Papers

ICMCTF2003 Session TS3-2: Computational Studies in Thin Films Science

Monday, April 28, 2003 1:30 PM in Room San Diego

Monday Afternoon

Start	Invited?	Item
1:30 PM		TS3-2-1 STM Studies of Nucleation Kinetics During Homoepitaxial Growth of TiN(001) by Reactive Magnetron Sputtering M.A. Wall, D.G. Cahill, I. Petrov (University of Illinois); D. Gall (Rensselaer Polytechnic Institute); J.E. Greene (University of Illinois) Polycrystalline TiN thin films are vital in the microelectronics, optical, and hard coatings industries. Coating performance in all these applications is strongly affected by the texture and roughness of the layer, both of which are largely determined in the earliest stages of growth. We study the nucleation kinetics of TiN on TiN(001), grown via reactive magnetron sputtering at temperatures T_s from 510 to 1010°C, to extract the energetics, and use ab-inito calculations to determine the atomic processes which control nucleation. Following growth, we image the surface using in-situ UHV (~10^-10 Torr) scanning tunneling microscopy (STM). We determine as a function of temperature, the characteristic island size necessary to nucleate a second layer cluster on a growing island as well as the average separation between islands on a large terrace and fit the nucleation data using rate equation theory. From these results, we find the activation energy for surface diffusion to be E_s = 1.4 eV and the admolecule formation energy to be E_f = 1.4 eV. In addition, we show that the transition from diffusion-limited nucleation to cluster formation-limited nucleation occurs at T = 865°C. Ab-initio calculations combined with our experimental results suggest that the dominant diffusing adspecies are TiN_x admolecules.
1:50 PM		TS3-2-2 Structural Properties of Amorphous Carbon Films by Molecular Dynamics Simulation S.-H. Lee (Korea Institute of Science and Technology, South Korea); C.-S. Lee (Korea Institute of Science and Technology and Yonsei University, South Korea); S.-C. Lee, K.-H. Lee, K.-R. Lee (Korea Institute of Science and Technology, South Korea) Atomic level analyses are valuable methods in investigating the formation and structural characteristics of amorphous materials. In most of amorphous materials, amorphous carbon is one of the most important materials owing to many advantages in industrial applications. For this reason, structural simulation using molecular dynamics technique to analysis an amorphous carbon has increased in popularity. In the present work, we investigated the formation and characterization of amorphous carbon films grown by molecular dynamics simulation of energetic carbon atoms deposition on diamond (100) surface with the Tersoff's empirical potential. The incident energy of carbon atoms was varied from 1 eV to 300 eV. We investigated the relationship between incident energy and the structural properties such as coordination number, density, pair correlation function and so on. The physical properties of the simulated carbon film were compared with those of the real films deposited by filtered cathodic arc process. The simulated amorphous carbon film has high density, sp³ ratio, and stress at the optimum incident energy from 50 eV to 75 eV, which is similar to the experimental observation. We also found the metastable sites which were placed at 2.1 Å and the amount of carbon atoms at metastable site was increased at the optimum incident energy. This phenomenon could be observed from amorphous carbon formed by melting and rapid quenching simulation of diamond lattice. When the atoms were collided on substrate with high incident energy or the temperature of film was increased suddenly, the thermal spike was occurred locally. The dissipation of carbon atom due to the localized thermal spike leaded to the formation of metastable sites. These results show that the metastable site affected the structural properties of amorphous carbon films.
2:10 PM		TS3-2-3 Experimental and Molecular Dynamics Simulation Studies of Friction between Diamond-Like Carbon (DLC) Films S. Zhang, S.N. Medyanik, Y.-H. Yu, W.K. Liu, Y.-W. Chung (Northwestern University) Molecular dynamics (MD) calculations were performed to simulate deposition of diamond-like carbon films with different sp3 fractions. The interaction energy between two such surfaces was then calculated, from which the adhesion and friction were determined as a function of the degree of surface hydrogenation. These studies show that both adhesive and friction interactions exhibit highly nonlinear behavior and that they can be markedly reduced via surface hydrogenation. In parallel with these simulation studies, we synthesized DLC films with different hydrogen concentrations using magnetron sputtering. These films have hardness in the 25-35 GPa regime and ultralow friction behavior (m ~ 0.05 in humid air and < 0.01 in dry air) similar to that obtained by Erdemir and coworkers using plasma-enhanced chemical vapor deposition and consistent with the above theoretical results. Opportunities to reduce the moisture sensitivity of these DLC films and results of preliminary experiments guided by MD calculations will be presented and discussed.
2:30 PM		TS3-2-4 Simulating Diffusion Through Porous Materials Using Molecular Modeling N. Iwamoto, M. Thomas (Honeywell Electronic Materials) Molecular modeling has been proven to be a useful tool in the design of dielectric materials by enabling correlation studies between the molecular structure and the material property. For instance molecular modeling was recently applied in the understanding of modulus trends while designing low k dielectric materials [1]. Molecular considerations are also extremely important in understanding diffusion through porous thin film layers and analysis. Semiconductor roadmap projections suggest that as the feature sizes continue to shrink the atomistic ramifications of diffusion will become critical [2]. Because of this concern we have initiated molecular simulations of transport through porous materials in order to understand the structural limitations from both the thin film layer and the diffusant perspective. This study has found that molecular simulations can help in the general understanding of diffusion property trends. Properties such as relative diffusion coefficients and activation energies are derived and will be discussed in this presentation. This understanding will become useful in the future as we design better materials for the semiconductor industry. [1] Studying Ultra Low-k Dielectric Coatings: Challenges and Solutions; International SEMATECH Ultra Low K Workshop; N. Iwamoto, B. Bedwell, P. Apen, June 6-7, 2002, Burlingame, CA. [2] Transport Considerations in Porous Low k and Metal Interconnect Systems Approaching Atomistic Dimensions; M. Thomas, D. Smith, S. Wallace, N. Iwamoto; 2002 IEEE Interconnect Technology Conference June 3-5, 2002, Burlingame, CA.
2:50 PM		TS3-2-5 A Study of the Reactive Sputtering Process with 2 Reactive Gases S. Berg, T. Nyberg (Uppsala University, Sweden); W.D. Sproul (Advanced Energy Industries) The hysteresis effect in reactive sputter deposition processes causes some problems for stable process control. These problems may relatively easy be solved for the one target one reactive gas system. However, complications arise for more sophisticated reactive sputtering processes. During reactive co-sputtering from several targets it is generally not possible to create conditions for sputtering from non-poisoned targets and simultaneously obtain compound film formation. Reactive sputter deposition with several (2) reactive gases (oxy-nitrides) is an even more complex process. There will be a strong interaction between the reactive gases since both act on the same target and substrate areas thus competing for the same reaction sites. Both gases will simultaneously contribute to the hysteresis behaviour of the process. Partial pressure control of only one of the reactive gases will not be satisfactory to obtain full process control. The complex nature of the process may in principle generate 3 different operating points for every set of partial pressure of one gas and fixed gas supply level of the second reactive gas. We have found that it is only possible to fully control such a process if two individual single-valued parameters can be simultaneously monitored. For this process, however, the only singe-valued parameters are the partial pressures of the reactive gases. This will be experimentally verified with the commercially available control system IRESS . In addition we will present results from computer modelling of this process that clearly will illustrate the problems related to control of this reactive sputtering process.
3:10 PM		TS3-2-6 Stability Analysis of Reactive Sputtering Process C. Li, J.H. Hsieh (Nanyang Technological University, Singapore) Reactive sputtering is an important and commonly used physical vapor deposition (PVD) process for thin film. The introduction of reactive gas would create a transition from metal to compounds (oxides, nitrides and carbides, etc.) in both target and substrate. This compound formation consumes most reactive gas when the flow rate is below a certain critical value. Beyond that critical value, excessive reactive gas would result a sudden increase of its partial pressure. Furthermore, since the ion-induced secondary electron emission of compounds is higher than that of metal, the formation also triggers a sudden change of cathode voltage followed by the Ohm's law. All these lead to the well-known hysteresis loop in cathode voltage, sputtering rate and fraction of compound formation under different flow rates of reactive gas. Therefore, the stability issue of process control stands out naturally. In this paper, a simple mathematical model based on Berg's original proposal is used to study the stability of steady state solution of the hysteresis loop. Mathematically, the stability is investigated by using perturbation method. In order to facilitate the analysis, several non-dimensional parameters are identified for the criteria of stability. These non-dimensional parameters are also expected to be useful for process control in practices. To further examine the stability criteria, a dynamics simulation is performed for the system.
3:30 PM		TS3-2-7 Electron-Phonon Coupling and Transport Properties of Palladium Thin-films Loaded with Hydrogen N. Luo, G.H. Miley, A.G. Lipson, C. Carlos, T. Woo (University of Illinois) The electronic and phonon structures of palladium hydrides (PdH) are investigated using First Principles methods. Full potential linearized augmented plane wave (FLAPW) and pseudopotential plane wave (PPPW) techniques are used to derive the electronic structures of Pd thin-films at various H compositions (loadings). The two methods give similar band structures for PdH, which are also very close to previous theoretical studies [1-6]. This provides additional confidence as to the validity of the current results. The phonon structures, such as the frequencies and normal modes, are resolved by using the density-functional perturbation theory (DFPT) implemented in the PPPW basis. The pseudopotentials adopted in this calculation are of the norm-conversing type and special attention was taken in the computation to ensure reasonable transferability. The same DFPT technique is then used to give the electron-phonon coupling constants, as well as phonon linewidths, which in turn enable the authors to find out transport properties of PdH, such as resistivity, at different hydrogen loadings and temperatures. The current computations on electron-phonon coupling are also compared with a few previous results [7-8] in PdH and selected hydride systems. [1] A.C. Switendick, Ber. Bunsenges. Phys. Chem. 76 (1972) 535. [2] D.A. Papaconstantopoulos, B.M. Klein, J.S. Faulkner, L.L. Boyer, Phys. Rev. B 18 (1978) 2784. [3] M. Gupta, A.J. Freeman, Phys. Rev. B 17 (1978) 3029. [4] C.T. Chan, S.G. Louie, Phys. Rev. B 27 (1983) 3325. [5] G.H. Miley, N. Luo, C.H. Castano, and A.G. Lipson, Bult. APS, APS Spring Mtg., Indianapolis, IN, Vol. 47, No. 1,Pt. I, (2002) 368. [6] N. Luo, G.H. Miley, A.G. Lipson, AVS, Applied Surface Modeling, Cleveland, OH, August, (2002). (submitted to Journal of Surface Science). [7] D. A. Papaconstantopoulos and B. M. Klein, Phys. Rev. lett. 35 (1975) 110. [8] E. Orgaz, V. Mazel, and M. Gupta, Phys. Rev. B 54 (1996) 16124.
3:50 PM		TS3-2-8 Radiation Induced Processes in Surface Ion Treatment Technologies I.G. Marchenko (Scientific Center of Physical Technologies, Ukraine); I.M. Neklyudov (Kharkov Institute of Physics and Technology, Ukraine) Such technologies applications as ion beam assisted deposition, arc deposition, magnetron deposition, low energy ion implantation, including ion nitriding accompanies with radiation defects production in near surface layers of materials. The role of this radiation interstitials, vacancies and defect-impurities complexes is discussed in present work. Such physicals phenomena as radiation induced desorption, abnormally deep ion penetration, metastable phase formation, mixing interlayer formation and others are considered. In present study there is proposed the numerical model of structure-phase formation in growing film. The model taking into account radiation defects production, the diffusion of point defects and impurities and size distribution of phase precipitates. The role of point defect interaction with surface in structural formation of coatings is discussed.
4:10 PM		TS3-2-9 Local and Non-Local Models for Plane 2D EM Wave Propagation in Superlattices and Ferroelectric Layered Films V.S. Travkin (Hierarchical Technologies) We consider the two different scales electromagnetic wave fields in solid state. One is the atomic scale electron distribution electromagnetic fields in a finite volume of perfect crystalline substance (material). This is applied to both of the two or more neighboring substances in a superlattice. Substantially larger scale is the scale of external incident EM field. The problem is that in spite of the quasistatic relationship between the both manifolds the scale of fields of interest is the larger one. The measured properties and application characteristics in this problem correspond one to another and being formulated in terms of externally applied larger scale incidental EM influence. In view of this scheme the two problem are considered: 1) one is the interaction of the two scale EM fields in a separately taken perfect crystalline material within an infinite and finite volume consideration; 2) another problem is the interaction of the both scales EM fields in the vicinity and across the interface surface between the two substances. We also analyze the different structures of a ferroelectric film and superlattice with ferroelectric layers as one of the substances. Both phases in ferroelectric layer are dielectrics and are polarizable. We derive the scale related polarization governing equations. We show what are the relationships between the atomic scale, crystalline scale 10(-7) - 10(-6) [m], and a film scale 10(-6) - 10(-4) [m] EM field in the Bi₄Ti₃O₁₂ layered structure proposed as a nonvolatile ferroelectric random-access memory material.
4:30 PM		TS3-2-10 Finite Element Modeling of Machining with Sapphire Tools to Evaluate Friction Models A. Adibi-Sedeh, V. Madhavan (Wichita State University) Coupled thermo-mechanical Eulerian FE analysis of machining have been carried out using the ABAQUS/EXPLICIT code to simulate cutting with sapphire tools at cutting speeds up to 5.9m/s. The material properties of the work material used in the experiments, AL 7075-T375, are modeled using the Johnson-Cook material model. Friction along the tool-chip interface is assumed to be Coulomb friction with the coefficient of friction set to the value that gives close agreement with the experimental data. The adequacy of this simple friction model is investigated by comparison of the results obtained from FEA for cutting forces, chip thickness, contact length and temperature distribution along the tool-chip interface with those obtained experimentally using transparent sapphire tools. Insights obtained from this study can be used for development of more accurate friction models required for modeling cutting processes.