New Hot Topic in Cu CMP: Edge-Over-Erosion (EOE)
and erosion are the two most costly surface anomalies that come about
with copper CMP. Dishing occurs when the copper recedes below or protrudes
above the level of the adjacent dielectric. Erosion is a localized thinning
of the dielectric.
Recently, we have observed the new type of defects associated with the
reduction of feature size and integration of low-k materials through edge-over-erosion(EOE)
phenomenon. EOE is a defect that is where the erosion is higher at the
edge of the recessed region in a feature when compared to the center (figure
1). EOE is increasingly severe when the feature size is small (0.12-0.25µm)
and pattern density is high (>35%).
1:profile scan which shows edge-over-erosion(EOE) phenomenon
of EOE brings forth several experimental challenges. One of the first
challenges is the requirement of a very advanced atomic force profiler.
Secondly, software, which can level and extract the important metrics
such as dishing, erosion, and others, is required as well. Our experience
shows that in order to systematically investigate the EOE, a number of
profilers that scan up to 80 to 100 in number, have to be analyzed per
wafer. Without the aid of some sort of analysis software, the analysis
can be very tedious and time-consuming. Lastly, the design of test patterns
(which is sensitive to EOE after Cu CMP) is required. Our previous experience
shows that EOE is most pronounced for fine array line features.
Since the minimum feature size of our current SKW 6-5(which is developed
for 90nm technology node) is 0.12µm, we have chosen this patterned
wafer as the first test vehicle. With the aids of an advanced atomic force
profiler (XE-300P), advanced
pattern wafer (SKW 6-5 Cu/TEOS),
and in-house developed software ("ChampiAn"),
we have investigated EOE phenomenon in Cu CMP. Enclosed
is a document summarizing our experimental findings. Based upon these
data, we conclude EOE is a function of metal line width, pattern density
and array size. In addition, we also conclude that SKW 6-5 is an excellent
test pattern wafer for the investigation of EOE.