Four point probe

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Four point probe
4pp.jpg
Four Point Probe Diagram[1]
Technology Details
Technology Metrology
Equipment Miller FPP-5000 4-Point Probe


Four point probe is used to measure resistive properties of semiconductor wafers and thin films. If the thickness of a thin film is known, the sheet resistance measured by four point probe can be used to calculate the resistivity of the material; conversely, if the material's resistivity is known, the thickness of the thin film can be calculated.

Equipment

Miller FPP-5000 4-Point Probe


Method of operation

  • A four point probe is typically used to measure the sheet resistance of a thin layer or substrate in units of ohms per square by forcing current through two outer probes and reading the voltage across the two inner probes. Using this four-terminal configuration avoids measurement error due to the contact resistance between the probe and sample.
  • The probes are collinear and are equally spaced.
  • Probe spacing for the LNF tools is 1.59mm
  • For film thickness ≤ 0.5 x (probe spacing) and diameter or lateral dimensions > 40 x (probe spacing), the sheet resistance calculation simplifies to:
SheetRho1.jpg

[1]

V = measured voltage

I = force current
Where:

SheetRho2.jpg

[1]


  • Rearranging the equation for resistance of a rectangular thin film resistor helps illustrate the meaning of sheet resistance which is equal to the resistivity of the material divided by its thickness.
    • ρ = thin film material resistivity
    • L = length of resistor
    • W = width of resistor
    • t = thickness of thin film material
ThinFilmResistorEq.jpg


  • If the thickness of a film or material is known, its resistivity can be calculated from the sheet resistance measurement.
  • If the resistivity of the film or material is known (or assumed), a thickness can be calculated from the sheet resistance measurement.

Applications

Four point probes are used in nanofabrication to measure the resistive properties of conducting films which may include substrates, deposited films, and doped regions on a sample surface.


See also

References

  1. 1.0 1.1 1.2 [1] PV Education.org Four Point Probe Resistivity Measurements
  2. Four-point-probes.com

Further reading