Laser Annealing of Power Devices

Abstract

The discrete IGBT (Insulated Gate Bipolar Transistor) is the most important power semiconductor device for power conversion and control in the medium power range with voltages >400 V. Next generation IGBTs require low thermal budget p-n junction formation for the back side field stop and emitter layer. The requirement for the limited thermal budget is due to the fact that the front side metallization does not allow high temperature treatment for the activation of the field stop layer. Therefore, laser annealing experiments have been carried out using a frequency doubled Yb:YAG laser at a wavelength of 515 nm with an energy density up to 4 J/cm2. In order to find out appropriate process conditions for a single step Boron and Phosphorous laser annealing process, parameters for ion implantation as well as energy density and pulse duration of the laser have been varied. The doping profiles of Boron and Phosphorous were measured by Secondary Ion Mass Spectroscopy (SIMS) and Spreading Resistance Probe (SRP) in order to assess the dopant activation behaviour. The main interest was the activation of the Phosphorous doped field stop layer in a depth range of 1 mum. A strong dependency of Phosphorous activation on implanted Boron dose was observed with dopant activation up to 70%.