Contact Method
Electrical metrology techniques determine the electrical properties of thin semiconductor films without the influence of contact resistance. When evaluating silicon wafers, four point probe measurement utilizes four collinear, equally spaced metal tips to inject current through the outer pair and measure voltage across the inner pair. The method is limited by the probe spacing and the thickness of the layer being measured.
Geometric Correction
Boundary conditions such as wafer size and probe location relative to the wafer edge affect the current flow lines. Applying four point probe measurement to finite samples requires using correction factors to account for these geometric constraints. If these factors are omitted, the calculated resistivity will be artificially high.
Equipment Accuracy
System accuracy depends on probe tip wear, contact force, and current source stability. Calibrating the four point probe measurement system requires reference wafers with traceable sheet resistance values certified by national standards laboratories. The instrumentation must minimize thermoelectric effects by reversing the current direction and averaging the resulting voltage readings.
Process Validation
Routine testing with this probe tool monitors the uniformity of dopant distribution across the wafer surface. This step ensures that subsequent manufacturing stages proceed with consistent material properties.
