Forward Voltage Drop Induced by an Abnormal Threading Dislocation Aggregation in 4H-SiC GTO Devices

Area of Science:

• Materials Science
• Semiconductor Physics
• Solid-State Devices

Background:

• Silicon carbide (SiC) is a critical material for high-power electronic devices.
• Gate turn-off thyristors (GTOs) are power semiconductor devices requiring high reliability.
• Defects in SiC can significantly degrade device performance.

Purpose of the Study:

• To characterize an unusual star-like defect found in failed SiC GTO devices.
• To investigate the impact of this defect on the electrical characteristics of SiC GTOs.
• To understand the relationship between this defect, dislocations, and device performance.

Main Methods:

• Metal removal and potassium hydroxide (KOH) etching at 450 °C.
• Analysis of defect morphology and size using a LEXT OLS4000 3D laser confocal microscope.
• Evaluation of forward blocking characteristics and forward current-voltage (I-V) relationships.
• Correlation analysis between dislocation density and forward voltage drop.

Main Results:

• Discovery of large (210-580 µm) abnormal star-like defects on failed SiC GTOs.
• The defect consists of multiple penetrating dislocations, exhibiting six-fold symmetry.
• These defects severely degrade the forward blocking capability of SiC GTOs.
• The defect has minimal impact on the anode-gate forward I-V characteristics.
• The defect disrupts the typical correlation between forward voltage drop and dislocation density.

Conclusions:

• The abnormal star-like defect is a significant failure mechanism in SiC GTOs.
• Dislocations forming this defect critically impair forward blocking performance.
• Understanding this defect is crucial for improving the reliability of SiC power devices.