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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

Issue 3 • Date May 1997

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Displaying Results 1 - 25 of 244
  • Approach for a three-dimensional on-chip quantification by secondary-ion mass spectrometry analysis

    Page(s): 445 - 451
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    An attempt to perform a three-dimensional (3D) quantitative evaluation of the complete sample volume sputter removed in a secondary-ion mass spectrometry analysis is described. Using a focused (∼3 μm) 7 keV Cs+ primary-ion beam and detecting sputtered MCs+ ions (M stands for any sample element), a vertical Si–metal–oxide–semiconductor transistor structure (with a lateral size of ∼40 μm and a total vertical dimension of ∼3 μm) was analyzed by image depth profiling. Elemental concentrations of these micrographs were derived from relative sensitivity factors and the pertinent depth information in the 3D sample (data) volume could be estimated by utilizing these factors and an approximation of the atomic densities. The specimen’s surface topography both in the pristine state and upon completion of the sputter depth profile was recorded by two-dimensional stylus profilometry. By these means, a reconstruction of the sample volume eroded during the analysis appears feasible at a lateral resolution of a few μm and an in-depth resolution of about 10 nm. © 1997 American Vacuum Society. View full abstract»

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  • Effects of oxygen flooding on sputtering and ionization processes during ion bombardment

    Page(s): 452 - 459
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    The effects of oxygen flooding on the sputter and ionization yield of Si and SiO2 have been investigated. Additional processes in sputtering and ionization may be introduced by oxygen flooding beyond a simple chemical adsorption and knock-on process, leading to a larger reduction in sputter yield and a further enhancement in ionization yield for silicon sputtered from a Si substrate as compared to the values for silicon dioxide. A transient, particularly for the sputter yield, still remains, implying that the transient reduction is not as complete as desired. © 1997 American Vacuum Society. View full abstract»

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  • Optimized time-of-flight secondary ion mass spectroscopy depth profiling with a dual beam technique

    Page(s): 460 - 464
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    High resolution depth profiling has been performed in a time-of-flight secondary ion mass spectroscopy (TOF-SIMS) instrument equipped with independent ion sources for sputtering (crater formation) and for SIMS analysis. In this dual beam mode a low energy sputter gun (Cs or any gas ion) allows a free selection of optimum sputter conditions with regard to depth resolution and matrix optimization. For secondary ion generation an independent high energy ion beam, optimized with regard to focussing and secondary ion yield (Ga or gas ion source) is applied. For different sputter gases (Ar, Xe, O2, and SF6), energies (0.3–2 keV) and angles of incidence a systematic investigation of B layers in Si and GaAlAs multilayers has been carried out. Decay lengths of 0.53 nm were achieved for low energy sputtering of B layers in Si with 0.6 keV SF5+. In this dual beam mode the depth profiling performance of TOF-SIMS exceeds that of state of the art quadrupole and magnetic sector field instruments in several fields of application, important in particular in microelectronics. © 1997 American Vacuum Society. View full abstract»

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  • Nondestructive depth profiling in Auger electron spectroscopy by means of partial intensity analysis

    Page(s): 465 - 469
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    A recently developed method to gain information on the near-surface compositional depth profile via analysis of the spectral line shape of Auger or x-ray photoelectrons has been tested. Electron-excited Auger spectra of a series of thin Au films on a Pt substrate have been subjected to this so-called partial intensity analysis. The overlap of the MNN Auger lines of Pt and Au gives rise to quite complex spectra. Subjecting these spectra to a partial intensity analysis reveals that the Au is present as a homogeneous overlayer. The overlayer thickness provided by the analysis is in good agreement with the values expected from the sample preparation. © 1997 American Vacuum Society. View full abstract»

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  • Growth and characterization of aluminum oxide thin films for evaluation as reference materials

    Page(s): 470 - 477
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    With the aid of aluminum oxide reference films, analytical techniques that previously provided only relative thickness information can now report absolute mass thickness measurements for aluminum oxide films. These new reference films were dense, nonporous, anodic aluminum oxide films grown by the method of Haas with a thickness range from 12 to 135 nm. Dimensional thickness measurements were made by transmission electron microscopy and spectroscopic ellipsometry. Absolute mass thickness measurements were made by electron probe microanalysis and energy-dispersive x-ray microanalysis. Relative thickness measurements were made by infrared spectroscopy, x-ray photoelectron spectroscopy depth profiling, and wavelength-dispersive x-ray fluorescence spectroscopy. Characterization measurements show the growth recipe (1.35 nm/V) predicts the dimensional thickness within 5%–10% and the mass thickness within 10%. Little or no evidence of hydration or phase change is observed after five years storage. Numerous surface-processing procedures involving aluminum material, such as brazing, welding, wetting, bonding, stamping, and rolling, will benefit from improved measurements of oxide-layer thicknesses on aluminum or aluminum alloys. © 1997 American Vacuum Society. View full abstract»

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  • Factors causing deterioration of depth resolution in Auger electron spectroscopy depth profiling of multilayered systems

    Page(s): 478 - 484
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    We have investigated the effects of the sputter-induced roughness on the depth resolution Δz and on the interface position zc obtained by Auger electron spectroscopy (AES) depth profiling of a Ni/Cr multilayer and of an AlAs/GaAs superlattice. We also correlated the escape depth λ with Δz and zc. First, the sputter-induced roughness was evaluated by atomic force microscopy (AFM). Second, both Δz and zc were evaluated quantitatively using an error function fitting method of AES, depth profiles. The AFM observation shows that the height distribution of sputter-induced roughness is approximated to first order by a Gaussian distribution and is correlated with the resolution function which depends strongly on the sputter-induced roughness. The precise measured height distribution is, however, somewhat different from the Gaussian distribution. The computational simulation using the error function approximation fitting is in good agreement with experimental results. We also estimated the escape depth λ using the same computational simulation results. The results indicate that the error function approximation fitting is useful to evaluate Δz and zc as a practical method, but anomalies of Δz and zc are discernable at the specific interface. These anomalies are assumed to come from preferential sputtering. © 1997 American Vacuum Society. View full abstract»

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  • Surface chemical analysis: Comparing and exchanging data

    Page(s): 485 - 492
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    The current status of repeatability and reproducibility in interlaboratory studies in surface analysis using Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), dynamic and static secondary ion mass spectrometries (SIMS), and sputtering are briefly reviewed. Repeatabilities are governed by the quality of the instrument design and the procedure for instrument use. Reproducibility from laboratory to laboratory requires the use of transfer standards which may be technique wide, as in the cases of AES and XPS, or sample specific as in the case of dynamic SIMS. Repeatabilities of intensity ratios with good instruments and procedures should be better than 2% for all techniques for suitable samples. Repeatabilities of the energy scale in good electron spectrometers average around 0.025 eV. The reproducibilities in quantification have improved to around 10% relative standard deviation. The measurement infrastructure is developing well and it needs to be reinforced by the relevant documentary standards to enable analysts to transfer and exchange data, at the above levels, and to improve it where necessary. The analyst needs methods of validating both equipment and software and the laboratory management, in turn, needs methods of testing the analyst’s proficiency. These aspects need development of appropriate documentary standards, as pioneered by ASTM Committee E-42 on Surface Analysis and, at an international level, by the International Standards Organization Technical Committee 201 on Surface Chemical Analysis. © 1997 American Vacuum Society. View full abstract»

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  • MAXMIND—Data storage and evaluation environment in surface analysis

    Page(s): 493 - 499
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    The problem of surface-analytical data exchange for multi-method analysis has to be solved in order to use data from a number of different surface analytical instruments [such as Auger electron spectroscopy (AES), scanning Auger microscopy, x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy, scanning tunneling microscopy, atomic force microscopy, etc.] in a synergistic manner. As only a standardized data exchange format can guarantee the independence of proprietary measurement systems without adaptation of existing software, the public domain software package called the management and exchange of method independent data (MAXMIND), was developed based on the hierarchical data format. A first key feature of MAXMIND is the strict separation of the software design and the development of data dictionaries (sets of parameters for various methods); thus data dictionaries can be modified without recompiling the software. The data dictionaries included in the present version of MAXMIND are in the case of AES and XPS based on published guides.12345 Dictionaries for other methods have been set up by the authors and are to be considered as preliminary. Besides a graphical user interface based on the X11 interface, a second key feature is that interfaces have been made from MAXMIND to the “matrix laboratory” (MATLAB) and a processing package from Khoral Research, Inc. (KHOROS), which are both well-known data analysis environments in the surface analysis and image processing community. Using one of these interfaces, a combination of either MATLAB or KHOROS in conjunction with MAXMIND forms an integrated data storage and evaluation environment. © 1997 American Vacuum Society. View full abstract»

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  • Nanometer-scale structure of hectorite–aniline intercalates

    Page(s): 500 - 504
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    The inclusion of the organic guest aniline into Cu(II)-exchanged hectorite thin films has been investigated. The subsequent polymerization of aniline on the clay surface and in the intergallery regions are studied using scanning force microscopy (SFM), electron paramagnetic resonance (EPR) spectroscopy, powder x-ray diffraction (XRD), and impedance spectroscopy. EPR and XRD data show that in addition to strong polymerization of aniline on the clay surface, polymerization also occurs in the intergallery regions of the clay. Using standard lift-off techniques or razor cleaving, the exposed intergallery polyaniline is successfully imaged for the first time using noncontract SFM in phase-contrast mode. The nearly two-dimensional polymer sheets formed in these regions exhibit none of the nanometer-scale grain or bundle structure commonly associated with polyaniline synthesized using techniques such as electrochemical or vacuum deposition. The electrical response of the resulting clay-conducting polymer composites is also investigated for thin films fabricated on 15 μm interdigitated arrays. Preliminary results indicate that these composite materials may be highly suitable as chemical sensors for a variety of important gases and vapors such as ethanol and hexane. © 1997 American Vacuum Society. View full abstract»

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  • X-ray photoelectron spectroscopy study of the chemical interaction between BN and Ti/TiN

    Page(s): 505 - 512
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    Many nitrides, particularly BN and TiN, have stimulated commercial interest because of their extreme hardness, wear and corrosion resistance, and thermal and electrical properties. All of these features are enhanced by the resulting structures and the large degree of covalency exhibited by the metal–nitride bonds. Coatings of select nitrides with films of related materials may particularly influence these properties in critical surface and interface regions. Materials of interest include the deposition by plasma vapor deposition of Ti and TiN on BN substrates. Some of these systems were then subjected to varying degrees of physical and thermal alteration. Resulting structural and morphological features have been investigated with electron microscopy and x-ray diffraction. Critical importance is also attributed to the chemical behavior of species deposited and grown at the resulting interfaces. Detailed x-ray photoelectron spectroscopy has, therefore, been rendered of these interfaces using cross-sectional display and sputter etching. Movement of nitridation and interference from oxidation and carbide formation are of particular concern. © 1997 American Vacuum Society. View full abstract»

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  • Metal overlayers on organic functional groups of self-organized molecular assemblies: VII. Ion scattering spectroscopy and x-ray photoelectron spectroscopy of Cu/CH3 and Cu/COOCH3

    Page(s): 513 - 519
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    X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) were used to characterize octadecanethiol [ODT, HS(CH2)17CH3] and methylmercaptohexadecanoate [MMHD, HS(CH2)15COOCH3] self-assembled monolayers (SAMs) before and after depositing up to 1.0 nm Cu at ca. 10-7Torr. Results from XPS O 1s, Cu 2p, and C 1s spectra do not indicate that a complex is formed (no chemical shifts) between Cu and the COOCH3 of MMHD or ODT organic functional groups (OFG) at 295 K. Although no direct evidence for Cu/COOCH3 interactions is evident, the initial value for ISS Cu peak intensities for 1.0 nm of Cu on COOCH3 of MMHD requires 7 h before it disappears compared with less than 150 min for Cu on CH3 of ODT. These times are also bracketed from XPS results, which are less sensitive than ISS to loss of copper from the M/SAM surface. The longer penetration time through MMHD versus ODT might be explained by weak interactions between Cu and COOCH3 of MMHD by different defect densities in the SAMs. The actual Cu deposition versus a layer-by-layer growth model and narrowing of the XPS Cu 2p peaks both provide support for formation of Cu clusters on the OFGs prior to penetration to the SAM/Au interface. © 1997 American Vacuum Society. View full abstract»

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  • Extracting more chemical information from X-ray photoelectron spectroscopy by using monochromatic X rays

    Page(s): 520 - 525
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    Monochromatized X-ray sources have been available for use in commercial X-ray Photoelectron spectrometers for more than 20 years. Nevertheless most X-ray photoelectron spectroscopic (XPS) data are collected using achromatic radiation. The advantages of using monochromatized XPS combined with high resolution data collection for the study of core and valence band XPS are discussed, with a focus on the latter region. Examples discussed include studies of metals and oxides. The importance of eliminating X-ray satellite features in obtaining lead oxide valence band spectra is illustrated, and the resulting valence band spectra are shown to be able to distinguish between the oxides. While the valence band region can be well understood by using a cluster model for oxides, the importance of using a band structure model is illustrated for graphite and molybdenum spectra. Possible band structure effects are reported in oxide valence band spectra. © 1997 American Vacuum Society. View full abstract»

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  • Determination of the surface silanol concentration of amorphous silica surfaces using static secondary ion mass spectroscopy

    Page(s): 526 - 531
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    A novel method has been developed to determine the concentration of silanol (Si–OH) groups on planar, amorphous silica glass surfaces. This method involves neutral beam static secondary ion mass spectroscopy (SIMS) analysis as a function of sample temperature. The calibration necessary to achieve absolute quantification of the silanol concentrations with static SIMS was obtained using a combination of Fourier-transform infrared (FTIR) spectroscopy and x-ray photoemission spectroscopy (XPS). High purity, amorphous silica glass samples with varying silanol and molecular water concentrations were prepared ex situ, and in vacuo by fracturing and dosing silica rods with water in the sample preparation chamber of a UHV system. Static SIMS spectra collected as a function of sample temperature show a decreasing SiOH+/Si+ peak area ratio with increasing temperature due to desorption of physisorbed, molecular water. It is shown that the equilibrium SiOH+ signal intensity obtained after the heat treatment is proportional to the silanol concentration of the silica surface. XPS analysis of derivatized samples was used to confirm the results of the static SIMS experiments. In order to achieve absolute quantification of the silanol concentration in OH/nm2, FTIR was used to calibrate the SiOH+/Si+ peak area ratios measured from the static SIMS spectra. © 1997 American Vacuum Society. View full abstract»

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  • Structure and composition of oxidized aluminum on NiO(100)

    Page(s): 532 - 537
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    Aluminum was deposited on stoichiometric NiO(100) in 5×10-6Torr O2 at substrate temperatures of 250 and 800 °C, and the resulting film interfaces were studied by photoemission [x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS)] and electron diffraction [reflection high-energy electron diffraction (RHEED)]. At 800 °C, RHEED patterns indicate that the growing overlayer interacts with the NiO(100) substrate forming a NiAl2O4 spinel phase. This observation is further supported by XPS and UPS results where peak shapes and relative peak positions correspond to values reported for thick NiAl2O4 films. During film growth at 250 °C, the underlying NiO RHEED pattern becomes diffuse due to formation of an amorphous overlayer. XPS and UPS results indicate that the amorphous film is Al2O3 and that little interaction with the NiO substrate occurs. Postdeposition annealing of the amorphous Al2O3 film to 800 °C in O2 results in a strong reaction at the interface and film crystallization to the NiAl2O4 spinel phase. These results demonstrate that kinetic factors are significant in determining interactions in this system. © 1997 American Vacuum Society. View full abstract»

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  • High resolution electron energy loss spectroscopy study of vapor-deposited polyaniline thin films

    Page(s): 538 - 543
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    Vapor deposited polyaniline films on Cu(110) have been characterized using high resolution electron energy loss spectroscopy. Ultrathin films (⩽100 Å) were found to exist in an oxidation state close to that of the starting emeraldine powder. After doping with HCl, the films exhibited plasmon excitations in the far-ir, suggesting that they are highly crystalline and possess electrical conductivities higher than those of HCl doped emeraldine films produced by wet-chemical deposition techniques. In contrast, thicker vapor-deposited films (⩾1000 Å) were found to be highly reduced, less crystalline, and exhibited electrical conductivities lower than those of the thinner films upon doping. These results suggest that the interactions of emeraldine with a metal surface can play an important role in determining the chemical, structural, and electronic properties of polyaniline films near the polymer-substrate interface. © 1997 American Vacuum Society. View full abstract»

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  • Study of poly(ether sulfone)/metal interfaces by high energy x-ray photoelectron spectroscopy and x-ray absorption spectroscopy

    Page(s): 544 - 549
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    The metallization of high-temperature polymers like poly(ether sulfone) (PES) is important, especially for microelectronic purposes. The adhesion of metals to these polymers can be greatly improved by using ion implantation. The low ion doses required to improve adhesion, however, make it difficult to determine the mechanism of the adhesion enhancement. This work studies the buried interfaces of ion implanted and as-deposited metal films (Al, Fe, and Cu) on PES. The U.K. Synchrotron Radiation Source at Daresbury Laboratory was used to provide tuneable photon energies in the range of 2100 eV up to 4600 eV. Thus, the interface can be probed to greater depth than usual without being destroyed by peeling or sputter profiling. Adhesion improvement as measured by mechanical testing can, thus, be linked to the chemical changes occurring at the interface of the system. These findings are complemented by additional x-ray absorption spectroscopy (NEXAFS studies) of spincoated PES films. These experiments are designed to give a deeper understanding of the interaction of individual metal atoms with the polymer surface. © 1997 American Vacuum Society. View full abstract»

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  • Determination of electron temperatures in plasmas by multiple rare gas optical emission, and implications for advanced actinometry

    Page(s): 550 - 558
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    A method is described for determining the electron temperature of a low pressure plasma of the type used in microelectronics materials processing. A small amount of an equal mixture of He, Ne, Ar, Kr, and Xe is added to the process gas (in this example Cl2) and the intensities of optical emission lines from the Paschen 2p levels of the rare gases are recorded. The observed emission intensities are compared with those computed from a model that includes electron impact excitation from the ground state, as well as two-step electron impact excitation through intermediate metastable levels. This latter route is shown to be the dominant one for nearly half of the levels. Using adjusted, published electron impact excitation cross sections and assuming a Maxwellian electron energy distribution, the electron temperature (Te), the only adjustable parameter, was determined from the best match between the observed and computed intensities. For a high density, helical resonator Cl2 plasma at 10 mTorr, Te=2.2±0.5 eV was determined from this method. This value is about 1 eV lower than the typical values reported for high density inductively coupled Cl2 plasmas at similar pressures. While the precision of the method is expected to be high, the accuracy of Te determined from optical emission would likely be improved with more accurate cross section data. Implications for actinometric determination of species concentrations in plasmas are also discussed. © 1997 American Vacuum Society. View full abstract»

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  • Direct simulation Monte Carlo computation of reactor-feature scale flows

    Page(s): 559 - 563
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    The direct simulation Monte Carlo (DSMC) technique was used to model the flow around multiple features on a wafer. Since the DSMC technique is valid in both the continuum and rarefied flow regimes, the near-surface reactor flow was directly coupled with the features into a single reactor-feature scale model. This model was then used to determine the effects of operating conditions, feature geometry, and surface chemistry on the concentrations and fluxes to a flat and featured surface. The surface chemistry addressed both chlorine etching of aluminum and SiO2 deposition from a silane/oxygen/argon gas mixture. For both the etch and deposition cases, the concentration of products was higher near the featured surface than the flat surface. This was partially due to multiple molecular reflections between the horizontal and vertical surfaces of the features. While the reacting area of the features was greater than the flat surface with no features, the fluxes to the features were less due to the direction of the incoming flow. Thus, topography models using fluxes to flat surfaces, which are assumed in full reactor scale models, will overpredict deposition or etch rates. A simplified adjustment to the flat surface flux was made to obtain more accurate boundary conditions for topography models and thus, better predictions of deposition and etch rates. © 1997 American Vacuum Society. View full abstract»

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  • Effects of the axial external magnetic field on the reduction of the dielectric window damage due to capacitive coupling in the inductively coupled plasma

    Page(s): 564 - 567
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    The degree of the capacitive coupling in the radio frequency inductively coupled plasma was estimated by measuring the dc shift of the potential at the central inner side of the dielectric window. Its value was -82.2 V for the condition examined (1.1 kW, 1.5 mTorr, C4F8 plasma, flow rate 20 sccm) and the dielectric window was severely damaged owing to this potential difference from the plasma potential, which could be confirmed with the quadrupole mass spectrometry. When an axial external magnetic field was applied, the mass spectrometer signals, which indicate the damage of the dielectric window, decreased drastically in addition to the improvement of the power transfer efficiency. This was mainly caused by the transition from the etching of the dielectric window to polymer formation due to the reduced window potential as a result of the application of magnetic field. © 1997 American Vacuum Society. View full abstract»

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  • CFX(X=1–3) radical densities during Si, SiO2, and Si3N4 etching employing electron cyclotron resonance CHF3 plasma

    Page(s): 568 - 572
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    The roles of CFX(X=1–3) radicals in etching reactions of Si, SiO2, and Si3N4 in an electron cyclotron resonance (ECR) CHF3 plasma have been investigated using infrared diode laser absorption spectroscopy (IRLAS). CFX radical densities in the plasma were measured as functions of Si, SiO2, and Si3N4 etch rates. The radical densities decreased with increasing etch rates of Si3N4, SiO2, and Si. Influences of byproducts from the etched substrates and substrate biases on CFX radicals were also investigated. Moreover, the FCN molecular density was measured using IRLAS in the ECRCHF3 plasma in the presence and absence of Si3N4 film. It was found that the FCN molecule was abundantly formed in the plasma during etching of Si3N4. The IRLAS measurement of the FCN molecule is considered to be suitable for detecting the FCN molecule and in situ monitoring of Si3N4 etching. © 1997 American Vacuum Society. View full abstract»

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  • Study of shallow silicon trench etch process using planar inductively coupled plasmas

    Page(s): 573 - 578
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    Silicon shallow trenches applied to the shallow trench isolation of integrated circuits were etched using planar inductively coupled Cl2 and HBr/Cl2 plasmas and the effects of process parameters such as gas combination, inductive power, and bias voltage on etch rates, selectivities, and etch profiles of silicon trenches were investigated. Also, the physical damages on the trench bottom and sidewall in Cl2 and HBr/Cl2 plasmas were studied using cross-sectional high resolution transmission electron microscopy (HRTEM). The increase of inductive power and bias voltage in Cl2 and HBr/Cl2 plasmas increased polysilicon etch rates in general, but reduced the etch selectivity over nitride. In case of Cl2 plasmas, low inductive power and high bias voltage showed an anisotropic trench etch profile, and the addition of oxygen or nitrogen to chlorine also increased the etch anisotropy. The use of pure HBr plasmas showed a positively angled etch profile and the addition of Cl2 to HBr improved the etch profile more vertically. HRTEM study showed defects formed near the sidewall, bottom, and bottom edge of the silicon trenches etched in Cl2/N2 plasmas, and more dense defects in HBr/Cl2 plasmas possibly due to the penetration of hydrogen in HBr. No defects were found for the trenches etched in pure Cl2 or Cl2/O2 plasmas. © 1997 American Vacuum Society. View full abstract»

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  • Aspect ratio effects in submicron contact hole plasma etching investigated by quantitative x-ray photoelectron spectroscopy

    Page(s): 579 - 584
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    The submicron contact hole etching process using CHF3–CF4–Ar plasma was performed in a commercial parallel plate reactive ion etching reactor (LAM 4520). Response surface methodology was employed to correlate input parameters with etching results. For the aspect ratio investigations, a special test pattern consisting of line/space and contact/space arrays of various dimensions (1 and 0.6 μm) was used. Aspect ratio dependent etching effects were observed. The bottom surface chemistry of SiO2/Si patterned structures after plasma etching have been investigated by using quantitative x-ray photoelectron spectroscopy (XPS). After the SiO2 etching treatments, the silicon surface of the contact (or trench) bottom presents modifications similar to that observed on unpatterned SiO2/Si samples. These modifications are described by a two-layer model involving a fluorocarbon overlayer and an interfacial oxide layer. The fluorocarbon layer thickness strongly increases when the surface area of silicon substrate exposed to the plasma decreases whereas, as unexpected, the fluorine density of the fluorocarbon film decreases. A refluorination mechanism depending on the diffusion of the fluorine atoms from the plasma through the fluorocarbon overlayer is proposed. This work points out the interest of XPS surface analysis in improving the contact hole etching process. © 1997 American Vacuum Society. View full abstract»

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  • Hole-size dependent highly selective SiO2 etching with a hexthode-type wide-gap plasma etcher

    Page(s): 585 - 589
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    We carry out contact-hole etching of SiO2 with a high selectivity over the underlying Si using a hexthode-type wide-gap plasma etcher. In spite of the low power density in the plasma, heavy fluorocarbon deposition was observed. The amount of deposition is thought to depend on the bias voltage near the surface of the wafer. Selectivity is low in smaller holes (≪∅0.8 μm), since the deposition radicals are shaded and cannot reach the bottom of the holes. In larger holes (≫∅0.8 μm), however, selectivity is very high (≫50), and almost infinite in a hole of ∅2.0 μm in diameter. Moreover, sidewall deposition is enough to prevent retardation of the resist even in smaller holes. As a result, quite unique hole-size dependent etching characteristics were obtained, such as tapered etching for smaller holes and high selectivity etching for larger holes. This oxide etcher is applicable when large shallow holes and small deep holes must be etched at the same time. © 1997 American Vacuum Society. View full abstract»

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  • Physical damage and contamination by magnetized inductively coupled plasmas and effects of various cleaning and annealing methods

    Page(s): 590 - 595
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    Effects of various cleaning and annealing methods on the removal of the residue and physical damage remaining on the exposed silicon surface after the oxide overetching by C4F8 magnetized inductively coupled plasmas were studied. X-ray photoelectron spectroscopy, current–voltage characteristics of Au Schottky diodes, and high resolution transmission electron microscopy were used. The formation of Co silicide was also studied using x-ray diffraction, four-point probe, and Rutherford backscattering spectrometry to investigate the effectiveness of the cleaning and annealing methods on the residue and damage removal. Thicker than 65 Å of polymer and thicker than 40 Å of physical damage remained on the silicon surface etched by C4F8 magnetized inductively coupled plasmas. Among the investigated cleaning methods, SF6/O2 soft cleaning was the most effective in removing the residue. SF6/O2 soft cleaning was also the more effective method in removing the physical damage compared to the annealing methods used in the experiment. Stable Co silicide was formed on the silicon surface after O2 plasma cleaning followed by HF dipping or SF6/O2 soft cleaning. Sheet resistances measured on these silicides were close to those of the silicide formed on the clean control silicon surface. Surface residue not the physical damage appeared to affect the formation of Co silicides, and fluorine rich residue appears to p- - revent the formation of stable silicide more compared to carbon rich residue. © 1997 American Vacuum Society. View full abstract»

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  • Insight into the dry etching of fence-free patterned platinum structures

    Page(s): 596 - 603
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    An investigation was undertaken to characterize the time progression of the Pt etch process during the dry etching (DE) of fence-free patterned structures. The goal of this study was to clarify the mechanism of fence-free Pt etching. In particular an explanation was sought that could account for the origin of the extremely shallow sidewall angles typically reported in the literature for fence-free Pt etching. The experiment consisted of coprocessing two oxidized Si wafers possessing identical 250 nm thick Pt film layers, but different photoresist (PR) mask thicknesses. Etching was suspended at 20%, 40%, 60%, and 80% of the full etch process in order to cleave off small pieces of wafer for analysis by scanning electron microscopy (SEM). Using Cl2-based DE conditions known to produce fence-free etching for 250 nm thick film layers, we found that a severe fence actually coats the PR mask during the first 20% of the etch process! As the etch continues the fence structure evolves, achieving a maximum height and width followed by progressive recession until disappearing completely prior to process endpoint. SEM micrographs clearly reveal how the existence of these transient fence structures account for the formation of shallow Pt sidewalls. The data also shows that the final profile of an etched Pt structure possesses a functional dependence on the initial thickness and slope of the PR mask as well as on the initial thickness of the Pt layer. Finally, we believe that the observed behavior of the transient fence provides the strongest evidence to date supporting the existence of a chemically assisted physical sputtering component associated with the DE of Pt films in halogen-based plasmas. © 1997 American Vacuum Society. View full abstract»

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Aims & Scope

The Journal of Vacuum Science and Technology A is devoted to reports of original research, review articles, and Critical Review articles.

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Editor
G. Lucovsky
North Carolina State University