Passivation of Si wafers by Al2O3 films with different surface conditioning

Abstract

We investigate the passivation quality of Al2O3 thin films grown by atomic laver deposition on differently etched surfaces of ∼500 μm thick, 2.13 Ωcm p-type float zone silicon wafers with an (100) crystal orientation. The applied CP- and KOH-etches lead to differently shaped surface morphologies but almost equal root-mean-squared (rms) roughnesses of ∼0.95 nm (CP) and ∼1.07 nm (KOH) measured within an area of 1 × 1 μm2 on the Si surface. The lowest surface recombination velocities after passivation resulting in effective carrier lifetimes up to 10 ms are achieved for samples treated with CP-etching. The lifetime is determined using a WCT-120 in the transient mode. It is shown that these lifetimes slightly exceed the theoretical limit given by a parameterization of the Auger recombination. Furthermore, scanning electron microscope images show that Al2O3 thin films with a thickness of ∼29 nm and ∼58 nm fully cover random pyramid textured Si surfaces of (111) orientation leading to high effective lifetimes up to 6 ms. The temperature of the wafer surface during the deposition is determined by in situ spectroscopic ellipsometry to be ∼180 °C.