ICMCTF2009 Session F2/B7: In Situ Characterization for Deposition Proceess and Film Properties Modeling

Wednesday, April 29, 2009 1:30 PM in Room Sunrise

Wednesday Afternoon

Start	Invited?	Item
1:30 PM		F2/B7-1 Quantification of the Incorporation Coefficient of a Reactive Gas on a Metallic Film During Magnetron Sputtering: the Method and Results W.P. Leroy, S. Mahieu (Ghent University, Belgium); R. Persoons (Flemish Institute for Technological Research (VITO), Belgium); D. Depla (Ghent University, Belgium) Magnetron sputtering is a widely used technique to deposit thin films. Adding a reactive gas to the discharge allows one to deposit stoichiometric compound films from a metallic (or substoichiometric) target at a high deposition rate. However, the addition of this reactive gas makes the control of the deposition process a complex task. Huge efforts are going into the understanding of the fundamental phenomena of this reactive sputter process and into the simulation of the deposition process by e.g. PIC/MC. However, one of the most uncertain parameters in this reactive sputtering process is the incorporation coefficient of the reactive gas on the growing layer, i.e. the real-time sticking coefficient during deposition. In this work, mass spectrometry is used to deliver more insights on this complex matter. A method has been developed to determine the incorporation coefficient of the reactive gas onto the growing metal film, using mass spectrometry combined with thin film analysis. This method delivers a global, realistic incorporation coefficient and hence a correct parameter to be used in the models for the reactive sputtering process. We have determined the sticking coefficient of O₂ and N₂ on several metals during reactive magnetron sputtering, and relate these to the material properties of the different metals.
1:50 PM		F2/B7-2 Experimental and Numerical Plasma Characterization in a Deep Reactive Ion Etch System S.P. Koirala, M.H. Gordon (University of Arkansas); S.L. Burkett (The University of Alabama) Using deep reactive ion etch (DRIE) with a modified Bosch process, we create through-silicon-vias (TSVs) which have application in 3D interconnects. These interconnects allow the development of three-dimensional architectures which have several advantages including faster signal processing and overall system miniaturization. Our modified Bosch process uses alternating etch and passivation cycles with sulfur hexafluoride (SF₆)/Argon (Ar), and cyclofluorobutane (C₄F₈), respectively. Previous studies show that the coil power and pressure significantly affect the quality of the via shape. In this study, optical emission spectroscopy and a Langmuir probe are used to experimentally characterize the plasma conditions during the etch process, and numerical plasma models are used for comparison and optimization. Preliminary Langmuir probe studies show that the introduction of SF6 into an Ar plasma causes a slight decrease in the ion density and a signific ant decrease in electron density. This latter effect is attributed to the electro-negativity of SF₆. The optical emission studies provide information on the relative population of argon and fluorine excited states, species which both play an important role in the formation of TSVs. Numerically, the commercially available Boltzmann equation solver ELENDIF is used in conjunction with an Ar collision radiative model to simulate the experimental conditions. Good agreement with experimental data is obtained.
2:10 PM	Invited	F2/B7-3 Initial Stages of Polycrystalline Thin Film Growth as Seen by Scanning Probe Microscopy T. Michely (Universität zu Köln, Germany) The growth of Ag thin films deposited at 300 K on amorphized Si surfaces under ultra high vacuum conditions is investigated by in situ scanning tunneling microscopy (STM). The analysis of the film morphology as a function of film thickness together with additional annealing or low temperature experiments allow one to obtain a quite complete picture of the film formation processes. It is shown that the large kinetic stability of the trenches separating Ag islands strongly influences all the structural features during the initial growth stages, i. e., island density, grain size, roughness and texture evolution. Specifically it becomes understandable, why abnormal grain growth is initiated only when continuous films develop facets. Finally it is shown, how texture evolution and grain structure can be manipulated in ion assisted growth by using a grazing incidence ion beam. The contributions to this work by Celia Polop, Christian Rosiepen, Daniel Förster and Se bastian Bleikamp are acknowledged.
2:50 PM		F2/B7-5 Surface Mound Formation During Epitaxial Growth of CrN(001) X.Y. Zhang, D. Gall (Rensselaer Polytechnic Institute) Single crystal CrN(001) layers, 10 to 160 nm thick, were grown on MgO(001) by ultrahigh vacuum magnetron sputtering at growth temperatures T_s = 600 and 800°C. All layer surfaces exhibit mounds which evolve in both shape and size, as observed by in-situ scanning tunneling microscopy and quantified by statistical analyses using height-height correlation functions. For T_s = 600°C, the root mean square surface roughness σ initially increases sharply from 0.69±0.18 for a thickness t = 10 nm to 2.44±0.48nm for t = 20nm, but then remains constant at σ = 2.43±0.13nm for t = 40, 80 and 160 nm. The mounds exhibit square shapes with edges along <110> directions for t≤40 nm, but develop dendritic shapes at t = 80 nm which revert back to squares at t = 160 nm. This is associated with a lateral mound growth that is followed by coarsening, yielding a decrease in the mound density from 5700 to 700 µm^-2 and an initial increase in the coherence length L from 7.18±0.6 to 16.27±0.8 to 23.87±2.87 nm for t = 10, 20, and 40 nm, respectively, followed by a drop in L to 22.22±1.97 and 16.12±1.89 nm for t = 80 and 160nm, respectively. Growth at T_s = 800°C leads to opposite trends: σ decreases from 1.98±0.45 to 0.92±0.07 and 1.03±0.07 nm and L decreases from 20.48±3.67 to 10.27±0.37 and 9.84±0.45nm, for t = 10, 20, and 40 nm, respectively, while the mound density remains approximately constant at 900 μm^-2. These unexpected trends are associated with mounds that elongate and join along <100> directions, yielding long chains of interconnected square mounds for t = 40 nm. At larger t, coalescence causes a rapid mound growth with σ increasing to 2.54±0.2 and 2.52±0.11nm, L increasing to 23.77±2.52 and 40.02±2.34 nm, and the mound density decreasing to 280 and 100 µm^-2, for t = 80 and 160 nm, respectively.
3:10 PM		F2/B7-6 In Situ Stress Evolution in TiZrN and TiTaN Thin Films Grown by Reactive Magnetron Sputtering G. Abadias (Universite de Poitiers, France); Ph. Guerin (Université de Poitiers-CNRS, Laboratoire PHYMAT, France); L.E. Koutsokeras, P. Patsalas (University of Ioannina, Greece) Due to their inherent physical and mechanical properties transition metal (TM) nitride thin films are commonly used in various applications, such as contact layers in microelectronics or protective hard coatings on cutting tools.¹ Extensive studies have been carried out in binary compounds (TiN, ZrN or TaN) to relate deposition conditions, stress, microstructure and preferred orientation to films' properties. In particular, it is important to understand stress development during growth to tailor thin films with reduced stress levels to enhance device's lifetime and reliability. Current efforts are now made to synthesize functional and adaptative layers based on multicomponents TM-based systems. Among these, the TiN-ZrN and TiN-TaN systems arouse an increasing interest due to the possibility to stabilize ternary nitride solid solutions with enhanced properties. For example, conducting Ti_1-xTa_xN thin films (02 However, stress development during growth in these multinary systems remains unexplored. In the present work, we investigated the stress evolution during reactive magnetron cosputtering of TiTaN and TiZrN thin films using a real time wafer curvature measurement technique. Samples were grown at 300°C on Si wafers under an Ar/N₂ atmosphere. The influence of substrate bias voltage, deposition rate, N₂ and Ar partial pressures on stress buildup was studied. The obtained data showed the presence of stress gradients over film thickness, as a result of two competing stress producing mechanisms: atomic peening inducing compressive stress and void formation inducing tensile stress.³ Complimentary ex situ techniques using X-ray diffraction and atomic force microscopy were performed to correlate stress evolution with texture formation and film morphology. A comparison will also be made with thin films grown by pulsed laser deposition. ¹G. Abadias, Surf. Coat. Technol. 202, 2223 (2008) ²L. E. Koutsokeras, G. Abadias, Ch. E. Lekka,G. M. Matenoglou, D. F. Anagnostopoulos, G. A. Evangelakis and P. Patsalas, Appl. Phys. Lett. 93, 011904 (2008) ³G. Abadias and Ph. Guerin, Appl. Phys. Lett. 93, 111908 (2008).
3:30 PM		F2/B7-7 In Situ AFM Investigation on Tribo-Corrosion of CrSiN Film Adherent Tool Steel H.-H. Lin, C.-C. Chou (National Taiwan Ocean University, Taiwan); J.-C. Huang, J.-W. Lee, Y.-C. Chang, Y.-B. Lin (Tungnan University, Taiwan) A CrSiN film was coated on SKD61 to enhance the anti-corrosion capability by a bipolar symmetry pulsed DC reactive magnetron sputtering process. A series of mechanical and electro-chemical polishing processes were implemented to obtain various surface roughnesses before the CrSiN films were built. The adhesion of CrSiN-coated samples was evaluated by scratch test. The corrosive characteristics were studied by potentiodynamic test and electrochemical impedance spectroscopy (EIS) in a 3.5 wt.％ NaCl solution. An in-situ atomic force microscope (AFM) was then applied to detect their pitting corrosion in a 0.01 M NaCl solution. Two loading conditions were applied to investigate the corrosion induced by different stresses. The results demonstrate that the significant improvement of the CrSiN-coated SKD61 substrates either in tribological property and corrosion resistance as well. In the mean time, the in-situ corrosion behavior of sample’s microstructures was also discussed and addressed.
3:50 PM		F2/B7-8 Fast Characterization of Reaction Waves in Exothermic, Metal-Metal Multilayer Nanolaminates D.P. Adams, J. McDonald, M Hobbs (Sandia National Laboratories) Sputter-deposited, exothermic multilayer films and foils have generated a great deal of interest recently, because they exhibit rapid, high-temperature, self-sustained reactions characterized by tailorable average propagation speeds.¹ These multilayers often consist of two or more reactant layers (typically dissimilar metals) characterized by a large negative heat of formation. Layer thicknesses range from 5-300 nm and coatings may consist of thousands of individual layers. Despite much interest, a great deal of research is required to fully understand the behavior and performance of these materials. In this presentation, we describe the dynamics of reaction front propagation as these depend on multilayer design and composition. Using high-speed photography (1E5 frames per second with 5 um spatial resolution) and high-speed thermal imaging devices we show direct evidence for steady and unsteady modes. A few multilayer systems (e.g., those consisting of Al/Pt) exhibit a steady reaction mode with no evidence for unsteady behaviors. Co/Al, Ni/Ti and other lower-enthalpy metal-metal pairs exhibit various, unsteady modes - particularly when bilayer thickness is made large. We further show how reaction mode and flame morphology depends on the total thickness of a given multilayer system (varied in this study from 150 nm to 50 micrometers). In addition, the relationship of reaction mode to final foil microstructure and morphology is presented. Complimentary finite difference and finite element heat transport models explain some of the observed macroscopic behaviors. 1 U.S. Patent 5,538,795 T.W. Barbee, Jr. and T. Weihs.
4:10 PM		F2/B7-9 Quantitative Measurement of Ion Energy Distributions Impinging onto Arbitrarily Biased Substrates During Plasma Deposition T. Baloniak, A. von Keudell (Ruhr-Universität Bochum, Germany) Substrate biasing is an established technique to control and adjust material properties during thin film deposition from a plasma. The energy distribution function of the ions impinging onto the substrate (IEDF) is manipulated by the external bias voltage. Optimal ion bombardment can significantly improve film properties like hardness, adhesion, crystallinity, or wear resistance. In our contribution, we report about the quantitative measurement of ion energy distribution functions on arbitrarily biased substrates. The measurements are performed in a magnetically enhanced, capacitively coupled argon discharge, which is heated by 13.56 and/or 71 MHz. An aluminum target is mounted on the powered electrode. The substrates are placed on an arbitrarily biased electrode driven by RF waveforms at 1 MHz. A miniaturized, floating retarding field analyzer allows for IEDF measurements on the biased substrate holder. The energy distributions are found to be good replica of the bias waveforms applied to the substrate, eventually skewed by collisions at higher pressures. Our findings allow to design tailored waveforms for optimal ion bombardment and thus, optimal film properties.