The tungsten filled via plug process is commonly used in sub-half micron CM
OS process technologies. As process technologies shrink beyond the 0.25 mu
m generation, the metal overlap over the via also reduces. This results in
vias not fully covered by the overlying interconnect lines. In the evaluati
on of such structures, we have observed a new failure mechanism resulting i
n completely unfilled vias due to electrochemical corrosion accelerated by
a positive charge on specific structures. This positive charge is collected
by the metal connected to the via during metal plasma etch processing and
results in electro-chemical corrosion during a subsequent solvent strip pro
cess. The charge collection is found to be dependent on the geometry of the
test structure. The corrosion rate is dependent on the amount of charge an
d the solvent pH. Methods to limit this corrosion are discussed. (C) 1999 E
lsevier Science Ltd. All rights reserved.