# Difference between revisions of "Four point probe"

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*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. | *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. | *The probes are collinear and are equally spaced. | ||

− | *For film thickness ≤ 0.5 x (probe spacing), the sheet resistance calculation simplifies to: | + | *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: | ||

[[File:SheetRho1.jpg|frame|left|link=]]<ref name="PVEducation"></ref> | [[File:SheetRho1.jpg|frame|left|link=]]<ref name="PVEducation"></ref> | ||

V = measured voltage | V = measured voltage | ||

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*If the resistivity of the film or material is known (or assumed), a thickness 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. | ||

+ | *For samples with lateral dimensions or diameter < 40 x (probe spacing), correction factors need to be used to obtain accurate sheet resistance values. For correction factor values, please refer to information at [http://four-point-probes.com/finite-size-corrections-for-4-point-probe-measurements http://four-point-probes.com/finite-size-corrections-for-4-point-probe-measurements] <ref name="4pp">[http://four-point-probes.com/finite-size-corrections-for-4-point-probe-measurements Four-point-probes.com]</ref> | ||

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==Parameters== | ==Parameters== |

## Revision as of 12:27, 10 February 2016

Four point probe | |
---|---|

Four Point Probe Diagram ^{[1]} | |

Technology Details | |

Technology | Metrology |

Equipment | Miller FPP-5000 4-Point Probe |

Warning: | This page has not been released yet. |

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.

## Contents

## 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:

^{[1]}

V = measured voltage

I = force current

Where:

^{[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

- 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.

- For samples with lateral dimensions or diameter < 40 x (probe spacing), correction factors need to be used to obtain accurate sheet resistance values. For correction factor values, please refer to information at http://four-point-probes.com/finite-size-corrections-for-4-point-probe-measurements
^{[2]}

## 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.

## Equipment

### Miller FPP-5000 4-Point Probe

Main article: Miller FPP-5000 4-Point Probe

## See also

## References

- ↑
^{1.0}^{1.1}^{1.2}[1] PV Education.org Four Point Probe Resistivity Measurements - ↑ Four-point-probes.com