Route towards power MOSFET large thin die mechanical robustness

Route towards power MOSFET large thin die mechanical robustness: Masters thesis report

Gupta, Nikhil (TU Delft Electrical Engineering, Mathematics and Computer Science; TU Delft Electronic Components, Technology and Materials)

Poelma, René H. (mentor)
Zhang, Kouchi (graduation committee)
French, P.J. (graduation committee)
van Driel, W.D. (graduation committee)
van Zeijl, H.W. (graduation committee)

Delft University of Technology

2022-10-20

Today’s cars are undergoing the greatest transformation the industry has seen. Power MOSFETs play a crucial role in making electronics more energy efficient by driving down switching losses and Rdson using a combination of next-generation trench technology and ultra-thin dies. Power MOSFET dies are becoming larger ( > 5 X 5 mm ) and thinner ( < 50 μm ) to meet the high performance lifetime requirements of the automotive industry. The high aspect ratio and the new chip designs with trench technology offer challenges for assembly, packaging and testing.

The majority of the research performed in the past, aimed to reduce the risk of die crack by improving equipment and process strategies in back-end semiconductor processing. This thesis study aims at improving die
strength from a front-end approach (device fabrication process) by making dies stronger to stress from die frontside. New chip designs are presented with new metal layer layouts for improved stress distribution. Materials like polyimide are investigated as new die top material for mechanical strengthening of die frontside. Key factors which influence die strength like trench-metal interaction, wafer stress and warpage are also analyzed in this thesis report.

In this study, ultra-thin power MOSFET dies are realised on 100 mm diameter silicon wafers with dimensions of 6 X 3 X 0.050 mm. These dies are mechanical equivalent in design, robustness to commercial trench power MOSFETs. The processed wafers are grinded from the backside to realise 50 μm thin wafers which are then sawned to obtain singulated dies. The strength of the dies are characterized by three-point bending tests and analyzed using probability plots for weibull distribution.

Ultra-thin die
Weibull distribution
Three point bending
Power MOSFET

http://resolver.tudelft.nl/uuid:dab20245-4ad1-49e7-a87c-51f163fd2603

2024-10-31

Student theses

master thesis

© 2022 Nikhil Gupta