This paper describes the joint development and optimization of an advanced critical dimension (CD) control methodology at IBM’s 300 mm semiconductor facility. The work is initially based on 22 nm critical level gate CD control, but the methodology is designed to support both the lithography equipment (1.35 NA scanners) and processes for 22, 20, 18, and 14 nm node applications. Specifically, this paper describes the CD uniformity of processes with and without enhanced CD control applied. The control methodology is differentiated from prior approaches1 by combining independent process tool compensations into an overall CD dose correction signature to be applied by the exposure tool. In addition, initial investigations of product specific focus characterization and correction are also described.
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
Advanced 193 nm lithographic processes will require defocus control for product wafers in order to meet CD and profile
requirements in the future. Dose control is already required. The interaction of product wafer materials with lithography
requires additional controls beyond tool monitoring. While scatterometry has demonstrated excellent ability to extract
effective defocus and dose information from monitor wafers, the addition of product film stacks introduces several issues
for this technique. The additional complexity of model generation and the sensitivity to under-layer thickness and
optical property variation are among these. A CDSEM technique for lithography focus monitoring overcomes these
issues provided it has sufficient precision and relative accuracy. In this paper, we report on comparative studies of two
CDSEM techniques. One technique uses angled e-beam to better view the sidewall for edge width measurement. The
angle of the beam from normal incidence is considerably larger than previously explored thereby enabling sensitive
measurements on shallower structures. The other technique introduces new target designs particularly suited to CDSEM
measurement that have enhanced sensitivity to focus and dose. Implementation of these techniques requires expanded
sampling during the course of a single measurement in order to suppress roughness. The small target size of these
structures enables applications with targets in product kerf and embedded within the circuit. In summary, these methods
enable the measurement of dose and focus variations on product wafers.
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