Dislocation Dynamics Simulations of Dislocation Interactions in Thin Fcc Metal Films
- PDF / 529,168 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 41 Downloads / 229 Views
DISLOCATION DYNAMICS SIMULATIONS OF DISLOCATION INTERACTIONS IN THIN FCC METAL FILMS PRITA PANT*, K.W. SCHWARZ**, S.P. BAKER* *Materials Science & Engineering Department, Cornell University, Ithaca, NY 14853. ** IBM Research, Yorktown Heights, NY, 10598. ABSTRACT Mesoscopic simulations of dislocation interactions in thin, single crystal FCC metal films were carried out. Interactions between threading-misfit and threading-threading dislocation pairs were studied and the strength of the interactions determined. Threading-threading interactions were found to be significantly stronger than threading-misfit interactions. Dislocations with different possible combinations of Burgers vectors were studied under cyclic loading. Only annihilation of dislocations was seen to result in residual dislocation structure after complete unloading. No differences were observed in the nature of threading-misfit interactions in 111 and 001 oriented films.
Stress (MPa)
INTRODUCTION The mechanical properties of metals at small scales have been a topic of increasing interest as sizes of devices have been shrinking. A well known example is that of metallizations in integrated circuits. Common reasons for the failure of metallizations are stress controlled processes like decohesion, cracking, void formation and electromigration. It would be useful then, to be able to estimate stresses and, based on mechanisms of failure, predict the strength and/or lifetime of metallizations under given working conditions. But metal thin films have different dimensional and microstructural constraints than bulk metals and show quite different mechanical properties [1]. 400 A standard experiment for investigating mechanical properties 1 µm thick passivated Cu film 300 involves thermally cycling a thin metal Passivated Cu film film on a substrate. Stresses arise due to Thermoelastic line 200 differential thermal expansion. Fig. 1 shows the stresses measured in a 1µm 100 thick, passivated Cu film during a thermal cycle. Similar behavior has been 0 observed in other studies [2, 3]. Compared to bulk Cu, thin films support -100 higher stresses at both low and high temperatures and show higher strain -200 0 100 200 300 400 hardening rates on cooling. Also, thin Temperature (˚C) films exhibit "negative yielding" i.e. the film yields plastically (deviates from the Fig 1. Stresses measured in a passivated Cu thermoelastic line) in compression, while film during thermal cycling [9]. the stress is still tensile. Nix [1] and Freund [4] have proposed models that explain the high strength of thin films based on an energy argument. According to these models, a threading dislocation moving on its glide plane in a passivated film will deposit misfit segments at both interfaces (Fig. 2). The dislocation will move into the film
P2.2.1
glide plane when the critical or "channeling" stress ( σ ch ) is reached. This stress is determined by the point at which the strain energy relieved by the dislocation film is just equal to the energy needed to create the threading misfits mis
Data Loading...
