Latent interface-trap generation in commercial power VDMOSFETs

Abstract

Latent interface-trap generation is one of the most controversial post-irradiation effects in MOSFETs, which can have a significant impact on device performance and reliability in radiation environments. In this paper, we present new experimental evidence of latent interface-trap buildup in commercial power VDMOSFETs: its dependencies on dose, temperature and gate bias applied during irradiation and annealing. We discuss several models for latent interface-trap buildup and show that the most consistent is one which involves the diffusion of molecular hydrogen from structures adjacent to the gate oxide (CVD oxide, poly-Si gate), and its cracking on positive charge centers in the oxide. The cracking reaction liberates hydrogen ions, which drift to the Si/SiO/sub 2/ interface to form interface traps. Some hypothesis from the recently proposed H-W model for post-irradiation behavior of interface traps may help resolve the question of the source of hydrogen sufficient to cause up to 800% increase in interface-trap density, experimentally observed. The implications of latent interface-trap generation for hardness assurance test methods are also discussed.