Memory device and forming method thereof

A method of forming a memory device, comprising:

• providing a semiconductor substrate, wherein multiple active regions are formed in the semiconductor substrate, the multiple active regions are separated by multiple first trenches extending along a first direction and multiple second trenches extending along a second direction, and the first trench communicates with the corresponding second trench;
• forming, in the semiconductor substrate at a bottom of the first trench, a third trench extending along the first direction, wherein a width of the third trench is less than a width of the bottom of the first trench;
• forming a bit line doped region in the semiconductor substrate on two sides of the third trench and at the bottom of the first trench through an ion implantation process;
• forming a gate dielectric layer on a sidewall surface and a bottom surface of the first trench and a sidewall surface and a bottom surface of the second trench;
• forming a first dielectric layer that fills the third trench;
• forming a metal gate in the second trench and the first trench on the first dielectric layer, wherein a top surface of the metal gate is lower than a top surface of the active region;
• filling the second trench and the first trench above the metal gate with a second dielectric layer;
• etching a portion of the metal gate in the second trench, and segmenting the metal gate in the second trench along the second direction;
• forming a source region on the top surface of the active region;
• and
• forming, on a surface of the semiconductor substrate, a capacitor connected to the source region.