Fabricating a substantially self-aligned MOSFET

A method of fabricating a semiconductor device, comprising:

• providing a semiconductor substrate;
• disposing a first oxide layer on the substrate;
• disposing a nitride layer on the first oxide layer;
• removing portions of the first layers;
• removing portions of the substrate adjacent to the remaining first layers;
• disposing side walls on substantially coplanar surfaces of the first layers and the substrate;
• disposing second oxide layers on surfaces of the substrate which are substantially normal to the side walls;
• removing the side walls;
• disposing and planarizing a first layer of polysilicon on the second oxide layers;
• disposing a third oxide layer on the layer of polysilicon and on the nitride layer;
• removing the third oxide layer from a top of the nitride layer;
• removing the nitride layer to form a trench;
• disposing a second layer of polysilicon having a substantially uniform thickness over the trench and over the third oxide layer, so that the second layer of polysilicon forms a notch;
• disposing and planarizing a masking material into the notch so that the masking material substantially fills the notch;
• and then
• removing the second layer of polysilicon immediately adjacent to the masking material in a direction normal to the first layer of polysilicon, so that a vertical surface of the second polysilicon layer is substantially coplanar with a vertical surface of the first polysilicon layer.