This technology is divided into three parts: making the sample into a need
le shape with a focused ion beam, collecting atomic-level projection imag
es of the sample at various angles with a spherical aberration-corrected el
ectron microscope, and iteratively optimizing the three-dimensional tomo
graphic reconstruction with Fourier transform. In this way, the three-dime
nsional atomic structure can be obtained in a FinFET sample with a resolut
ion of 1.8 angstroms.
First, the target is to prepare the test piece into a needle-shaped sample w
ith a diameter of less than 50 nanometers. When preparing, we first positi

on the sample and use high-voltage ion beam current to roughly cut it int
o a needle shape with a diameter of about 5 microns. Then, the ion beam
current is reduced to 300 pA, and the cutting is carried out using a ring m
ask. Finally, the voltage of the ion beam is reduced to 5 kV, and the current
is reduced to below 100 pA so that the damage caused by the ion beam is
minimized, reaching a needle with a diameter of 50 nanometers.
Then, use a scanning transmission electron microscope (STEM) with a sph
erical aberration corrector and an annular dark field detector (ADF) to coll
ect atomic projections of the needle-shaped sample at all angles. STEM-A
DF images are dark field images, also known as Z-contrast images, and do
not have the problem of contrast reversal caused by changing the focus. T
herefore, the SiGe thin film, high dielectric constant thin film, ferroelectric
layer, and metal gate are promising for observation.
Finally, 3D images were obtained using optimized tomographic reconstru
ction techniques. Since the experimental data are on the polar grid points,
and the reconstruction is on the Cartesian grid points, using all the experi
mental data to perform global interpolation in the Fourier space and then
performing inverse Fourier transform will obtain the 3D reconstruction wi
th a better resolution.