Wafer testing

Wafer testing is a step performed during semiconductor device fabrication after back end of line (BEOL) and before IC packaging.

Two types of testing are typically done. Very basic wafer parametric tests (WPT) are performed at a few locations on each wafer to ensure the wafer fabrication process has been carried out successfully. Discrete test structures are provided for WPT to test parameters like transistor threshold voltage or gain, interconnect resistance, capacitance, diodes, etc. Considerable information about device performance is obtained from WPT using structured typically provided in the scribe lines.

After WPT, all individual integrated circuits on the wafer are given extensive wafer functional testing (WFT) (also called die sort) by applying special test patterns. The testers used for WFT are typically quite expensive (see Teradyne for an example of a semiconductor test system). The WFT "yield" is recognized as the key test in determining the economic outcome of the entire fabrication process.