Method for preparing contact plug structure

摘要

In a further embodiment of the present invention, a method for preparing a contact structure includes the steps of forming a conductive stack on the semiconductor substrate; forming a patterned mask on the conductive stack; forming a depression in an upper portion of the conductive stack; forming a spacer layer on the surface of the depression and the patterned mask; forming a mask block filling the depression; removing a portion of the spacer layer not covered by the mask block; and removing a portion of the conductive stack by using the mask block and the patterned mask to form the contact structure including at least one tall contact plug under the patterned mask and at least one the short contact plug under the mask block.