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

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.