| 摘要 |
A multiple LOCOS (local oxidation) process shapes a surface of a substrate to form a series of planar regions which are vertically separated from each other. One exemplary process forms a hard mask layer for each LOCOS operation. Another exemplary process includes forming a silicon nitride mask layer and repeatedly changing the pattern of that mask layer. Each change in the pattern corresponds to a planar region to be formed; and after each change, oxide is grown in openings through the mask layer. The growth of oxide consumes part of the substrate and provides a vertical separation between the planar level corresponding to the pattern and a next higher planar level. Regions of the substrate once exposed by a mask pattern can remain exposed so that subsequent LOCOS operations maintain previously established separations between levels. A hard mask layer can include a polysilicon layer which protect a silicon nitride layer from conversion to oxide during the repeated LOCOS operations.
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