Papers

AVS2001 Session DI-WeM: Atomic Layer Deposition for Silicon Devices

Wednesday, October 31, 2001 8:20 AM in Room 130

Wednesday Morning

Start	Invited?	Item
8:20 AM		DI-WeM-1 Growth of Tantalum Oxide Films by Chemical Vapor and Atomic Layer Deposition S. Prasertchoung, S.-Y. Yang, J.N. Kidder (University of Maryland) The nucleation and growth of tantalum oxide thin films by chemical vapor and atomic layer deposition was studied. In the CVD process, the films were deposited using Ta(C₂H₅O)₅ and O₂ as precursors, where tantalum source was delivered to the process using direct liquid injection. Films with thickness of 1 to 50 nm were deposited on Si and Pt-coated Si substrates and characterized using ellipsometry, atomic force microscopy, X-ray diffraction, and electrical measurements. In the CVD process it was observed that the deposition rate was kinetically-limited at substrate temperatures up to 475 C with an activation energy of approximately 1 eV. At temperatures greater than 475 C the growth rate decreased significantly and film properties were poor with rough morphology. This behavior was characteristic of gas phase reaction effects, although similar behavior was observed even with sequential delivery of the oxygen and tantalum ethoxide, where reactions between the precursors were minimized. This effect may stem from reactions with by-products of the alkoxide decomposition, such as water and ethanol, which can have a large effect on the nucleation and growth. In this work we investigated the effect of water on the initial nucleation, the growth kinetics, and the film morphology for ultra thin films of tantalum oxide deposited in both chemical vapor deposition and atomic layer deposition processes where the precursors (Ta(C₂H₅O)₅, O₂, H₂O) were delivered under various sequences and conditions. This work was supported by the NSF through the University of Maryland MRSEC(DMR 00-80008).
8:40 AM		DI-WeM-2 Quantum Chemical Study of Zirconium Oxide Atomic Layer Deposition Y. Widjaja, C.B. Musgrave (Stanford University) As gate oxide thickness in MOS device decreases, new high-κ materials are being investigated to substitute for silicon oxide. However, unlike silicon oxide, the oxide layers being investigated do not react readily on silicon surfaces. Here, we use density functional theory to examine the atomic layer deposition of zirconium oxide, one of the high-κ materials candidates, on the Si(100)-(2x1) surface. The reactants investigated in this study are ZrCl₄ and H₂O. The atomistic mechanisms of two different deposition cycles are investigated: 1) ZrCl₄ is first deposited on the clean Si(100)-(2x1) surface. Upon adsorption, ZrCl₄ is shown to dissociate into ZrCl₃(a) and Cl(a) with an activation barrier that is below the entry level. Water is deposited next and various surface reactions and configurations are investigated. We find that the most stable species consists of ZrCl₃(a) and OH(a) attached to the two silicon atoms of silicon dimers. Alternatively, 2) H₂O is first deposited on the Si(100)-(2x1) surface. As determined previously, we also find that H₂O dissociates into OH(a) and H(a) upon adsorption. Subsequent reactions with ZrCl₄ are then investigated. Upon investigation of the two different deposition cycles, the properties of the interfacial layer between silicon and zirconium oxide are then investigated. Subsequent half cycle reactions on the zirconia surface will also be presented.
9:00 AM		DI-WeM-3 Effect on In-situ H₂ Plasma Treatment of ZrO₂ Gate Dielectric Deposited by Plasma Enhanced Atomic Layer Deposition Method J.H. Koo, Y. Kim, H. Jeon (Hanyang University, Korea) As the metal oxide semiconductor device continues scale down, the high-k gate dielectrics become one of the solutions in providing increased capacitance and reduced leakage currents without significantly increasing the actual equivalent oxide thickness (EOT) of gate dielectrics. Among the high-k materials, ZrO₂ is considered as one of the alternatives to SiO₂ gate dielectric due to the relatively high dielectric constant (~25), low leakage current and its compatibility with the manufacturing of integrated circuits.¹ Here, we focus on the in-situ H₂ plasma effect on ZrO₂ gate dielectric deposited by plasma enhanced atomic layer deposition (PEALD) method. ZrO₂ were deposited on p-type Si (100) substrates at 200-300°C using t-butoxide as Zr precursor and oxygen as reactant gas at the process pressure of about 1 Torr. Initial native oxide layer was removed by in-situ hydrogen plasma treatment before ZrO₂ deposition at the same processing temperature. Oxygen reactant gas was introduced both as in gas and plasma states. About 1000Å layer of Platinum (Pt) as gate electrodes were deposited by e-beam evaporator. The electrical properties of this MOS capacitor were measured after post metal annealing. The physical and chemical characteristics of ZrO₂ film were analyzed by cross-sectional transmission electron microscope, atomic force microscope, Auger electron spectroscopy, X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. The results of electrical properties and reliability characteristics including EOT, hysteresis, leakage current and capacitance were measured by I-V and C-V. This paper presents the plasma effect on ZrO₂ films deposited by PEALD method and its potential applications for gate dielectric in ultra large-scale integrated circuit devices. ¹ ¹W. Qi, R. Nieh, B. H. Lee, L. Kang, Y. Jeon and J. C. Lee, Appl. Phys. Lett., 77, 3269-3271 (2000).
9:20 AM		DI-WeM-4 Nucleation and Growth Chemistry during Tungsten Atomic Layer Deposition on Oxide Surfaces R.K. Grubbs (University of Colorado, Boulder) The nucleation and growth chemistry during tungsten (W) atomic layer deposition (ALD) on SiO₂ and Al₂O₃ surfaces were studied using Auger electron spectroscopy and quadrupole mass spectrometry. W ALD was performed using sequential exposures of WF₆ and Si₂H₆. Differences in the nucleation process and the film growth mode were observed for the two oxide substrates. The nucleation of W ALD on SiO₂ required 8-9 WF₆/Si₂H₆ reaction cycles. A much shorter nucleation period was observed on Al₂O₃. W ALD on SiO₂ followed a Frank-Van der Merwe, layer-by-layer, growth mode while W ALD on Al₂O₃ occurred with a Volmer-Weber growth mode. These results indicate that the identity of the underlying substrate has an affect on the nucleation and growth of W ALD films. The growth chemistry of W ALD was studied using quadrupole mass spectrometry. The reaction products from each sequential reaction were identified and correlated with the Auger results. The reaction products suggest the stoichiometry of the surface reactions during tungsten atomic layer deposition.
9:40 AM		DI-WeM-5 Atomic Layer Deposition of Al₂O₃/ZnO Nanolaminates and Alloys: Fabrication and Properties J.W. Elam, M.D. Groner, Z.A. Sechrist, S.M. George (University of Colorado) Atomic layer deposition (ALD) of Al₂O₃ and ZnO films can be accomplished using sequential exposures to Al(CH₃)₃/H₂O and Zn(CH₂CH₃)₂/H₂O, respectively. ALD Al₂O₃ is smooth, amorphous and insulating. ALD ZnO is rough, crystalline and conducting. Composite mixtures of Al₂O₃ and ZnO may have unique and interesting properties. Al₂O₃/ZnO nanolaminates and alloys were deposited by ALD in a viscous flow reactor. The Al₂O₃/ZnO composite film growth was monitored using an in situ quartz crystal microbalance. A series of Al₂O₃/ZnO nanolaminates was prepared where the total thickness of Al₂O₃ and ZnO was kept constant while varying the number of individual Al₂O₃/ZnO bilayers. Atomic force microscopy was used to measure the root mean squared (RMS) surface roughness of the Al₂O₃/ZnO nanolaminate films. The RMS roughness of the nanolaminate films decreased dramatically versus the number of Al₂O₃/ZnO bilayers. A series of Al₂O₃/ZnO alloy films was also grown using ALD by varying the relative number of Al(CH₃)₃/H₂O and Zn(CH₂CH₃)₂/H₂O sequential exposures. Four-point probe and mercury probe measurements were performed to determine the resistivity of the Al₂O₃/ZnO alloys. The resistivity of the Al₂O₃/ZnO alloy films decreased with small Al₂O₃ percentage and then increased greatly with increasing Al₂O₃ percentage. These studies of the fabrication and properties of ALD composite films will serve as a model for the future development of ALD aluminates and silicates.
10:20 AM		DI-WeM-7 Radical Enhanced Atomic Layer Deposition of TiN Diffusion Barriers F. Greer, D. Fraser, J.W. Coburn, D.B. Graves (University of California, Berkeley) Atomic Layer Deposition (ALD) has been proposed as one way to deposit highly conformal thin films for copper diffusion barriers due to the self-limiting, layer-by-layer growth that can be achieved with this technology. One problem with thermally activated ALD is that the deposition temperatures that are required to achieve reasonable growth rates and good quality films with low impurity concentrations can be relatively high. This may make the integration of these barrier films with temperature-sensitive films, such as organic low-k films, impossible. One potential alternative to thermal ALD is to use more reactive species such as radicals to catalyze film deposition at lower substrate temperatures. In this work, TiN films are deposited using Radical Enhanced Atomic Layer Deposition (RE-ALD) using separate, alternating pulses of TiCl₄ and various combinations of hydrogen and/or nitrogen radicals with or without additional pulses of NH₃. By directing independent beams of each of these species at a given surface (in this case, silicon dioxide coated on Quartz Crystal Microbalances), kinetic parameters of interest such as the sticking and reaction probabilities of these species have been measured as a function of surface temperature, and will be used to predict the conformality of films deposited using RE-ALD in features of arbitrary aspect ratio. Ex-situ XPS analysis of the deposited films will be presented, paying particular attention to the low residual chlorine content that can be achieved with sufficient hydrogen radical exposure (~0.3%) at deposition temperatures as low as 100°C. In-vacuo Auger Electron Spectroscopy film composition measurements will be presented from different stages during the deposition process. Various measurements of the film quality will also be presented including the dependence of the films' resistivity and crystallinity on deposition conditions.
10:40 AM		DI-WeM-8 Characteristics of Tungsten Nitride Atomic Layer Deposition H.S. Sim, Y.T. Kim (Korea Institute of Science and Technology); H. Jeon (Hanyang University, Korea) Atomic layer deposition method for binary or ternary metal nitride film such as TiN, W-N, TaN, and TiSiN has been proposed to get a nano-scale diffusion barrier thin film. In this work, we have deposited W-N atomic layer with multiple cycles of introducing WF₆, N₂, NH₃, and N₂ gases in order. A cycle time was varied from 1 - 5 sec for an atomic layer. Deposition rate per cycle, crystal structure, and atomic lattice image for interface of W-N and Si were determined with high resolution transmission electron microscopy (HR-TEM). We have investigated atomic deposition windows at temperatures between 250 - 450 °C. As a result, deposition rate per cycle was nearly the same and the resistivity of as deposited W-N was about 100 ~ 300 µΩ-cm. The diffusion barrier performance of both as-deposited and post-annealed W-N films at temperatures between 500 and 700 °C were investigated in the view points of Cu diffusion mechanisms through surface and grain boundary. As a nano scale diffusion barrier for Cu interconnect, we have investigated correlations between Cu diffusion and texture, composition change and crystalline structures of W-N atomic layer during post-annealing with medium energy ion spectrometry (MEIS) as well as HR-TEM.
11:00 AM		DI-WeM-9 Deposition of Ultra Thin Films by Atomic layer Deposition (ALD) M.A. Leskela (University of Helsinki, Finland) In ALD the precursors are pulsed to the substrate alternately one at the time and between the reactant pulses the reactor is purged with an inert gas. With a proper adjustment of the conditions the process can proceed via saturative steps. The precursors chemisorb on the surface or react with the surface groups and form a tightly bound monolayer. Under such conditions the growth is stable and the thickness increase is constant in each deposition cycle. The layer-by-layer principle facilitates the growth of ultra thin films with accurate thickness and conformality on large areas. These advantages of the ALD method are just those required in microelectronics for the manufacturing of future generation integrated circuits. In microelectronics ALD has been studied for deposition of oxide films for dielectrics, nitride films for diffusion barriers for metallizations, and metal films. Examples of those processes will be given. The key issue in a successful ALD process is the precursor chemistry. The development of new precursors is a challenge for the further progress of ALD. ALD can also be used to modify interfaces of thin film structures and surfaces of powder samples. Examples from the use of ALD in preparation of heterogeneous catalysts will be highlighted.