7/28/2019 Magnetron Sputtering of Ni-ti Thinfilmsimulation by Using Embedded Atom Model

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MAGNETRON SPUTTERING OF NI-TI THIN FILM SIMULATION BY USING EMBEDDED ATOM MODEL*Ajit Behera, M. Gupta, S. Aich and S. Ghosh

Department of Metallurgical and Materials Engineering, Indian Institute of Technology,Kharagpur 721302, INDIA

*E-mail address: ajit.behera88@gmail.comABSTRACTNickel-Titanium Thinfilm shape memory alloys formed by sputtering have been promising

candidates for the realization of powerful actuators in microelectromechanical systems(MEMS) such as micro valves, micro fluid pumps and micromanipulators. In order toincrease the actuation response of the microactuator utilizing SMA thin films, it isnecessary to study the sputtering process parameter. The present work simulates themovement of Ni and Ti atoms on NiTi film During impingement, revealed re-sputtering,which is manipulated by Classical molecular dynamics simulation.

CONCLUSIONSThe conclusions that can be drawn from the results of classical molecular dyn

simulations are: (1) Reflection and re-sputtering were observed only when the colliding veexceeded a critical value. (2) The critical velocity was found to decrease with increase idensity of adatoms in the plasma just above the film surface. (3.) The number of re-sputtatoms or the atoms ejected from the interior of the film was much higher than the numb

reflected atoms. The lower number of reflected atoms was attributed to the inelastic collisio

RESULTSIt was found that the adatoms, which strike the film, seldom got reflected, irrespective

striking velocity. The resputtered atoms were mostly those which were within the film sand possessing high mechanical energy. High vertical speed of the adatoms and gas ionshave two effects on the thin film; (1) attrition due to the mechanical energy of atoms and sputtering or ejection of atoms from thin film. Both the phenomena have been explopossible causes for the formation of amorphous phase during resputtering using clasmolecular dynamics (MD) simulation.

OBJECTIVE The main aim of the present studies is to Understand the structural changes of NiTi thin

films during sputtering and resputtering.

FIG 2: Snapshots showing the sputteriresputtering process with tim

FIG 1: Preliminary Model for Sputtering

REFERENCES[1]T. Mineta, and Y. Haga, Materials and Processes in Shape Memory Alloy, in: MMaterials and Processes Handbook, MEMS Reference Shelf: Springer, 1, 355-402 (2011).[2 ] R.M.S. Martins,et. al., Study of graded Ni-Ti shape memory alloy film growth on Ssubstrate, Appl. Phys. A 91, 291 299 (2008), DOI: 10.1007/s00339-008-4397-2.

INTRODUCTIONCurrent intensive research demonstrated that thin films unique fine microstructure is

responsible for superior shape memory characteristics in films, compared to that of bulkmaterials [1]. The shape memory characteristics of NiTi films depends significantly onmetallurgical factors such as: alloy composition, annealing or aging temperatures; andsputtering conditions such as: target power, Ar gas pressure, plasma powers, substratetemperatures, bias voltage, etc. These films are attractive materials for microfabricationand integration in micro-miniature systems composed of mechanical elements, actuators,

sensors and electronics made on one chip [2].

MODELING THE SPUTTERING PROCESSFirst of all we are trying to make a preliminary model to simulate the process of deposition

of thin films on a substrate. For this the initial phase space was divided into 3 regions:1.Upper region containing the plasma phase. Middle region containing the deposited filmon the substrate. Lower Region containing the substrate2. Boundary Conditions: Boundary conditions was set as pps i.e (periodic, periodic andshrink). This means periodic in x and y direction so that the adatoms are connectd in thesputter region and they dont spread out. Shrink in z direction because the adatoms coming

towards the substrate may cause reflection of adatoms and resputtering of the depositedatoms. Due to this the z-direction box size may change accordingly.3. Assumptions for modeling (Inputs): Substrate Target Distance: This is not required hereas we are giving velocity data of adatoms to the simulated model. Substrate BiasVoltage=0, Substrate Temp= 300K, Gaseous phase temp= 3000K, Velocity of adatoms:1km/sec, 2.5km/sec, 5km/sec and 10km/sec (modeled at different velocities)Concentration of adatoms in gaseous phase : 20% , 10% , 5% and 1% (modeled at dierentconcentrations)