Importance

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Abstract

A DRAM cell structure with extended trench, the DRAM cell structure comprises: a NMOS transistor and a trench capacitor connected with the source electrode of the NMOS transistor; the trench capacitor comprises: a semiconductor substrate; a multilayer structure as the bottom plate of the trench capacitor, formed over the semiconductor substrate, which is composed of N-type SiGe layers and N-type Si layers arranged alternatively; a trench formed through the multilayer structure deeply into the semiconductor substrate, whose sidewall cross section is serrate-shaped; a dielectric layer formed on the inner face of the trench; a first polycrystalline silicon layer which is filled in the trench as the top plate of the trench capacitor; and a P-type Si layer formed over the multilayer structure. The present invention adopts doping epitaxial growth process to fabricate a multilayer structure composed of N-type SiGe layers and N-type Si layers arranged alternatively as the bottom plate of the trench capacitor. Compared with the traditional buried plate, the fabricating process is simplified. In addition, the present invention adopts selective etching process to form a sidewall having a serrate-shaped cross section. This improved structure increases capacitor plate area and thus even thick dielectric layer will achieve required capacitance.

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First Claim