Line width roughness and cross sectional characterization of sub-50 nm structures using CD-SAXS and CD-SEM
Chengqing Wang 1, Ronald L. Jones 1, Kwang-Woo Choi 2 , Derek Ho1, Eric K. Lin1, Wen-li Wu 1 , James S. Clarke 3, John S. Villarrubia 4, Benjamin Bunday 5
Polymers Division, MSEL
Bldg 224, Rm B304, MS 8541
Mentors: Eric K. Lin, Wen-li Wu
Sigma Xi member: Yes
1 Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD
2 Intel Corporation, Santa Clara, CA
3 Intel Corporation, Hillsboro, OR
4 Precision Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD
5 International SEMATECH Manufacturing Initiative (ISMI), Austin, TX
Critical dimension small angle x-ray scattering (CD-SAXS) is a new metrology platform which is capable of measuring the average cross section and sidewall roughness in patterns ranging from (10 to 500) nm in pitch with a sub-nm precision. These capabilities are obtained by measuring and modeling the scattering intensities of a collimated X-ray beam with sub-Angstrom wavelength from a periodic pattern, such as those found in optical scatterometry targets.
In this work, we evaluate the capability of both a laboratory scale and synchrotron based CD-SAXS measurements for line-width roughness (LWR) characterization from measurement of periodic line-space patterns fabricated with EUV lithography with sub-50 nm line widths and designed with programmed roughness amplitude and frequency (Fig. 1). For these patterns, CD-SAXS is capable to provide high precision data on cross section dimension, including sidewall angle, line height, line width and pitch, as well as the amplitude of LWR. A representative CD-SAXS result is given in Fig. 2 where two orders of off-equatorial scattering peaks are clearly visible. These off-equatorial peaks are the direct consequence of the programmed LWR of the sample. From the amplitude ratio of these peaks with respect to the equatorial peaks, one can unambiguously determine the amplitude of LWR. For this data, the best fit parameters are line width = 51.8 +/-0.5nm, LWR amplitude = 4.4 +/-0.2 nm and pitch = 149.7 +/- 0.5 nm. We will also discuss the status of ongoing efforts to compare quantitatively the CD-SAXS data with top-down scanning electron microscopy (CD-SEM) measurements.
Key words: line width roughness, line edge roughness, small angle x-ray scattering
1. Characterization of correlated line edge roughness of nanoscale line gratings using small angle x-ray scattering, C.Q. Wang, R.L. Jones, E.K. Lin, W.L. Wu, B.J. Rice, K.W. Choi, G. Thompson, S.J. Weigand, and D.T. Keane, J. Appl. Phys. 102, 024901 (2007).
Fig. 1 Top down SEM images of a wafer with (a) programmed LWR pattern with fixed roughness amplitude and frequency (b) no programmed roughness. The scale bar reprensents 0.2 µm for (a) and 0.5 µm for (b).
Fig. 2. CD-SAXS results from a sample with programed LWR.