Octadecyltrichlorosilane self-assembled-monolayer islands as a self-patterned-mask for HF etching of SiO2 on Si

Octadecyltrichlorosilane (OTS), self-assembled-monolayer (SAM) grown on SiO2 in the submonolayer region is investigated by atomic force microscope (AFM), which is further applied to SiO2 characterizations technique. OTS-SAM forms characteristic dendrite-shaped islands in its submonolayer region, whose shape and size significantly depend on the surface roughness of SiO2 formed at different temperatures in the range of 700–1100 °C. Moreover, OTS-SAM islands have practical usefulness as a self-patterned-mask for HF etching. When an oxidized Si wafer covered by OTS-SAM islands is dipped into HF, SiO2 in the area uncovered by the islands is selectively removed. This technique is successfully applied for the precise SiO2 thickness measurement in ultrathin (50 Å) regions by AFM. In addition, this technique enables a simultaneous observation of the morphologies of SiO2 surface and SiO2/Si interface. The result shows, for the first time, the continuity of the steps on SiO2 surface and SiO2/Si interface, indicating no lateral step motion of Si (111) surface during oxidation.