Effective SiN$_{\bf x}$ :H Capping Layers on 1-nm Al2O3 for p$^{\bf +}$ Surface Passivation

Abstract

Passivation of p + regions is typically achieved by Al 2 O 3 layers with thicknesses in excess of 10 nm. Given the expense of commonly used Al 2 O 3 precursors and, in some cases, the deposition time, it is desirable to minimize the layer thickness. We achieve recombination factor J 0p+ in the order of 22 fA/cm 2 with 1 nm of Al 2 O 3 capped with ~70-nm amorphous silicon nitride (SiNx :H) films on 85 Ω/□ boron diffusions. The passivation performance of ultrathin-Al 2 O 3 /SiN x :H stacks depends critically on both the alumina thickness and the SiN x :H composition. It was found that to achieve low J 0p+ with 1-nm-Al 2 O 3 /SiN x :H stacks, the SiNx :H hydrogen concentration ([Si-H]+[N-H]) was required to be low: less than 8×1021 cm -3 . Fourier transform infrared measurements indicated that the initial hydrogen content is more appropriate to evaluate the hydrogen release process of SiNx :H layers than Si-N bond density, at least in this study. Both the Al 2 O 3 -Si interface and charge density of 1-nm-Al 2 O 3 /SiN x :H stacks can be impacted by the SiN x :H capping layer. The outstanding passivation quality of 1-nm-Al 2 O 3 /SiN x :H stacks is due to a combination of both chemical and electrostatic passivation.