Manipulation of Stresses in Metallic Thin Films by Alloying
- PDF / 2,191,460 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 108 Downloads / 226 Views
A. S. NANDEDKAR CASA Engineering,15 Dartantra Dr., Hopewell Junction, NY 12533, U. S. A. ABSTRACT
Atomistic simulations were used to study the configurations of defects in copper aluminum alloy (2% copper, 98% aluminum). In the presence of free surface, the copper atoms migrated towards the surface. When the aluminum cell (about 2000 atoms) contained a dislocation, copper atoms segregated near the dislocation core on the compressional side. In presence of a grain boundary, copper atoms moved into the boundary plane. The segregation in these simulations resulted from reduction in localized strain near the structural defects. INTRODUCTION
Alloying elements are often used for enhancing the desired properties of materials, such as hardness, toughness, yield strength, resistivity, etc. Alloying element's atoms and vacacnies are essentially point defects and they interact with other structural defects inthe host material. Agglomeration of vacancies inAl thin films (interconnects) in this fashion can nucleate voids [1]. Earlier studies [1, 2, 3] identified the parameters influencing the void formation mechanism. Itwas concluded that some of these parameters were stress levels, activation energy for migration of vacacnies, grain size and temperature. The activation energy for vacacny migration depended on the stress in aluminum lines [3]. The stresses included both long range (average) stresses and local stresses because of structural defects (grain boundaries, dislocations etc.). Recently, in place of pure aluminum, copper aluminum alloy is being tested for making interconnects. Point defects (alloying elements) are known to segregate near dislocations and grain boundaries [1, 2]. The driving force for the segregation is the
reduction of local stresses near the defects. The change in local stresses may influence the activation energy for migration of vacanclies near defects such as grain boundaries and dislocations. Hence inthis paper, effect of alloying (Cu) on local stress levels in Al cells is evaluated. Depending upon the size of the alloying atom compared to the host atom, it will also introduce local compressive or tensile stresses. In thin films, compressive stresses often result in formation of misfit dislocations [4]. Adding smaller alloying elements in the compressed film may reduce coherent stresses in the film and hence formation of misfit dislocations. In an earlier study, we had demonstrated spontaneous formation of misfit dislocations in Au/Ni heterostructures (4]. In this paper, we will evaluate the effect of using an Au+Ni alloy on a Ni substrate. To investigate effect of tensile stresses in the film, we will simulate a Ni film on an Au substrate. METHOD
Acommercially available software package ADESH (Atomistic DEfect Simulation Handler) was used. About thirty hours of CPU time was required for calculations on a personal computer with 486 DX2, 66 MHz microprocessor. Three dimensional aluminum cells containing about 2000 atoms were simulated. A 900 dislocation was introduced roughly at the center of th
Data Loading...
