Micro-probe Auger Analysis of Si Migration in Al Metallization for LSI

Abstract

The Si migration in Al metallization during a sintering process in LSI fabrication has been analyzed by means of electron microprobe Auger spectroscopy (EMAS). The spatial and depth resolutions of the equipment are about 0.5 µm and 10 to 20 Å, respectively. The lateral profiling shows the high Si concentration at the contact hole edges. The anomalous pit growth is caused by the diffusion of a large amount of Si in the extending Al interconnections from the contact hole. The Si/Al peak ratio in the equilibrium region at 45°C is about 55% lower than that at 500°C. The Si in-depth profiles reveal the existence of a Si rich layer at the surface on the center of a contact hole, whereas the Si concentration is relatively uniform throughout the Al layer over SiO2. The sintering time should be shorter than 30 min at 450°C and 13 min at 500°C to prevent the Al spearing through a diffused n+ layer of 1.2 µm in depth.