Sheet Resistance and the Calculation of Resistivity or Thickness relative to Semiconductor Applications

Four point probe based instruments use a long established technique to measure the average resistance of a thin layer or sheet by passing current through the outside two points of the probe and measuring the voltage across the inside two points.

If the spacing between the probe points is constant, and the conducting film thickness is less than 40% of the spacing, and the edges of the film are more than 4 times the spacing distance from the measurement point, the average resistance of the film or the sheet resistance is given by:

Rs = 4.53 x V/I

The thickness of the film (in cm) and its resistivity (in ohm cm) are related to Rs by:

Rs = resistivity/thickness

Therefore one can calculate the resistivity if the thickness of a film is known, or one may calculate the thickness if the resistivity is known.

Glossary of Terms

Ohms-per-square: The unit of measurement when measuring the resistance of a thin film of a material using the four point probe technique. It is equal to the resistance between two electrodes on opposite sides of a theoretical square. The size of the square is unimportant.

Read more here at Wikipedia: http://en.wikipedia.org/wiki/Sheet_resistance

Ohms-Centimeter (Ohms-cm): The unit of measurement when measuring the bulk or volume resistivity of thick or homogeneous materials such as bare silicon wafers or silicon ingots, using the four point probe technique.

Read more here at Wikipedia: http://en.wikipedia.org/wiki/Resistivity

Four-Point-Probes is a division of Bridge Technology. To request further information please call Bridge Technology at (480) 988-2256 or send e-mail to Larry Bridge at: sales@bridgetec.com