In multilevel metallization processes, stress induced void and hillock formations cause serious problems with respect to the reliability of metal line, such as pitting corrosion of metal during the pad etching step, mask misalignment due to surface roughness, and open or short failure of metal line. It is generally known that these types of metal-film related problems are due to stress relaxation process in the metal line stress-induced by thermal expansion mismatch between metal and over/underlayer oxide film or compressive stress of overlayered passivation dielectric film.
In this study, the stress behavior of phosphosilicate glass (PSG) film on the Al-l%Si film, deposited by different CVD methods, is investigated. Here we found that the degree of PSG film stress is related with the suppression of hillock growth, void formation, and cracking of passivation layer, depending on the heat treatment and heat treatment. Using stress measurement, surface profilometer, and SEM, the relation between passivated PSG film stress on metal line and the metal line failures is analyzed. In addition, an effective method of hillock suppression is suggested, which is the use of PECVD-PSG film on the metal line before heat treatment of 400°C or that of any type of PSG film before 350°C.