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2.3.5.3 Coaxial Sample Holders
Coaxial holders offer the ability to define the voltage potential on the conductive
sample mounting surface in addition to isolating it from system ground. They are
useful when it is desired to maintain the back side of a substrate at a potential other
than chassis ground. They are recommended for applications such as guarding the
sample to reduce leakage current, bringing a bias voltage to the back side of the
sample or isolating and shielding the sample to reduce noise.
Coaxial holders are constructed as laminations of metal/insulator/metal in the
sample plane. The conductive sample surface has a contact pin that can be driven at a
user defined potential. Wiring for the sample holder requires an FT-BNC or FT-TRIAX
feedthrough option. Moderate thermal gradients between the sample stage and
sample mounting surface should be expected. The maximum operating temperature
is 350 K.
2.3.5.4 Triaxial Sample Holders
Triaxial holders offer the ability to define two different voltage potentials between
the conductive sample mounting surface and system ground. They are recommended
when two of the features supported by the coaxial sample holder are used at the
same time. Examples include guarding to reduce leakage current and shielding to
reduce noise or voltage biasing and guarding at the same time.
Triaxial holders are constructed as laminations of metal/insulator/metal/insulator/
metal. The conductive sample surface and center metal plane both have contact pins
that can be driven at user defined potentials. Wiring for these signals requires an FT-
TRIAX feedthrough option. Moderate to medium thermal gradients between the
sample stage and sample mounting surface should be expected. The maximum
operating temperature is 350 K.
2.3.6 Vision System
Configuration
The probe station’s vision system is critical for distinguishing characteristics of the
sample and properly landing probes. The vision system can be optimized for the type
of sample that is most frequently probed. There are four configurations available for
the probe station, two different microscopes each with two lighting choices. The
choice of an appropriate lighting type is especially important because it strongly
influences the behavior of the vision system.
2.3.6.1 Microscopes
There are two microscopes available for the probe station, the standard Zoom 70 and
the optional Zoom 160. The Zoom 70 has a ratio of magnification change (zoom) of
7:1 and the Zoom 160 has a ratio of magnification change (zoom) of 16:1. The
maximum magnification of the vision system is different than the magnification
ratio. Vision system magnification is dependent on the microscope magnification and
other factors such as the camera, monitor size and the optical elements necessary to
overcome the probe station’s relatively large working distance. Resolution is often a
more useful specification than magnification when choosing a microscope.
Lake Shore specifies resolution for the two different microscopes in Chapter 1. The
specified resolution indicates the smallest feature that can be reasonably
distinguished on the sample’s surface. (The sample’s texture and contrast also affect
resolution.) Although the Zoom 160 always offers a higher magnification than the
Zoom 70, the usable resolution of the two microscopes is often similar. This is
primarily a result of the relatively large working distance between the microscope
and sample, which limits the resolution of the Zoom 160.
