Yoann Buvat, Characterization and Modelling Senior Engineer, STMicroelectronics

Yoann Buvat joined STMicroelectronics in 2008. He holds a bachelor’s degree in electronic and microelectronic and a master’s degree in embedded computer science from Tours University. He serves as a characterization and modelling engineer inside the WLR & DC laboratory, which is part of R&D department. His main missions are the support on the development and the production of power discrete technologies as well as the management of laboratory equipment. Since 2017, he pursues a Ph.D. thesis with Tours University studying the characterization and reliability of passivation layers used in power electronic devices. His fields of topic are wafer-level reliability and characterization of power discrete, passivation materials electrical characterization and wafer-level testing.

High Forward Current Characterization Tests at Wafer Level on Vertical Discrete Power Technology

Characterization of power discrete devices such as rectifiers can be difficult to carry out due to high current or high voltage values to handle. Today, electrical sorting at high current is performed only after back-end process. The forward voltage extraction at high current directly at wafer level could enable to increase significantly the final yield and growth margin of rectifier products. However, forward voltage tests at current levels up to 200 A, is a key challenge at wafer level. Considering vertical power technology, as a matter of fact, current bias is generally limited to a few amps.

Two factors have been identified to impact forward voltage measurement on vertical power technology: the frontside contact resistance between tips and pad metallization on the one hand, and the backside contact resistance between the chuck and the backside wafer metallization on the other hand. The present study is dedicated to backside contact resistance issues. To address this challenge, FormFactor proposes a new generation of high current chucks with an optimized vacuum technology which enables to significantly reduce backside resistance. This new generation of chucks was evaluated and very promising results were obtained up to 40 A. Investigations are still on-going to achieve measurements up to 200 A.