Passivation of Si Wafers by ALD-Al2O3 Films with Different Surface Conditioning

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 CPand 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 μm 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. Keyords: Passivation; Al2O3; ALD; wet chemical treatments