To fully characterize the lithography process, it is critical to have accurate CD and profile of photo
resist structure at ADI stage. Traditionally, CDSEM can only provide limited profile information, and
is extremely challenged to be integrated for real-time in line wafer level process control because of
throughput issue. Over the past few years, optical digital profilometry (ODP(R)) developed by Timbre
Technologies, Inc., has been adopted for real-time process control in Litho for optical CD and shape
monitoring. In this paper, the integrated ODP(R) reflectometer is applied to study process signatures of
3D complicated ADI and AEI structures of a 70nm DRAM process. The DT structures from the 70nm
node process studied in this paper, are elliptical photo resist via developed over a thin film stack at
ADI, and via etched deeply through the thick (over 5um) dielectric film at AEI. At ADI, the ODP(R)
library is qualified by careful cross check with CDSEM data. CD results from iODP(R) show very good
correlation to that from CDSEM. The iODP® measurement for a FEM wafer shows smoother and
cleaner Bossung curves than the CDSEM does. At AEI, the library is then qualified for top CD
measurement in comparison to CDSEM, and also to results at ADI. With implementing iODP(R)
measurements into both ADI and AEI structures, their signature patterns from ADI to AEI for 70nm
DT process can be matched successfully. Such a signature pattern match indicates the strong
correlation between ADI and AEI processes and can be fully made use of for APC. It is a significant
step toward IM APC control considering ADI and AEI process steps together.
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