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edfas.org ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 24 NO . 3 26 For this analysis, a platinum-iridium coated silicon probe witha constant forceof 0.2N/manda resonance frequency of 13 kHz was used. SSRM is also an AFM contact mode, where the analy- sis is based on the measurement of the local resistance between the tip and a back contact of the sample. A DC voltage (V DC ) is applied between the conductive tip and the sample, and through a logarithmic current amplifier, the local resistance is recorded. For the electrical modes based on AFMmeasurements, a very flat surface with low roughness is necessary to assure a constant tip-contact with the sample surface during the scan. To access the DTI structures, a cross- sectional sample is prepared using a hand-polishing technique. The analysis focuses on the area with the layers, the location of an n-silicon device, for example. For the SCM mode, a thermal oxide with a thickness of a few nm is formed on the surface by a heat treatment under ambient conditions. Measurements are performed using an AFM (the Dimension Iconmodel fromBruker) operated at room temperature. A vibration-free table is used to eliminate any ground vibrations and/or acoustic noise. For SCMmeasurements (Fig. 2), a Pt/Ir coated, highly n-doped silicon probe (SCM-PIC) was employed (spring constant k = 0.1 N/m and radius = 25 nm). SSRM measurements (Fig. 3) were conducted with a highly conductive full diamond tip of Adama with an apex of 10 nm (AD-40-AS). The stiffness of the cantilever was determined by the thermal tune method. The spring constant (k) of the can- tilever of the used probe was 42 N/m. TOPOGRAPHY OF THE CROSS-SECTIONAL SAMPLE Figure 4 shows the 2D and 3D views of the surface topography obtained in contact mode on the cross-sec- tional sample. The metal contacts, Si-epitaxial layer and silicon substrate canbe distinguished. Without any chemi- cal layer revelation, the morphology of the DTIs stands out against the silicon substrate, and the metal contacts show a surface being positioned at about 170 nm below that of the silicon zones. This is the effect of the difference of mechanical hardness of the metallic layer compared to the silicon, polysilicon, and oxide, leading to different abrasion speeds in the polishing step. The holes observed in the poly-Si filling in themiddle of the trenches are prob- ably due to some incomplete filling. The mapping of the deflection error (signal error of the cantilever deflection Fig. 3 SSRM technique based on an AFM, measurements of the local resistance between the conductive AFM tip and the back contact of the sample. Fig. 4 Topography signals, scan size: 15 µm × 15 µm, (a) 2D and (b) 3D-view of the studied surface, and (c) deflection signal. (a) (b) (c) (a) (b)