Method for forming semiconductor device structure

A method for forming a semiconductor device structure, comprising:

• forming a first isolation structure and a second isolation structure penetrating into the substrate, wherein the first isolation structure has a first upper surface and a first protruding edge extending away from the substrate, the first upper surface has a first recess extending below a first top of the first isolation structure, and the first recess is between the first top and the first protruding edge;
• forming a gate dielectric layer over the substrate between the first isolation structure and the second isolation structure, a first sidewall of the first isolation structure, and the first recess;
• forming a first gate over the gate dielectric layer, wherein the first gate has a lower portion, an upper portion over the lower portion, and a neck portion between the lower portion and the upper portion, and a first width of the lower portion is greater than a second width of the neck portion;
• forming a dielectric layer over the first gate;
• and
• forming a second gate over the dielectric layer and above the first gate.

A method for forming a semiconductor device structure, comprising:

• forming a first isolation structure and a second isolation structure penetrating into the substrate, wherein the first isolation structure has a first upper surface and a protruding edge extending away from the substrate, the first upper surface has a first recess extending below a top of the first isolation structure, and the first recess is between the top and the protruding edge;
• forming a gate dielectric layer over the substrate, the first isolation structure, and the second isolation structure;
• forming a first gate over the gate dielectric layer, wherein the first gate has a lower portion, an upper portion over the lower portion, and a neck portion between the lower portion and the upper portion, and a first width of the lower portion is greater than a second width of the neck portion;
• forming a dielectric layer over a second upper surface and a first sidewall of the first gate, a second sidewall of the gate dielectric layer, the first isolation structure, and the second isolation structure;
• and
• forming a second gate over the dielectric layer and above the first gate.