On-wafer production testing

Introduction

On-wafer production testing is an important step in semiconductor manufacturing. Testing the electrical performance and functionality of RF transistors while they are still in wafer form, before they are cut into individual chips and packaged, ensured the quality and reliability of the transistors by identifying defects or deviations from required specifications. This is typically done by mounting the wafer onto a prober with multiple probes making contact with the device on the wafer.

However, depending on the size of the wafer and transistor density, there can be anywhere from hundreds to millions of devices per wafer. Because of this, time efficiency is extremely important leaving only seconds to be spend on each die, in which basic parametric analysis such as IV curves and S-Parameters are performed. Spending additional seconds for matched 50-ohm devices can yield additional RF parameters such as power and efficiency but becomes increasingly more time consuming for non-50-ohm production tests due to slower testing times associated with traditional mechanical impedance tuning methods. Open-loop active load pull methods can improve test times by eliminating mechanical tuners, but can still only achieve a few impedance points per second.