ICMCTF2015 Session PL: Plenary Lecture
Time Period MoPL Sessions | Abstract Timeline | Topic PL Sessions | Time Periods | Topics | ICMCTF2015 Schedule
| Start | Invited? | Item |
|---|---|---|
| 8:00 AM | Invited |
PL-1 Connecting Residual Stress and Thin Film Growth Processes: Real-time Experiments and a Kinetic Model
Eric Chason (Brown University, USA) Polycrystalline thin films often develop residual stress during growth. Since it can be large enough to impact performance or cause failure, there is a need to understand and control it. Stress evolution can be measured in real-time during film growth using wafer curvature techniques. A large number of studies have been performed that quantify the dependence of the stress on deposition rate, grain size, temperature and microstructure in numerous materials systems. These show that the residual stress may depend strongly on the processing conditions, e.g., electrodeposited Ni films can be 400 MPa (tensile) if the film is grown rapidly and -500 MPa (compressive) if the film is grown slowly. The stress can also go through a series of states during deposition, even changing sign as the microstructure evolves from individual islands to a continuous film. But why do they develop stress at all, since strained films have higher energy than relaxed ones? To understand the non-equilibrium state of the film, we consider the kinetic processes that occur during thin film growth. We have developed a model that explains the stress evolution in terms of competing mechanisms that operate as the boundary forms between adjacent grains. The stress changes because the balance between these mechanisms changes with different processing conditions or with the evolving microstructure. The model predicts a dependence on the dimensionless parameter D/LR where D is the diffusivity, R is the growth rate and L is the grain size. We compare the calculations from the model with measurements on different films as a function of growth rate, temperature and grain size. More recently, studies of stress in patterned films have been performed in which the microstructure of the film is known precisely, allowing for direct comparison with the model. |