MOSFET with decoupled halo before extension

A method of forming at least one field effect transistor having an inverse-T gate structure with at least two ledges extending along a transistor axis from the sides of a central gate structure by a ledge distance, comprising the steps of:

• forming a gate dielectric on a portion of a semiconductor substrate having a first polarity;
• and
• forming a gate electrode disposed above the gate dielectric and having an inverse-T structure;
• in which said step of forming a gate electrode comprises the steps of:
• forming a gate dielectric on a semiconductor substrate having a first polarity:
• depositing a ledge layer of a first material over said gate dielectric;
• depositing a temporary layer of a second material over said gate dielectric;
• forming a first damascene aperture having vertical interior walls and extending down to said ledge layer in said temporary layer;
• forming a set of vertical spacers of a third material different from said second material on said interior walls of said damascene aperture, thereby forming a second damascene aperture;
• forming a gate electrode disposed above the ledge layer in said second damascene aperture;
• stripping the vertical spacers and thereby forming an inverse T gate electrode from the gate electrode and the ledge layer;
• implanting a halo implant of said first polarity and a halo concentration in the substrate on opposite sides of the gate electrode, self-aligned to the central gate structure and passing through said ledges to a halo depth;
• forming a pair of disposable spacers adjacent to said central gate structure and extending past said ledge distance over a portion of the halo implant;
• implanting a self-aligned S/D region of a second polarity opposite said first polarity in the substrate and self-aligned to said disposable spacers, said S/D region having a concentration greater than said halo concentration and having a S/D depth greater than said halo depth;
• activating the S/D implant;
• implanting in the substrate an extension implant of said second polarity self-aligned to said ledges;
• and
• activating the extension implant.