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edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 21 NO. 4 8 At the 700 eV step, one metal and one fin layer were removed in 15 minutes; the milling rates of the metal and fin layer at 700 eV can be estimated as 10 minutes and 5 minutes, respectively. It is expected that longer milling times at 500 eV are required and, in this case, a 20-minute milling timewas required to remove oneMandone F layer. ITERATIVE ION MILLING The concentratedbeamof argon ionswas rastered and directed toward the leading edge of the specimen, which was the Si substrate (Fig. 3). The change in SED (Figs. 3a and 3c) and STEM (Figs. 3b and d) image contrast after Ar + milling of the Si substrate indicates the reduction in specimen thickness. TEMimages acquiredbetweenmilling steps at decreas- ing energies show the transition fromthe epitaxial source/ drain (S/D) after 700 eV to the metal gate structure of the FinFET after 500 eV milling (Fig. 4a). Disappearance of the W intermetallic layer and SiGe S/D from 700 to 500 eV (Fig. 4b) indicates controlledmilling, which enables target- ing of specific integrated circuit features. HIGH RESOLUTION IMAGING AND ANALYSIS Figure 5 shows atomic resolution dark field STEM images of the PMOS area (top) and the NMOS area (bottom) of the device after Ga + milling and after Ar + milling. These images show electron-transparent speci- mens of differing specimen quality. Low magnification images after Ga + milling show that the FinFETwas covered withparticles (Figs. 5aand c)while theAr + milled specimen was of significantly better quality (Figs. 5b and d). Higher magnification images at the fin from the PMOS region show that the Si atoms on the fin in Fig. 6a are unclear due to the bright haze over the surface, which Fig. 3 SED and STEM images acquired using the Ar + milling systembefore (a-b) andafter Ar + milling (c-d) showing specimen thickness reduction. Fig. 4 TEMimagesafter700eV(a)and500eV(b)millingshow the ability to precisely control the progression of milling through the fin structure. Figure reproduced from Reference 11. POST-FIB CLEANING OF TEM SPECIMENS (continued from page 6) (continued on page 10)