Thorough characterization of a EUV mask Page: 2 of 11
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In this paper, we have studied one EUV mask in great detail, a so-called NOVACD mask which was developed for
ASML Alpha Demo Tool characterization and for OPC modeling of 22-nm and beyond node logic devices. We show
data from the NOVACD mask obtained with a scanning electron microscope (SEM), an atomic force microscope
(AFM), and an actinic inspection tool (AIT) and will discuss the following topics:
LER analysis: We compare the LER of a 200-nm line/space feature on the NOVACD mask to the LER of the 4x
reduction printed line/space image using an SEM.
Surface analysis: We show AFM images of mirror and absorber areas on the mask for comparison with AIT images.
From the AIT images, we have calculated the reflectance ratio of an absorbing area and a reflecting area of the
NOVACD mask.
32nm technology node SRAM analysis: We show mask SEM images, AIT images, data from a TEMPEST simulation,
and resist images printed with the ADT for comparison with each other.
2. LER ANALYSIS BY MASK SEM, MASK AFM AND RESIST SEM IMAGE
2.1 200nm line and space evaluation patterns
The LER analysis of the NOVACD mask was carried out at the center of a 400pm square area which was filled with
200nm lines or spaces at various densities (1, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 99%). For example, the 1% pattern
density includes a 200nm space and a 19800nm (200x 99) line; 20% pattern density includes a 200nm space and a
800nm (200x 4) line; 50% pattern density includes a 200nm space and a 200 nm line; and 99% pattern density includes a
200nm line and a 19800nm space.
2.2 Mask SEM evaluation and mask AFM evaluation
The mask AFM measurement was carried out using the following steps: (1) the 200nm line/space pattern was scanned
256 times at the scan pitch values shown in Table 1 (see Figure 2(a)); (2) the edge positions for each scan were
determined (see Figure 2(b) and (c)); and (3) the 3-sigma and Power Spectral Density (PSD) for each scan pitch were
calculated.
Scan pitch (nm) 2.0 3.9 9.8 19.5 48.8
Total length (pm) 0.5 1.0 2.5 5.0 12.5Table 1. AFM measurement conditions.
1
2
3
256
(times)(a)
1
2
3
256
(times)1
2
3
256
(times)X X'
(b)
X X'
J X
...(c)
Figure 2. Procedure for mask AFM measurement. (a) Schematic of top-down view of line (white) and space (gray). Dashed lines
shows direction of AFM scanning. (b) Schematic of AFM measurement data; x and x' are the edges of lines. (c) Line edge profile
from the 256 measurements of the locations of x and x'..- ---- - - -
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Mizuno, H.; McIntyre, G.; Koay, C.-W.; Burkhardt, M.; He, L.; Hartley, J. et al. Thorough characterization of a EUV mask, article, June 25, 2009; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc929242/m1/2/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.