Measuring and mapping sheet resistance
The sheet resistance of a layer, along with derived parameters such as specific resistance, charge carrier density, or layer thickness, are fundamental characteristics required in many areas of the semiconductor and photovoltaic industries. A proven method for determining these values is the four-point probe technique.
Polytec offers probe heads for all common four-point measurement devices. Upon request, we also provide resistance measurement instruments for universities, laboratories, and research institutions.
Cylindrical Four-Point Probe
The cylindrical four-point probe is compatible with Jandel instrument stands as well as some OEM mapping systems.
It can be integrated into customer-specific four-point measurement systems using an optional mounting adapter. Alternatively, the cylindrical design is also suitable for customers who manufacture their own probe holders.
The needle forces for the probe are set to a load between 10 g and 200 g. For probes with a spacing of 0.5 mm, the load is defined between 60 g and 100 g.
All probes are manufactured with high mechanical precision. Specifications for radii, spacing, and flatness are checked using video inspection systems and optical interferometers, and the load is measured with electronic force gauges. Each probe features upper and lower diamond needle guides.
Optimal Probe Pressure
The probe features an acrylic insulating pad on the measurement tip. This pad comes into contact with the sample during measurement, ensuring that the needles achieve the correct spacing and optimal pressure.
Specification
| Feature | Value |
|---|---|
| Probe Spacing | 0.500 mm; 0.635 mm; 1.00 mm; 1.591 mm (needle to needle) |
| Tolerance | ± 10 micrometers |
| Arrangement | Linear or square |
| Needles | Tungsten carbide, 0.4 mm diameter (0.3 mm diameter for close spacing) |
| Radii | 12.5; 25; 40; 100; 150; 200; 300; 500 micrometers |
| Retraction to Pad | 0.5 mm |
| Planarity | ± 0.025 mm or better |
| Loads | Between 10 g and 200 g. For probes with 0.500 mm spacing, between 60 g and 100 g |
| Cables | 4-fold shielded cable, Teflon insulated |
| Electrical Leakage | 10¹³ Ohm resistance between needles at 500 volts |