1. Procedure for Pro4 using Keithley
Four Point Probe
Procedure for Pro4 using Keithley

2. Overview What is Four Point Probing How the system works Pro 4 Set Up
Simple Calculations behind Four Point Probing
Procedure for using Pro4

3. What is Four Point Probing
Four Point Probing is a method for measuring the resistivity of a substance.
Impurity concentrations can be estimated from the resistivity

4. Resistivity vs Resistance
Bulk or volume resistivity is measured in ohms-cm
Independent of sample size or shape
Sheet resistance is measured in ohms-per-square
Used for measuring resistivity of thin films

5. Pro-4 Set Up The 4 point probing setup consists of 3 key components
Pro-4 probing station from LUCAS LABS with 4 point probe head
KEITHLEY 2400 power/source meter
Computer with Pro4 software and interface
Probing Station
Source Meter
Pro-4 Software
The 4 point probing setup can measure resistivity or the thickness of a film. But, either one has to be known.

6. Resistivity Probe Stand
Contact Lever
Probe head electrical connection
Probe Head
Mounting Chuck (Aluminum base with Teflon surface

7. How the system works Current is passed through the two outer probes
Voltage is measured between the two inner probes
Resistance is measured using ohms law
The thickness of the film must be known

8. Calculations Rs = Resistivity of the substance
If the spacing between the probe points is constant, and the conducting film thickness is less than 40%, and the edges of the film are more than 4 times the spacing distance from the measurement point, the average resistance of the substance is given by
Rs= k x V/I
For bulk resistivity, the sample is much larger than the spacing of the probes, the sheet resistance is defined as the resistance equal to the bulk resistivity divided by the sample thickness. The equation is given by…
Rs= P/t
Rs = Resistivity of the substance
K = constant for the average resistivity that is equal to 4.53
P = Resistance
t = thickness of the substance

9. Resistivity measurements
The Pro-4 can be used to measure resistivity or the thickness. But, either one has to be known.
The # of points to be tested and the shape of the sample can be selected.
A single point or multiple points on the sample can be tested to obtain the average resistivity

10. Procedure for using the Pro-4
Click on the Auto Test tab for multiple measurements or Single Test tab for a single reading.
Select size and shape of the sample using the tabs at the bottom of the page. Type in the required information.
Place the sample on the mounting table and then move the sample to position it at the required location
Turn down the lever so that all the needles on the probe head are in contact with the wafer.

11. Saving the data
After the measurement is completed, the resistivity at each location will be displayed on the left hand side of the screen.
When all the points are tested, the data can be saved and read using excel