Event Scheduled for Jan 27, 2012
Event: ME Spring 2012 Seminar Series, ‘Understanding stress evolution in thin films,’ Prof. Eric Chason, Brown University
Location: UTEB 150
Time: 02:00 pm
Details of Event:
Thin films go through a range of stress states during deposition, often changing from compressive to tensile and back again. The resulting residual stress and stress gradients can severely limit performance (due to cracking, delamination and other failure mechanisms) which provides significant motivation for understanding and controlling stress evolution. In this talk, we will describe a simple analytical model that we have developed to describe thin film stress evolution in terms of a kinetic competition between different generation and relaxation mechanisms. The balance between them shifts as the microstructure evolves from isolated islands, through coalescence and finally into a steady state uniform film. We will discuss models for both high mobility and low mobility films and show that the steady state stress scales with the dimensionless parameter D/LR where D is the diffusivity, R is the growth rate and L is the grain size. We will compare our model results with real-time measurements of stress using wafer curvature to show that they are consistent. Results of kinetic Monte Carlo simulations will also be described (from LLNL) that show how the film porosity can be used as a surrogate for stress evolution since the same kinetic mechanisms control both porosity and stress.
Eric Chason is a professor in the School of Engineering at Brown University. He received his PhD in physics from Harvard University in 1985 and was a staff member at Sandia National Labs in Albuquerque before joining Brown in 1998. His major research interests are in the evolution of morphology and stress in thin films. This includes the development of a multi-beam optical technique for monitoring stress evolution in situ during processing. In recent years, his work has focused on stress in thin films, whisker formation in Pb-free Sn, growth of large area single crystals and ion-induced nanopatterning.
Sponsored By: Mechanical Engineering
Pamphlet/Flyer: View file here