what causes Breakdown voltage (BVces) to drift after HTRB reliability test? I do understand HTRB is an accelerated test which eventually leads to carrier's mobility degradation in the field depletion structure. But what is the main reasion causing BVces to reduce from 650V to 550V after 1000 hours?
is there any recommendation to reduce the decrease the BVces after HTRB test?
Hello Zhi,
HTRB combines electrical and thermal stress to test for junction integrity, crystal defects, and ionic contamination revealing (amongst others) weaknesses or degradation effects in field depletion structures at the device edges and in the passivation (BVCES drift, Vth drift).
The cause of the drift are space charges that emerge from charge carriers being attracted to the interface between the chip and its insulator.
Those charge carriers have been attracted by ions (in many cases contamination introduced by packaging process) that have diffused through the layers above the chip insulator, finally reached the insulator surface.
Under the influence of the electric field, ions with different charges move parallel to the chip surface or separate from each other. They finally accumulate in areas of high field strength on the chip surface, forming a charged plane (space charge) there.
All in all: Space charges add an electrical field strength on top affecting the blocking behavior and threshold voltage.
Kind regards,
Christian
...regarding your 2nd question:
Space charges do not naturally introduce (visible) structural changes or damages in the metal-oxide-hard passivation sandwich since the voltage drift is not caused by chemical reactions. It is caused by field distortions.
As long as the field stress did not cause significant thermal issues (those can be very localized) during HTRB, you can try to heat out (at 125, without applied voltage) or just wait some days, so ions should have redistributed... ;)
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