Integrated circuits with laterally diffused metal oxide semiconductor structures and methods for fabricating the same

A method for forming an LDMOS integrated circuit comprising:

• forming an n-type reduced surface field region and a p-type body well in a semiconductor substrate, wherein the p-type body well is disposed on a lateral side of the n-type reduced surface field region;
• forming a first trench within the n-type reduced surface field region;
• forming a shallow trench isolation structure within the trench;
• forming a second trench within the shallow trench isolation structure;
• and
• forming a gate structure over the n-type reduced surface field region, over the p-type body well, over the shallow trench isolation structure, and within the second trench.

A laterally diffused metal oxide semiconductor (LDMOS) integrated circuit structure comprising:

• a p-type semiconductor substrate;
• an n-type deep well region disposed over and in contact with the p-type semiconductor substrate;
• an n-type reduced surface field region disposed over and in contact with the n-type deep well region;
• a p-type body well disposed on a lateral side of the n-type reduced surface field region;
• a shallow trench isolation structure disposed within the n-type reduced surface field region;
• and
• a gate structure disposed partially over the p-type body well, partially over the n-type reduced surface field region, partially over the shallow trench isolation structure, and partially within the shallow trench isolation structure,
• wherein the shallow trench isolation structure comprises first and second silicon oxide layers separated by the at least one silicon nitride layer,
• wherein the gate structure extends into the shallow isolation trench structure below an upper surface defined by the p-type body well and the n-type reduced surface field region, and
• wherein the gate structure extends into the shallow trench isolation structure through the second silicon oxide layer to contact with the silicon nitride layer, but does not extend through the silicon nitride layer.