Papers

ICMCTF2003 Session F5-1: Characterization of Thin Film Growth Mechanism and Evolving Film Properties

Thursday, May 1, 2003 8:30 AM in Room Royal Palm 4-6

Thursday Morning

Start	Invited?	Item
8:30 AM		F5-1-1 Nucleation, Growth and Annealing Processes for Thin Film Properties Part 1 J.A. Venables (Arizona State University and CPES, University of Sussex, Brighton, United Kingdom) Nucleation and growth models are well developed for nucleation on homogeneous substrates, and can typically be described in terms of three energy parameters. Nucleation on substrates containing point defect traps and steps have been investigated, at the cost of introducing more energy parameters. This talk describes such growth models, using rate and rate-diffusion equations, in terms of energies for individual surface processes, with examples taken from metal-metal, metal-insulator, metal-semiconductor and elemental semiconductor growth; these models will be illustrated by running (relatively simple) MatLab programs. The main challenge to modeling is to describe the large range of length and time scales in thin film fabrication and degradation, without relying on too many (mostly unknown) material parameters. There may be opportunities to control thin film properties on an industrial scale, as currently rate equation solutions are already fast enough to vary parameters and compute results in real time.
9:10 AM		F5-1-3 Nucleation Growth and Annealing Processes for Thin Film Properties Part 2 J.A. Venables (Arizona State University and CPES, University of Sussex, Brighton, United Kingdom) SEE ABSTRACT ABOVE
9:50 AM		F5-1-5 OH-Mediated Metal Nucleation and Growth at Dielectric Surfaces J.A. Kelber (University of North Texas); D.R. Jennison (Sandia National Laboratories, Albuquerque) The fabrication of conformal metal/dielectric interfaces is of broad and growing importance in microelectronic interconnect technology, the fabrication of nanoelectronic tunneling devices, catalyst preparation and MEMS technology. Metals deposited in vacuum on metal oxide and other dielectric surfaces normally grow in 3-D clusters due to weak ad-atom/substrate interactions. Recent state-of-the-art density functional theory (DFT) calculations, and experimental (XPS, AFM) studies have revealed the role of surface OH groups in inducing the transition from 3-dimensional to 2-dimensional growth for Cu and Co on Al₂O₃ surfaces under UHV conditions. In both cases, surface hydroxylation enhances charge transfer from the metal to the substrate, promoting conformal growth, with first-layer metal cation coverage controlled by surface OH coverage. In the case of Cu on hydroxylated sapphire(0001), ( Θ(OH)_max ~0.45) surface hydroxyls remain intact during deposition¹. In the case of Co on fully hydroxylated Al₂O₃(poly), the presence of adjacent OH groups results in an exothermic reaction resulting in Co(II) formation and H₂ formation². These results point towards a novel method for the engineering of laminar interfaces. The extension of theory and experiment to more complex interfaces, including liquid/solid interfaces, will be discussed. ¹. C. Niu, K. Shepherd, D. Martini, J. Tong and J. A. Kelber, and D. R. Jennison and A. Bogicevic, Surface Science 465, 163-76 (2000) ² J. A. Kelber, Chengyu Niu and K. Shepherd, D. R. Jennison and A. Surface Science 446, 76-88 (2000)³ S. A. Chambers, T. Droubay, D. R. Jennison and T. R. Mattsson, Science, 297 827-31(2002) * Acknowledgements: Work at UNT was supported by the Welch Foundation. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000
10:30 AM		F5-1-7 Effects of Lattice Mismatches in ZnO/Substrate Structures on the Orientation of ZnO Film and the Characteristic of SAW Device J.B. Lee, M.H. Lee, C.K. Park, J.S. Park (Hanyang University, South Korea) High-quality piezoelectric thin film-based surface acoustic wave (SAW) filters have several advantages over the conventional single-crystalline substrate-based SAW filters, mostly due to circuit miniaturization through integration with monolithic microwave-integrated circuit (MMIC) technology and high-frequency applications. Among recently developed piezoelectric materials, thin film ZnO is considered to be very promising for fabricating small-sized high-frequency SAW devices. To achieve a high-quality ZnO film for SAW devices, selection of suitable substrate materials that are well lattice-matched and thermally compatible with ZnO films is very essential since the structural and thermal stresses lying at the ZnO/substrate interface may significantly deteriorate the piezoelectric properties of ZnO films. However, this issue has failed to be profoundly investigated, which may hinder the production of high-performance ZnO-based SAW devices. In this research we intensively examine the effect of several types of substrate materials in the ZnO/substrate structure on the crystal orientation of deposited ZnO films as well as the frequency response characteristic of ZnO-based SAW devices. ZnO films are deposited using RF magnetron sputtering at a nominal condition of RF power = 100 W, O₂/(Ar+O₂) ratio = 10 %, substrate temperature = 200°C, and working pressure = 5 mTorr. Various substrate materials including Si (111), SiO₂/Si, DLC/Si, sapphire, and AlN/Si are used to compare the structural properties of ZnO films grown on those substrates. XRD spectra and their rocking curves are monitored to estimate the texture coefficient (TC) for (002)-orientation, crystallite size, and full-width at half-maximum (FWHM) for (002)-peak. To fabricate SAW devices, interdigital-transducer (IDT) electrodes with 2μmm-line width are patterned on ZnO using a lift-off method. Frequency response characteristics (including S₂₁) for fabricated SAW devices are measured and the device parameters such as insertion loss and side-lobe rejection level are estimated. It is to be noted from the experimental results that among all the ZnO/substrate combinations used in this research the ZnO/AlN/Si configuration may be the most desirable for SAW device applications since it shows an excellent (002)-preferred growth nature for deposited ZnO films and superior characteristics for fabricated SAW devices. This is attributed to the small lattice mismatch (~ 4.3 %) and structural resemblance (hexagonal-closed packed) between ZnO and AlN. The relationship between the properties of ZnO films and the characteristics of SAW devices are also discussed in terms of substrate materials.
10:50 AM		F5-1-8 The Growth of High-quality Uniform SiGe Films by Introducing an Intermediate Si Layer S.-W. Lee (National Tsing Hua University, Taiwan, ROC); P.S. Chen (Industrial Technology Research Institute, Taiwan, ROC); C.W. Liu (National Taiwan University, Taiwan, ROC); L.J. Chen (National Tsing Hua University, Taiwan, ROC) The growth of high-quality uniform SiGe films has been achieved by introducing a thin Si interlayer in a commercial multi-wafer hot wall UHV/CVD system. The SiGe films were characterized by transmission electron microscopy, atomic force microscopy, high-resolution x-ray diffraction and Raman spectroscopy. It was found that an intermediate Si in the SiGe films reduces the threading dislocation density in relaxed Si_0.8Ge_0.2/Si heterostructures from 10⁷ down to 5.2x10⁴ cm^-2. The rms surface roughness was measured to be about 3.2 nm and formation of pits related to strain relaxation on the surface was suppressed. The degree of strain relaxation is 89 %, which compares favorably with those grown with conventional compositionally graded buffer layer. In comparison with conventional compositionally graded buffer layer, it has the advantages of having thinner buffer layer for required degree of relaxation, smoother surface and lower threading dislocation density. A strain relaxation mechanism for the Si interlayer is proposed.
11:10 AM		F5-1-9 Study of a-Si/SiO₂ Interface Deposited by RF Magnetron Sputtering N. Tomozeiu, A. Palmero-Acebedo, E.E. van Faassen, W. Arnoldbik, A.M. Vredenberg, F.H.P.M Habraken (Utrecht University/Debye Institute, The Netherlands) Silicon oxides are basic materials for many industrial applications. They are widely used as optical coatings, passivation layers or microelectronic and optoelectronic devices. It is known that in microelectronic the SiO₂/Si interface largely affects the performance of silicon devices. There is still a lack in understanding the interface structure and its chemistry. a-Si/SiO₂ interfaces have been prepared by reactive sputtering from a polysilicon target in an Ar/O₂ gas mixture using an RF magnetron deposition system. Two series of samples with various thickness of SiO₂ (1, 2, 4 and 8 nm) have been deposited by two procedures: a) plasma on for a-Si deposition and the oxygen was introduced for SiO₂ layers (plasma on); b) each layer has been deposited separately after a background pressure of 10^-7 mbar (plasma on/off). The composition and the structure of the interface layer are studied by x-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). The presence of Si⁺ⁿ (with n=0,1,2,3,4) species and their evolution with the layer thickness is studied using Si 2p OES spectra. The plasma during deposition has been monitorized by optical emission spectroscopy (OES). A correlation between the plasma characteristics revealed by OES and structural building blocks at the interface is proposed and discussed. More oxidized entities (higher n values in Si⁺ⁿ) are found in samples plasma on/off deposited.