurrences of these two simultaneous processes results in the formation of nanometer sized Si pillars (typical basewidth 100–150 nm and height 5–15 nm) capped by silicon nitride. These pillar structures are separated by clean Si areas as shown by the clear presence of two domains. We also show that the height of these Si pillars can be increased by ex situ chemical etching.
Photoemission spectromicroscopy studies on epitaxial lateral overgrowth GaN surfaces
Authors: Yang Y. , Mishra S. , Cerrina F. , Xu S. H. , Cruguel H. , Lapeyre G. J. , Schetzina J. F.
Published: July 2002

Photoemission spectromicroscopy is employed to investigate the inhomogeneities of surface electronic structures of epitaxial lateral overgrowth GaN material. The image, acquired on a clean surface, shows the surface morphology and agrees with the atomic force microscopy image. The dominant contrast mechanism is attributed to the angular dependence of the quantum yield for regions at different angles. Energy distribution curves localized to a submicron region for the Ga 3d core level demonstrate that growth-front areas have different Fermi level pinning behavior compared with window areas and overgrowth regions. The sample exposed to atomic hydrogen shows the same Fermi level position for all areas of the surface. Photoemission spectromicroscopy reveals island formation when about 10 monolayers of Mg is deposited on the surface.
Comparison of sensitivity and exposure latitude for polymethylmethacrylate, UVIII, and calixarene using conventional dip and ultrasonically assisted development
Authors: Yasin Shazia , Hasko D. G. , Ahmed H.
Published: July 2002

Experiments are reported on the characteristics of electron-beam exposed polymethylmethacrylate (PMMA), UVIII, and calixarene resists for ultrasonically assisted development and conventional dip development. Ultrasonically assisted development provides improvements in sensitivity and contrast compared to conventional dip development, for the same development time in the case of 10 μm wide features in PMMA and UVIII, whereas no appreciable change is seen for calixarene. Also, we observe a substantial improvement in exposure dose latitude for smaller linewidths with ultrasonically assisted development compared to dip development for PMMA, UVIII, and calixarene. This improvement decreases somewhat as the linewidth increases. The increases in sensitivity and exposure dose latitude may be significant also in improving ultimate resolution. Isolated lines of 36 nm width have been obtained with UVIII using ultrasonically assisted development.
NANOJET: Nanostructuring via a downstream plasmajet
Authors: Voigt J. , Reinker B. , Rangelow I. W. , Mariotto G. , Shvets I. , Guethner P. , Löschner H.
Published: July 2002

A novel high-fidelity pattern transfer and microfabrication method using a scanning micro-/nanonozzle is presented. Reactive species created in a downstream plasma source are transported through a capillary which is pulled to form a nozzle. Due to the high directionality of the emerging particle beam, a strongly localized etching or deposition is induced. By scanning the sample a small distance under the nozzle a pattern transfer is performed. Fundamental principles of this technology, such as transport of free radicals through high aspect ratio capillaries, localized etching, and high etching rates without ion bombardment, are demonstrated in this work. The achieved etching rates are up to 1.1 μm per minute in silicon. Combining the microplasma source with scanning probe techniques provides an instrument for simultaneous in situ structuring and imaging.
High density plasma deposition of device quality silicon nitride. II. Effects of thickness on the electrical properties
Authors: Hugon M. C. , Delmotte F. , Agius B. , Irene E. A.
Published: July 2002

Dielectric behavior of SiNx films, fabricated by microwave electron cyclotron resonance discharge, has been studied as a function of film thickness on the basis of the current–voltage and the capacitance–voltage characteristics. In the thickness range (20 nm<d<80 nm), the resistivity and the critical field for SiNx were found not to be sensitive to the film thickness (d) and which was opposite to strong dependence of the dynamic dielectric constant εd on thickness. To explain the εd behavior as a function of d, a model based on trapped space charge effects is proposed. The dominant mode of electronic conduction, determined from J–E1/2 curves and Arrhenius plots of leakage current, appears to be Poole–Frenkel emission only for thicker films (d>20 nm). Finally, the spatial profile of fixed charges reveals that SiNx/Si interface has a much greater concentration of defects than the bulk film.
Fluorinated amorphous carbon films for low permittivity interlevel dielectrics
Authors: Theil Jeremy A.
Published: July 2002

The need to substitute SiO2 with low dielectric constant (κ) materials increases with each complementary metal–oxide–semiconductor process generation as interconnect RC delay, crosstalk, and power dissipation play an ever larger role in high-performance integrated circuits. Fluorinated amorphous carbon films (a-C:F,H) with low-κ properties (κ∼2.0–2.4) deposited by plasma-assisted chemical vapor deposition (CVD) techniques provide several advantages including low temperature processing, good gap fill capabilities, minimal moisture absorption, and simple implementation. Several deposition techniques have been examined, including high-density plasma and parallel-plate plasma-assisted CVD. In each case, it is possible to deposit a-C:F,H films with widely varying properties, such as κ and thermal stability. This has led to a good deal of confusion as to what is required to produce useful material. Results from many different sources are examined to develop a coherent picture of the relationships between deposition techniques, microstructural features, and macroscopic properties, and to summarize the scientific and technical challenges that remain for a-C:F,H implementation. The relationships between film deposition parameters such as applied substrate bias and film properties are presented in the discussion. In addition, x-ray photoelectron spectroscopy and network constraint theory are used to develop connections between microstructural and macroscopic properties, as well as to show how deposition parameters can be used to create a predictive model. This will demonstrate what process parameters are important in film formation. Finally, efforts to incorporate this material into integrated circuits, as well as measurements of the reliability and performance will be reviewed.
Scanning tunneling microscopy of defects in NbSe2
Authors: Prodan A. , Marinković V. , Gril R. , Ramšak N. , van Midden H. J. P. , Boswell F. W. , Bennett J. C.
Published: July 2002

Defects in the quasi-two-dimensional compound NbSe2 were studied by scanning tunneling microscopy. Atomic vacancies as well as substitutional and interstitial defects, which require an accommodation of the surrounding chalcogen atoms, were identified in as-grown crystals. Defects were also introduced after growth, both by heating the crystals and by bombarding their surfaces with Ar+ ions. Heating the crystals for only 2 min to about 470 K causes in addition to Se vacancies local changes in the surface structure with reduced symmetry as compared to that of the bulk. Ar+ ions with energies and doses not exceeding 400 eV and 1013 ions/cm2 form large surface craters as well as Se vacancies accompanied by mobile adatoms.