We report the first detailed study of dishing effects in chemical mechanical polishing (CMP) of oxide films, observed during the development of an advanced CMP-only trench isolation process. The degree of dishing has been determined for field widths ranging from 0.3 μm to 4 mm and was found to be highly pattern geometry (field width) sensitive, increasing from ∼0 nm at a field width of 5 μm and below to 200 nm at 4 mm. Although this dishing effect makes complete planarization in a large field oxide region (on the order of 1 mm) difficult, it poses no serious problem for trench isolation in narrow field regions due to its reduced effect at small field geometries.

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Ultrathin dielectric materials that provide high capacitance values are needed for 64-and 256-Mb stacked DRAM's. This paper shows that capacitance values as high as 12.3 fF/pmZ can be obtained with ultrathin nitride-based layers deposited on rugged polysilicon storage electrodes. In addition, these films present the reliability and low leakage current levels required for 3.3-V applications. The nitride thickness, however, cannot be scaled much below 6 nm to avoid the oxidationpunchthrough mechanisms that appear when too-thin films are unable to withstand the reoxidation step.

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