We present a summary of various methods for inverting top and bottom critical dimension (CD) data to extract dose and
focus information. We explain analytical, numerical, and library inversion techniques in detail, and explore their relative
merits for the purposes of online and offline focus monitoring use models. We also detail the modeling requirements
associated with each inversion technique, and -- for cases where the model form is flexible -- present a cross-validation
methodology for optimizing the response model to fit experimental data. We present modeling and inversion results
from seven exemplary photolithography processes, and study the results from each methodology in detail. While each
method has its own set of advantages and disadvantages, we show that the library method represents the optimum choice
to satisfy a variety of use models while minimizing cost.
In this paper, three different types of spectral scatterometry hardware are compared using Timbre Technologies' Optical Digital Profiler (ODP) as a common software platform. The hardware under consideration includes a spectroscopic reflectometer (R), polarizing spectroscopic reflectometer (RP) and a spectroscopic ellipsometer (SE). Four advanced lithographic applications are evaluated-two from Spansion's 110-nm Flash memory technology line, and two from AMD's 90-nm logic process. ODP models are developed and optimized for each application and each type of hardware. Results include static and dynamic repeatability, throughput, correlation to incumbent metrology and correlation to cross-section. For each application, the authors also attempt to determine the level of model complexity supported by each hardware type, with special attention paid to the relative sensitivity of each system to changes in critical dimension (CD) and resist profile. The results generally indicate that the SE is the most sensitive hardware type while the R is the most stable. The RP occupies some form of middle ground on both counts. These generalizations are largely application dependent and clear differentiations do not always exist. Selecting the right spectral scatterometry hardware, therefore, is a function of one’s application complexity and control objectives.
KEYWORDS: Semiconducting wafers, Critical dimension metrology, Metrology, Particles, Time metrology, Control systems, Metals, Scanning electron microscopy, Tin, Process control
As the semiconductor industry continues the transition to 300mm wafer factories, not only does the cost per wafer increase dramatically, but the number of eligible die (assuming equal die size) more than doubles. Given the parallel transition to design rules of 90nm and below, both the cost of production and the potential revenue from a 300mm wafer are vastly higher than that of a current 200mm wafer. For this reason alone, it is essential that wafer jeopardy, or the
number of wafers processed between metrology events, be reduced dramatically from the levels in a typical 200mm wafer line. The most promising method for achieving this is process tool-integrated metrology. Such systems allow rapid (in some cases near instantaneous) feedback on the process. Such a data stream, as input to an Advanced Process Control (APC) system, provides a volume of data and feedback lag time unparalleled by standalone metrology. In this case, critical dimension (CD) metrology is provided by a scatterometer integrated on a 200mm TEL CLEAN TRACK - ACT 8. The data, available on a wafer-by-wafer basis, is uploaded to the factory host where the APC application can update its state estimation before the entire lot has even completed processing.
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