Laser annealing of double implanted layers for IGBT Power Devices

Abstract

As microelectronic Power Devices increase their performances, there is a need to implement low thermal budget annealing processes on thin silicon wafers, typically few tenth of micron thick. To enhance the performance of these devices, particularly for Insulated Gate Bipolar Transistor (IGBT), there is a need to activate two different layers of doped silicon at different depth from the backside of the wafers, one P-doped and another N-doped (buffer layer). These annealing processes have to be able to localize a high temperature heat front limited to a very thin layer not to damage the other side of the wafer, where metallic structures would not allow temperature above 400°C. In this work, we annealed wafers implanted with Boron and Phosphorous with Excico Long Pulse Exciplex laser (308nm excimer laser, 180ns pulse) to induce two different silicon phases where both a liquid and a solid phase process activate the 2 different dopant layers. SIMS and SRP measurements were performed to quantify the amount of dopant activated during the laser annealing. The rate of defects in the silicon was measured by RBS. Depending on the laser energy density and implantation conditions, we were able to identify a process window within we achieve a high activation rate of Boron in the melting phase and of the Phosphorus in the solid phase.