|
This paper discusses the controls benefit accomplished on both product wafers and process tools at IBM's 300mm
wafer manufacturing line by using integrated auto-macro defect inspection in all the photolithography tool clusters
for after-develop-inspection (ADI). Inspection is supported on all production wafers (with possibility to sample
wafers if desired). To get to this level of control the overall 'ADI process' in the line had to be first rendered
manufacturable. Therefore, significant effort had to be focused towards decreasing false fails and nuisance holds.
As a result, over the last year inspection software related false fails were reduced 3X, hardware related PC
communication fails were decreased 5X, and fab automation related nuisance wafer holds were reduced 12X. Fail
rate has been sustainable at 6% (± 2%) for over two quarters. At this point only 20% of the fail rate is false and is
mostly attributable to hardware related wafer alignment issues during inspection. By decreasing false fails and hold
rates, sensitivity and effectiveness in the line towards correctly reacting to real fail signals significantly improved.
Product wafers with real fails are now consistently reacted to real-time in the line leading to rework and elimination
of photo sector generated macro defects. Contribution of this integrated metrology system to fab rework rate in
eliminating yield impacting macro defects from product wafers, as well as examples of captured defects that have
identified several process tool problems are also presented. Majority of rework contributors are defects generated
from intermittent photo process tool issues that randomly occur and disappear (versus systematic process tool issues
that typically end up being flagged within two consecutive failed lots). Typically 0.5 to 1% of the ADI inspected
wafers get reworked for macro defectivity translating to a significant number of wafers - thus justifying ADI return-on-
investment. Note that real fails as a result of defectivity propagation from prior photolevels - estimated at 15% of
the fail rate, do not get reworked. Additionally, real fails determined to be non-reworkable as a result of defectivity
from the current photolevel - estimated at 50% of the fail rate, also do not get reworked. Further, by analyzing real
fails for intra/inter wafer signatures systematic process tool issues are being consistently flagged on the line.
Overall, ADI at IBM's 300mm wafer fab has evolved into a real-time wafer level go/no-go control for both product
and process tools.
|
