Study of Over-Etching Behaviors on Silicon Nitride Patterned Wafers

To ensure the reliability of passivation etch in wafer fabrication, behaviors of over-etching (OE) on silicon nitride (SiN) patterned wafers were investigated under various chamber conditions in a capacitively coupled plasma (CCP) etching system. C 4 F 8 /O 2 /Ar gas chemistry is used. It was found the etch rate (ER) was dependent not only chamber conditions but also the previous process. Copper (Cu) is inevitably sputtered onto the chamber wall during passivation etch. It was observed the etch rate raised from 796 to 1060 Å/min with the accumulation of copper. Moreover, ER would be quite stable if no prior waferless clean (WLC) process was performed, regardless of the residual copper amount. OES intensity data indicated the surface loss of CF 2 radicals was significant in idle or clean chamber, but was inhibited by fluorocarbon (CF) polymer coatings. Finally, it was confirmed copper could promote the formation of and thus affect the etch rate.