Four-Point Probe Sheet Resistance Calculator
Semiconductor wafer metrology & doping characterization: Compute sheet resistance ($R_s$), bulk resistivity ($ ho$), and active carrier concentration from four-point probe ($V/I$) measurements.
Probe Electrical Readings & Geometry
Sheet Resistance & Resistivity
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Frequently Asked Questions
Why does four-point probe eliminate contact resistance?
In a standard 2-point probe, the measured resistance includes probe-to-semiconductor contact resistance and lead resistance. In a 4-point probe, the inner voltage sensing probes carry almost zero current due to the voltmeter giga-ohm input impedance, preventing contact resistance voltage drops.
What is the physical meaning of ohms per square (Ω/□)?
Sheet resistance is independent of the size of the square. For a square thin film of length L and width W = L, resistance R = ρ · L / (t · W) = ρ / t = Rs. Whether a square is 10 µm × 10 µm or 10 cm × 10 cm, its end-to-end resistance is always exactly Rs.
When must geometric correction factors be applied?
The standard constant 4.532 applies to infinitely large sheets where thickness t < s/2. When measuring near a wafer edge (distance < 5s) or on small test dies, current cannot spread symmetrically in 2D, requiring edge correction factors F(d/s) to prevent overestimating resistivity.