Method of forming a self-aligned contact hole on a semiconductor wafer

A method of forming a self-aligned contact hole in a semiconductor wafer, the semiconductor wafer comprising:

• a silicon substrate;
• an array area located on the substrate comprising memory cells of a DRAM, at least one active area, a first gate electrode adjacent to a side of the active area, and a second gate electrode adjacent to an opposite side of the active area;
• and
• a periphery area located on the substrate comprising a control circuit of the DRM, the control circuit comprising at least one third gate electrode;
• the method comprising:
• forming a first doped area over each of two opposite sides of each gate electrode, each of the first doped areas adjacent to the third gate electrode serving as a lightly doped drain (LDD) of the third gate electrode;
• forming a first silicon oxide layer to cover the substrate and all of the gate electrodes on the surface of the substrate;
• forming a first photoresist layer on the surface of the first silicon oxide layer;
• performing a lithographic process to remove the first photoresist layer over the periphery area;
• performing a first dry etching process to remove a portion of the first silicon oxide layer in the periphery area, the remainder of the first silicon oxide layer in the periphery area thereby forming the first spacers on the walls of two opposite sides of the third gate electrode;
• removing the first photoresist completely;
• performing an ion implantation process to form a doped area on the surface of the substrate adjacent to each of the two first spacers, these two doped areas serving as source and drain for the third gate electrode;
• forming a silicide layer on the surface of the source and the drain;
• and
• forming a second spacer on a wall of each of the two opposite sides of the first gate electrode and the second gate electrode in the active area;
• wherein the first spacers are thicker than the second spacers, and the second spacers between the first and second gate electrodes are used as internal walls of a self-aligned contact hole between the first and second gate electrodes.