Nanoscale oxide structures are very important for the study of functional nanodevices. Local oxidation induced by electric field with scanning probe microscopy is a promising method. Some oxide lines and dots on Si surface were fabricated using conductive atomic force microscope in this paper. Nanoscale oxide lines induced by dc voltages exhibit the characteristic of single peak, but the hollow structures with higher aspect ratio are observed under the effect of square wave voltages. We present the hollow structures result from the finite diffuse speed and concentration of oxygen ion, and the higher aspect ratio results from the effect of dynamic electric field in the conductor-nonconductor-semiconductor junction formed in the course of fabrication.