Interfacial CuAl2 precipitate nucleation and growth during the deposition of Al-4% Cu-1.5% Si alloys

Publisher Website
Google Scholar
Abstract
A series of experiments was performed to evaluate the effects of varying substrate temperature on the vertical distribution of Cu in S‐Gun■ sputtered films of Al‐4% Cu‐1.5% Si. Films having a thickness of 1 μm were sputtered onto substrates of SiO2 and Ti:W alloy films which were heated to temperatures between 25 and 360 °C. Rutherford backscattering and AES depth profile data indicated that a large fraction of the Cu was present near the substrate interface when deposited at elevated temperatures. Films prepared on substrates at room temperature exhibited little segregation. Placement of a Ti:W alloy barrier between the Al–Cu–Si film and the SiO2 substrate did not affect the Cu distribution. Cross‐sectional transmission electron micrographs of samples prepared at 360 °C revealed the presence of Cu‐rich precipitates approximately 4000 Å in size at the substrate interface. Precipitates formed in the room‐temperature deposited films were approximately 1500 Å in size. These results suggest that, if sufficient thermal energy is available, Cu‐rich precipitates which nucleate at the substrate interface will grow rapidly by depleting adjacent film regions of copper. The deduced driving force behind this phenomena is the desire of the system to reduce its precipitate surface to volume ratio and consequently free energy via an Ostwald ripening process. A surface diffusion mechanism is proposed to explain the interfacial precipitate nucleation and growth for the alloys deposited under cold substrate conditions.