598
6 Reverse Engineering of Microcircuits
at their boundaries. The relief from polishing is often minimized by using polishing
cloths with low nap and high values of disk rotation speed. If the polishing-etchingpolishing procedure is used, the best option is to apply the etchant that creates the
least prominent relief.
Another problem is the analysis of samples containing inclusions that can be
torn out during preparation of samples. The use of smaller amounts of polishing
compound is the commonly accepted method of preserving inclusions. The entire
transition area between the matrix and inclusions can be examined with the help of an
optical microscope at high magnification. If the sample is properly prepared, both the
matrix and the inclusions are precisely in focus. Another problem is the penetration
of polishing abrasive into the examined material. This is especially important when
examining cracked or porous samples. In this case, the use of another method of
sample preparation, such as electro-polishing, is justified. Thus, greater attention is
required to obtain a flatter surface. As for special methods of preparation of thin
sections, the literature describes an entire range of such method.
6.6.1.3 Dusting of Non-conductive Samples
Almost all non-conductive samples examined in a scanning electronic microscope
need to be covered with a thin film of conductive material. Such coating is required
to eliminate or reduce the electrical charge that is quickly accumulated on a nonconductive sample when it is scanned using a high-energy electron beam. In the study
of non-conductive samples without a conductive coating in the SEM with the optimal
parameters of the device, the charging phenomenon invariably appears, which leads
to image distortion, as well as to its thermal and radiation damage, which can lead
to a significant loss of material from the sample. In some cases, a sufficiently high
charge can accumulate on the sample, and the sample can act as an electron mirror,
slowing down the electron beam. Thus, the most important reason for applying a
conductive coating is increasing electrical conductivity of the samples. Materials
with high resistance will be quickly charged under the incident beam and can charge
up to the potential sufficient for breakage of the dielectric. This causes a change
in the surface potential that forms complex artifacts on the image, which are often
referred to as charging. These artifacts appear in the form of deviations of low-energy
secondary electrons and periodic bursts of secondary electron emission, which leads
to a deviation of the primary electron beam and reduces resolution of the SEM. Thus,
conductivity of the thin film shall be sufficient to ensure current discharge from the
sample to the ground without charging the surface to a significant potential.
6.6.1.4 Examination of Non-decorated IC Cleavages
The simplest and most “humane” way of studying vertical topology of an IC is
examining the sample without any additional chemical effect. This applies both to
the surface of the studied material and to its cleavage. As an example of IC study, let
6 Reverse Engineering of Microcircuits
at their boundaries. The relief from polishing is often minimized by using polishing
cloths with low nap and high values of disk rotation speed. If the polishing-etchingpolishing procedure is used, the best option is to apply the etchant that creates the
least prominent relief.
Another problem is the analysis of samples containing inclusions that can be
torn out during preparation of samples. The use of smaller amounts of polishing
compound is the commonly accepted method of preserving inclusions. The entire
transition area between the matrix and inclusions can be examined with the help of an
optical microscope at high magnification. If the sample is properly prepared, both the
matrix and the inclusions are precisely in focus. Another problem is the penetration
of polishing abrasive into the examined material. This is especially important when
examining cracked or porous samples. In this case, the use of another method of
sample preparation, such as electro-polishing, is justified. Thus, greater attention is
required to obtain a flatter surface. As for special methods of preparation of thin
sections, the literature describes an entire range of such method.
6.6.1.3 Dusting of Non-conductive Samples
Almost all non-conductive samples examined in a scanning electronic microscope
need to be covered with a thin film of conductive material. Such coating is required
to eliminate or reduce the electrical charge that is quickly accumulated on a nonconductive sample when it is scanned using a high-energy electron beam. In the study
of non-conductive samples without a conductive coating in the SEM with the optimal
parameters of the device, the charging phenomenon invariably appears, which leads
to image distortion, as well as to its thermal and radiation damage, which can lead
to a significant loss of material from the sample. In some cases, a sufficiently high
charge can accumulate on the sample, and the sample can act as an electron mirror,
slowing down the electron beam. Thus, the most important reason for applying a
conductive coating is increasing electrical conductivity of the samples. Materials
with high resistance will be quickly charged under the incident beam and can charge
up to the potential sufficient for breakage of the dielectric. This causes a change
in the surface potential that forms complex artifacts on the image, which are often
referred to as charging. These artifacts appear in the form of deviations of low-energy
secondary electrons and periodic bursts of secondary electron emission, which leads
to a deviation of the primary electron beam and reduces resolution of the SEM. Thus,
conductivity of the thin film shall be sufficient to ensure current discharge from the
sample to the ground without charging the surface to a significant potential.
6.6.1.4 Examination of Non-decorated IC Cleavages
The simplest and most “humane” way of studying vertical topology of an IC is
examining the sample without any additional chemical effect. This applies both to
the surface of the studied material and to its cleavage. As an example of IC study, let