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.
Historically, in a volume production environment, process induced variation in optical property (n&k) of film stack was
not significant for the most of applications using scatterometry. Many papers presented before addressed the CD variation
in the production by adopting the fixed optical property approach [1-8]. However, with shrinkage of device size, and
introduction of new material and process, n&k variation of some critical layers can not be ignored. In this paper, it presents
impacts on measured optical CD due to n&k variation of one critical film in a 70nm DRAM ArF lithography process at a
patterned area (A-layer). A solution to minimize the impacts using floating n&k in the scatterometry model is discussed,
developed and verified.
KEYWORDS: Transmission electron microscopy, Copper, Etching, Reflectometry, Metrology, Chemical mechanical planarization, Critical dimension metrology, Back end of line, Photomasks, Metals
In this paper, a scatterometry software named ODP(R) by Timbre Technologies was used to develop
BEOL applications to measure the trench and complicated dual damascene structures. Diffraction
spectra were collected with Nanometrics normal incidence polarized reflectometer system in the
wavelength range of 220~800nm. The measured spectra were analyzed and used as target spectra by
ODP-PAS(R) system. Then the associated models were built to generate the simulated spectra which
were used to match the measured spectra. We studied four different structures related to the post
trench-and-via etch and post copper CMP processes, including two two-dimensional (2D) line\space
structures and two three-dimensional (3D) trench-over-via dual damascene structures. Cross-section
TEM (transmitted electron microscopy) measurements were performed to evaluate the performance
of ODP measurements. The results show that the correlation between TEM and ODP of CD
measurements is good, and the correlation between TEM and ODP of the trench depth
measurements is also good. ODP is able to measure the trench and complicated dual damascene
structures and further to be used to optimize the process conditions.
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