Joachim Krumrey

A novel SIMS based approach to the characterization of the channel doping profile of a trench MOSFET

We present here a new technique which for allows the accurate characterization of the channel doping profile using secondary ion mass spectrometry (SIMS) analysis within the active area cells of a trench MOSFET. The technique involves the chemical removal of the entire structure apart from the silicon mesas and trenches, followed by the deposition of undoped silicon (polycrystalline or epitaxial) to refill the trenches. The SIMS profiles obtained are then corrected for the trench geometry to reveal the underlying doping profile within the MOSFET cells.

Simulation of the failure mechanism of power DMOS transistors under avalanche stress

The failure mechanism caused by avalanche stress in power devices consisting of large DMOS cell arrays is investigated using electrothermal device simulation. To this end, we use the approximation of an infinitely large array, but allow for thermal interaction among the cells. The numerical analysis demonstrate the occurrence of unstable states, where a single hot spot and a current filament evolve in one particular ‘weak’ cell, thus confirming earlier work. We also demonstrate that the maximum temperature rise in the first cell exhibiting filamentary current flow can easily exceed the destructive level. Subsequent current and temperature redistributions observed in simulation thus turn out to be of no practical relevance.