bluuebunny/crossref_metadata_2025 huggingface dataset:
A high vacuum system for laser induced deposition of tungsten
Authors: van Maaren A. J. P. , Krans R. L. , de Haas E. , Sinke W. C.
Published: July 2002

A new high vacuum system for laser induced chemical vapor deposition of tungsten on silicon is presented in this paper. In this apparatus, tungsten depositions have been performed in the 0.5–15 mbar pressure range at substrate temperatures up to 400 °C. The base pressure of the system is 10−8 mbar after baking. Samples can be transferred via a sample loading system to maintain a low concentration of impurities. 193 nm UV photons are supplied by an ArF excimer laser (0–50 Hz, 160 mJ). A nitrogen window purge prevents tungsten deposition on the laser entrance and exit windows. Reaction product analysis can be performed with a quadrupole mass spectrometer which has been installed in a separate, differentially pumped, vacuum chamber close to the sample and the laser beam. Tungsten films have been analyzed with Rutherford backscattering spectrometry and scanning electron microscopy. Sheet resistivities less than twice the bulk value have been obtained with this setup.
Electron cyclotron resonance plasma preparation of GaAs substrates for molecular beam epitaxy
Authors: Choquette Kent D. , Hong M. , Freund Robert S. , Mannaerts J. P. , Wetzel Robert C.
Published: July 2002

We report the preparation of GaAs substrates, using only electron cyclotron resonance plasma techniques, and the subsequent growth of GaAs by molecular beam epitaxy, accomplished within an integrated processing facility. Exposure of the substrates to a hydrogen plasma with an ion current density less than 3 mA/cm2 for 1 h removes the native GaAs oxide leaving a smooth crystalline surface as revealed by streaky (1×1) reflection high energy electron diffraction patterns. At a greater ion current density a spotty diffraction pattern is obtained; a subsequent SiCl4 plasma etch restores a streaky (1×1) diffraction pattern. After plasma processing, evidence of surface reconstruction is observed at substrate temperatures greater than 400 °C in an As overpressure and during GaAs overgrowth. Impurity concentrations at the epilayer/substrate interfaces of plasma-prepared samples are found to be comparable to those of chemically prepared wet etched substrates. This vacuum substrate preparation scheme is a first step toward realizing the benefits of integrated device processing.
In overlayers on Sb passivated GaAs
Authors: Green A. M. , Yamada M. , Kendelewicz T. , Herrera-Gomez A. , Spicer W. E.
Published: July 2002

Photoemission spectroscopy has been performed on Sb/GaAs. We have shown that Sb/nGaAs returns to near flatband (∼0.3 eV below the conduction-band minimum) upon annealing. This is in contrast to previous results which demonstrated this behavior on p type (movement to ∼0.1 eV above the valence-band maximum) but not on n-type substrates [F. Schaffler, R. Ludeke, A. Taleb-ibrahimi, G. Huges, and D. Rieger, J. Vac. Sci. Technol. B 5, 1048 (1987); R. Cao, K. Miyano, T. Kendelewicz, I. Lindau, and W. E. Spicer, Surf. Sci. 206, 413 (1988)] and in agreement with the results of Zahn et al. [T. Zahn, Technische Universitat Berlin (private communication)] showing analogous behavior in n-type GaAs. Indium overlayers have been deposited on these surfaces and band bending, chemistry and overlayer morphology have been studied. Analysis of Ga (3d) and As (3d) spectra indicate that much stronger clustering is observed on p-type than on n-type substrates. Consistent with this assertion is that stronger chemistry is observed on n-type substrates as is evident from the In (4d) and Sb (4d) spectra. The fact that the same clustering behavior is observed for In/GaAs for both n- and p-type substrates suggests that the Sb interlayer is primarily responsible for the inequivalent clustering observed. Band bending results indicate that for Sb passivated substrates the Fermi-level pins at 0.6 and 0.4 eV as opposed to 0.75 and 0.5 eV above the VBM for n and p-type GaAs on the unpassivated surface.
Hafnium dioxide etch-stop layer for phase-shifting masks
Authors: Shih K. K. , Chieu T. C. , Dove D. B.
Published: July 2002

Phase-shift masks were prepared using sputter deposited films for the phase-shift layer and etch stop layer on fused quartz silica substrates. It has been found that the combination of SiO2 for the phase-shift layer and HfO2 for the etch-stop layer offers a unique combination of properties advantageous for the preparation of phase-shift masks. The optical transmission properties of HfO2 layers with or without a SiO2 phase-shifting layer on quartz substrates are presented.
Water soluble conducting polyanilines: Applications in lithography
Authors: Angelopoulos Marie , Patel Niranjan , Shaw Jane M. , Labianca Nancy C. , Rishton Stephen A.
Published: July 2002

A new class of water soluble conducting polyanilines has been developed. This is accomplished by oxidatively polymerizing aniline monomers on a template such as a polymeric acid. The resulting polyanilines readily dissolve in water. These materials can be applied as removable discharge layers for electron-beam lithography and for mask inspection by scanning electron microscopy. They can be spin-applied directly on top of resists without any interfacial problems. Image distortion as a result of charging during resist exposure is not observed with these materials. After exposure the polyaniline is readily and cleanly removed during the resist develop. By incorporating cross-linkable functionality on the polyaniline backbone, water soluble polyanilines that are radiation curable are attained. Upon irradiation these materials cross-link and become insoluble and thus can be utilized as permanent conducting coatings for electrostatic discharge applications. In addition, the cross-linkable polyanilines can be used as water developable conducting resists. 1.0 μm conducting lines have been patterned with electron-beam irradiation.
Carbon doping by a compact electron beam source
Authors: Van Hove J. M. , Chow P. P. , Rosamond M. F. , Carpenter G. L. , Chow L. A.
Published: July 2002

Carbon doping in III–V compounds has generated much attention because of applications in high temperature and high current devices. We present results using a novel electron beam carbon source for doping GaAs and GaSb. The source construction allows normal effusion cell geometry and utilizes electron bombardment for evaporation from a carbon rod. Mass spectrometer data showed the carbon flux contained C1, C2, and C3 species. For GaAs, controllable hole doping densities between 3×1015 cm−3 and 5×1019 cm−3 were obtained. For GaSb, carbon doping resulted in P-type material with hole densities ranging from the background level of 2×1016 to 3×1020 cm−3 for specular film morphology. Hole mobility values for GaAs and GaSb are comparable to published data.
Secondary ion mass spectrometry depth profiling of boron and antimony deltas in silicon: Comparison of the resolution functions using oxygen bombardment at different energies and impact angles
Authors: Wittmaack K.
Published: July 2002

Codeposited delta doping distributions of B and Sb in Si, with areal densities on the order of 1×1013 atoms/cm2, were used to determine the resolution functions for depth profiling of these dopants under 2 and 5 keV O2 bombardment at impact angles θ between 0° (normal incidence) and 60°. The resolution functions are described by the first and second moments and by the characteristic inverse slopes, which define the exponential rise and decay of the signal at the profile’s leading and trailing edges, respectively. The decay lengths λd(0°) agree very well with numbers reported recently. The up-slope parameters λu(0°) are the same for B and Sb (0.65 and 1.0 nm at 2 and 5 keV, respectively), but significantly smaller than the previously published data, which showed differences for B, Sb, and Ge. This discrepancy could be due to differences in roughness of the as-grown samples. Moreover, the high doping densities used in the previous work might have caused profile distortions during growth. Variations of θ between 0° and 60° have only a very small effect on λu(B, Sb) and on λd(B); e.g., at 5 keV λd(B)=3.3 nm at 0° and 60° with a broad maximum in between, where λd=3.7 nm. By contrast, λd(Sb) is quite large in the range 0°≤θ≤25°, 5.6–6.0 nm, then decreases rapidly with increasing impact angle to fall below λd(B) as θ exceeds 40°. Significant differences between B and Sb are also seen in the first moments 〈z〉 of the resolution function. At 5 keV, e.g., 〈z〉Sb−〈z〉B varies from 3.5 nm (0°) to −1.5 nm (60°). The square root of the second moments can be approximated as σ=λu+λd. The difference in the angular dependence of the resolution parameters for B and Sb is thought to be due to differences in the redistribution of the two dopants within the silicon dioxide layer (θ≤25°) and the silicon suboxide (θ≳25°) generated by oxygen bombardment.
Lateral variation in the Schottky barrier height of Au/PtSi/(100)Si diodes
Authors: Talin A. Alec , Williams R. Stanley , Morgan Brent A. , Ring Ken M. , Kavanagh Karen L.
Published: July 2002

The lateral variation in the Schottky barrier height (SBH) formed at UHV prepared Au/PtSi/(100)Si (n=4.5×1014) diodes was measured on length scales ranging from a few to several hundred nanometers using ballistic electron emission microscopy (BEEM). The spatial profile and the statistical distribution of the SBHs thus obtained were compared to broad area current–voltage (I–V) and capacitance–voltage (C–V) characteristics of these metal–semiconductor contacts. This comparison showed that the macroscopic SBHs obtained from I–V and C–V measurements can be successfully interpreted using the parallel conduction model applied to the BEEM derived barrier height distribution. In addition, we found that the variations in the SBH were strongly correlated, with an autocovariance length of ∼20 nm at short wavelengths and with a strong peak in the spectral density at a spatial frequency of ∼(225 nm)−1.
Imaging of cells with atomic force microscopy operated at a ‘‘tapping’’ mode
Authors: Shibata-Seki Teiko , Watanabe Wakako , Masai Junji
Published: July 2002

This paper reports direct imaging of cells with a new scanning mode for atomic force microscopy (AFM), a tapping mode for AFM (TMAFM). Two kinds of cells, Escherichia coli (E. coli) and cultured hamster ovary (CHO) cells, prepared on indium tin oxide (ITO) glasses were observed in air. The TMAFM yielded very reproducible images without appreciable modifications of the sample surfaces. The images were examined in two modes of the data representation; normal height-mode and deflection-mode (similar to a first derivative of height-mode data) representations. The deflection-mode image of the E. coli sample showed much finer surface details than the conventional height-mode one, while the height-mode image of the CHO sample provided more detailed structure than the deflection-mode one.
Simulation and visualization of scanning probe microscope imaging
Authors: Pingali Gopal Sarma , Jain Ramesh , Kong Lai-Cheng
Published: July 2002

This article presents a model for the interaction of probe and sample geometries in scanning probe microscope (SPM) imaging. The model is in terms of mathematical morphological operations and serves as a powerful tool for simulating SPM images given the geometric shapes of the scanning probe and the scanned sample. The artifacts produced due to probe geometry can clearly be seen in such simulated images. The model also serves as a basis for a tool through which SPM users can visualize how different probe shapes image a sample of interest. Based on the visualization, users can, for example, choose the most suitable probe shape for scanning a sample. We present several simulated SPM images produced using the model. The model is verified by comparing predicted images of spheres and cylindrical patterns with actual scanning force microscope images of polystyrene spheres and microfabricated cylindrical structures.
Resist pattern fluctuation limits in extreme-ultraviolet lithography
Authors: Scheckler Edward W. , Ogawa Taro , Yamanashi Hiromasa , Soga Takashi , Ito Masaaki
Published: July 2002

Extreme ultraviolet (EUV) projection lithography has been proposed to achieve features as small as L=180 nm to 70 nm for 1 G to 16 G DRAMs. Application will require high-sensitivity resists and pattern fluctuation control to less than 10% of nominal linewidth. To evaluate low-dose, resist material, and resist process dependent resist roughness limits in EUV lithography, a roughness model originally by Neureuther and Wilson is extended, and a new model for chemical amplification resists is presented and applied to EUV lithography. Analyses of molecular scale simulation and EUV exposures of novolac negative chemical amplification resists complete the study. For 13 nm exposure wavelengths, 180 nm lithography with positive chain-scission resists requires at least 0.69 mJ/cm2, which scales to 54.3 mJ/cm2 for 70 nm features, accounting for both intrinsic resist polymer roughness and absorption in 100 nm PMMA. At 4.5 nm exposure, the dose minima are 15.9 mJ/cm2 and 1254 mJ/cm2, for 1 G and 16 G respectively. Novolac negative chemical amplification resists have a theoretical minimum linewidth of 115 nm, dependent on postexposure bake conditions and resist composition. Printability criteria limit the extent to which process variation can improve roughness. Existing novolac-based negative chemical amplification resists are not suitable for EUV lithography in the 16 G regime, but may be suitable for the 4 G regime under certain conditions.
Atomically resolved image of cleaved surfaces of compound semiconductors observed with an ultrahigh vacuum atomic force microscope
Authors: Ohta M. , Sugawara Y. , Osaka F. , Ohkouchi S. , Suzuki M. , Mishima S. , Okada T. , Morita S.
Published: July 2002

An atomically resolved image of a cleaved InP(110) surface with an ultrahigh vacuum atomic force microscope (UHV AFM) was obtained under the contact mode for the first time. The rectangular lattice could be clearly observed. The distances and corrugation amplitudes between the protrusions along the [001] and [11̄0] directions are estimated to be 5.8±0.6 and 4.1±0.4 Å, and 1.3±0.2 and 0.7±0.2 Å, respectively. These results suggest that the UHV AFM has potential for investigating III–V compound semiconductor surfaces on an atomic scale.
Lens and deflector design for microcolumns
Authors: Thomson M. G. R. , Chang T. H. P.
Published: July 2002

The designs of the deflector and the final focusing lens for an electron beam microcolumn are constrained by the extremely small physical size (less than 4 mm overall), and the low energy of the beam (1 keV). Electrostatic lenses are more suitable than magnetic lenses because their field strengths are more practical. For simplicity of construction, the deflector is also electrostatic. It must be designed in concert with the focusing lens to achieve the largest possible deflection field at these low beam energies. Strategies have been developed to optimize the performance of symmetric and unsymmetric Einzel lenses together with deflection systems. The lens and deflector dimensions are varied subject to constraints which ensure that the final design can be fabricated, and nonlinear constraints on the voltages and fields ensure that operation is practical. The properties of symmetric and unsymmetric Einzel lenses have been evaluated. Immersion lenses (in which the beam energy is higher in the column than at the target plane) have also been considered, although they may not be practical in a microcolumn. Another key factor for high performance is the alignment tolerances, since fabrication errors may be a more significant fraction of the lens bore than for conventional lenses. The aberrations produced by misalignment have been predicted for the different lens types, and designs can be selected which can tolerate electrode misalignments of approximately 1 μm for the probe sizes and working distances of interest. The field which can be covered with a prelens double-deflection system is analyzed, and strategies for improving the deflection field are discussed.
Combining transmission electron microscopy with focused ion beam sputtering for microstructural investigations of AlGaAs/GaAs heterojunction bipolar transistors
Authors: Snyder C. W. , Frei M. R. , Bahnck D. , Hopkins L. , Hull R. , Harriott L. , Chiu T. Y. , Fullowan T. , Tseng B.
Published: July 2002

Transmission electron microscopy (TEM) and focused ion beam sputtering have been used for investigations of microstructure and defect formation in AlGaAs/GaAs heterojunction bipolar transistors. The use of focused ion beam sputtering to prepare nearly ideal thin membranes within the active region of transistors for cross-sectional electron microscopy is described. Results are obtained from as-fabricated devices, devices annealed at temperatures of 400 °C, and devices for which ‘‘aging’’ is accelerated by operating at high-bias conditions and heating in combination. We find that electrical operation leads to significant microstructural changes which are distinct from those observed in devices which are annealed. TEM images of the metal/semiconductor contact reveal ‘‘metal spiking’’ and facetted structures associated with alloy interpenetration. Characterization of the semiconductor heterojunctions reveal precipitates at the emitter-base junction. Mechanisms for the formation of these defects under high-biased operation are discussed.
Fabrication and physics of 2 nm islands for single electron devices
Authors: Chen Wei , Ahmed Haroon
Published: July 2002

Multiple tunneling junctions consisting of metal islands about 2 nm in diameter and <2 nm gaps were fabricated by a combination of high resolution electron-beam lithography and an ionized beam deposition technique. The effective tunneling capacitance of this structure is calculated to be about 0.2 aF, implying that the charging energy associated with an electron tunneling on or off the islands is well above the thermal energy at room temperature. Electrical measurements showed clear Coulomb blockade effects in this structure. Coulomb gaps of 0.16 V were observed at 77 K in the source–drain current–voltage characteristics and the nonlinearity persisted up to room temperature although the Coulomb gaps disappeared as the temperature was raised. When the voltage applied to the gate electrode was swept, the drain–source current showed strong oscillations at constant drain–source bias voltage, confirming the existence of single electron charging effects. This process can be used to fabricate single electron devices operating at liquid nitrogen temperature or perhaps even at room temperature and is compatible with the methods used in integrated circuit processes.
Role of interface microstructure in rectifying metal/semiconductor contacts: Ballistic electron emission observations correlated to microstructure
Authors: Morgan Brent A. , Ring Ken M. , Kavanagh Karen L. , Talin A. Alec , Williams R. Stanley , Yasuda Takashi , Yasui Takanari , Segawa Yusaburo
Published: July 2002

Ballistic electron emission microscopy (BEEM) is a technique for the measurement of nanoscopic spatial variations in the barrier height of metal-semiconductor contacts. We have used BEEM in conjunction with simultaneous scanning tunneling microscopy observations of topography, as well as cross-sectional and plan-view transmission electron microscopy, to investigate diode nonidealities and relate them to microstructure. Au/ZnSe and PtSi/Si diodes were examined using these techniques. When analyzed with the parallel conduction model, distributions of barrier heights observed by BEEM in area scans agree well with values measured by conventional techniques and reported in the literature. The wider Au/ZnSe barrier height distribution is thought to be correlated with a rougher interface structure than the PtSi/Si.
Chemical vapor deposition of copper from CuI hexafluoroacetylacetonate trimethylvinylsilane for ultralarge scale integration applications
Authors: Braeckelmann Gregory , Manger Dirk , Burke Aaron , Peterson Gregory G. , Kaloyeros Alain E. , Reidsema Cindy , Omstead Thomas R. , Loan James F. , Sullivan John J.
Published: July 2002

In this article, the authors report the results of a study aimed at optimizing a manufacturable thermal copper-chemical vapor deposition process, using (tmvs) CuI (hfac) as the source, where tmvs=trimethylvinylsilane and hfac=hexafluoroacetylacetonate, and establishing associated material and process characteristics and performance. This study employed a two-stage design of experiments approach in conjunction with actual deposition runs on unpatterned silicon (Si) and titanium nitride (TiN) surfaces, as well as SEMATECH patterned TiN structures with feature sizes as small as 0.30 μm with aspect ratio 6:1. All samples were analyzed by Auger electron spectroscopy, Rutherford backscattering, four-point resistivity probe, and cross-section scanning electron microscopy. The results of these analyses showed that precursor concentration, substrate temperature, and in situ predeposition substrate surface plasma treatment play a key role in achieving good conformality and complete filling at high growth rates in aggressive via and trench structures. Based on these findings, an optimum process window was identified and employed to demonstrate complete high growth rate (∼2000 Å/min) filling of 0.3 μm, 6:1 aspect ratio, devices structures with pure copper at as-deposited resistivities of 1.8 μΩ cm.
Control of emission characteristics of silicon field emitter arrays by an ion implantation technique
Authors: Kanemaru Seigo , Hirano Takayuki , Tanoue Hisao , Itoh Junji
Published: July 2002

Conical Si field emitter arrays with gate electrodes have been fabricated. Emitter tips were doped by using an ion implantation technique so as to control the emission characteristics. The doped emitters with n-type surfaces showed typical field emission characteristics. However, the p-type emitters did not work well with the Fowler–Nordheim theory and showed plateaus in the Fowler–Nordheim plots. It is speculated from the capacitance–voltage measurements and the experiment of photoenhanced emission that the emission current is limited due to the supply of electrons from depletion layers near the emitter tips and from inversion layers under the gate electrodes.
Atomic force microscopy for cross section inspection and metrology
Authors: Wilder Kathryn , Quate Calvin F. , Singh Bhanwar , Alvis Roger , Arnold William H.
Published: July 2002

Images of integrated circuit cross sections may be acquired with the atomic force microscope (AFM) by introducing material-dependent topography through a series of selective etches. AFM images of a fully processed complementary metal–oxide–semiconductor inverter structure show excellent qualitative agreement with high resolution scanning electron microscope (SEM) images. Measurements of layer thicknesses and lateral dimensions, however, do not precisely correlate. These discrepancies are attributed to tip–sample convolution due to the finite cone angle and rounding of the probe. We describe a one-dimensional computer simulator that models the nonlinear geometrical interaction between a tip and sample. Simulation results are used to determine the tip shape from an AFM image of a feature of known dimensions. The tip influence can be subsequently deconvolved from a cross section AFM image, generating a more faithful reflection of the surface topography. We demonstrate that this scheme yields measurements that correlate well with those made by the SEM and suggest that AFM imaging may be a viable alternative for the inspection and metrology of IC cross sections.
Thermal stability and desorption of Group III nitrides prepared by metal organic chemical vapor deposition
Authors: Ambacher O. , Brandt M. S. , Dimitrov R. , Metzger T. , Stutzmann M. , Fischer R. A. , Miehr A. , Bergmaier A. , Dollinger G.
Published: July 2002

We present results on the thermal stability as well as the thermally induced hydrogen, hydrocarbon, and nitrogen–hydrogen effusion from thin films of Group III nitrides prepared by low-pressure chemical vapor deposition from organometallic precursors. We have deposited amorphous, polycrystalline, and epitaxial InN, GaN, and AIN films on (0001) Al2O3 substrates using the chemical reaction of azido[bis(3-dimethylamino)propyl]indium, triethylgallium, and tritertiarybutylaluminium with ammonia. The substrate temperature was varied between 400 °C and 1100 °C. The elemental composition, in particular its dependence on the growth temperature, was investigated by elastic recoil detection analysis (ERDA). The influence of growth rate and crystallite size on the concentration of surface adsorbed hydrocarbons and carbon oxides is determined by a combination of ERDA and thermal desorption measurements. In addition, the stability of and the nitrogen flux from the InN, GaN, and AIN surfaces was determined by x-ray diffraction and thermal decomposition experiments.
Method for the determination of the angular dependence during dry etching
Authors: Hedlund C. , Strandman C. , Katardjiev I. V. , Bäcklund Y. , Berg S. , Blom H.-O.
Published: July 2002

Process simulation is going to play an ever increasing role in the development, process optimization, and production of integrated circuit devices, yielding shorter development times and reduced costs as compared to traditional development methods. One of the most notorious problems one faces in topography simulations in particular is the determination of the erosion/growth rates of materials exposed to a variety of complex physicochemical processes. The latter evolve continually to satisfy the needs of the ever advancing microelectronic industry, while our understanding about these processes is often incomplete and insufficient for their description. Existing theoretical models, which are often semiempirical, include a set of fitting parameters which are generally unknown and their determination in most cases involves guesswork. Another much more pragmatical approach to the problem is to measure these etch/growth rates directly in situ in the production equipment and feed the data into a topography simulator. In this article we present a simple and general method for measuring the angular dependence of the etch rate of a variety of materials using specially patterned silicon wafers. With anisotropic wet etching of silicon wafers it is possible to create structures defined by specific crystallographic planes, thus producing a variety of planar orientations on one and the same wafer. The structures can be oxidized and coated with the material of interest and processed under standard operating conditions. The method will be presented together with angular dependence data from typical dry etching processes. The results will be used as an input to the topography simulation program DINESE.
Electron beam defined surface gratings in AlGaAs with precisely controlled duty cycle using a multiple line exposure technique
Authors: Eriksson N. , Hagberg M. , Larsson A.
Published: July 2002

We describe the fabrication of surface gratings in AlGaAs with precise control of duty cycle using a multiple line electron beam exposure technique. Using the electron beam resist as an etch mask for the subsequent chemically assisted ion beam etching, we have fabricated near ideal rectangular gratings with a periodicity of 290 nm and a duty cycle ranging from 34% to 73%. The duty cycle is conveniently controlled by utilizing the linear dependence of the duty cycle on the line spacing during the electron beam exposure.
Two-dimensional dopant profiling of submicron metal–oxide–semiconductor field-effect transistor using nonlinear least squares inverse modeling
Authors: Khalil N. , Faricelli J. , Huang C.-L. , Selberherr S.
Published: July 2002

We present an inverse modeling technique to determine the two-dimensional (2D) dopant profile of a metal–oxide–semiconductor field-effect transistor from electrical measurements. In our method, the profile is formulated using two tensor product splines (TPSs). This analytical representation is general, compact, and flexible. It simplifies the profile determination problem to the extraction of the TPS coefficients from experimental data. We show the results of applying the new technique on data collected from a sub-0.5 μm complementary metal–oxide–semiconductor technology with various source/drain implants. We also compare the measured and simulated I–V and C–V characteristics. The results illustrate the importance of accurate 2D dopant profiles for short-channel device simulation and modeling.
Study of molecular scale friction on stearic acid crystals by friction force microscopy
Authors: Takano Hajime , Fujihira Masamichi
Published: July 2002

We observed two types of stearic acid single crystals having different lattice constants with a friction force microscope to study the molecular scale friction. Molecularly resolved friction force microscope images and molecularly periodic stick-slip motions of the cantilever were observed. The stick-slip motion of the cantilever was measured in terms of the normal load acting on the silicon nitride cantilever and scanning directions over the single crystals.
Atomic force microscopy and lateral force microscopy using piezoresistive cantilevers
Authors: Linnemann R. , Gotszalk T. , Rangelow I. W. , Dumania P. , Oesterschulze E.
Published: July 2002

In this article a novel probe for atomic force microscopy will be introduced. It is based on a conventional micromachined silicon cantilever with an integrated electronic sensor which determines the cantilever deflection. The principle setup of this probe is described and a theoretical and an experimental investigation of the sensitivity of the probe will be presented. The probe is suitable for operation in the static as well as in the dynamic mode and was employed for imaging various materials. To enhance the sensitivity of the detection system and to obtain simultaneously a cantilever with a small spring constant, the geometry of the cantilever was modified. Finite element method calculations were performed to get the optimum sensor design. Furthermore, a different cantilever concept was designed to perform lateral force microscopy as well.
Real-time process sensing and metrology in amorphous and selective area silicon plasma enhanced chemical vapor deposition using in situ mass spectrometry
Authors: Chowdhury Ashfaqul I. , Read Walter W. , Rubloff Gary W. , Tedder Laura L. , Parsons Gregory N.
Published: July 2002

We have used mass spectroscopy to observe and analyze, in real-time, gas phase reactants and product species in plasma enhanced chemical vapor deposition (PECVD) of silicon. We describe a doubly differentially pumped mass spectrometry system to sample the exhaust stream of a large area plasma CVD reactor operating at 0.4–1.5 Torr. We show real-time quantitative analysis of silane consumption and hydrogen production for deposition of hydrogenated amorphous silicon and for pulsed-gas selective area silicon deposition. The ability of mass spectrometry to observe process faults in real time is also demonstrated. Mass spectroscopy is a useful nonintrusive process-state sensor for real-time metrology of plasma deposition, for example, to quantify gas phase species, and to characterize reactions occurring on the substrate surface. Based on our results, we discuss potential advanced manufacturing applications of real-time mass spectrometry in amorphous silicon and selective area silicon plasma deposition, including indirect wafer-state sensing, fault analysis and classification, and run-to-run and real-time process control.
Structural characterization of thin Ni films deposited on (001) ZnSe
Authors: Ruvimov Sergei , Liliental-Weber Zuzanna , Bourret Edith D. , Swider Wendy , Washburn Jack , Duxstad Kristin J. , Haller E. E.
Published: July 2002

Transmission electron microscopy and x-ray diffraction have been used to study the evolution of the structure during thermal annealing of thin Ni films deposited on ZnSe. 30-nm-thick Ni layers were deposited, and then annealed at temperatures ranging between 300 and 475 °C for 0.5 or 1 h in a N2 atmosphere. The as-deposited Ni layer was found to be polycrystalline. Annealing results in Ni diffusion into the ZnSe and outdiffusion of the Zn and Se toward the sample surface. The Se reacts with Ni to form NixSe phases at the Ni–ZnSe interface and in the Ni layer. Formation of a metastable tetragonal NixSe phase detected after annealing at 425 °C was found to be suppressed at higher annealing temperatures. The cubic NixSe phase (x∼1) with a=4.23 Å dominates in the samples after annealing at temperatures above 425 °C. Both phases are crystallographically oriented with respect to the matrix so as to provide the best lattice match with the ZnSe.
Scattering with angular limitation projection electron beam lithography for suboptical lithography
Authors: Harriott Lloyd R.
Published: July 2002

There are several candidate lithography technologies for the postoptical era early in the next century. The scattering with angular limitation projection electron-beam lithography (SCALPEL) approach combines the high resolution and wide process latitude inherent in electron beam lithography with the throughput of a parallel projection system. In the SCALPEL system, a mask consisting of a low atomic number membrane and a high atomic number pattern layer is uniformly illuminated with high energy (100 keV) electrons. The entire mask structure is essentially transparent to the electron beam so very little of the beam energy is deposited in it. The portions of the beam which pass through the high atomic number pattern layer are scattered through angles of a few milliradians. An aperture in the back focal plane of the electron projection imaging lenses stops the scattered electrons and produces a high contrast image at the plane of the semiconductor wafer. This article describes how a lithography system based on the SCALPEL principle can be used for semiconductor manufacturing lithography for feature sizes beyond the capabilities of optical lithography.
Role of atomic hydrogen in argon plasma-assisted epitaxy of InGaAsP/InP
Authors: LaPierre R. R. , Robinson B. J. , Thompson D. A.
Published: July 2002

Epitaxial layers of InP and InGaAsP have been grown on (100) InP substrates by gas source molecular beam epitaxy over the temperature range 400–480 °C while simultaneously exposed to an Ar plasma stream produced by electron cyclotron resonance (ECR). Transmission electron microscopy, x-ray diffraction, and photoluminescence studies indicate improved structural and optical properties of the InGaAsP layers as compared to layers grown by conventional epitaxy without plasma. This improvement is attributed to a reduction in lateral composition modulation (LCM), which develops at the surface during growth due to the existence of a miscibility gap. Comparison of these results with that achieved by an independent thermal hydrogen cracker suggests that the reduced LCM results from molecular hydrogen, produced from the cracking of the group V hydride sources, backflowing into the ECR chamber and resulting in a flux of atomic hydrogen toward the growth front. Atomic hydrogen exposure of the growing surface may then result in surfactant-mediated epitaxy, thereby, reducing the adatom surface diffusion length and, hence, the LCM. Atomic hydrogen, therefore, appears to be the sole actor in reducing the LCM, while the effects of the plasma itself are negligible.
Coverage-dependent etching pathways for Br–GaAs(110)
Authors: Brake J. , Cha C. Y. , Han B. Y. , Owens D. W. , Weaver J. H.
Published: July 2002

Scanning tunneling microscopy was used to characterize Br-exposed GaAs(110) surfaces that were heated to 700 K to induce surface etching. Areal analysis of etched surfaces showed that the etch yield (number of substrate atoms removed per adsorbed Br atom) decreased as the initial coverage increased. This reflects competition between reaction channels involving GaBr and GaBr3 evolution which are determined by the local surface Br concentration. A kinetic model demonstrates that the percentage removed by GaBr3 increases with initial coverage but that most of the Ga atoms are removed as GaBr. Arsenic desorbs spontaneously.
Extraordinary growth of C60 on a GaAs(001) As-rich 2×4 surface
Authors: Sakurai T. , Xue Qikun , Hashizume T. , Hasegawa Y.
Published: July 2002

We have systematically investigated, by using scanning tunneling microscopy, the adsorption and film growth of C60 on the various GaAs(001) surface phases prepared by molecular-beam epitaxy. For most phases, the C60 overlayer exhibits the usual close-packed fcc(111) configuration with its lattice constant close to that of the bulk C60 crystal. However, in the case of C60 on the As-rich 2×4 substrate, the epitaxial growth is found to be quite different and unique; C60 film takes its (110) crystalline axis; the C60 overlayer is highly strained with a lattice expansion of ∼13%, and this structure is very stable at least up to 10 ML. We will address the underlying formation mechanism of this new structure in terms of a charge transfer from the As-dangling bonds to C60s and a site-specific C60-substrate interaction, as confirmed by molecular dynamic simulations. The present system provides a unique opportunity to study fullerene and/or noble-gas related two-dimensional phenomena, and demonstrates a potential for fabrication of novel fullerene-based devices, such as strained superlattice structures.
Correlated electrical and optical measurements of firing semiconductor bridges
Authors: Kim Jongdae , Kim Sang Gi , Jungling K. C.
Published: July 2002

Description is given of a high-resolved optical multichannel analyzer (OMA) system and of a firing set whereby OMA records and electrical measurements from a single discharge of a semiconductor bridge (SCB) may be accurately correlated in time. Such a correlation obtained by the novel experimental system is used in order to explain the dynamic discharge behaviors, especially the plasma formation, of the bridges. From the results of the experiments, the minimum electric field to generate a plasma from the W-land SCB is about 0.77×103 V/cm and the time required to evolve the plasma from the bridge is about 1.5 μs, for the SCB 47 μm long and 140 μm wide.
Conductive polyaniline: Applications in x-ray mask making
Authors: Lawliss M. S. , Rocque J. M. , Angelopoulos M. , Puisto D. M. , Henry R. W.
Published: July 2002

Image-placement control with electron-beam lithography is directly influenced by charging effects during exposure. One of the primary charging sources is the buildup of electrons in the nonconductive resist film. We have evaluated the use of a conductive-polyaniline film as a topcoat over the resist during exposure. Critical parameters including image-size variation, image placement, and defect density were compared for masks with and without the conductive-polyaniline topcoat. It was found that the performance is dependent on the resist exposure dose. For a low-sensitivity resist (i.e., a resist requiring high exposure dose), significant improvements for image size and image placement can be achieved with the implementation of a conductive topcoat. For a high-sensitivity resist (i.e., a resist requiring low exposure dose) with single-pass writing, preliminary results show that charging is currently not the primary driver of image-placement errors.
Sub-20 nm x-ray nanolithography using conventional mask technologies on monochromatized synchrotron radiation
Authors: Simon G. , Haghiri-Gosnet A. M. , Bourneix J. , Decanini D. , Chen Y. , Rousseaux F. , Launois H. , Vidal B.
Published: July 2002

The optimal wavelength range for x-ray lithography is usually estimated between 0.8 and 1.4 nm. In this work, the use of a monochromator working at 1.1 nm on synchrotron radiation is reported. Replication results in this monochromatic mode are compared with results obtained for a polychromatic synchrotron radiation centered at 0.8 nm in terms of resolution and image contrast. Two conventional mask technologies are used for this study. The influence of the mask contrast is also studied. A nondestructive soft contact system was chosen to lower the gap below 1 μm. An ultimate resolution of 20 nm is shown in PMMA resist as well as 35 nm in PMMA/MAA (8.5%) resist for the monochromatic mode. The effect of photoelectrons created in the substrate is also investigated by replications on Si substrates coated with a Cr/Au bilayer. In addition, the daughtering of high resolution masks at 1.1 nm is successfully performed in the 20 nm range by Au electroplating.
Fabrication of nanoelectromechanical systems in single crystal silicon using silicon on insulator substrates and electron beam lithography
Authors: Carr D. W. , Craighead H. G.
Published: July 2002

We have demonstrated a process for fabricating nanometer-scale electromechanical structures of diverse geometries in single crystal silicon, using silicon on insulator substrates. We pattern the substrate using high resolution electron beam lithography with 100 keV electrons followed by Al evaporation and liftoff. The Al is used as an etch mask in CF4 reactive ion etching to pattern the top silicon layer. We then undercut structures using a buffered oxide etch. The structures were made from substrates having a top silicon thickness of 200 or 50 nm, and a buried oxide thickness of 400 nm. With this process we have made a variety of movable structures. We describe the performance of an electrostatically driven Fabry–Perot interferometer that consists of a μm sized pad suspended by wires that are 100–200 nm wide. We have also made much smaller mechanical structures such as suspended silicon beams as narrow as 30 nm.
Secondary ion mass spectrometry depth profiling of ultralow-energy ion implants: Problems and solutions
Authors: van Berkum J. G. M. , Collart E. J. H. , Weemers K. , Gravesteijn D. J. , Iltgen K. , Benninghoven A. , Niehuis E.
Published: July 2002

The use of oxygen flooding and an amorphous Si capping for secondary ion mass spectrometry (SIMS) depth profiling of ultralow-energy implants is discussed in terms of the accuracy of the depth and concentration scale. Further, the advantages of a lower primary ion energy and the simultaneous mass registration on a time-of-flight-SIMS with dual beam mode is illustrated. Finally, the effects of ultrahigh top concentrations on the tail of implantation profiles is investigated.
Fabrication of metal field emitter arrays for low voltage and high current operation
Authors: Oh Chang Woo , Lee Chun Gyoo , Park Byung Gook , Lee Jong Duk , Lee Jong Ho
Published: July 2002

This article describes a new fabrication process for a metal field emitter to achieve low voltage and high current operation. The key element of the fabrication process is that the isotropic silicon etching and oxidation process used in silicon tip fabrication are utilized for gate hole size reduction and gate oxide layer formation. A reliable structure with a small gate hole can be easily obtained. Metal field emitter arrays were fabricated in order to demonstrate the validity of the new process and submicron gate apertures were successfully obtained from 2.25-μm-diam disk patterns defined by a conventional contact mask aligner. The required gate voltage to obtain an anode current of a 0.1 μA/tip was 54 V, and emission currents above 20 μA/tip were stable at a gate bias of 96 V without any disruption.
Model calculations of internal field emission and J–V characteristics of a composite n-Si and N–diamond cold cathode source
Authors: Lerner Peter , Miskovsky N. M. , Cutler P. H.
Published: July 2002

A model to describe internal field emission through the interface between highly n-doped Si and nitrogen (N)-doped diamond is presented. We describe the roughness on the Si surface as a collection of sharp, spherically pointed Si asperities embedded in the diamond film. These “tips” provide enhancement of the applied electric field, which, in conjunction with the high N doping of diamond, results in the formation of a Schottky barrier which allows for tunneling or internal field emission from the Si into the conduction band of diamond. This enhanced electric field is also sufficient to induce valence band tunneling from the Si into the diamond conduction band. In our model limitations on the field mediated transport of holes from the n-doped Si/diamond interface to the cathode base leads to charging of the Si asperities. This charge accumulation results in band bending in Si and a significant reduction in the valence band current. The calculated J–V characteristics for the internal field emission lead to nonlinear behavior when plotted in Fowler–Nordheim coordinates. This is a consequence of the limitation of the conduction band current due to density of states effects at high fields in addition to the suppression of the valence band current. The calculated results are in qualitative agreement with recent field emission studies of Okano et al. [K. Okano, S. Koizumi, S. Ravi, P. Silva, and G. A. J. Amaratunga, Nature 381, 140 (1996)] for a composite n-Si and N–diamond cold cathode source. A plausible geometric argument suggests that there is also reasonable quantitative agreement.
Monolithic integration of resonant tunneling diodes and heterojunction bipolar transistors on patterned InP substrates
Authors: Chow D. H. , Hafizi M. , Stanchina W. E. , Roth J. A. , Zinck J. J. , Dubray J.-J. , Dunlap H. L.
Published: July 2002

We report the successful fabrication of coplanar, monolithic integrated circuits based on heterojunction bipolar transistors (HBTs) and resonant tunneling diodes (RTDs). Molecular beam epitaxy growth of the integrated device structure is performed on an InP wafer, which is patterned by photolithography and dry etching prior to growth. The substrate pattern consists of pedestals, which support RTDs after postgrowth device fabrication, and a lower level which ultimately supports HBTs. In situ sensors for layer thickness (photoemission oscillations) and substrate temperature (absorption-edge spectroscopy) play a critical role in controlling key growth and structural parameters for the HBT and RTD devices. Utilization of the photoemission oscillation sensor during deposition of the AlAs barrier layers of the RTD structure has enabled control of peak currents to a design tolerance of ±20% for devices with current densities in the mid-104 A/cm2 range. Implementation of proportional–integral–derivative control based on a transmission-mode absorption-edge spectroscopy sensor has enabled regulation of the substrate temperature to a precision of ±1 °C throughout deposition of the RTD/HBT structure.
Widely changing probability of surface damage creation induced by a single ion in the MeV ion energy range
Authors: Ogiso Hisato , Tokumoto Hiroshi , Nakano Shizuka , Yamanaka Kazushi
Published: July 2002

We report widely changing probability of surface damage creation induced by a single ion on highly oriented pyrolytic graphite specimens, each implanted with 3.1 MeV Si, Cu, As, Sr, Ag, or Au ions at a dose of 1.9×1011 cm−2. By using a friction force microscope, we observed lattice disordered surface damage, and found the probability of surface damage creation varying from 0.02 to 0.54 depending on the variation in the ion species. To determine the reason for the larger dependence on ion species, we calculated the probabilities of knock-on atom generation by nuclear collision. The calculated probability of knock-on atom generation agreed well with the observed probability of surface damage creation.
Fabrication of GaN field emitter arrays by selective area growth technique
Authors: Kozawa T. , Suzuki M. , Taga Y. , Gotoh Y. , Ishikawa J.
Published: July 2002

Selective area growth technique has been used to fabricate field emitter arrays of GaN. Uniform micro-sized hexagonal pyramids of Si-doped GaN were obtained on dot-patterned GaN(0001)/sapphire substrates using metalorganic vapor phase epitaxy at atmospheric pressure, and the tip radius of the pyramids was less than 100 nm. Measurement of the emission was performed at the pressure of 10−7 Pa range. The Fowler–Nordheim plot obtained from current–voltage characteristics shows a linear relationship, indicating that the emitted current is apparently due to field emission.