Method for fabricating small-size two-step contacts for word-line

Abstract

A method using a two-step contact process for making word-line strapping on DRAM devices was achieved. The method replaces a single-step contact process in which it is difficult to etch the smaller contact openings. After partially completing the DRAM cells by forming gate electrodes and word lines having a first hard mask, a planar first insulating layer is formed. Capacitor node contact openings are etched and capacitors with a protective second hard mask are completed. A thin first photoresist mask with improved resolution is used to etch small first contact openings in the first insulating layer to the word lines, while the second hard mask protects the capacitors from etching. Tungsten plugs are formed in the openings, and an interlevel dielectric layer is deposited over the capacitors. A thin second photoresist mask with improved resolution is used to etch second contact openings to the tungsten plugs. The word-line strapping for the DRAM is completed by forming tungsten plugs in the second contact openings. Since the tungsten plugs are formed after forming the capacitors, they are not subjected to high-temperature processing that could adversely affect the DRAM devices. The two thin photoresist masks replacing a thicker photoresist mask used in the single-step process allow smaller contact openings to be etched.