Hydrogen induced passivation of Si interfaces by Al2O3 films and SiO2/Al2O3 stacks

Abstract

The role of hydrogen in Si surface passivation is experimentally identified for Al2O3 (capping) films synthesized by atomic layer deposition. By using stacks of SiO2 and deuterated Al2O3, we demonstrate that hydrogen is transported from Al2O3 to the underlying SiO2 already at relatively low annealing temperatures of 400 °C. This leads to a high level of chemical passivation of the interface. Moreover, the thermal stability of the passivation up to 800 °C was significantly improved by applying a thin Al2O3 capping film on the SiO2. The hydrogen released from the Al2O3 film favorably influences the passivation of Si interface defects.

Effective passivation of Si surfaces by plasma deposited SiOx/a-SiNx:H stacks

“…We recently reported similar observations for SiO 2 / Al 2 O 3 stacks. 17,18 These results in combination with the lifetime data in Fig. 1 suggest that recombination in the inversion layer plays less of a role for the stacks than for single-layer SiN x on p-type Si.…”

“…We consider the decrease in passivation at high annealing temperatures to be indicative of the dehydrogenation of the Si/ SiO x interface. 11,18 The observed differences between Si-rich and N-rich SiN x capping films are consistent with the fact that the diffusion and release of hydrogen, initially bonded as Si-H and N-H in SiN x , are very sensitive to film composition. [23][24][25] Effusion of hydrogen in Si-rich SiN x was shown to occur at lower temperatures compared to more compact SiN x , 24,25 which led to a reduced availability of hydrogen at high annealing temperatures.…”

“…The deposition of the SiN x capping films on top of as-deposited SiO x led to a significantly improved surface passivation, e.g., S ef f Ͻ 27 cm/ s for SiN x with n = 2.05 on n-type Si. This can be related to the incorporation of hydrogen, e.g., from the plasma, 18 which reduces the interface defect density during "in situ annealing" at the deposition temperature of ϳ350°C. After postdeposition annealing of the SiO x / SiN x stacks at 400°C ͑10 min, N 2 ͒, the surface passivation performance improved even more.…”

Er3+ and Si luminescence of atomic layer deposited Er-doped Al2O3 thin films on Si(100)

“…Figure 12 reveals that a small fraction of hydrogen can leave the film by effusion into vacuum at moderate temperatures of $350-450 C. The mobilized hydrogen can also diffuse toward the interface and passivate defects, as was recently demonstrated by a secondary ion mass spectroscopy study on deuterated Al 2 O 3 thin films. 48 Accordingly, very low interface defect densities 10 11 eV À1 cm À2 have been reported for Al 2 O 3 thin films annealed at 400 C. 22 By increasing the annealing temperature > 450 C, significant amounts of OH groups are removed from the (Er-doped) Al 2 O 3 films. While this represents the removal of quenching centers coinciding with the activation of the Er 3þ luminescence, the hydrogen loss will also take place at the interface, which leads to a drop of the Si PL and a decreasing level of surface passivation.…”

“Zero-charge” SiO2/Al2O3 stacks for the simultaneous passivation of n+ and p+ doped silicon surfaces by atomic layer deposition

“…It is hypothesized that for these stacks the SiO 2 interlayer acts as a (trap-assisted) electron tunnel barrier, preventing charge-injection from the c-Si base into the electron trap sites in the Al 2 O 3 [13,28]. The Al 2 O 3 plays a key role in the reduction of Si/SiO 2 interface defect states, which are effectively passivated by the diffusion of hydrogen from the Al 2 O 3 film to the Si/SiO 2 interface during annealing [33]. ALD SiO 2 /Al 2 O 3 stacks have the advantage that they can be prepared at relatively low temperatures (e.g., 200°C), are conformal even over high-aspect ratio structures and can be prepared in a single deposition run [13,28,34].…”