Yield Management
exposure time, humidity level and chemical high throughput.
concentration. Through these tests, engineers The Puma 9150
determined that sidewall void formation was, in was able to detect
fact, related to exposure to AMCs and that the sidewall void defects
severity of the sidewall voids increased with the at a throughput of
amount of time the wafers were exposed to the ~15wph providing
AMCs. Transferring these results to the fab, it appropriate
was determined that sidewall void formation was throughput levels.
directly related to lot queue times. (fig 3) Using detailed
Utilising the darkfield imaging inspector decision trees and the
Hynix was able to optimize process flow and darkfield imaging
timing. This helped to minimize exposure of post inspector as an
Issue III 2009
metal etch lots to the production environment, excursion monitor at metal 1 and metal 2 etch, Figure 4. Example of a
square4
significantly reducing the number of reliability Hynix was able to successfully track excursions production trend chart
.com
issues related to sidewall void defects. and produce data that confirmed the reduction for metal 1 etch
Additional measures were taken to prevent in sidewall void defect formation (fig 4) . generated using the
the formation of sidewall voids. When lots have This metal etch excursion monitoring inspection results from
to wait longer than the optimal time due to a strategy also produced results that alerted the Puma 9150
down post etch processing tool, wafers are engineers to changing production conditions so
stored in inert environment glove boxes and a that early corrective action could be taken to
post etch oxide layer has been added. prevent reliability issues and maintain high
oasiasemiconductor
device quality.
.eur
Void Defect Inspection Strategy Through reliability testing and failure
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In addition to optimising process flow and queue analysis, Hynix identified a metal sidewall void
times to prevent the formation of large numbers defect as the root cause of a reliability issue.
15
of sidewall void defects, Hynix implemented an Using a darkfield imaging inspector to track
excursion monitoring step at metal etch. The sidewall void defectivity on post metal etch
purpose of this monitoring step was twofold: to layers, engineers were able to correlate sidewall
validate that the process flow optimization steps void defect levels to corrosion caused by
had, in fact, eliminated the sidewall void environmental factors related to process flow. By
reliability issue; and to flag any metal etch defect optimising queue times and implementing an
issues that could lead to future reliability excursion monitor using the darkfield inspector,
problems. Increased sidewall void defectivity was sidewall void defect levels were significantly
linked to increased queue times so it was reduced, resulting in improved device reliability
important that post metal etch inspections have and quality.
ACKNOWLEDGEMENTS
The authors wish to thank ChangHo Lee and JaeHa Ryu at Hynix M10 for sharing data and tool time for data collection.
REFERENCES
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