KEYWORDS: Metrology, Scatterometry, Critical dimension metrology, Semiconducting wafers, Data modeling, Atomic force microscopy, Transmission electron microscopy, Inspection, 3D metrology
Shrinking design rules and reduced process tolerances require tight control of critical dimension (CD) linewidth, feature shape, and profile of the printed geometry. The holistic metrology approach consists of utilizing all available information from different sources such as data from other toolsets, multiple optical channels, multiple targets, etc., to optimize metrology recipe and improve measurement performance. Various in-line CD metrology toolsets such as scatterometry optical CD, CD-SEM, and CD-AFM are typically utilized individually in fabs. Each of these toolsets has its own set of limitations that are intrinsic to specific measurement technique and algorithm. Here we define "hybrid metrology" to be the use of any two or more metrology toolsets in combination to measure the same dataset. We demonstrate the benefits of the hybrid metrology on two test structures: 22-nm-node gate develop inspect and 32-nm-node fin-shaped field effect transistor gate final inspect. We will cover measurement results obtained using typical BKM (nonhybrid, single toolset standard results) as well as those obtained by utilizing the hybrid metrology approach. Measurement performance will be compared using standard metrology metrics; for example, accuracy and precision.
Shrinking design rules and reduced process tolerances require tight control of CD linewidth, feature shape, and profile of
the printed geometry. The Holistic Metrology approach consists of utilizing all available information from different
sources like data from other toolsets, multiple optical channels, multiple targets, etc. to optimize metrology recipe and
improve measurement performance. Various in-line critical dimension (CD) metrology toolsets like Scatterometry OCD
(Optical CD), CD-SEM (CD Scanning Electron Microscope) and CD-AFM (CD Atomic Force Microscope) are typically
utilized individually in fabs. Each of these toolsets has its own set of limitations that are intrinsic to specific
measurement technique and algorithm. Here we define "Hybrid Metrology" to be the use of any two or more metrology
toolsets in combination to measure the same dataset. We demonstrate the benefits of the Hybrid Metrology on two test
structures: 22nm node Gate Develop Inspect (DI) & 32nm node FinFET Gate Final Inspect (FI). We will cover
measurement results obtained using typical BKM as well as those obtained by utilizing the Hybrid Metrology approach.
Measurement performance will be compared using standard metrology metrics for example accuracy and precision.
Optical properties (n and k) of the material films under measurement are commonly assumed invariant and fixed in scatterometry modeling. This assumption keeps the modeling simple by limiting the number of floating parameters in the model. Such scatterometry measurement has the potential to measure with high precision some of the profile parameters (critical dimension, sidewall angle). The question is: if the optical properties modeled as "fixed" are actually changing, would this modeling assumption impact the accuracy of reported geometrical parameters? Using the example of a resist profile measurement, we quantify the "bias" effect of unmodeled variation of optical properties on the accuracy of the reported geometry by utilizing a traditional fixed n and k model. With a second model, we float an additional optical parameter and lower the bias of the reported values, at the expense of slightly increased "noise" of the measurement (more floating parameters, less precision). Finally, we extend our multistack approach (previously introduced as an enabler to the product-driven material characterization methodology) to augment the spectral information and increase both precision and accuracy through the simultaneous modeling of multiple targets.
Optical properties (n&k) of the material films under measurement are commonly assumed invariant and fixed in
scatterometry modeling. This assumption keeps the modeling simple by limiting the number of floating parameters in
the model. Such scatterometry measurement has the potential to measure with high precision some of the profile
parameters (CD, Sidewall angle). The question is: if the optical properties modeled as "fixed" are actually changing -
would this modeling assumption impact the accuracy of reported geometrical parameters?
Using the example of a resist profile measurement, we quantify the "bias" effect of un-modeled variation of optical
properties on the accuracy of the reported geometry by utilizing a traditional fixed n&k model. With a second model we
float an additional optical parameter and lower the bias of the reported values - at the expense of slightly increased
"noise" of the measurement (more floating parameters - less precision). Finally, we extend our multi-stack approach
(previously introduced as enabler to the product-driven materials characterization methodology) to augment the spectral
information and increase both precision and accuracy through the simultaneous modeling of multiple targets
This paper discusses a novel methodology of material characterization that directly utilizes the scatterometry targets on
the product wafer to determine the optical properties (n&k) of various constituent materials. Characterization of optical
constants, or dispersions, is one of the first steps of scatterometry metrology implementation. A significant benefit of
this new technique is faster time-to-solution, since neither multiple single-film depositions nor multi-film depositions on
blanket/product wafers are needed, making obsolete a previously required-but very time-consuming-step in the
scatterometry setup. We present the basic elements of this revolutionary method, describe its functionality as currently
implemented, and contrast/compare results obtained by traditional methods of materials characterization with the new
method. The paper covers scatterometry results from key enabling metrology applications, like high-k metal gate (postetch
and post-litho) and Metal 2 level post-etch, to explore the performance of this new material characterization
approach. CDSEM was used to verify the accuracy of scatterometry solutions. Furthermore, Total Measurement
Uncertainty (TMU) analysis assisted in the interpretation of correlation data, and shows that the new technique provides
measurement accuracy results equivalent to, and sometimes better than, traditional extraction techniques.
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