X‐ray photoelectron spectroscopy and surface charge build‐up used to study residue on aluminum contacts on integrated circuits

Abstract

AbstractX‐ray photoemission induced surface charge build‐up with a charge control screen and small spot analysis was used to study processing residue layers deposited on aluminum–silicon metallization as found in high aspect ratio via regions on silicon integrated circuits. Chemically vapor deposited silicon dioxide on Al: 1% Si metallization is commonly found in double level metallization of intergrated circuits. An interdigitated fine‐line test pattern with lines ranging from 500 nm to 2000 nm and variable spacing was used to simulate a typical integrated circuit structure. X‐ray photoemission studies of processed test circuits have led to the following conclusions. Line patterns CHF3 plasma etched into 800 nm SiO2 to expose Al were found to be contaminated with a dominant carbide and a minor oxyfluoride compound. Both Al carbides and Al oxyfluorides are non‐volatile compounds and hence are not readily removed during plasma etching or ashing. This surface layer is deposited by a combination of fluorine in the plasma interacting with the aluminum surface, side wall deposition of carbon from the photoresist, and ion induced mixing of the surface region. Deposits found on similarly processed planar structures were contaminated with Al oxyfluoride and no detectable amount of carbide. Back‐scattered Al(OF)x was observed on the SiO2 surface due to the plasma ashing photoresist removal step.