The influence of self heating on the measurement of hot carrier degradation in high voltage n-channel LDMOS

A systematic study of self heating caused by hot-carrier (HC) stress in packaged thick gate oxide HV LDMOS devices (Laterally Diffused MOSFETs), and how self heating significantly affects HC degradation characteristics is presented. The time delay between the removal of the HC stress and the parameter measurement significantly affected the measured HC Idlin/Rdson degradation with longer delay times resulting in less observed Idlin degradation. We show the recovery of degradation observed with longer delay times was mostly due to self heating effects, as opposed to interface trapped charge related recovery. HC stress at wafer level with different relaxation times exhibits almost no recovery on Idlin/Rdson degradation. The HC Idlin degradation caused by the self heating effect is observed in packaged HV LNDMOS devices but not in wafer level tests. A method is proposed to eliminate the influence of the self heating effect on HC measurement.