Thermal and free carrier concentration mapping during ESD event in smart Power ESD protection devices using an improved laser interferometric technique

Abstract Spatial distribution of temperature and free-carrier concentration during high-current stress is studied in smart power electrostatic discharge (ESD) protection devices using a backside laser interferometric technique. The method is based on detecting changes in the refractive index of silicon due to thermo-optical and plasma-optical effects. We use a modified version of a heterodyne interferometer, where the reference beam is reflected from an external mirror outside the sample chip, which allows one to perform measurements without any restriction to the size of the scanning area. We have found two pronounced heat dissipating regions due to a vertical and a lateral current flow path in the device. In addition, two regions with increased current density due to carrier injection related to the two current paths have been found. These temperature and carrier concentration distributions found by the experiment agree very well with the results of 2D device simulation.

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