High Speed Atmospheric Pressure ALD for Industrial Scale Solar Cell Passivation

A next generat ion material for surface passivat ion is atomic layer deposit ion (ALD) Al2O3. However, convent ional t ime-resolved ALD is limited by its low deposit ion rate. Therefore, an experimental high - deposit ion-rate prototype ALD reactor based on the spat ially-separated ALD principle has been developed. This reactor leads to deposit ion rates up to 1.2 nm Al2O3/s. In this work, the passivat ion quality and uniformity of the experimental spat ially-separated ALD Al2O3 films are evaluated and compared to convent ional temporal ALD Al2O3, by use of quasi-steady-state photo-conductance (QSSPC) and carrier density imaging (CDI). It is shown that spat ially-separated Al2O3 films of increasing thickness provide an increasing surface passivat ion level. Moreover, on p-type CZ Si, 10 and 30 nm spat ial ALD Al2O3 layers can achieve the same level of surface passivat ion as equivalent temporal ALD Al2O3 layers. In cont rast , on n-type FZ Si, spat ially-separated ALD Al2O3 samples generally do not reach the same opt imal passivat ion quality as equivalent convent ional temporal ALD Al2O3 samples. Nevert heless, aft er “ firing”, 30 nm of spat ially -separated ALD Al2O3 on 250 μm t hick n-type (1-5 Ω.cm) FZ Si wafers can lead t o effect ive surface recombinat ion velocit ies as low as 2.9 cm/s, compared t o 1.9 cm/s in the case of 30 nm of temporal ALD Al2O3.