Vertical MOSFET with dual work function materials

Details Vertical MOSFET with dual work function materials Vertical MOSFET with dual work function materials

2007-11-13

2007-11-13

Ngô, Ngân V. (Department: 2818)

Active solid-state devices (e.g., transistors, solid-state diode

Field effect device

Having insulated electrode

C257S301000, C257SE27084, C257SE21655

Reexamination Certificate

active

10622477

ABSTRACT:
A vertical pass transistor used in a DRAM cell for maintaining a low total leakage current and providing adequate drive current is described together with a method of fabricating such a device. The transistor gate is engineered in lieu of the channel. The vertical pass transistor for the DRAM cell incorporates two gate materials having different work functions. The gate material near the storage node is n-type doped polysilicon. The gate material near the bit line diffusion is made of silicide or metal having a higher work function than the n-polysilicon. The novel device structure shows several advantages: the channel doping is reduced while maintaining a high Vt and a low sub-threshold leakage current; the carrier mobility improves with the reduced channel doping; the body effect of the device is reduced which improves the write back current; and the sub-threshold swing is reduced because of the low channel doping.

REFERENCES:
patent: 6696717 (2004-02-01), Chang et al.
patent: 2005/0139884 (2005-06-01), Lane
H. Akatsu et al., “A highly manufacturable 110nm DRAM technology with 8F2 vertical transistor cell for 1Gb and beyond”, IEEE 2002 Symposium on VLSI Technology Digest of Technical Papers.
K. McStay et al., “Vertical pass transistor design for sub-100nm DRAM technologies”, IEEE 2002 Symposium on VLSI Technology Digest of Technical Papers.
J. A. Mandelman et al., “Challenges and future directions for the scaling of dynamic random-access memory (DRAM)”, IBM Journal of Research and Development, vol. 46, No. 2/3, Mar./May 2002, pp. 187-208.

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