Specific Process Knowledge/Characterization/Four-Point Probe: Difference between revisions
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[[Image:Probe_diagram.PNG|thumb|200x200px|Probe diagram]]The set-up of the four point probe is four the tungsten carbide electrodes/probes.The power source (DC) sends a current through the two outer electrodes. A digital voltage meter (DVM) measures the potential drop between the two inner electrodes. | [[Image:Probe_diagram.PNG|thumb|200x200px|Probe diagram]]The set-up of the four point probe is four the tungsten carbide electrodes/probes.The power source (DC) sends a current through the two outer electrodes. A digital voltage meter (DVM) measures the potential drop between the two inner electrodes. | ||
The sheet resistance can then be calculated using the equation below: | |||
(Unit ohms/square) | |||
This equation is only valid if: i) the material being tested is no thicker than 40% of the spacing between the probes, and ii) the lateral size of the sample is sufficiently large. If this is not the case, then geometric correction factors are needed to account for the size, shape, and thickness of the sample. | |||
Bulk resistivity for wafers and films = sheet resistance x wafer thickness in cm (Unit ohm.cm) | |||
Bulk resistivity for a semi-infinite volume = 2 x π x S x V/I where is S is the probe spacing in cm (Unit ohm.cm) | |||
A sample is usually defined as a “semi-infinite volume” if it extends to infinity in all directions below a plane on which four probes are located. | |||
'''Note:''' | |||
Volume Resistivity = Volume Resistance = Bulk Resistivity = Bulk Resistance | |||
Sheet Resistivity = Sheet Resistance = Surface Resistivity = Surface Resistance | |||