Mixed Aluminum Precursor in the Atomic Layer Deposited Al2O3 for Effective Silicon Emitter Passivation

In this contribution, we have studied the impact of
aluminum precursor of atomic layer deposited (ALD) Al2O3 on
the passivation quality of silicon solar cell emitters. Aluminum
precursors, Trimethylaluminum (TMA) and Dimethylaluminum
chloride (DMACl), and their different combinations were used to
deposit Al2O3 layers on both phosphorus and boron implanted
emitters. In addition to measuring the passivation quality, the
wafers experienced thermal stability investigation. In all wafers,
Al2O3 resulted in better emitter saturation current as compared
to thermal oxide resulting from ion implantation drive-in anneal.
On industrial type of emitters, values around Joe at 60 fA/cm2
were obtained. The impact of aluminium source was not as high
as expected, however, we found that aluminium precursor has a
high impact on the formation of so-called blisters. We show that
the blisters can be greatly suppressed using DMACl as the
aluminium precursor while TMA results in the formation of high-
density and large-size blisters. Our PERC solar cell with the
DMACl in the ALD process showed similar passivation quality as
the TMA-based process.