Papers

AVS1996 Session TF-WeA: In Situ and Ex Situ Characterization II

Wednesday, October 16, 1996 2:00 PM in Room 107B

Wednesday Afternoon

Start	Invited?	Item
2:00 PM		TF-WeA-1 Characterization of the LPCVD Grown Rugged Polysilicon Surface using Atomic Force Microscopy M. Schroth, J. Sweeney (Bruce Technologies International) As DRAM areal density increases to 64Mbit and beyond and critical dimensions decrease to deep sub-half micron, the surface area left for the DRAM charge storage capacitor shrinks. It is about 1.4 /mu/m/super 2//cell in the 64Mbit DRAM. The capacitance required, however, remains about the same from generation to generation. This requires some means to increase the capacitance per unit area of wafer surface. "Rugged" polysilicon is a form of polysilicon which has a high surface area per planar surface area used. Its high spatial frequency roughness produces specific surface area increase factors of 1.5 and greater. It is deposited in a state-of-the-art LPCVD vertical reactor with multiple gas inlets, a flat temperature distribution, and wafer rotation. The films are deposited at temperatures in the vicinity of 575 degrees C, which produces amorphous Si films and then allowed to crystallize during the purge and unloading steps. This produces (311) textured films as opposed to the (110) texture which exists in as-deposited polysilicon deposited at temperatures above 600 degrees C. These (311) textured films have a much higher surface roughness than the as-deposited (110) polysilicon. Atomic force microscopy (AFM) measurement of these films poses a challenge since films with such high roughness must be measured with sharp probes which are typically made of silicon. Sharp Si probes measuring rough Si surfaces results in damage to one or the other unless scanned at low speeds. A solution was found which uses probes coated with diamond like carbon to reduce damage to probes and surfaces. Using these probes has allowed us to characterize these films as a function of critically controlled growth temperature, pressure, rotation, and gas delivery conditions. Rms roughnesses, specific surface area increases, and power spectra are used to specify the surfaces as a function of critical parameters
2:20 PM		TF-WeA-2 Diode-like Behavior of Silicon-Phthalocyanine Junctions Investigated with Scanning Tunneling Microscopy/Spectroscopy L. Ottaviano, S. Santucci, S. Di Nardo, L. Lozzi, M. Passacantando, P. Picozzi (Universit\ag A\ Dell'Aquila, Italy) We present ultra high vacuum Scanning Tunneling Spectroscopy (STS) and Ultraviolet Photoemission Spectroscopy (UPS) measurements on an ultrathin film (5 \Ao\) of Nickel-Phthalocyanine (Ni-PC) deposited onto a clean "metallic" Si(111)7x7 surface. STS spectra (I-V curves) were taken at constant tip-sample separation showing highly reproducibility at different submicrometric topographical features of the sample. In particular three typical spectra have been repeatedly observed: i) I-V curves with a slow exponential increase of the current up to +2 eV (I\<=\ 5 nA) where the current steeply increases (I\>=\ 50 nA), ii) highly noisy I-V curves symmetric with respect to the applied bias and, iii) curves which show a marked rectifying behavior with negligible current (I\<=\ 10 pA) at negative (sample to tip) voltages and steeply increasing current when applying a positive bias (I\>=\ 50 nA for V\>=\ .5 Volt). We explain the different electronic behaviors in terms of the different morphological features observed (different Ni-PC crystallites height and different Ni-PC molecular plane orientation with respect to the substrate) and starting from the density of states below the Fermi energy of the Ni-PC/Si(111)7x7 interface as measured with UPS. The diode-like behavior observed is explained in terms of resonant tunneling of electrons from the tip through the PC layer to the Silicon substrate. STS spectra of clean Si(111)7x7 are also presented for comparison.
2:40 PM		TF-WeA-3 Deconvolution of Tip Effected Atomic Force Microscope Images and Comparison to Rutherford Backscattering Spectrometry M. Tabet, F. Urban III (Florida International University) There is distortion in atomic force microscope (AFM) images caused by a non-ideal shape and size of the probe tip. This tip effect is also known as convolution of the tip and sample. AFM images of nanometer size islands of zinc deposited on silicon substrates by the ionized cluster beam deposition technique were used to investigate this effect by comparing the number of zinc atoms per unit area determined by each of two methods, the AFM images and Rutherford backscattering spectrometry (RBS). This Comparison showed on offset, with the AFM reporting more zinc than RBS. A partial explanation for this difference is a convolution of the tip and sample making the islands appear larger. Previously reported convolution and deconvolution algorithms were implemented to study and simulate the interaction between tip and sample in the AFM. The deconvolution algorithm removes part of the distortion by taking into account the physical volume occupied by the tip which exposes a more accurate image. After deconvolution of the zinc islands images there was better agreement between AFM and RBS results. Deconvolution of other images, will also be presented.
3:00 PM		TF-WeA-4 In Situ Optical Emission Spectroscopic Study of the Plumes Produced during Pulsed-laser Deposition of Metal Oxide Films P. Kung (AFR, Inc.) An optical emission spectroscopy (OES) system has been developed as an in-situ process monitor for Nd:YAG pulsed-laser (266 nm, 10 Hz) deposition of metal oxide films onto Si substrates. The spectrometer is designed for use with optical fibers, equipped with 1024 element array of Si CCD detectors, and coupled with an auto-ranging software/hardware interface. The effects of oxygen pressure, laser fluence, and distance from the target surface on excited state population distributions for atomic, ionic, and molecular species within the expanding laser-induced plume are studied systematically. The metal oxide films under investigation include SiO\sub 2\, YSZ, SrTiO\sub 3\, YBa\sub 2\Cu\sub 3\O\sub 7\, Bi\sub 2\Sr\sub 2\CaCu\sub 2\O\sub 8\, La\sub 0.5\Sr\sub 0.5\CoO\sub 3\, Ba\sub 0.4\Sr\sub 0.6\TiO\sub 3\, Pb(Zr,Ti)O\sub 3\, and La\sub 0.67\Ca\sub 0.33\MnO\sub 3\. These films of multilayered structures are fabricated for various applications in gas sensing, magnetic field detection, and dynamic random access memory cells. Their microstructural, electrical, and magnetic properties are measured and correlated with the qualitative features of plume emission spectra and of infrared reflectance spectra collected on themselves during deposition. The OES system provides a low-cost and sensitive diagnostic for optimization and monitoring of deposition conditions. Details on the development of spectrum analysis methods and software routines as well as the realization of real-time, closed-loop process control schemes will be discussed.
3:40 PM		TF-WeA-6 In Situ Monitoring of Molecular Beam Epitaxy using Specularly Scattered Ion Beam Current Oscillations J. Labanda, S. Barnett (Northwestern University) A 3 keV He ion beam was focused on a GaAs(001) surface 2\super o\ from the GaAs(001) surface plane along the <110> direction. Specular scattering, measured using a Faraday cup and observed as a local maximum in the current, was observed at a scattering angle of 4\super o\ with a 2-3\super o\ spread. The scattered current measured during molecular beam epitaxy (MBE) oscillated with periods that decreased with increasing Ga cell and agreed with measured reflection high energy electron diffraction oscillation periods, i.e., they corresponded to the monolayer growth rate. For growth at 520 \super o\C and 0.28 ML/s, for example, the measured ion current dropped rapidly by ~40% upon opening the Ga shutter, oscillated 17 times with an initial amplitude of ~14% of the initial ion current, and then increased gradually upon closing the Ga shutter. The oscillation intensity decreased as the substrate temperature was increased above ~570 \super o\C, indicating a transition to step-flow growth. The ion scattering oscillations are not a diffraction effect, as indicated by the fact that they do not vary strongly with scattering angle or ion energy. The initial ion current decrease is due to scattering of ions from the specular beam by adatoms, step edges, and surface vacancies, since a locally flat surface is required for a specular reflection. Calculations of the scattering cross section for single adatoms, using a Thomas-Fermi-Moliere potential, provide reasonable agreement with the results. One possible advantage of this method is that simple geometrical scattering models can be used to obtain adatom and step densities. Another advantage is the weak dependence on azimuthal scattering angle, such that measurements during substrate rotation are possible.
4:00 PM		TF-WeA-7 In Situ Characterization of Oxygen Incorporation during Initial Growth of Pb(Zr\sub x\Ti\sub 1-x\)O\sub 3\ Thin Films using Time of Flight (ToF) Ion Beam Analysis Methods J. Im, A. Krauss (Argonne National Laboratory); O. Auciello (Microelectronics Center of North Carolina); V. Smentkowski, D. Gruen (Argonne National Laboratory); R. Chang (Northwestern University) The synthesis of ferroelectric thin multicomponent oxide films, via physical or chemical deposition requires a background of ambient oxygen pressure, typically 5x10\super -4\ Torr or greater. This background gas limits the use of most current surface analytical methods for the characterization of thin film surfaces during growth. Therefore, Time-of-Flight Ion Scattering and Direct Recoil Spectroscopic (ToF-ISARS) methods have been developed which permit monolayer-specific surface analysis under the conditions appropriate for the growth of ferroelectric thin film materials. In this paper, oxygen incorporation during the early stages of film growth via ion beam sputtering of Pb(Zr\sub x\Ti\sub 1-x\)O\sub 3\ (PZT) targets onto substrates consisting of a thin layer of Pt and RuO\sub 2\ on MgO at 570 \super o\C in an oxygen ambient of 5x10\super -4\ Torr is studied via ToF-ISARS. The oxygen concentration at the surface of a PZT film, monitored during deposition onto a Pt/MgO substrate, was found to be nearly zero during the initial stage of film growth, increasing continuously with film thickness during the deposition of a 45 \Ao\ thick PZT layer. A PZT film deposited onto a RuO\sub 2\/MgO substrate under the same conditions was found to have a constant and higher oxygen signal during growth to a similar thickness. These results are discussed in the context of a model involving the presence of oxygen vacancies at the PZT/electrode interface as contributors to the fatigue phenomenon for PZT capacitors with Pt electrodes, and the observed suppression of fatigue for PZT capacitors with oxide electrodes.Work supported by the U.S. Department of Energy, BES-Materials Sciences, under Contract W-31-109-ENG-38.The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory ("Argonne") under Contract No. W-31-109-ENG-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid-up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.
4:20 PM		TF-WeA-8 Core-Level Photoabsorption Characterization of Diamond and Carbon Films L. Terminello, J. Carlisle (Lawrence Livermore National Laboratory); C. Zuiker, A. Krauss, D. Gruen (Argonne National Laboratory); F. Himpsel (University of Wisconsin, Madison) We have used synchrotron radiation core-level photoabsorption to characterize the electronic structure and morphology of carbon thin-films and determined the relative ratio of sp2 vs. sp3 bonding. The diamond, diamond-like, and carbon films characterized were prepared by a variety of methods including sputtering, CVD, microwave plasma CVD, and laser ablation. We have also measured these films using Raman spectroscopy and have found that in cases where the domain size of the crystallites in the carbon films was nanoscopic (less than 100 nm), Raman spectroscopy gave indeterminate results. In these cases, as well as with larger crystallite size films, core-level photoabsorption was able to unambiguously identify the bonding in the film. We will present photoabsorption data obtained from these materials. These experiments and prospects for other experiments that can identify the unique electronic properties and bonding of such novel thin films will be discussed. This work was supported by the U. S. Department of Energy under Contract No. DE-AC03-76SF00098 for the Advanced Light Source, Lawrence Berkeley National Laboratory, contract number W-31-109-ENG-38 for Argonne National Laboratory, and under Contract No. W- 7405-ENG-48 for the Lawrence Livermore National Laboratory.
4:40 PM		TF-WeA-9 Quantification of BPSG Films Compared using Quadrupole SIMS, RBS, WDX and Wet Chemistry G. Mount, J. Kirchoff, V. Chia, M. Edgell (Charles Evans & Associates) Consistent BPSG film stoichiometry across wafer and from run to run are important in achieving predictable etch back rates. Film thickness must also be controlled and reproducible to ensure sufficient dielectric remains after etch processing. It is therefore important to quantify accurately, precisely and routinely, boron and phosphorous concentrations, and film thickness both across the wafer, and from wafer to wafer. Four methods of boron and phosphorous quantification are compared and discussed. These are Quadrupole Secondary Ion Mass Spectrometry (SIMS), Wavelength Dispersive X-ray analysis (WDX), wet chemistry (colorimetry), and Rutherford Backscattering Spectrometry (RBS). The accuracy and precision of the quantification and film thickness measurement of each method are presented and compared. Multi-stage BPSG deposition can lead to changes in film chemistry from one layer to the next and at the interfaces of each deposited layer. The ability of each technique to discern changes in film chemistry with depth is also investigated and presented.