Impurity Gettering by Atomic‐Layer‐Deposited Aluminium Oxide Films on Silicon at Contact Firing Temperatures (Phys. Status Solidi RRL 3/2018)

Aluminium oxide (Al2O3) thin films are well known for their excellent passivation on silicon surfaces, and are therefore commonly used in silicon solar cells, such as in industrial Passivated Emitter and Rear Cell (PERC) solar cells. However, little is known about their ability to remove metal impurities from the silicon wafer bulk. The work by Liu and Macdonald (article no. 1700430) shows that the Al2O3 films, from plasma-assisted atomic layer deposition, generate strong impurity gettering effects at temperatures that are typically used for contact firing in cell fabrication. Iron is used as a marker impurity in silicon to study the gettering effectiveness and to illustrate the impurity redistribution during different process conditions. It is found that a reduction in the bulk iron concentration is accompanied by a corresponding increase in the iron accumulation at the Al2O3/Si interfaces, which clearly demonstrates the gettering effects of the Al2O3 passivation films. A longer annealing time drives some iron into the bulk of the Al2O3 films. Impurity segregation to the Al2O3 regions (interface and/or bulk of the film) is identified as the main gettering mechanism.