New material innovations such as Embedded Silicon Germanium (eSiGe) provide a substantial metrology challenge for
the 45 nm node technology and beyond. We discuss the details of how scatterometry provides in-line metrology solution
to measure key features of the eSiGe structure. Critical features to measure are eSiGe to gate proximity and the un-etched
silicon on insulator (SOI) thickness. The proximity measurement is particularly vital because it has a major
influence on device performance, yet there was no high throughput in-line metrology solution until scatterometry.
Results from multiple scatterometry platforms (three) are presented along with a summary of various metrology
performance metrics like precision and accuracy. We also show how scatterometry measurements have been
instrumental in supporting process development efforts. The comparison of scatterometry measurements to reference
data from multiple metrology techniques is presented in order to evaluate the accuracy performance of various supplier
platforms. Reference metrology techniques used are thin-film measurements from un-patterned targets, transmission
electron microscopy (TEM) and cross-section scanning electron microscopy (XSEM). Tool matching uncertainty
(TMU) analysis and weighted reference measurement system (wRMS) technique have been utilized to assist in the
interpretation of correlation data. Scatterometry results from various wafers that were generated to modulate spacer
width and etch cavity are also presented. The results demonstrate good sensitivity for key measurement features,
especially eSiGe proximity and un-etched SOI thickness, which have very tight process control requirements.
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.
KEYWORDS: Data modeling, Scatterometry, Critical dimension metrology, Lithography, Finite element methods, Reticles, Semiconducting wafers, Metrology, Process control, Systems modeling
In this paper, results and analysis are presented from Advanced Micro Devices' (AMD) efforts at calculating lithography
dose and focus parameters using scatterometry metrology and semi-physical CD models. The system takes advantage of
the accurate and precise top and bottom CD data produced by scatterometry to differentiate dose and focus variation. To
build the lithography process model, scatterometry data is generated for each field of a focus-exposure matrix (FEM)
wafer, and the resulting top and bottom CD data is used to fit the parameters of series expansions relating CD to dose
and focus. When new CD data is generated, the models can be inverted to solve for dose and focus independently. Our
methodology employs a flexible modeling and inversion approach in an attempt to make the technique applicable to any
production film stack and any line spacing regime. The quality of the inversion results are highly correlated to the
degree of focus observability present in the system. Our results will show how a series of litho process with varied film
stacks and line/space ratios respond to this technique, and we will report some best practices for a variety of use cases
ranging from equipment characterization to focus monitoring on product.
This paper discusses the use of scatterometry for scanner focus control in hyper-NA lithography. A variety of techniques
based on phase shift technology have been traditionally used to monitor scanner focus. Recently scatterometry has
offered significant promise as an alternate technique to monitor both focus and dose. In this study, we make careful
comparisons of a Scatterometry-based Focus-Dose Monitoring (SFDM) technique to Phase-grating Focus Monitoring
(PGFM). We discuss the operating principles of these techniques and compare the sensitivity of SFDM to PGFM. In
addition, the variation observed in characterizing intra-field and across-wafer behavior of a hyper-NA immersion
scanner is described when using these different techniques.
Scatterometry techniques are used to characterize the CD uniformity, focus and dose control, as well as the image
contrast of a hyper-NA immersion lithography scanner. Results indicate very good scanner control and stability of these
parameters, as well as good precision and sensitivity of the metrology techniques.
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.
A series of experiments were performed to determine if the ThermaWave INTEGRA CCDi reflectometer combined with Timbre Technologies’ Optical Digital Profiler (ODP) software could meet the requirements for lithography cell integration and process control of critical 0.13-micron Flash memory applications. Shallow Trench Isolation (STI), First Poly Gate, Stacked Gate and Aluminum Interconnect layers were examined as a part of this study. ODP models were developed for each of these applications and their output was compared to Critical Dimension Scanning Electron Microscopy (CDSEM) and cross-section SEM to demonstrate adequate correlation to incumbent metrology techniques. ODP is shown herein to correlate to CDSEM while providing the throughput required to measure every wafer without creating a bottleneck for the lithography cell. Experimental results also suggest that, in many cases, ODP can deliver profile determination beyond the fundamental capability of standard in-line metrology techniques.
One goal of CD metrology is to monitor lithographic process control and how it relates to post-etch results. At present, in-fab process control for this purpose is achieved through top-down CD measurements. To acquire profile information requires destructive cross-section SEM measurements or time-consuming AFM measurements. To find height and profile information about a resist or etched structure directly on a CD-SEM, techniques using the combination of in-column beam tilt and stereographic imaging have been developed, implemented and improved on the Applied Materials NanoSEM-3D. This work is an extension of results previously published, although the tool used is greatly improved and the target feature stacks more thorough. The column of the NanoSEM-3D is designed to be able to electronically tilt the incident beam at small angles as it approaches the sample, through bending the beam within the column. Two images can be captured of the sidewall of the feature target, one at a smaller tilt angle and one at a larger tilt angle. Through matching common features between these two images, a reconstructed profile can be mathematically generated. A feature height and sidewall angle can be calculated, and general shape information such as top-rounding, footing and undercutting can also be displayed. To benchmark the effectiveness of this new technique, an experiment has been conducted to quantify the repeatability and reproducibility of height and sidewall angle measurements of lines of resist-on-poly and the resulting etched-poly lines, and correlate these to measurements of the these same profiles using XSEM to determine the accuracy of the technique. This study will span a reasonable lithographic process window. We hope to demonstrate the necessary precision and accuracy capability to non-destructively replace some cross-section work. In applying these techniques to a common etch bias problem, we also hope to demonstrate a strong correlation which can be used to directly predict post-etch behavior and serve as a model for other etch processes, work with which XSEM cross-sections have typically been used until now. The profile measurement technique is also applied to other CMOS features such as etched STI trench, resist and etched contact holes, and resist and etched damascene trenches and vias, with calculated tool precisions for feature height and sidewall angle.
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