FN-degradation of S-RCAT with different grain size and oxidation method

• We realized Sphere-shaped-recess-cell-array-transistor to improve short channel effect.
• Negative shift of threshold voltage and increase of swing were observed after FN stress.
• The degradation was improved by small grain sized gate electrode and radical oxidation.
• We suggested the modeling of hole-trap in S-RCAT using energy band diagram.

Sphere-shaped-recess-cell-array-transistor (S-RCAT) has played a major role in the sub-80 nm design-rule DRAM. The Fowler–Nordheim (FN) degradation of gate oxide in S-RCAT has been studied with the gate electrode grain size and gate oxidation method. Negative shift of threshold voltage and increase of sub-threshold swing in NMOS cell transistor were observed under certain process conditions. As the grain size of gate poly-Si decreases, the negative shift of threshold voltage and increase of sub-threshold swing were decreased. In addition the negative shift perfectly disappeared in the radical oxidation instead of the thermal oxidation. It is assumed that the negative shifts of threshold voltage and the possibility of hole-trap originate from the curvature of energy band bending of S-RCAT. From our study, the electric filed in the recessed channel transistor must be reduced by the small grain sized electrode, and the radical oxidation which has low interface-trap is suitable for 3D-transistors.

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