Chengqing Wang

Determination of the Internal Morphology of Nanostructures Patterned by Directed Self Assembly

The directed self-assembly (DSA) of block copolymers (BCP) is an emerging resolution enhancement tool that can multiply or subdivide the pitch of a lithographically defined chemical or topological pattern and is a resolution enhancement candidate to augment conventional lithography for patterning sub-20 nm features. Continuing the development of this technology will require an improved understanding of the polymer physics involved as well as experimental confirmation of the simulations used to guide the design process. Both of these endeavors would be greatly facilitated by a metrology, which is capable of probing the internal morphology of a DSA film. We have developed a new measurement technique, resonant critical-dimension small-angle X-ray scattering (res-CDSAXS), to evaluate the 3D buried features inside the film. This is an X-ray scattering measurement where the sample angle is varied to probe the 3D structure of the film, while resonant soft X-rays are used to enhance the scattering contrast. By measuring the same sample with both res-CDSAXS and traditional CDSAXS (with hard X-rays), we are able to demonstrate the dramatic improvement in scattering obtained through the use of resonant soft X-rays. Analysis of the reciprocal space map constructed from the res-CDSAXS measurements allowed us to reconstruct the complex buried features in DSA BCP films. We studied a series of DSA BCP films with varying template widths, and the internal morphologies for these samples were compared to the results of single chain in mean-field simulations. The measurements revealed a range of morphologies that occur with changing template width, including results that suggest the presence of mixed morphologies composed of both whole and necking lamella. The development of res-CDSAXS will enable a better understanding of the fundamental physics behind the formation of buried features in DSA BCP films.

Three-dimensional x-ray metrology for block copolymer lithography line-space patterns

Abstract. We report on the development of a new measurement method, resonant critical-dimension small-angle x-ray scattering (res-CDSAXS), for the characterization of the buried structure of block copolymers (BCP) used in directed self assembly (DSA). We use resonant scattering at the carbon edge to enhance the contrast between the two polymer blocks and allow the determination of the three-dimensional shape of the native lamella in a line–space pattern by CDSAXS. We demonstrate the method by comparing the results from conventional CDSAXS to res-CDSAXS on a 1:1 DSA BCP sample with a nominal 50-nm pitch. The res-CDSAXS method provides substantially improved uncertainty in the fit of the line shape and allows the determination of the buried structure.

Intercomparison between optical and x-ray scatterometry measurements of FinFET structures

In this paper, we present a comparison of profile measurements of vertical field effect transistor (FinFET) fin arrays by optical critical dimension (OCD) metrology and critical dimension small angle X-ray scattering (CD-SAXS) metrology. Spectroscopic Muller matrix elements measurements were performed at various azimuthal angles for OCD, and X-ray diffraction intensities were collected for different incident angles in CD-SAXS measurements. A common trapezoidal model was used to compute the OCD and CD-SAXS signatures, using rigorous coupled wave (RCW) analysis and a 2D Fourier transform, respectively. Profile parameters, some material parameters, and instruments parameters were adjusted by a non-linear fitting procedure of the data. Results from both measurement techniques were compared and found in reasonable agreement with one another, although some of the parameters have differences that exceed the estimated uncertainties.

Critical dimension small angle X-ray scattering measurements of FinFET and 3D memory structures

We have demonstrated that transmission critical dimension small angle X-ray scattering (CD-SAXS) provides high accuracy and precision CD measurements on advanced 3D microelectronic architectures. The competitive advantage of CD-SAXS over current 3D metrology methods such as optical scatterometry is that CD-SAXS is able to decouple and fit cross-section parameters without any significant parameter cross-correlations. As the industry aggressively scales beyond the 22 nm node, CD-SAXS can be used to quantitatively measure nanoscale deviations in the average crosssections of FinFETs and high-aspect ratio (HAR) memory devices. Fitting the average cross-section of 18:1 isolated HAR contact holes with an effective trapezoid model yielded an average pitch of 796.9 ± 0.4 nm, top diameter of 70.3 ± 0.9 nm, height of 1088 ± 4 nm, and sidewall angle below 0.1°. Simulations of dense 40:1 HAR contact holes and FinFET fin-gate crossbar structures have been analyzed using CD-SAXS to inquire the theoretical precision of the technique to measure important process parameters such as fin CD, height, and sidewall angle; BOX etch recess, thickness of hafnium oxide and titanium nitride layers; gate CD, height, and sidewall angle; and hafnium oxide and titanium nitride etch recess. The simulations of HAR and FinFET structures mimic the characteristics of experimental data collected at a synchrotron x-ray source. Using the CD-SAXS simulator, we estimate the measurement capabilities for smaller similar structures expected at future nodes to predict the applicability of this technique to fulfill important CD metrology needs.

CD-SAXS measurements using laboratory-based and synchrotron-based instruments

Critical dimension small angle X-ray scattering (CD-SAXS) is a metrology platform capable of measuring the average cross section and line width roughness (LWR) with a sub-nm precision in test patterns with line widths ranging from 10 to 500 nm. The X-ray diffraction intensities from a collimated X-ray beam of sub-Angstrom wavelength were collected and analyzed to determine line width, pitch, sidewall angle, LWR, and others structural parameters. The capabilities of lab-scale and synchrotron-based CD-SAXS tools for LWR characterization were tested by measuring a set of identical patterns with designed roughness amplitude and frequency. These test patterns were fabricated using EUV lithography with sub-50 nm linewidths. To compensate for the limited photon flux from the lab-based X-ray source, the incident beam of the lab system was collimated to a less extent than the synchrotron beam-based tool. Consequently, additional desmearing is needed to extract information from data obtained from lab-based equipment. We report the weighted nonlinear least-squares algorithm developed for this purpose, in addiiton to a comparison between the results obtained from our lab system and the synchrotron beam-based tool.

A Laboratory Scale Critical-Dimension Small-Angle X-ray Scattering Instrument

New methods for critical dimension (CD) measurements may be needed to enable the detailed characterization of nanoscale structures produced in the semiconductor industry and for nanotechnology applications. In earlier work, small angle x‐ray scattering (SAXS) measurements with synchrotron sources have shown promise in meeting several grand challenges for CD metrology. However, it is not practical to depend upon x‐ray synchrotron sources, which are large national facilities with limitations in the number of available instruments. To address this problem, a laboratory scale SAXS instrument for critical dimension measurements on periodic nanoscale patterns has been designed, installed, and tested. The system possesses two configurations, SAXS and ultra‐small‐angle x‐ray scattering (USAXS), with a radiation target of either copper or molybdenum. With these configurations, the instrument is capable of accessing scattering angles that probe length scales ranging from ca. 0.5 nm to 2 μm. In this work, we compare CD‐SAXS measurements taken from a synchrotron‐based SAXS at the Advanced Photon Source of the Argonne National Laboratory with those from the National Institute of Standards and Technology laboratory‐scale SAXS instrument. The results from standard line/space gratings possessing periodic line‐space patterns with CDs of tens to hundreds of nanometers show that the laboratory‐scale system can quantitatively measure parameters, such as the pitch, line width, height, line‐width roughness and sidewall angle. These results show that laboratory‐scale measurements are feasible and can be used for research and development purposes or to assist calibration of optical scatterometry and CD‐scanning electron microscopy instruments. The primary limitation of the measurement is that the data collection rate is unacceptably slow for production metrology because of the significantly lower x‐ray beam fluxes currently available.New methods for critical dimension (CD) measurements may be needed to enable the detailed characterization of nanoscale structures produced in the semiconductor industry and for nanotechnology applications. In earlier work, small angle x‐ray scattering (SAXS) measurements with synchrotron sources have shown promise in meeting several grand challenges for CD metrology. However, it is not practical to depend upon x‐ray synchrotron sources, which are large national facilities with limitations in the number of available instruments. To address this problem, a laboratory scale SAXS instrument for critical dimension measurements on periodic nanoscale patterns has been designed, installed, and tested. The system possesses two configurations, SAXS and ultra‐small‐angle x‐ray scattering (USAXS), with a radiation target of either copper or molybdenum. With these configurations, the instrument is capable of accessing scattering angles that probe length scales ranging from ca. 0.5 nm to 2 μm. In this work, we compare...

Line Edge Roughness of Directed Self‐Assembly PS‐PMMA Block Copolymers—A Candidate for Future Lithography

Directed self‐assembly (DSA) of block copolymers (BCPs) is a technology that combines lithographically defined physical or chemical features to guide self‐assembled polymers to create features smaller than those possible with conventional lithography. To the semiconductor industry DSA represents a possible lithography solution below 22–16 nm node where the targeted line edge roughness (LER) is 1.4 nm or less. This LER requirement presents a challenge for DSA to become a viable lithography solution. Hitherto the LER of DSA block copolymers was measured mostly using SEM and AFM, hence the results represent only the top surface characteristics. In addition, the observed LER using SEM or AFM is often greater than 1.3 nm. The purpose of this work is to demonstrate the use of transmission X‐ray scattering to quantify LER as well as the critical dimensions in BCP patterns created with the DSA technique. Experimental results from poly(styrene‐b‐methyl methacrylate) copolymer line gratings with 23 nm half pitch will be presented and the theoretical developments needed to extract LER from X‐ray scattering will also be discussed.

Linewidth roughness and cross-sectional measurements of sub-50 nm structures with CD-SAXS and CD-SEM

Critical dimension small angle X-ray scattering (CD-SAXS) is a measurement platform that is capable of measuring the average cross section and sidewall roughness in patterns ranging from (10 to 500) nm in pitch with sub-nm precision. These capabilities are obtained by measuring and modeling the scattering intensities of a collimated X-ray beam with sub-nanometer wavelength from a periodic pattern, such as those found in optical scatterometry targets. In this work, we evaluated the capability a synchrotron-based CD-SAXS measurements to characterize linewidth roughness (LWR) by measuring periodic line/space patterns fabricated with extreme ultraviolet (EUV) lithography with sub-50 nm linewidths and designed with programmed roughness amplitude and frequency. For these patterns, CD-SAXS can provide high precision data on cross-section dimensions, including sidewall angle, line height, line width, and pitch, as well as the LWR amplitude. We also discuss the status of ongoing efforts to compare quantitatively the CD-SAXS data with topdown critical dimension scanning electron microscopy (CD-SEM) measurements.

Line Edge Roughness and Cross Sectional Characterization of Sub-50 nm Structures Using Critical Dimension Small Angle X-ray Scattering

The need to characterize line edge and line width roughness in patterns with sub‐50 nm critical dimensions challenges existing platforms based on electron microscopy and optical scatterometry. The development of x‐ray based metrology platforms provides a potential route to characterize a variety of parameters related to line edge roughness by analyzing the diffracted intensity from a periodic array of test patterns. In this study, data from a series of photoresist line/space patterns featuring programmed line width roughness are measured by critical dimension small angle x‐ray scattering (CD‐SAXS). For samples with designed periodic roughness, CD‐SAXS provides the wavelength and amplitude of the periodic roughness through satellite diffraction peaks. For real world applications, the rate of decay of intensity, termed an effective “Debye‐Waller” factor in CD‐SAXS, provides an overall measure of the defects of the patterns. CD‐SAXS data are compared to values obtained from critical dimension scanning electron microscopy (CD‐SEM). Correlations between the techniques exist, however significant differences are observed for the current samples. A tapered cross sectional profile provides a likely explanation for the observed differences between CD‐SEM and CD‐SAXS measurements.The need to characterize line edge and line width roughness in patterns with sub‐50 nm critical dimensions challenges existing platforms based on electron microscopy and optical scatterometry. The development of x‐ray based metrology platforms provides a potential route to characterize a variety of parameters related to line edge roughness by analyzing the diffracted intensity from a periodic array of test patterns. In this study, data from a series of photoresist line/space patterns featuring programmed line width roughness are measured by critical dimension small angle x‐ray scattering (CD‐SAXS). For samples with designed periodic roughness, CD‐SAXS provides the wavelength and amplitude of the periodic roughness through satellite diffraction peaks. For real world applications, the rate of decay of intensity, termed an effective “Debye‐Waller” factor in CD‐SAXS, provides an overall measure of the defects of the patterns. CD‐SAXS data are compared to values obtained from critical dimension scanning electr...