Abstract
The isolation characteristics of COB (capacitor over bit-line)-DRAMs was degraded, only when TEOS (tetraethyl orthosilicate)-BPSG (boron phosphor silicate glass) film was used for the interlayer oxide, which was covered with the silicon nitride film. The measurement of V fb (flat band voltage) of the capacitor indicated that there were the positive charges around the SiO 2 Si interface, which made the substrate n-type. SIMS (Secondary Ion Mass Spectrometry) by detecting MCs + ions showed that the amount of piled-up carbon at the interface increased with increasing annealing temperature, and this increase was consistent with the V fb shift. Therefore, the isolation degradation was considered to be caused by positive charges which were originated from piled-up carbon. The SIMS analysis also showed that the total amount of carbon in the oxide seemed to be unchanged by the heat treatment, indicating that residual organic compounds migrated from the TEOS-BPSG layer to the SiO 2 Si interface during the heat treatment, since the silicon nitride layer prevented their out-diffusion.
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