Al₂O₃/SiN_x-stacks at increased temperatures : avoiding blistering during contact firing

We investigate the passivation stability and blister formation during firing at 800°C of an Al2O3/SiNx stack deposited on p-type float zone silicon at different Al2O3 deposition set temperatures ranging from 170°C to 400°C. The actual wafer temperatures during Al2O3 deposition in the FlexAL reactor are determined using spectroscopic ellipsometry. After the firing step blistering can be observed for stacks featuring 15 nm thick Al2O3 layers grown at 170°C set temperature. We show that the deposition of the layer at higher set temperatures of 250°C, 300°C and 400°C reduces blister formation significantly. After firing, stacks with 15 nm thick Al2O3 layers deposited at set temperatures of 250°C and 300°C show the best passivation resulting in effective surface recombination velocities below 5 cm/s without significant blister formation