Determination of optimal parameters for CD-SEM measurement of line-edge roughness (original) (raw)
Related papers
Journal of Applied Physics, 2012
With the constant decrease of semiconductor device dimensions, line width roughness (LWR) becomes one of the most important sources of device variability and thus needs to be controlled below 2 nm for the future technological nodes of the semiconductor roadmap. The LWR control at the nanometer scale requires accurate measurements, which are inevitably impacted by the noise level of the equipment that causes bias from true LWR values. In this article, we compare the capability of two metrology tools, the critical dimension scanning electron microscopy (CD-SEM) and critical dimension atomic force microscopy (CD-AFM) to measure the true line width roughness of silicon and photoresist lines. For this purpose, we propose several methods based on previous works to estimate the noise level of those two equipments and thus extract the true LWR. One of the developed methods for the CD-SEM technique generalizes the power spectral densities (PSD) fitting method proposed by Hiraiwa and Nishida with a more universal autocorrelation function, which includes both correlation length and roughness exponent. However, PSD fitting method could not be used with CD-AFM due to the time consuming character of this technique. Hence, other experimental protocols have been set up for CD-AFM in order to accurately characterize the LWR. Our study shows that the CD-SEM technique combined with our PSD fitting method is much more powerful than CD-AFM to get all roughness information (true LWR, correlation length, and roughness exponent) with a good accuracy and efficiency on hard materials such as silicon. Concerning materials degradable under electron beam exposure such as photoresist, the choice is more disputable, since ultimately they are impacted by the electrons. Fortunately, our PSD fitting method allows working with low number of integration frames, which limits the resist degradation. Besides, we have highlighted some limitations of the CD-AFM technique due to the tip diameter. This technique can underestimate LWR if the roughness presents significant amount of high frequency components, as it is the case for photoresist patterns. So far, there is no universal technique to accurately estimate the LWR on any materials. Nevertheless, the CD-SEM protocol we propose opens a way for a better characterization of the photoresist LWR after lithography and a better understanding of the LWR transfer during the plasma etching steps involved in gate patterning processes. V
Photoresist line-edge roughness analysis using scaling concepts
Journal of Micro/Nanolithography, MEMS, and MOEMS, 2004
We focus on the problem of obtaining and characterizing the edge roughness of photoresist lines by analyzing top-down scanning electron microscope (SEM) images. An off-line image analysis algorithm detecting the line edge, and an edge roughness characterization scheme, based on scaling analysis, are briefly described. As a result, it is suggested that apart from the rms value of the edge (sigma), two more roughness parameters are needed: the roughness exponent ␣ and the correlation length. These characterize the spatial complexity of the edge and determine the dependence of sigma on the length of the measured edge. Completing our previous work on the dependencies of the roughness parameters (sigma,␣,) on various image analysis options, we examine the effect of the type of noise smoothing filter. Then, a comparative study of the roughness parameters of the left and right edges of resist lines is conducted, revealing that the sigma values of the right edges are larger than those of the left edges (due to an imperfect SEM beam alignment), whereas the roughness exponents and the correlation lengths do not show such a trend. Finally, the relation between line width roughness and line edge roughness is thoroughly investigated with interesting conclusions. © 2004 Society of Photo-Optical Instrumentation Engineers.
2D and 3D photoresist line roughness characterization
Microelectronic Engineering, 2013
Lithographic scaling is approaching 16 nm feature dimensions. Besides the manufacturing challenges, metrology is also suffering with feature scaling: Scanning microscopy is struggling to capture the roughness of the new photoresist platforms for ArF and extreme-UV lithography, thinner and more sensitive to electron bombardment. Moreover, standard figure of merit such as feature dimensions and line roughness should be integrated with fractal analysis and frequency evaluation, both needed to understand the root-causes of resist roughness. For this purpose, 3D sidewall information are likely to be required in order to choose the best process settings to reduce the roughness after exposure and during pattern transfer.
About the influence of Line Edge Roughness on measured effective–CD
Optics Express, 2011
Various reports state that Line Edge/Width Roughness (LER/LWR) has a significant impact on the integrated circuits fabricated by means of lithography, hence there is a need to determine the LER in-line so that it never exceeds certain specified limits. In our work we deal with the challenge of measuring LER on 50nm resist gratings using scatterometry. We show by simulation that there is a difference between LER and no-LER scatter signatures which first: depends on the polarization and second: is proportional to the amount of LER. Moreover, we show that the mentioned difference is very specific, that is-a grating with LER acts like a grating without LER but showing another width (CD, Critical Dimension), which we refer-to as effective-CD.
Bias reduction in roughness measurement through SEM noise removal
The importance of Critical Dimension (CD) roughness metrics such as Line and Contact edge roughness (LER, CER) and their associated width metrics (LWR, CWR) have been dealt with widely in the literature and are becoming semiconductor industry standards. With the downscaling of semiconductor fabrication technology, the accuracy of these metrics is of increasing importance. One important challenge is to separate the image noise (present in any SEM image) from the physically present roughness. An approach for the removal of the non-systematic image noise was proposed by J. Villarrubia and B.Bunday [Proc. SPIE 5752, 480 (2005)]. In the presented work this approach is tested and extended to deal with the challenge of noise removal in the presence of various types of systematic phenomena present in the imaging process such as CD variation. The study was carried out by means of simulated LWR and using real measurements.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2003
An off-line image analysis algorithm and software is developed for the calculation of line-edge roughness (LER) of resist lines, and is successfully compared with the on-line LER measurements. The effect of several image-processing parameters affecting the fidelity of the off-line LER measurement is examined. The parameters studied include the scanning electron microscopy magnification, the image pixel size dimension, the Gaussian noise-smoothing filter parameters, and the line-edge determination algorithm. The issues of adequate statistics and appropriate sampling frequency are also investigated. The advantages of off-line LER quantification and recommendations for the on-line measurement are discussed. Having introduced a robust algorithm for edge-detection in Paper I, Paper II [V. Constantoudis etal, J. Vac. Sci. Technol. B 21, 1019 (2003)] of this series introduces the appropriate parameters to fully quantify LER. © 2003 American Vacuum Society.
Effects of different processing conditions on line-edge roughness for 193-nm and 157-nm resists
2004
The control and minimization of resist line edge (or width) roughness (LER or LWR) is increasing in importance. It requires first a complete and reliable characterization scheme of LER, including frequency dependency, and then an investigation and understanding of its origins and methods for improvement. A new characterization method, introduced by Demokritos and based on the offline analysis of top-down SEM pictures, has been evaluated and compared to more conventional inline measurements. This enables us to include additional parameters that quantify the spatial aspects of LER, next to the classical LER 3σ value. The spatial frequency dependence can also be determined from the inline measurements. Both techniques are applied to several test cases: the impact on LER of changing softbake (SB) and post-exposure bake (PEB) temperature, and changing aerial image contrast (AIC). Also, the improvements in an etch optimization experiment are quantified. The majority of the work is concentrating on 193nm resists, but initial experiments with a 157nm resist will be shown. This work has led to a better understanding of some of the contributors to line edge roughness and gives the possibility to quantify process improvements in a better way.
Determination of the line edge roughness specification for 34 nm devices
Digest. International Electron Devices Meeting,, 2002
The impact of gate line edge roughness (LER) on 70 nm MOS devices was measured experimentally and used to validate an enhanced statistical technique for evaluating LER effects on devices. The technique was used to determine that LER in 34 nm devices will need to be limited to 3 nm. Effect of LER spectrum on wide and narrow devices is discussed, as well as an approach for correcting experimental current measurements for LER.
Unbiased roughness measurements: Subtracting out SEM effects
Microelectronic Engineering, 2018
Most scanning electron microscope (SEM) measurements of pattern roughness today produce biased results, combining the true feature roughness with noise from the SEM. Further, the bias caused by SEM noise changes with measurement conditions and with the features being measured. The goal of unbiased roughness measurement is to both provide a better estimate of the true feature roughness and to provide measurements that are independent of measurement conditions. Using an inverse linescan model for edge detection, the noise in SEM edge and width measurements can be measured and removed statistically from roughness measurements. This approach was tested using different pixel sizes, magnifications, and frames of averaging on several different post-lithography and post-etch patterns. Over a useful range of metrology conditions, the unbiased roughness measurements were effectively independent of these metrology parameters.
Line edge roughness detection using deep UV light scatterometry
Microelectronic Engineering, 2007
Line edge roughness (LER) is one of the problems that reported to affect the final fab products and most of the time it occurs in the photo lithography process. The industry requirements call for an in-line nondestructive and very fast measuring tool. We report on a possible in-line integrated metrology solution for alarming when LER has grown out-of a specified