Nanoporous SiO2 made by atomic layer deposition and atomic layer etching

n this study, Al2O3:SiO2 composite films were grown using atomic layer deposition (ALD) with the thicknesses of Al2O3 and SiO2 being between 1 Å - 20 Å. The composition of the films was varied by changing the relative number of ALD cycles from 1 to 20. The optical properties of the layers were investigated with spectroscopic ellipsometry (SE). The experimental refractive indices of the composite films with Al2O3 and SiO2 ALD cycles of 1-10 were shown to be higher than the calculated values. This was attributed to the hampered growth of the SiO2 during the first ALD cycles. On the other hand, the experimental and calculated refractive indices of the mixture 20 cycles:20 cycles agreed very well indicating a nanolaminate behavior. Selective etching of the alloys 1:1 and 2:2 resulted in a nanoporous SiO2 films. The refractive index of the final porous SiO2 films was dependent on the thickness of the initial alloy layer.