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1 - Characterization by C-V
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A well-known method which consists of measuring the capacitance in function of the voltage while varying the frequency of the applied signal (sinusoidal signal in most cases, square pulses with the C-V mercury probe)
The graph obtained can reveal a number of interesting parameters useful to understand the characteristic of the measured layer and its interfaces.
The contact with the layer is made by probe needles contacting metal deposited pads, which in certain cases is an added and complex operation only to get a metal contact. Another interesting technique is to use a "Mercury contact", the Mercury is a liquid elastic metal which allows contacting on certain types of layers (oxide, epitaxied layers) without need of preliminary metal deposition (link to Mercury probe systems).
Measurement graphs
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Measurement graphs #2
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C-V classical probe station
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Associated Articles : USJ (Ultra-Shallow Junction) characterization by mercury probe (IIT2006 Marseille)
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2 - Measurement of sheet resistivity by Four point probe method
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The four point probe method will measure the sheet resistivity of a semiconductive layer deposited onto a substrate. Depending upon the probes spacing, the size of the measured substrate and the possible interference caused by another below layer, the measurement can be considered a surface resistivity measurement. The unit is typically ohm/quare but can be ohm-cm if knowing the layer thickness.
The Four point systems are available in several configurations upon the expected average values, the substrate size, the need of mapping (measurement on a number of points on the substrate to calculate the homogeneity and uniformity)…
The Four point probe heads are typically 4 needles inline, they can be of different materials (tungsten, Osmium), the needle pressure is adjustable.
- 4 point probe systems
- 4 point Mercury probe systems
Manual basic 4 Point Probe
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4 Point Probe Heads
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Automatic system with mapping
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Example of mapped wafer
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Articles :
Four-Point Probe Theory of Operation from the University of California, Berkeley, EECS web site.
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3 - Hall effect measurement
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The Hall effect was discovered by M. Hall, A Johnes Hopkins university professor. If a magnetic flux is applied to a conductor in which a current is flowing, it creates an electronic stress which traduces by a voltage called "Hall voltage". The Hall effect technique allows the measurements of numerous parameters of an electronic layer, carriers mobility, density, resistivity, magneto-resistance, Hall coefficient…
The traditional Hall effect measurement systems were built with very big magnets offering variable magnetic flux. A new range of fixed-magnet "low-cost" systems have appeared on the market and start to be very popular with universities, lab research…(link to Hall effect systems). These systems allow measuring the Hall effect and associated parameters at a low cost while keeping the necessary technicity and variable current ranges, different fixed magnet, temperature measurements…
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Easy Clipping Sample holder
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Hall effect measurement systems
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Compact Magnet Box
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low temperature (77k) measurement
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Electrical characterization of semiconductor layers
