Pad oxide protect sealed interface isolation

摘要

Field oxide regions are formed between drive regions of a silicon substrate by forming over the substrate a sandwich of silicon dioxide, silicon nitride and silicon dioxide layers, opening the layers to expose a portion of the silicon substrate, removing a layer of the exposed substrate, forming side wall spacers on the edges of the opening, removing a layer of the silicon substrate exposed between the side wall spacers, and then reaching the exposed substrate for the thermal oxidation of the exposed substrate for forming the field oxide region. In those structures in which the field oxide is buried in the substrate as shown in FIG. 12, it may be feasible to use thicker field oxide regions and thereby to reduce the need for the heavily doped surface layer under the field oxide.