Time-Resolved Short Circuit Failure Analysis of SiC MOSFETs

Abstract

High-speed optical imaging is used in conjunction with fast electrical measurements to advance the understanding of the development of short circuit failures in silicon carbide power MOSFETs. Special samples are manufactured, which are compatible and comparable to TO-247 packages, but do not have any encapsulation. This allows optical observation of die surface during the test. The information on visible processes on the die allows for a better understanding of the sequence of events leading up to a failure. Imagery of destructive drain-source failures is also obtained, as well as post-failure images of surface and cross-sections. Aluminum metal melting is observed even for very short tests, before electrical indications of damage. The onset and completion of melting are used as information on the temperature of the die surface. Using this data for calibration, a detailed electro-thermal model is then used to simulate the temperature distribution and evolution during the short circuit.

Accurate Temperature Estimation of SiC Power mosfets Under Extreme Operating Conditions

“…Clearly, the presented TCAD modeling can be used to accurately estimate the time needed for the temperature at the point P to reach the melting temperature of aluminum, with a time reference at the start of the SC event, t M,P , for V dc = 200 V and 400 V as well as for typically operating dc voltages of 600 and 800 V, as summarized in Table IV. The estimation of t M,P for 400 and 800 V in TCAD-SIMREF is close to the experimental results from [47] obtained using a high-speed camera. SC failure of SiC power MOSFETs is typically ascribed in the literature to either oxide degradation or semiconductor failure at temperatures above 1000 K [48].…”

Measurements and Review of Failure Mechanisms and Reliability Constraints of 4H-SiC Power MOSFETs Under Short Circuit Events

“…The accuracy of the results was verified by comparing the chip surface roughness with the estimated temperature that may potentially induce the melt of Al. In [82], a novel method was proposed to observe the failure process of the SiC MOSFET chip during the short circuit transient. A SiC MOSFET device was specially made without packaging, and a high-speed camera was used to record the fast dynamic process.…”

Review of Methodologies for Evaluating Short-Circuit Robustness and Reliability of SiC Power MOSFETs

“…Upon that happening, three terminals are shorted, and the surface of the die is expected to change significantly. For example, in [93], [117], a visible burn mark has been seen at the source pad, and in [118], [119], a cross-sectional image of the damaged die has revealed severe damages within the SiC material. In [30], observation with a scanning-electron microscope (SEM) has also confirmed the wide melting of the aluminum layer above the source pad of a 1200V die burdened by thermal runaway.…”

“…More innovative observing methods are thus necessary. One of them mentioned in [119] uses a high-speed camera with a macro lens to record a particular sample's complete change of surface during SC tests. The particular sample is comparable to the Cree 2 nd generation 1200 V, 80 mΩ die but has not been encapsulated.…”