Focused Ion Beam Metrology

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Mat. Res. Soc. Symp. Proc. Vol. 396 0 1996 Materials Research Society

following sections. In addition, the use of FIB to produce cross sections for visualizing resist profiles is also described. FIB CD METROLOGY DEMONSTRATIONS A finely focused ion beam can be raster scanned over a sample to produce high resolution images, similar to the Scanning Electron Microscope (SEM). These ion images can be analyzed to determine the size of features in the same way that optical and electron microscopes are used. Ion images of resist structures were obtained with a JEOL 106D focused ion beam system, using a 15pA, 50nm diameter, 100kV gallium ion beam. The ion beam was scanned over the resist 3 sample with a pixel step rate of 4MHz, delivering a total ion dose of approximately 6x10" ions per cm' per image. The ion images were captured, converted into appropriate image formats (e.g. TIFF & RAS), and stored digitally. The resist was a chemically amplified deep UV resist (IBM Apex resist), and the exposures were done using X-ray lithography. The resist was coated with a thin layer of gold palladium to eliminate beam induced charging effects during FIB and SEM measurements. The stored ion images were analyzed off line using a Princeton Gamma Technology (PGT) linewidth measurement system. The PGT system is also connected to a Hitachi S-4000 low voltage SEM. This allows direct comparison of ion beam measurements with SEM based measurements using the same analysis system and analysis algorithms as indicated below in Fig. 1. SEM

PGT Linewidth Measurement

Image

System

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Mean = 252 nm

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Sigma = 5 nm

Fig 1: Procedure for measuring resist linewidth using the SEM and FIB. Examples of FIB measurements are shown in Fig. 2. Figure 2(a) shows an ion image of a 250nm nominal trench capacitor resist structure. The mean width of the capacitor trenches determined from the ion image is 267nm, with a 3cr deviation of l6nm. Figure 2(b) shows an ion Site A image of a 250nm nominal gate conductor pattern. Two sites are identified (A and B) on the straight spaces in the image, corresponding to The different neighboring resist structures. measured mean line widths were 205nm and 216nm for Site A and B respectively, with 3c (b) (a) The ion measurement deviations of I lnm. Fig 2: FIB Images of Apex Resist

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results shown in Figure (2) are comparable or superior to the precision obtained with the Hitachi SEM on the same samples. A more direct comparison of SEM and FIB measurements is shown in Figure 3. Figure 3(a) shows measurements of 0.25 to 1.0 um spaces in a line space array taken with the ion beam, while Figure 3(b) shows measurements from the Hitachi SEM of the same samples. The figure Gold Absorber Thickness (a) 340nm . 480nm .---- ----------A590nm -- -5 0m 0-0-

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