Characterization of MoSi<inf>2</inf>-gate buried channel MOSFET's for a 256K-bit dynamic RAM

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MoSi 2 -gate buried channel MOSFETs as a transfer gate of a memory cell and an element of peripheral circuits of a 256k-bit dynamic RAM have been investigated. Two-dimensional numerical analysis predicts that MoSi 2 -gate buried channel MOSFETs have inherently larger subthreshold leakage current than conventional Si-gate MOSFETs, but it can be improved by a deep ion-implantation. Experimental results which support the analytical predictions will be presented. It is found by BT-stress test that MoSi 2 -gate MOSFETs are much more reliable than Si-gate MOSFETs concerning the oxide breakdown. This is due to the buried channel structure, and hence, is one of very attractive features of MoSi 2 -gate MOSFETs. To verify the applicability of MoSi 2 - gate MOSFETs to a 256k-bit dynamic RAM, memory cell arrays with a unit cell area of 5.6 × 13 µm2were fabricated. The measured memory holding time is 6 ∼ 8 msec at 100°C, which assures the 4 msec refresh time of a 256k-bit dynamic RAM.

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