Abstract
A method for forming a semiconductor device structure is provided. The method includes forming a first gate stack, a second gate stack, and a third gate stack, which are positioned over a semiconductor substrate and spaced apart from each other. The method includes removing portions of the semiconductor substrate to form a first recess, a second recess, and a third recess in the semiconductor substrate. The method includes forming a first doped structure, a second doped structure, and an isolation structure in the first recess, the second recess, and the third recess respectively. The first gate stack, the second gate stack, the first doped structure, and the second doped structure together form a memory cell. The isolation structure is wider and thinner than the second doped structure. A top surface of the isolation structure has a fourth recess.