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 , INDIA * address: ABSTRACT Nickel-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 to increase the actuation response of the microactuator utilizing SMA thin films, it is necessary to study the sputtering process parameter. The present work simulates the movement of Ni and Ti atoms on NiTi film During impingement, revealed re-sputtering, which is manipulated by Classical molecular dynamics simulation. CONCLUSIONS The conclusions that can be drawn from the results of classical molecular dynamics simulations are: (1) Reflection and re-sputtering were observed only when the colliding velocity exceeded a critical value. (2) The critical velocity was found to decrease with increase in the density of adatoms in the plasma just above the film surface. (3.) The number of re-sputtered atoms or the atoms ejected from the interior of the film was much higher than the number of reflected atoms. The lower number of reflected atoms was attributed to the inelastic collision. RESULTS It was found that the adatoms, which strike the film, seldom got reflected, irrespective of the striking velocity. The resputtered atoms were mostly those which were within the film surface and possessing high mechanical energy. High vertical speed of the adatoms and gas ions will have two effects on the thin film; (1) attrition due to the mechanical energy of atoms and (2) re- sputtering or ejection of atoms from thin film. Both the phenomena have been explored as possible causes for the formation of amorphous phase during resputtering using classical molecular 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 sputtering and resputtering process with time FIG 1: Preliminary Model for Sputtering REFERENCES [1]T. Mineta, and Y. Haga, Materials and Processes in Shape Memory Alloy, in: MEMS Materials and Processes Handbook, MEMS Reference Shelf: Springer, 1, (2011). [2 ] R.M.S. Martins,et. al., Study of graded Ni-Ti shape memory alloy film growth on Si(100) substrate, Appl. Phys. A 91, 291–299 (2008), DOI: /s INTRODUCTION Current intensive research demonstrated that thin films’ unique fine microstructure is responsible for superior shape memory characteristics in films, compared to that of bulk materials [1]. The shape memory characteristics of NiTi films depends significantly on metallurgical factors such as: alloy composition, annealing or aging temperatures; and sputtering conditions such as: target power, Ar gas pressure, plasma powers, substrate temperatures, bias voltage, etc. These films are attractive materials for microfabrication and integration in micro-miniature systems composed of mechanical elements, actuators, sensors and electronics made on one chip [2]. MODELING THE SPUTTERING PROCESS First 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 film on the substrate. Lower Region containing the substrate 2. Boundary Conditions: Boundary conditions was set as pps i.e (periodic, periodic and shrink). This means periodic in x and y direction so that the adatoms are connectd in the sputter 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 deposited atoms. Due to this the z-direction box size may change accordingly. 3. Assumptions for modeling (Inputs): Substrate Target Distance: This is not required here as we are giving velocity data of adatoms to the simulated model. Substrate Bias Voltage=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 dierent concentrations)