Observation of impurity diffusion defect in IGBT using a laser terahertz emission microscope technique

• Femtosecond laser pulses are applied to the p-n junction, and THz waves are observed by a photoconductive antenna.
• THz waves emit from the wiring connected to the p-n junction.
• Covering with alminum foil blocks opposite-phase THz waves, and improves the detection sensitivity of the THz waves.
• The LTEM technique is capable of measuring impurity diffusion defects in power devices such as IGBTs.

This paper describes a technique for observing impurity diffusion defects in IGBTs using laser terahertz emission microscopy (LTEM). In this method, femtosecond laser pulses are applied to the p-n junction of a trench IGBT structure and terahertz (THz) waves emitted from the wiring connected to the p-n junction are observed by a photoconductive antenna. Furthermore, covering the measurement sample with aluminum foil blocks opposite-phase THz waves emitted from the sample and improves the detection sensitivity of the THz waves emitted from the IGBT wiring. This technique enables impurity diffusion defects, which were created by deliberately omitting a portion of the resist pattern used in the IGBT emitter n+ ion implantation process, to be recognized as contrast differences on an LTEM image.