Memory device and method for manufacturing the same

A method for manufacturing a memory device, comprising:

• preparing a substrate, wherein the substrate comprises an array region and a peripheral region;
• forming two first gate structures in the array region;
• forming a multilayer insulating structure on the first gate structures, wherein the multilayer insulating structure comprises:
• a first insulating layer formed on and covering the first gate structures;
• a second insulating layer formed on the first insulating layer, wherein a width of the second insulating layer is smaller than a width of the first insulating layer;
• a third insulating layer formed on the second insulating layer, wherein a width of the third insulating layer is the same as the width of the second insulating layer;
• and
• a fourth insulating layer formed on the third insulating layer, wherein a width of a bottom surface of the fourth insulating layer is greater than a width of a top surface of the third insulating layer;
• and
• forming a capacitor contact plug between the first gate structures, wherein the capacitor contact plug comprises:
• a first contact element formed on the substrate;
• a second contact element formed on the first contact element, wherein a width of a top surface of the second contact element is greater than a width of a bottom surface of the second contact element;
• and
• a buffer layer formed between the first contact element and the second contact element.