Directed self-assembly (DSA) is a potential patterning solution for future generations of integrated circuits. Its main advantages are high pattern resolution (∼10 nm), high throughput, no requirement of high-resolution mask, and compatibility with standard fab-equipment and processes. The application of Mueller matrix (MM) spectroscopic ellipsometry-based scatterometry to optically characterize DSA patterned contact hole structures fabricated with phase-separated polystyrene-b-polymethylmethacrylate (PS-b-PMMA) is described. A regression-based approach is used to calculate the guide critical dimension (CD), DSA CD, height of the PS column, thicknesses of underlying layers, and contact edge roughness of the post PMMA etch DSA contact hole sample. Scanning electron microscopy and imaging analysis is conducted as a comparative metric for scatterometry. In addition, optical model-based simulations are used to investigate MM elements’ sensitivity to various DSA-based contact hole structures, predict sensitivity to dimensional changes, and its limits to characterize DSA-induced defects, such as hole placement inaccuracy, missing vias, and profile inaccuracy of the PMMA cylinder.
KEYWORDS: Line edge roughness, Silicon, Scatterometry, Data modeling, Optical components, Scanning electron microscopy, Picosecond phenomena, Chemical elements, Line width roughness, Optical properties
Measurement and control of line edge roughness (LER) is one of the most challenging issues facing patterning technology. As the critical dimensions (CDs) of patterned structures decrease, an LER of only a few nanometers negatively impacts device performance. Here, Mueller matrix (MM) spectroscopic ellipsometry-based scatterometry is used to characterize LER in periodic line-space structures in 28-nm pitch Si fin samples fabricated by directed self-assembly patterning. The optical response of the MM elements is influenced by structural parameters like pitch, CDs, height, and side-wall angle, as well as the optical properties of the materials. Evaluation and decoupling MM element response to LER from other structural parameters requires sensitivity analysis using scatterometry models that include LER. Here, an approach is developed that can be used to characterize LER in Si fins by comparing the optical responses generated by systematically varying the grating shape and measurement conditions. Finally, the validity of this approach is established by comparing the results obtained from power spectral density analysis of top down scanning electron microscope images and cross-sectional transmission electron microscope image of the 28-nm pitch Si fins.
Patterning based on directed self-assembly (DSA) of block copolymer (BCP) has been demonstrated to be a cost-effective manufacturing technique for advanced sub-20-nm structures. This paper describes the application of Mueller matrix spectroscopic ellipsometry (MMSE) based scatterometry to optically characterize polystyrene-b-polymethylmethacrylate patterns and Si fins fabricated with DSA. A regression-based (inverse-problem) approach is used to calculate the line-width, line-shape, sidewall-angle, and thickness of the DSA structures. In addition, anisotropy and depolarization calculations are used to determine the sensitivity of MMSE to DSA pattern defectivity. As pattern order decreases, the mean squared error value increases, depolarization value increases, and anisotropy value decreases. These specific trends are used in the current work as a method to judge the degree of alignment of the DSA patterns across the wafer.
Measurement and control of line edge roughness (LER) is one of the most challenging issues facing patterning
technology. As the critical dimensions (CD) of patterned structures decrease, LER of only a few nanometers can
negatively impact device performance. Here, Mueller matrix spectroscopic ellipsometry (MMSE) based scatterometry is
used to determine LER in periodic line-space structures in 28 nm pitch Si fin samples fabricated by directed selfassembly
(DSA) patterning. The optical response of the Mueller matrix (MM) elements is influenced by structural
parameters like pitch, CD, height, and side-wall angle (SWA), as well as the optical properties of the materials.
Evaluation and decoupling MM element response to LER from other structural parameters requires sensitivity analysis
using simulations of optical models that include LER. Here, an approach is developed that quantifies Si fin LER by
comparing the optical responses generated by systematically varying the grating shape and measurement conditions.
Finally, the validity of this approach is established by comparing the results obtained from top down scanning electron
microscope (SEM) images and cross-sectional TEM image of the 28 nm pitch Si fins.
We have used synchrotron-based critical dimension small-angle x-ray scattering (CD-SAXS) to monitor the impact of hydrogen annealing on the structural characteristics of silicon FinFET structures fabricated using self-aligned double patterning on both bulk silicon and silicon-on-insulator (SOI) substrates. H2 annealing under different conditions of temperature and gas pressure allowed us to vary the sidewall roughness and observe the response in the two metrology approaches. In the case of the simpler bulk Si FinFET structures, the CD-SAXS measurements of the critical dimensions are in substantive agreement with the top–down critical dimension scanning electron microscopy metrology. Corresponding characterizations on SOI-based FinFET structures showed less agreement, which is attributed to the more complex structural model required for SOI FinFET CD-SAXS modeling. Because sidewall roughness is an important factor in the performance characteristics of Si FinFETs, we have compared the results of roughness measurements using both critical dimension atomic force microscopy (CD-AFM) and CD-SAXS. The measurements yield similar estimates of sidewall roughness, although the CD-AFM values were typically larger than those generated by CD-SAXS. The reasons for these differences will be discussed.
The novel method of sub-nanometer uncertainty for the line width measurement and the line profile measurement using STEM (Scanning Transmission Electron Microscope) images is proposed to calibrate CD-SEM line width measurement and the standardization of line profile measurement as reference metrology. In accordance with the proposed method, we already have established the methodology of profile of Si line and photoresist feature for reference metrology. In this article, we applied the proposed method to the sidewall roughness measurement of photoresist features and line profile measurement of finFET features. Using the proposed method, specimens of photoresist feature and finFET feature are sliced as thin specimens of 100 nm thickness by FIB (Focused Ion Beam) micro sampling system. Then the cross-sectional images of the specimens are obtained by STEM and TEM. The sidewall roughness of photoresist features is estimated by the maximum slope of the image intensity graph at the edge. Then, the sidewall roughness is also measured by CD-AFM (Critical Dimension Atomic Force Microscope); we compared the results by STEM image and CD-AFM. Moreover, the line profile of finFET features is defined using TEM images for reference metrology. We compared the line width of fin measured by the proposed method and CD value by CD-SEM measurement.
Directed self-assembly (DSA) shows considerable promise as a cost-effective manufacturing technique for advanced sub-20 nm patterning. Along with continued progress, the patterning process requires advances in both CD metrology and high-speed characterization of DSA defectivity. This work is a report on the study of Mueller matrix spectroscopic ellipsometry (MMSE) scatterometry measurements of 28 nm pitch DSA line/space patterns consisting of polystyrene-block- polymethylmethacrylate (PS-b-PMMA) block copolymer sample fabricated using a chemical epitaxy process. Generalized ellipsometric data (all 16 Mueller elements) is collected over a spectral range from 245 to 1700 nm for various different pre-pattern pitch/guide strip combinations created by modulating the pre-pattern photoresist CD. Scatterometry is used to evaluate and calculate the CD, line shapes, and thicknesses of the plasma developed PS patterns (PMMA removed). Likewise, spectral comparisons based on anisotropy and depolarization are used to determine the DSA pattern defectivity. CD-SEM metrology and imaging is also conducted as a comparative metric for scatterometry. The sensitivity of MMSE to pre-pattern pitch and pitch multiplication on PS line CD and defectivity is demonstrated. Slight imperfections in the line/space pattern as well as fingerprint like patterns (undirected assembly) can be distinguished from aligned patterns using MMSE scatterometry.
Although fin metrology presents many challenges, the single crystal nature of the fins also provides opportunities to use a combination of measurement methods to determine stress and pitch. While the diffraction of light during a scatterometry measurement is well known, X-ray diffraction from a field (array) of single crystal silicon fins can also provide important information. Since some fins have Si1-xGex alloys at the top of the fin, determination of the presence of stress relaxation is another critical aspect of fin characterization. Theoretical studies predict that the bi-axially stressed crystal structure of pseudomorphic alloy films will be altered by the fin structure. For example, one expects it will be different along the length of the fin vs the width. Reciprocal space map (RSM) characterization can provide a window in the stress state of fins as well as measure pitch walking and other structural information. In this paper, we describe the fundamentals of how RSMs can be used to characterize the pitch of an array of fins as well as the stress state. We describe how this impacts the optical properties used in scatterometry measurement.
The uses of strained channel became prevalent at the 65 nm node and have continued to be a large part of logic device performance improvements in every technology generation. These material and integration innovations will continue to be important in sub-22nm devices, and are already being applied in finFET devices where total available in-channel strains are potentially higher. The measurement of structures containing these materials is complicated by the intrinsic correlation of the measured optical thickness and variation of optical properties with strain, as well as the dramatic reduction in total volume of the device. Optical scatterometry has enabled characterization of the feature shape and dimensions of complex 3D structures, including non-planar transistors and memory structures. Ellipsometric methods have been successfully applied to the measurement of thin films of SiGe and related strained structures. A direction for research is validating that the thin film stress results can be extended into the much more physically complex 3D shape. There are clear challenges in this: the stress in a SiGe fin is constrained to match the underlying Si along one axis, but the sides and top are free, leading to very large strain gradients both along the fin width and height. Practical utilization of optical techniques as a development tool is often limited by the complexity of the scatterometry model and setup, and this added material complexity presents a new challenge. In this study, generalized spectroscopic ellipsometric measurements of strained grating was undertaken, in parallel with reference cross sectional and top down SEM data. The measurements were modeled for both anisotropy calculations, as well as full scatterometry calculations, fitting the strain and structure. The degree to which strain and CD can be quickly quantified in an optical model is discussed. Sum decomposition method has been implemented to extract the effective anisotropic coefficients and a discussion on the effect of anisotropy toward modeling is presented. Finally, errors in the scatterometry measurement are analyzed, and the relative strengths and limitations of these optical measurements compared.
Optics contamination remains one of the challenges in extreme ultraviolet (EUV) lithography. Dependence of
contamination rates on key EUV parameters was investigated. EUV tools have optics at different illumination angles. It
was observed that at shallower angles, the carbon contamination rate and surface roughness was higher on the optics
surface. This is a concern in EUV optics as higher roughness would increase the scattering of the EUV radiation.
Secondary ion time of flight mass spectrometer (TOF-SIMS) data indicated that the carbon contamination film might be
a polymer. Three chemical species were used to investigate the dependence of polymerization and reactivity on the
contamination rate. Acrylic acid was found to have a measurable contamination rate above background compared to
propionic acid and methyl methacrylate. Secondary electron dissociation is one of the mechanisms considered to be a
cause for the growth of the carbon contamination film. Multiple experiments with two substrates having different
secondary electron yields were performed. The substrate with the higher secondary electron yield was found to give a
higher contamination rate.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.