Identification of internal stresses may improve transistor fabrication in high-voltage components

Vertical double-diffused metal-oxide-semiconductor transistors have become the go-to for integrated circuits within high-voltage and high-frequency electronics. The hallmark deep trenches in silicon chips can help isolate voltages as high as 500 V, but they are also responsible for some of the chips’ greatest weakness. During trench processing, internal stresses can induce point defects, dislocations and micro-cracks, which can lead to chip failure.

Seeking to create silicon chips less prone to failure, Hieckmann et al. studied the mechanical internal stresses of the chips during the fabrication process of the trenches. They measured the local strains via electron backscatter diffraction using a scanning electron microscope, and then analyzed the diffraction images of the deep trench regions and nearby stress-free regions during different steps in the chip manufacturing process.

“Our objective was to optimize the manufacturing process and to reduce chip failures,” said author Ellen Hieckmann. “The most satisfying result concerning the suitability of the experimental method is the good correlation between the stresses determined in different process states, each obtained on different samples.”

The results showed that the range and distribution of tensile and compressive stresses are in agreement with finite element simulations in the framework of linear theory of elasticity, however, the observed stresses were higher than expected for all the states.

The authors hope the work will help develop a silicon chip fabrication process optimized for higher reliability. In the future, they plan to continue investigating how different geometries and thermal oxidization conditions affect the stress field of deep trenches during processing.

Source: “Investigations of internal stresses in high-voltage devices with deep trenches,” by Ellen Hieckmann, Uwe Mühle, Paul Chekhonin, Ehrenfried Zschech, and Jeff Gambino, Journal of Vacuum Science & Technology B (2020). The article can be accessed at https://doi.org/10.1116/6.0000515 .

This paper is part of a closed special collection: Reliability and Stress-related Phenomena in Nano and Microelectronics, learn more here .