Passivation of n$^{+}$-Type Si Surfaces by Low Temperature Processed SiO$_{2}$/Al $_{2}$O$_{3}$ Stacks

The surface passivation of SiO
₂
/Al
₂
O
₃
stacks prepared at low process temperatures was investigated on phosphorous diffused n
⁺
-type Si surfaces with a broad range of sheet resistances. Two kinds of SiO
₂
films were prepared, the first with plasma-enhanced chemical vapor deposition (PECVD) and the second in a wet chemical process. After atomic layer deposition of the Al
₂
O
₃
capping layer, the resulting SiO
₂
/Al
₂
O
₃
stacks differ in the polarity of their fixed charge density, i.e., the PECVD SiO
₂
stacks had a positive and the wet chemically grown SiO
₂
stacks a negative fixed charge density. The PECVD SiO
₂
/Al
₂
O
₃
stacks resulted in a high surface passivation over a broad range of sheet resistances whereas the wet chemically grown SiO
₂
stacks were only feasible for diffused surfaces with low sheet resistances (<; 100 Ω/□). By corona charging experiments, it was established that the field effect based on a negative fixed charge density was the reason for the loss in surface passivation in the specific range of diffused surfaces.