High voltage field effect transistors with different sidewall spacer configurations and method of making the same

A semiconductor structure, comprising:

• a first field effect transistor located over a substrate in a first device region and comprising first active regions laterally spaced from each other by a first semiconductor channel, a first gate dielectric overlying the first semiconductor channel, a first gate electrode overlying the first gate dielectric, and a first gate spacer having first laterally-straight outer sidewalls that have first laterally-straight bottom edges that coincide with top edges of first laterally-straight sidewalls of the first gate dielectric;
• and
• a second field effect transistor located in a second device region of the substrate and comprising second active regions laterally spaced from each other by a second semiconductor channel, a second gate dielectric overlying the second semiconductor channel and the second active regions, a second gate electrode overlying the second gate dielectric, and a second gate spacer comprising:
• a first portion located on a first side of the second gate electrode and having a second laterally-straight outer sidewall that has a first laterally-straight bottom edge that coincides with a top edge of a second laterally-straight sidewall of the second gate dielectric;
• and
• a second portion located on a second side of the second gate electrode and having a contoured portion that overlies a portion of a top surface of the second side of the second gate electrode and that laterally surrounds the second gate electrode, and a horizontally-extending portion that overlies one of the second active regions and including a discrete gate-spacer opening therethrough that overlies a discrete gate-dielectric opening through the second gate dielectric.