A study of LAO nanopatterns on Si substrates of different crystallographic orientations

Oxide nanopatterns have been drawn on Si (100), (110) and (111) substrates using the AFM based method of local anodic oxidation (LAO) employing negative tip voltages of 5, 8 and 10 V. The same tip was used in all the cases and experimental parameters such as tip velocity and humidity were kept fixed. The total volume occupied by the oxide estimated based on the z-profiles of the raised patterns as well as of the trenches obtained after removing the oxide by treating with dilute HF, is similar to that of vitreous SiO2 at a moderate tip voltage of 8 V. A smaller voltage of 5 V produced a defect oxide (SiOx) as seen on the (111) surface while, a tip voltage of 10 V gave rise to a porous oxide that occupied, in relation to vitreous SiO2, ∼14% more volume in the case of (100) and (111) surfaces and ∼35% with the (110) surface. The nature of the oxide is related to the surface densities of the substrates, the (110) surface being dense requires more voltage to initiate oxidation but produces voluminous oxide. Nanoindentation on the LAO pattern yielded a hardness value of 4.3 GPa.