Method of forming a level silicon oxide layer on two regions of different heights on a semiconductor wafer

The present invention relates to a method of forming a level silicon oxide layer on a semiconductor wafer. The semiconductor wafer comprises a substrate having a first region containing no silicon nitride on its surface and a second region which is higher than the first region and contains a silicon nitride layer on its surface. The method comprises performing a cleaning process on the semiconductor wafer with an alkaline solution to uniform the deposition rate over the surface of the first region; and performing a deposition process employing ozone as a reactive gas with a flow capacity of 80-200 g/L to form a silicon oxide layer above the first and second regions wherein the deposition rate of the silicon oxide layer on the first region is higher than that on the second region and the silicon oxide layer above the first region is leveled with that above the second region after a predetermined period of time.