bluuebunny/crossref_metadata_2025 huggingface dataset:
Barrier properties of Ta–RuO2 diffusion barrier for dynamic random access memory capacitor bottom electrodes
Authors: Yoon Dong-Soo , Baik Hong Koo , Lee Sung-Man , Lee Sang-In
Published: July 2002

We proposed the Ta–RuO2 diffusion barrier for oxygen in the dynamic random access memory capacitor bottom electrode, and investigated the barrier and electrical properties of the developed diffusion barrier. The Ta–RuO2/TiSi2/poly-Si/SiO2/Si contact system deposited with and without the SiO2 capping layer showed the lower total resistance and ohmic characteristics up to 800 °C. For the Ta–RuO2/TiSi2/poly-Si/SiO2/Si contact system, no other phases observed except for the formation of conductive RuO2 phase in the barrier film by reaction with the indiffused oxygen after annealing in air, but the thin oxidized layer at the Ta–RuO2/TiSi2 interface was formed by external oxygen. However, a large number of the crystallites in the annealed samples compared to that of as-deposited film were observed even after depth profile. The crystallites consisted of Ru and O containing a small amount of Ta. In addition, the embedded RuO2 crystalline phase was observed in the thin oxidized TiSi2 surface layer. Correspondingly, we suggest that the ohmic mechanism of the Ta–RuO2/TiSi2/poly-Si/SiO2/Si contact system is an embedded RuO2 crystalline phase involving a small amount of Ta in a Ta amorphous structure.
Microfabrication and testing of suspended structures compatible with silicon-on-insulator technology
Authors: Ayón A. A. , Ishihara K. , Braff R. A. , Sawin H. H. , Schmidt M. A.
Published: July 2002

The footing or notching effect arises during the dry overetching of silicon layers on top of dielectric films. The visible consequence of this effect is the resulting etch that propagates along the interface between the underlying dielectric films and the silicon layer. Footing is usually considered an undesirable artifact during etching. Thus, the vast majority of efforts made to date have been oriented towards reducing or eliminating the aforementioned effect. There is, however, another alternative that has not been fully exploited: the application of the notching effect in the microfabrication of released structures. Furthermore, with deep reactive ion etching (DRIE) tools it is also feasible to deposit fluorocarbon films for electrical isolation purposes in situ. Thus, it is possible to microfabricate suspended structures by combining the footing effect with the capabilities offered by DRIE. For this purpose, we have developed, built, and tested suspended electrostatic actuators applying this new microfabrication scheme. The process is well suited for applications involving silicon-on-insulator wafers. Electrostatic actuators microfabricated with this passivation film subsequently underwent 105 pull-in cycles without failure.
Atomic structure of stacked InAs quantum dots grown by metal-organic chemical vapor deposition
Authors: Flebbe O. , Eisele H. , Kalka T. , Heinrichsdorff F. , Krost A. , Bimberg D. , Dähne-Prietsch M.
Published: July 2002

We present a detailed cross-sectional scanning-tunneling microscopy investigation of threefold stacked InAs quantum dots in a GaAs matrix grown by metal-organic chemical vapor deposition. The dots are vertically aligned and show a layer-dependent size. Detailed images with atomic resolution indicate that the dots consist of pure InAs with a shape well described by prisms with {110} and additional {111} side faces as well as a (001) top face. The wetting layer is found to be inhomogeneous, while no In diffusion into the overgrowing GaAs layer is observed. These findings demonstrate that growth in the present sample is more related to kinetics than to equilibrium conditions. Furthermore it is demonstrated that the image contrast is strongly influenced by a cleavage-induced outward relaxation of the strained quantum dots.
Epitaxial growth and electronic structure of lanthanide silicides on n-type Si(111)
Authors: Vandré S. , Kalka T. , Preinesberger C. , Dähne-Prietsch M.
Published: July 2002

We present an investigation of Gd, Dy, Er, and Lu silicides epitaxially grown on n-type Si(111) using scanning-tunneling microscopy, low-energy electron diffraction, and core-level photoemission. With varying silicide film thickness, we observe structurally, electronically, and chemically different silicide phases. In particular we found that the Si-2p photoelectron spectra from monolayer silicides are different from those at higher coverages. This observation is attributed to the structure of the layered hexagonal silicide, with a Si vacancy lattice only present in case of multilayer films. Furthermore, we observe peculiar electronic properties: An extremely low band bending is found in the monolayer range, with a Fermi-level position of only 0.08±0.05 eV below the conduction-band minimum of silicon, representing the lowest value ever observed on n-type silicon. With increasing coverage, a final Schottky-barrier height of 0.32±0.05 eV is obtained. This behavior is interpreted as a consequence of the developing metallicity of the silicide overlayer and will be discussed in the framework of theoretical models for Schottky-barrier formation.
Real time monitoring and control of wet etching of GaAs/Al0.3Ga0.7As using real time spectroscopic ellipsometry
Authors: Cho Sang-Jun , Snyder P. G.
Published: July 2002

Real time spectroscopic ellipsometry (RTSE) was used to monitor etching of GaAs/Al0.3Ga0.7As/GaAs heterostructures in citric acid:hydrogen peroxide:de-ionized water (25:1:75). Etch rates of GaAs and AlGaAs of 15.3 and 17.6 nm/min, respectively, were determined by numerically fitting the RTSE data. A variable delay in the onset of etching was observed, and was related to variations in surface cleanliness and the initial oxide thickness. Real time monitoring was also used to control stopping of the nonselective etch after removal of the GaAs cap layer. In addition, etch depth control in the AlGaAs layer was demonstrated. Etching was stopped with 100 nm of AlGaAs remaining. Finally, RTSE was used to monitor wet etching of a patterned sample (75% of the surface area was covered by photoresist).
Phantom exposures of chemically amplified resists caused by acids generated in environmental air in synchrotron radiation lithography
Authors: Deguchi K. , Nakamura J. , Kawai Y. , Nakanishi K. , Okada I. , Fukuda M. , Oda M. , Kochiya H.
Published: July 2002

In this article, we discuss the phantom exposure of chemically amplified resists in x-ray lithography, which is attributable to acids in environmental air induced by x-ray irradiation. Since the acids generated in the air diffuse into the resist film from the top to the bottom like so many catalytic acids, they cause cross linking in a negative resist and decomposition in a positive resist. The phantom exposure in flood exposures of a 20 mm square increases as the exposure dose increases, and expands more than 10 mm outside the exposure field when the exposure dose is ten times greater than the optimum exposure dose for patterning. Dependence of the phantom exposure on the exposure dose and resist material are evaluated.
Effects of surface topography on oxide deposition rates using TEOS/O2 chemistry
Authors: Doyle James R. , Feng G. F. J.
Published: July 2002

The effect of surface topography on TEOS/O2 oxide deposition rates is investigated. It is found that the oxide thickness is significantly less on the top layers of topography used in static random access memory device structures compared to flat wafers for fixed conditions of power, flow, and pressure. The total mass deposition increases, however, in the presence of topography. These effects can be understood from the perturbation on the precursor radical densities near the surface caused by the surface topography. A simple model based on the diffusion-reaction equation with an appropriate boundary condition is proposed to explain the effect. The boundary condition is developed as an effective macroscopic reflection coefficient that takes into account trapping effects of film precursors in the topography. The application of the model to the experimental data gives an estimate for the effective microscopic surface reflection coefficient of r≈0.87 for the oxide film precursors.
Dependence of the performance and reliability of n-metal-oxide-silicon field effect transistors on interlayer dielectric processing
Authors: Trabzon L. , Awadelkarim O. O. , Werking J.
Published: July 2002

This article reports on the impact of interlayer dielectric (ILD) deposition and processing on the characteristics and reliability of n-channel metal-oxide-silicon field-effect transistors (n-MOSFETs). The ILD materials used were silicon dioxide prepared from tetra-ethyl-ortho-silane, fluorinated silicon oxides (FSOs), and low-k polymers. The ILDs were deposited by means of plasma enhanced chemical vapor deposition (PECVD), PECVD and high density plasma (HDP), and spin coating, respectively. The devices with 90 Å gate oxide and 0.35 μm channel lengths were sensitive to poly-Si gate definition etching steps with antenna ratio 5 and 70 K. To assess the degree of degradation, charge pumping (CP), gate-oxide integrity as well as transistor’s parameters were measured after Fowler–Norheim (FN) stressing. It is found out that PECVD deposition of FSO resulted in the highest degradation to the MOSFETs, whereas spinning-on and processing polymer ILD yielded the best performing and the most reliable MOSFETs. It is also found that device degradation in wafers with FSO as ILD depends on the deposition method of FSO, and that this degradation bears a reverse charging-antenna correlation. It is argued that this correlation is caused by the interaction between fluorine and plasma-charging damage.
Selectivity switch concept in Cu chemical mechanical planarization and its implementation on orbital tools
Authors: Gotkis Y. , Alamgir S. , Yang L. , Dai F. , Mitchell F. , Nguyen J. , Shumway L. , Walesa L. R. , Yang J. , Nunan P. , Holland K.
Published: July 2002

Cu and barrier removal peculiarities were studied and a differential multislurry (DMS) chemical mechanical planarization (CMP) process for dual damascene technology was developed. Process shows Cu removal rates up to 1.2 μm/min with an average nonuniformity <5%. Annealing was shown to have impact on process stability. Details of Cu removal mechanism were studied. Cu removal process was found to be temperature insensitive and following Preston’s law that indicates its pseudo-mechanical nature. Abrasive enhancement of chemical activity was shown to be important for Cu removal. Phenomenon of metal feature thinning (MT) and dielectric erosion (DE) in heterogeneous CMP was analyzed and compared with data obtained for various conditions. It was shown that properties of all major acting CMP characters: the tool (loading), the slurry (selectivity), and the pad (hardness) are contributing to MT. Hard pad, slurry selectivity ⩽1 in the end of Cu clearance phase and low polishing pressure help to minimize MT. Some MT and DE related process integration issues are discussed, as well.
Spectroscopic ellipsometry investigation of silicide formation by rapid thermal process
Authors: Hu Yaozhi , Tay Sing Pin
Published: July 2002

Titanium, cobalt, and nickel silicides have been considered as self-aligned silicides (salicides) for contact and interconnect metallization in ultralarge scale integrated circuits. A CoSi2 salicide process using TiN or Ti capping, which is superior to the conventional cobalt salicidation, has been found to be a good solution for producing a lower sheet resistance value and a tighter sheet resistance distribution. In this work cobalt silicidation with and without a TiN and Ti cap has been performed in temperature range of 300–800 °C. In order to extensively study the phase sequence of silicide formation, a spectroscopic ellipsometry (SE) technique has been used to characterize the thin silicide films. The measurement of the optical properties and thicknesses of thin cobalt, stacked TiN/Co, and cobalt silicide layers has been compared with four point probe measurements. Also, a technique employing a SE optical method has been successfully developed to measure the thickness of thin Co and CoSi films and the selective etch rates of TiN and CoSi, which showed 0.45 and 0.009 nm/s, respectively, for TiN capped Co silicidation. The results obtained by the SE nondestructive technique are also compared with the results of Rutherford backscattering spectrometry.
Integration methodology of chemical vapor deposition TiN, chemical vapor deposition W and W chemical mechanical planarization for sub-quarter micron process application
Authors: Wu Jun , Wang Y. L. , Dun Jowei , Wu Y. L. , Zhang H. , Wang Arthur
Published: July 2002

Chemical vapor deposition (CVD) W plugs have been widely used for device metallization with excellent conformity in small contacts/vias with high aspect ratio [J. E. J. Schmitz, Chemical Vapor Deposition of Tungsten and Tungsten Silicides (Noyes, 1991)]. However, some unexpected plug fill such as plug loss and key hole exposing post tungsten chemical mechanical planarization (WCMP) still happened while going to smaller plug size and using metalorganic chemical vapor deposition (MOCVD) TiN barrier. In this study, MOCVD TiN and CVD W fill followed by WCMP for plug metallization were investigated. Extensive analysis had been conducted on various types of defective W plugs. Organic contaminants (hydrocarbon by-products) in MOCVD TiN deposition would prevent W deposition taking place inside the plug. For W wise, lower process temperature, carefully adjusted WF6/SiH4 and WF6/H2 partial pressure ratios had demonstrated better plug fill and electrical performance [T. E. Clark et al., J. Vac. Sci. Technol. B 9, 1478 (1991)]. In the WCMP approach, the effects of different oxidizer concentration in slurry were characterized. Eliminating the seam formation during the CVD W process can help avoid slurry attack in WCMP. The optimized integration scheme of MOCVD TiN barrier, CVD W, and WCMP was successfully achieved and is applied on 0.20 μm Logic production.
Optical endpoint detection for chemical mechanical planarization
Authors: Bibby Thomas , Adams John A. , Holland Karey
Published: July 2002

We present product wafer and laboratory test results of a production worthy, in situ, broadband optical endpoint system in the context of a simple model that describes the reflectance of semiconductor wafers during chemical mechanical planarization. Broadband and single wavelength approaches are presented. The challenges of extracting precise endpoint measurements on patterned product wafers in an intrinsically noisy environment are addressed. Finally, the benefits of using such an endpoint system are presented. Experimental data on tungsten, copper, shallow trench isolation, and interlevel dielectric layers is presented.
Radio frequency plasma chemical vapor deposited thin films of diamond-like carbon/SiO2 nanocomposites by way of tetraethoxysilane
Authors: Senkevich Jay J. , Leber Donald E. , Tutor Michael J. , Heiks Noel A. , Ten Eyck Greg A. , Scherrer David W.
Published: July 2002

Diamond-like carbon (DLC) has gained recent interest since it can be easily deposited at room temperature with a conventional radio frequency (rf) plasma. DLC has the potential benefits of a low coefficient friction, high hardness, and can be deposited with common inexpensive precursors. However, for optical applications used in the visible spectrum DLC has the problem of having a peak absorbance at 305–330 nm. This absorbance with thicker films or for higher volume fractions of DLC in a nanocomposite structure monotonically decreases into the visible spectrum where the film appears yellowish to brownish. The work here has focused on using a common alkoxy silane precursor, tetraethoxysilane, to deposit DLC/SiO2 nanocomposites at room temperature using an ion-assisted process to deposit transparent antiscratch films in the visible spectrum. The highest scratch resistant nonabsorbing films were deposited at low pressures (∼15 mTorr), high flows of oxygen (>120 sccm), at modest power densities (∼0.2 W/cm2), and low flows of argon (15 sccm) keeping the TEOS bubbler temperature constant. Under these conditions very little SP2 carbon is deposited, hence, little absorption. However, more important argon bombardment allows the SiO2 to be nearly hydroxyl free and the carbon that is left may allow the films to retain a lower coefficient of friction and their hydrophobicity. At higher system pressures (∼200 mTorr) the films deposited were much softer than the films deposited at lower system pressures (∼30 mTorr), hence, the importance of ion bombardment. At higher power densities (∼1.4 W/cm2) DLC is deposited independent of other system parameters. The measured absorbtivity of DLC was 31 600 cm−1 at 305–330 nm.
Comparison of silicon stencil mask distortion measurements with finite element analysis
Authors: Ehrmann A. , Struck T. , Chalupka A. , Haugeneder E. , Löschner H. , Butschke J. , Irmscher M. , Letzkus F. , Springer R. , Degen A. , Rangelow I. W. , Shi F. , Sossna E. , Volland B. , Engelstad R. , Lovell E. , Tejeda R.
Published: July 2002

Stencil mask fabrication processes using silicon-on-insulator (SOI) mask-wafer blanks have already been established. In order to meet the stringent requirements of pattern placement both mask distortion measurements and finite element analyses serve as tools to understand the sources of the pattern distortions. In this article experimental results from LMS IPRO measurements in intermediate process steps and comparison to corresponding finite element analyses of two stencil masks are presented, demonstrating the decisive influence of SOI mask-wafer blank quality, in particular with respect to the warp of the wafer substrate and thickness homogeneity of the silicon membrane layer.
Thin film stress mapping using an integrated sensor
Authors: Schlax M. P. , Jachim A. F. , Engelstad R. L. , Lovell E. G. , Liddle J. A. , Novembre A. E.
Published: July 2002

The integrated sensor complementary electrode (ISCE) stress mapping tool has been created for process development and characterization of blank SCALPEL masks (4-in. format). The SCALPEL mask design incorporates a 0.1-μm-thick SiN membrane with a Cr/W scattering bilayer supported by a grillage of Si struts. The ISCE was used to determine the resonant frequency and consequently the stress of each freestanding window (or membrane) created by the grillage. Discrete stress values for each window were combined to develop a stress contour map across the complete mask membrane area. The ISCE tool utilizes 120 sensor pads integrated into and multiplexed on a two-sided computer numerically controlled (CNC) milled circuit board. The gap between the sensor board and the mask is fixed so there are no moving parts. Advantages to this design are increased speed and reduced cost and size. Stress mappings for two 4-in. SCALPEL masks were completed using the integrated sensor board and results are shown. The worst case repeatability of window resonant frequency was 1.0%. A detailed uncertainty analysis of the stress mapping results is presented.
Field size versus column shortness in high throughput electron beam lithography
Authors: Han L. , Pease R. F. W. , Meisburger W. D. , Winograd G. I. , McCord M. A.
Published: July 2002

In electron beam projection systems there are competing requirements for column length. Shorter lengths lead to reduced space charge interactions while longer columns allow larger field sizes. Other parameters include the convergence angle and beam voltage. We have used a generic 4:1 reduction telecentric system as a test vehicle to study these tradeoffs. To determine the lens aberrations we employed a thick lens configuration with constant magnetic fields; space charge blur was estimated with a Monte Carlo simulation using a thin lens approximation. For a given beam voltage V, field size F, convergence angle α, and current I, there is a maximum value of column length L that satisfies a given resolution requirement. For example, if V=100 kV and I=20 μA then L must be less than 30 cm for 100 nm resolution. The use of a retarding field just upstream of the target can lead to greatly improved performance in terms of resolution, field size, and throughput; e.g., the minimum resolved feature size is approximately proportional to the ratio of landing voltage over beam voltage.
PREVAIL: Theory of the proof of concept column electron optics
Authors: Stickel W. , Langner G. O.
Published: July 2002

The PREVAIL proof-of-concept (POC) system is described elsewhere in these proceedings. For theoretical as well as practical reasons, the operating conditions of POC were restricted to the special, albeit not necessarily optimum case, of the deflected beam following a particular trajectory in the lens doublet forming the backbone of the POC optics; this trajectory is referred to in optics as the “fundamental off-axis imaging ray.” To provide guidance for and evaluation of its operation, the necessary computer simulation software was developed in-house. The interaction between modeling and experimentation proved fruitful in achieving the primary objective, demonstration of feasibility of large-area reduction projection and beam scanning for next-generation lithography. Beyond that, the theory provides the means to investigate variations of the optics regarding configuration as well as setup, their impact on performance, and the direction for further improvements.
Characteristics for negative and positive tone resists with direct write electron beam and SCALPEL exposure systems
Authors: Sato Mitsuru , Ocala L. E. , Novembre A. E. , Ohmori Katsumi , Ishikawa Kiyoshi , Katsumata Katsuhiko , Nakayama Toshimasa
Published: July 2002

High acceleration voltage electron beam exposure is one of the possible candidates for post optical lithography, where tighter resolution and wide process latitude is required. The use of highly accelerated electrons instead of photons prevents optical related problems, such as standing waves, because the interaction mechanisms between the resist and photons and electrons are different. The present work will describe results obtained with a 50 kV direct write e-beam exposure tool and SCALPEL, which operates at 100 kV acceleration voltage on positive and negative chemically amplified resists from Tokyo Ohka Kogyo (TOK). TOK has designed a positive tone resist, EP-004, with 100 nm resolution for line and space patterns. The dose to print on SCALPEL is 6 μC/cm2 and process latitude is about 10%. The TOK negative resist, EN-009, has 100 nm resolution for isolated lines. The dose to print on SCALPEL is 7 μC/cm2 and process latitude is about 15%. These results are the first to meet high throughput requirements for SCALPEL in terms of resist sensitivity and process latitude, which are: dose between 5 and 10 μC/cm2 and process latitude greater than 10%.
Tribological behavior of TiC/DLC multilayers prepared on Ti–6Al–4V alloy by plasma-based ion implantation
Authors: Ji Hongbing , Xia Lifang , Ma Xinxin , Sun Yue , Sun Mingren
Published: July 2002

Plasma-based ion implantation (PBII) of carbon (time 1–3 h) and subsequent glow discharge deposition of carbon produced TiC/DLC multilayers on Ti–6Al–4V samples (TiC second phase formed in the near surface region plus DLC surface layers). The as-modified samples showed higher hardness than the uncoated sample especially at low plastic penetrations in the order of the 1, 2, and 3 h carbon implantation, but had brittle wear appearances. When the implantation time was increased, the brittleness increased, hence the tribological properties in most cases deteriorated. A tribofilm transferred from a disk wear surface was formed on the wear surface of a counterbody made of bearing steel AISI 52100, lowering the friction coefficient, and reducing the ball wear. When the wear load was decreased and sliding speed increased, the function of the tribofilm became more important; the friction decreased, and the wear properties improved, with a stable friction coefficient ranging from 0.1 to 0.2. But when the counterbody AISI 52100 was changed to Ti–6Al–4V modified as the disk, the tribological behavior surprisingly deteriorated, with wear changing from only disk to both disk and ball abrasive dominated, and it is probably the transferred disk wear debris that caused wear weight increases of the counterbody Ti–6Al–4V.
Critical tool performance analysis for SCALPEL extensibility
Authors: Stanton Stuart T. , Liddle J. Alexander , Waskiewicz Warren K. , Mkrtchyan Masis M.
Published: July 2002

An important feature of any advanced lithography technology is its cost-effective extension over several device generations beyond its introduction. Since SCALPEL is an electron imaging system with resolution not limited by diffraction, a unique extensibility analysis is needed to establish development pathways for the evolution of SCALPEL to the 50 nm generation and beyond. A combination of modest progress in four performance areas—effective optical field width, aberrations, acceptable dose latitude, and stage performance—will allow SCALPEL to maintain good throughput over several lithography generations without aggressive optical design scaling.
Material and process studies in the integration of plasma-promoted chemical-vapor deposition of aluminum with benzocyclobutene low-dielectric constant polymer
Authors: Talevi Robert , Gundlach Heidi , Bian Zailong , Knorr Andreas , van Gestel Maarten , Padiyar Sumant , Kaloyeros Alain E. , Geer Robert E. , Shaffer Edward O. , Martin Steve
Published: July 2002

The integration of low-temperature plasma-promoted chemical-vapor deposition (PPCVD) of aluminum, using dimethylethylamine-alane (DMEAA) as the source precursor, with benzocyclobutene (BCB) low-k polymers has been investigated to explore the feasibility of BCB-based Al metallization for sub-quarter-micron integrated circuitry. The study examined the thermal, chemical, and structural compatibility of PPCVD Al interconnects with the BCB polymer, including the feasibility of barrierless aluminum–BCB multilevel metallization stacks. Studies were conducted on a range of BCB surfaces, consisting of untreated (UNT), reactive-ion etched (RIE), and SiO2-capped BCB (SiO2–BCB) surfaces. The purpose was to mimic the actual BCB surfaces encountered during damascene processing. Each BCB surface was treated with argon or hydrogen plasma prior to aluminum processing to ensure reduction in the barrier to aluminum formation, leading potentially to enhanced Al nucleation mechanisms. In all cases, the direct deposition of Al on BCB films via PPCVD was successfully demonstrated, with the RIE-BCB substrate providing the best Al nucleation characteristics. Compositional analyses of the Al films indicated that carbon and nitrogen contaminants, which could have resulted from the dissociation reaction of the DMEAA molecule, were below the detection limits of the techniques used. Alternatively, oxygen inclusion was highly dependent on the chemical state and type of plasma treatment of the BCB surface, with only the PPCVD Al on plasma pretreated RIE BCB exhibiting bulk oxygen levels below the detection limits of x-ray photoelectron spectroscopy. Oxygen incorporation in the PPCVD Al films on UNT BCB and SiO2–BCB could be attributed to the diffusion of oxygen through intergranular voids upon air exposure, resulting in increased Al film resistivity. In all cases, the study indicated that an appropriate diffusion barrier/adhesion promoter is required to ensure viable BCB integration in Al metallization schemes.
Thermal stability and etching characteristics of electron beam deposited SiO and SiO2
Authors: LaRoche J. R. , Ren F. , Lothian R. , Hong J. , Pearton S. J. , Lambers E. , Hsu C. H. , Wu C. S. , Hoppe M.
Published: July 2002

We have studied the thermal stability and etching characteristics of electron beam deposited SiO and SiO2. Scanning electron microscopy, Auger, atomic form microscopy, and ellipsometry were used to analyze the surface morphology, roughness, and film composition as a function of annealing temperatures. Both SiO and SiO2 showed excellent thermal stability up to 400 °C anneal and refractive index, surface morphology and pattern edge definition of both films barely changed. For higher temperature anneal, based on Auger analysis results, the ratio of Si/O of SiO2 film stayed constant after 700 °C. However, the Si/O ratio of SiO film increased from 0.54 to 0.62 due to oxygen outdiffusion. Dry etch characteristics of SiO and SiO2 were investigated using SF6 and NF3 discharges in a Plasma Therm inductively coupled plasma system. Wet etches were performed using buffered HF and HF/H2O solutions. Dry etch rates of SiO2 were comparable with that of conventional plasma enhanced chemical vapor deposition SiO2. SiO2 etched faster than SiO under all etch conditions.
Compensation effect during water desorption from siloxane-based spin-on dielectric thin films
Authors: Proost J. , Baklanov M. , Maex K. , Delaey L.
Published: July 2002

It is the aim of this report to show experimental evidence for the compensation effect during water desorption from siloxane-based spin-on dielectrics. A single linear relationship was obtained between the activation entropy ΔS# and the activation enthalpy ΔH# for the elementary water desorption components in the degassing spectra for siloxane-based dielectric thin films. From this observation, an isokinetic temperature was derived at which all desorption rates become equal. It is argued that this temperature can be considered as a fundamental materials characteristic, governing the thermal stability of the dielectric thin film.
Extraction of two-dimensional metal–oxide–semiconductor field effect transistor structural information from electrical characteristics
Authors: Richards W. R. , Shen M.
Published: July 2002

As metal–oxide–semiconductor technology continues to scale to deep submicron feature sizes, the two-dimensional nature of the implanted impurity profiles becomes a critical component of the device design. Device performance in both the off state and on state, as well as device manufacturability, yield, and reliability, depend heavily on a good understanding of the depth, spread, and shape of these profiles. It is often necessary for the device designer to obtain quick, accurate information about these junctions based upon test structures and metal–oxide–semiconductor field effect transistor (MOSFET) electrical characteristics. With junction depths required well below 100 nm for source/drain and lightly doped drain features of very deep submicron MOSFETs, characterization with spatial resolutions on the order of 10 nm is required. In this work, a summary of the techniques used for extracting lateral profile information in a MOSFET channel are presented and compared with physical measurements from the literature. A technique is reviewed which allows extraction of lateral source/drain profile information from the electrical characteristics of a single transistor nondestructively.
Two-dimensional dopant profile of 0.2 μm metal–oxide–semiconductor field effect transistors
Authors: Wang X.-D. , Mahaffy R. , Tan K. , Shih C. K. , Lee J. J. , Foisy M.
Published: July 2002

In this article, we report our progress in two-dimensional (2D) dopant profiling of metal–oxide–semiconductor field effect transistor devices fabricated with 0.2 μm technology by using dopant selective etching followed with atomic force microscope imaging (DSE/AFM). By comparing device simulation results based on our measurement with electrical measurement results, we have found that in these small devices the depletion region can have a significant effect on the results of dopant concentration conversions from the selective etching data, and the necessary correction can be found by a proper estimation of the depletion width. Here we discuss the factors that affect the etching reproducibility and reliability and show our approaches to these challenges. Our results show that DSE/AFM is a useful technique for 2D dopant profiling with certain advantages if it is dealt with properly.
Optical emission spectroscopy of microscopic gas discharges using a high-pressure scanning tunneling microscope
Authors: Möller D. , Eckert R. , Haefke H. , Güntherodt H.-J.
Published: July 2002

A high-pressure scanning tunneling microscope (STM) unit was used to produce electrical discharges on a mesoscopic scale. Piezoelectric positioning elements allow to adjust the electrode gap with the precision needed. Optical emission spectroscopy was performed in high-pressure environments of helium and argon in a range of 5–20 bar. Spectra were recorded at different gas pressures and discharge currents. The increase of gas pressure changed line intensities and caused broadening of spectral lines of helium and argon. Increasing the discharge current yielded a higher intensity of the emitted light. The use of different electrode materials had no significant influence on the spectra. Electrical gas discharges on the microscopic scale can be used not only as a lithographic tool, but also as a compact light source of high luminance with emission of well-defined line spectra.
Atomic force microscope tip sharpening and evaluation by electric field confinement using a metal grid close to the tip
Authors: Arai Toyoko , Tomitori Masahiko
Published: July 2002

By setting a metal grid close to a Si tip on an atomic force microscope (AFM) cantilever and applying voltage between the grid and the tip, electrons were field emitted from the tip apex, where a high electric field was induced confining the metal grid. The pattern of field-emitted electrons was projected at high magnification by a shadow of the grid onto the phosphor screen of a field emission microscope (FEM). The FEM image shows the tip radius and the cleanliness. The confined electric field was also used to sharpen the tip by a thermal-field (TF) treatment, in which the tip is heated under a high electric field. The change in the FEM images before and after the treatment is reported, and the faceting of the Si tip apex by the treatment is discussed. The noncontact-AFM image of Si(111) 7×7 with atomic resolution was observed with the TF treated tip immediately after the tip came near to the sample.
Fabrication of Spindt-type tungsten microtip field emitter arrays with optimized aluminum parting layers
Authors: Park Y. J. , Choi J. H. , Lee H. W. , Lee N. S. , Kim J. W. , Hong S. S. , Park N. S. , Jung J. E. , Kim J. M.
Published: July 2002

Spindt-type field emitter arrays of tungsten microtips have been fabricated by optimizing aluminum parting layers. The aluminum parting layers, which play a crucial role in the subsequent deposition of peeling-free tungsten films, are characterized by varying the deposition conditions. The aluminum parting layer deposited at a high vacuum level has a good stress relaxation effect, and tungsten microtip field emitter arrays, free of peeling, are successfully fabricated and show good electrical characteristics.
Study on local stability of field emitter arrays by using an emission microscope
Authors: Nakane Hideaki , Muto Yasufumi , Yamane Koichi , Adachi Hiroshi
Published: July 2002

Electron emission from a field emitter array (FEA) was magnified by making use of an emission microscope, and the stability of the individual microtip was examined. The number of observable microtips increased with the total emission current of the whole FEA, and approached 90% of it. Some microtips showed unstable emission and the number of such unstable microtips increased with the total emission current. Gas molecules, which adsorbed locally to inside the microtip, would be caused by the instability of the electron emission.
Proposal and modeling of a novel thermal microprobe using n-Si/nitrogen doped diamond cathodes
Authors: Nicolaescu Dan , Filip Valeriu , Itoh Junji , Okuyama Fumio
Published: July 2002

A novel thermal microprobe is proposed and its operation is theoretically analyzed. The thermal sensitivity of the microprobe is assured by a field emission diode using n-Si/nitrogen doped as a cathode. The cathode layer is placed on the atomic force microscope cantilever on the opposite side of the sharp sensing stylus, thus allowing for both mechanical and thermal maps of the sample to be obtained. A model to characterize the temperature dependence of the emission current has been developed, which shows good agreement to reported experimental data. The current-temperature exponential dependence allows a high temperature sensitivity of the microprobe. The developed model is further used to characterize the thermal microprobe properties and derive design hints.
Electrical properties and defect states in undoped high-resistivity GaN films used in high-power rectifiers
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Dang G. , Zhang A. P. , Ren F. , Cao X. A. , Pearton S. J. , Wilson R. G.
Published: July 2002

The electrical properties and spectra of deep centers in high-resistivity undoped GaN samples used to fabricate high-power Schottky diode rectifiers with breakdown voltages exceeding 2000 V are reported. It is shown that the Fermi level in such material is pinned by defects with energy levels close to Ec−0.6 eV. Thermally stimulated current measurements revealed the presence of unidentified traps with activation energies of 0.3 and 0.7 eV. The important role of hole traps with energy levels Ev+0.3 eV and Ev+0.9 eV was confirmed by measurements of temperature quenching of photocurrent and by photoinduced transient current spectroscopy measurements. Prominent persistent photoconductivity was observed even for temperatures above 300 K. Imaging of the sample using microcathodoluminescence showed the existence of cellular nonuniformities with characteristic dimensions of the cells of about 3 μm.
Normal-incidence SiGe/Si photodetectors with different buffer layers
Authors: Jiang R. L. , Lo Z. Y. , Chen W. M. , Zang L. , Zhu S. M. , Liu X. B. , Cheng X. M. , Chen Z. Z. , Chen P. , Han P. , Zheng Y. D.
Published: July 2002

Normal-incidence SiGe/Si p–i–n photodetectors with relaxed GeSi alloy layers grown on Si buffer layers at low temperature and fraction-graded Si1−xGex buffers were fabricated by rapid thermal process/very-low-pressure chemical-vapor deposition. The response wavelength of these detectors ranges from 0.7 to 1.55 μm. The peak wavelengths are 0.98 and 1.06 μm, at which the responsivities are 2.7 and 1.8 A/W (−2 V), respectively. The responsivities at 1.3 μm are 0.15 and 0.07 A/W (−5 V), and the dark current densities are 0.05 and 0.03 μA/mm2 (−2 V), respectively. The influences of the Ge fraction, epilayer thickness, and bias voltage on the detectors are discussed.
Electronic structure, growth, and structural and magnetic properties of magnetic semiconductor Fe/GaAs heterostructures
Authors: Hirose Shingo , Haneda Shigeru , Yamaura Masaaki , Hara Kazuhiko , Munekata Hiro
Published: July 2002

In this article we describe a study of the magnetic semiconductors of Fe/GaAs, undertaken theoretically and experimentally. We discuss the structural advantage of body-centered-cubic-Fe structure lattice matching to GaAs (001). Theoretical calculations using the self-consistent linear augmented-plane-wave method indicate the existence of an energy state of the quantum well in Fe layers in a GaAs/Fe/GaAs double heterostructure. We then present the preparation of Fe/GaAs heterostructures by using molecular beam epitaxy. α-Fe and δ-Fe could be grown epitaxially on (001) GaAs at a substrate temperature of 290 and 580 °C, respectively, which was confirmed from the results of reflection high energy electron diffraction and x-ray diffraction measurements. We also found that, in order to obtain α-Fe/GaAs, a low-temperature GaAs growth must be induced before the Fe growth can occur. Differences in magnetic properties were observed in the magnetic measurements, indicating that α-Fe dominates the ferromagnetic state, while the δ-Fe shows relatively slight ferromagnetic behavior.
Closed-loop control of resonant tunneling diode barrier thickness using in situ spectroscopic ellipsometry
Authors: Roth J. A. , Williamson W. S. , Chow D. H. , Olson G. L. , Johs B.
Published: July 2002

We examine the use of spectroscopic ellipsometry (SE) for fully automated, in situ real-time control of the barrier thickness for resonant tunneling diodes (RTDs) grown by molecular-beam epitaxy (MBE). The RTDs in this study utilize AlAs barriers, an InGaAs well with an InAs subwell, and lattice-matched InGaAs spacer layers, grown on an InP(100) substrate. Pseudodielectric functions for the strained AlAs barriers were generated from SE data acquired during MBE growth, using simultaneous photoemission oscillation measurements for in situ thickness calibration. For closed-loop control, the measured dielectric functions were utilized in conjunction with a virtual substrate model to derive the instantaneous layer thickness from real-time SE data. Repeatability was tested by growing several series of AlAs barriers and complete RTDs under fully automated control, with shutter actuation based on the real-time thickness determined from SE. The results show that by using SE for real-time control, barrier thickness repeatability on the order of ±0.1 ML can be achieved.
Precise and efficient ex situ technique for determining compositions and growth rates in molecular-beam epitaxy grown semiconductor alloys
Authors: Peiris F. C. , Lee S. , Bindley U. , Furdyna J. K.
Published: July 2002

A technique based on the principle of coupling an evanescent wave via a prism into a semiconductor thin film has been used to determine simultaneously the composition and the thickness of II–VI semiconductor ternary alloys. This approach, which determines the indices of refraction n with high precision (at least 0.1%), and also concurrently determines the epilayer thicknesses with an uncertainty of less than 0.5%, has been applied to a series of molecular-beam epitaxy grown ternary alloy families; Zn1−xCdxSe, Zn1−xMgxSe, Zn1−xBexSe, Zn1−xMnxSe, and ZnSe1−xTex. The composition determined by x-ray measurements allows one to generate a calibration between n and the alloy composition, which is used subsequently to derive the alloy composition of the ternary specimen by measuring only its value of n. Since the prism coupler method also determines the thickness of the film, the growth rates are also obtained concurrently.
Investigation of e–h pair compression in molecular beam epitaxy grown ZnCdSe/ZnSe multiquantum wells at volume excitation by electron beam
Authors: Kozlovsky V. I. , Sadofyev Yu. G.
Published: July 2002

Comparative cathodoluminescence (CL) study of the molecular-beam epitaxy grown ZnCdSe/ZnSe multiquantum well (MQW) structures differing by the number of QWs (4, 15, 30, 100) has been carried out. The total thickness of MQW part for all structures equals 1.5 μm. The CL intensity of the four QW structure has been found to be the highest, which provides evidence on the high efficiency of the carrier collection into QWs even in the case when the ZnSe barrier thickness is as large as 0.5 μm. Cleaved edge cavities for transverse e-beam pumping have been cleaved from these structures but a lasing action has been achieved on the four QW structures only because of the highest carrier compression in this structure. Based on the independence of the carrier collection efficiency on the barrier thickness, the estimation of the optimal number of QWs in the e-beam pumped MQW vertical cavity surface emitting lasers has been carried out. The MQW structure with only five QWs should be used for the cavity losses to be as small as 0.01 in a single pass of the cavity.
Resonant Raman scattering and photoluminescence enhancement in ZnCdSe quantum wells
Authors: Hernández-Ramírez L. M. , Hernández-Calderón I.
Published: July 2002

We have observed resonant Raman scattering (RRS) and photoluminescence (PL) enhancement due to resonant absorption of the exciting light in low temperature experiments on a 50 Å Zn0.74Cd0.26Se quantum well (QW) confined by ZnSe barriers. The spectra presents a sharp and very intense Stokes longitudinal optical (LO) phonon at 31.1 meV and also a weak 2LO mode. We show that the RRS is due to a double resonance: the first is produced by the matching of the exciting laser line (488 nm, 2.5407 eV) with the 1hh→1e absorption transition of the QW; the second is due to the coincidence of the exciton binding energy (determined as 32.6±2 meV) and the LO phonon energy. A selective increase of the intensity of one of the PL excitonic peaks takes place when islands of 50 Å thickness of the QW are resonantly excited with the 488 nm laser line; the relative intensity of this peak increases one order of magnitude in relation to other excitonic peak situated around 9 meV below.
InGaAs/AlGaAs intersubband transition structures grown on InAlAs buffer layers on GaAs substrates by molecular beam epitaxy
Authors: Katzer D. S. , Rabinovich W. S. , Beadie G.
Published: July 2002

We report on the use of InAlAs linearly graded buffer layers for improving the performance of InyGa1−yAs (y>0.42)/AlGaAs intersubband transition (ISBT) superlattice structures grown on GaAs substrates by molecular beam epitaxy. Linearly graded InAlAs buffer layers give better optical confinement in the active superlattice region, similar intersubband transition linewidths, and comparable surface morphology compared to linearly graded InGaAs buffer layers. The best surface morphology for our ISBT superlattices was obtained by growing the linearly graded InAlAs buffer layer at 360 °C.
Molecular beam epitaxial growth of vertical cavity surface emitting lasers with digital alloys and digital gradings
Authors: Newman P. G. , Pamulapati J. , Shen H. , Taysing-Lara M. , Liu J. , Chang W. , Simonis G. , Koley B. , Dagenais M. , Feld S. , Loehr J.
Published: July 2002

Electrical resistance through vertical cavity surface emitting lasers (VCSELs) grown by molecular beam epitaxy is generally higher than in VCSELs grown by metalorganic chemical vapor deposition (MOCVD). The better performance of MOCVD-grown material is attributed to the fact that MOCVD can continuously grade the composition between the high index (narrow band gap) and low index (wide band gap) materials that constitute the Bragg mirror stack. This leads to a lower resistance for the charge to traverse through the mirror stack. In addition, the oxidation of VCSEL apertures dramatically reduces threshold current Ith; however, the oxidation process requires a low index layer with a high aluminum mole fraction for reasonable oxidation rates and for good material stability. The MOCVD process benefits from its ability to tailor the high mole fraction AlGaAs material that is crucial for creating the oxide apertures. The majority of these problems can be alleviated using digital alloys and digital grades.