Manufacturing method of memory device

A method for manufacturing a memory device is provided, the method includes the following steps: firstly, providing a dielectric layer, then simultaneously forming a contact window and an alignment mark trench in the dielectric layer, wherein the contact window exposes a lower metal line, then forming a conductive layer on the surface of the dielectric layer, in the contact window and in the alignment mark trench, performing a planarization step on the conductive layer, and leaving a residue in the alignment mark trench. Subsequently, a nitrogen plasma step (N2 plasma) is performed on the dielectric layer, a cleaning step is performed to remove the residue in the alignment mark trench, and a patterned magnetic tunneling junction, MTJ) film is laminated on the contact window.