On the mechanism of aluminum via fill by reflow and forcefill as studied by transmission electron microscopy

A comparison has been made between the Al via fill mechanisms in both reflo w and forcefill processes. Cross-sectional transmission electron microscopy has been used to study the Al transport into the vias as a function of tim e. Our analysis shows that reflow and forcefill results can be explained by a stress relaxation model. We propose that the transport of aluminum into the vias as a function of time is described by both diffusion and dislocati on movement. In the case of reflow at high temperature, the vias may be fil led completely, after closure, by high-temperature creep of Al. In the case of forcefill, an additional high stress has been applied which raises the strain levels such to activate the dislocation glide and climb mechanism. T he results from detailed investigations of the microstructure by cross-sect ional transmission electron microscopy support these new insights. (C) 1999 American Institute of Physics. [S0021-8979(99)02401-9].