TEM, XPS and EDX Characterization of the Si Wafer Backside Sputtered Cr/Au Metallization Films

摘要

A detailed study of sputtered thin film Cr/Au metallization on the back side of Si wafers was performed using high magnification TEM assisted by XPS and EDX analysis. Au films with and without Cr barrier were annealed at 400deg C to simulate the die-attach temperature cycle. It was observed that without the Cr barrier even a 1 min. anneal resulted in de-wetting of Au film and formation of polycrystalline Au islands surrounded by Au-Si eutectic. However, a 340nm Cr barrier preserves a dense and uniform Au film even after 20 min.anneal, while allowing some Si diffusion to the Au surface, as needed for reliable die-attach. The study reveals the details of the grain structure of the films and of their interfaces, as well as suggests the grain boundary Au/Cr/Si inter-diffusion mechanism.