Impurity Gettering by Atomic‐Layer‐Deposited Aluminium Oxide Films on Silicon at Contact Firing Temperatures

Abstract

Aluminium oxide (Al2O3) thin films deposited on silicon surfaces, synthesised by plasma‐assisted atomic layer deposition, are recently reported to possess impurity gettering effects for the silicon wafer bulk during annealing at 425 °C, a typical temperature used for activating the surface passivation quality of the Al2O3 films. This paper investigates the gettering effects of Al2O3 films at higher temperatures of 700–900 °C, which are commonly used for contact firing in silicon solar cell fabrication. Iron is used as a marker impurity in silicon to study the gettering effectiveness. Results show that Al2O3 films also generate strong impurity gettering effects at 700–900 °C, through a segregation gettering mechanism. The as‐deposited Al2O3 films are found to be more effective at gettering than the 425 °C‐activated Al2O3 films, demonstrating gettering processes that are largely limited by the impurity diffusivity in silicon. For both as‐deposited and activated Al2O3 films, gettering during high temperature annealing occurs by impurity accumulation at the Al2O3/Si interfaces, similar to the gettering action at 425 °C. However, some iron is found to redistribute into the bulk of the Al2O3 films after long annealing at a high temperature.