Laser Thermal Annealing for Power Field Effect Transistor by using Deep Melt Activation

For chips with vertical flow of electrical current, an ohmic contact and/or emitter on the backside of the wafer are required. The formation of this electrical contact can be done using a laser annealing method in overlapping mode. Test on bare wafers and on productive chips were carried out using an excimer laser (lambda = 308 nm) with a laser energy density of more than 2 J/cm₂ and a laser pulse duration of 180ns. Owing to the long pulse duration, deep melt activation with a molten zone with up to 400nm could be reached and an efficient emitter could be achieved