Threshold Voltage Control at Double-Gate Devices

One of technological challenges for thin body MOSFETs is threshold voltage (Vt) control. Ideally, the FinFET body should be lightly doped in order to achieve high carrier mobility for high transistor drive current, as well as immunity to dopant-fluctuation-induced variations in Vt. The required range of gate work functions for a fully-depleted CMOS FinFET technology is 4.4 V (NMOS) ~ 5.0 V (PMOS), which precludes poly-Si as a gate material. A metal gate with a tunable technology and dual gate work function was announced [1-4]. However, manufacturability and reliability of a gate dielectric should be considered for implementation of metal gate technology to FinFETs.

In this work, molybdenum (Mo) will be used for PMOS and Mo2N will be used for NMOS gate material after selective nitrogen implantation and annealing. Multiple threshold voltages can be achieved by changing a dosage of nitrogen. As an alternative, separated double gates at narrow silicon fins will be formed by chemical-mechanical polishing. Threshold voltages can be adjusted by different gate biases at both gates.

[1]

I. Polishchuk, P. Ranade, T.-J. King, and C. Hu, "Dual Work Function Metal Gate CMOS Technology Using Metal Interdiffusion," IEEE Electron Device Lett., Vol. 22, 2001.

[2]

Q. Lu, R. Lin, P. Ranade, T.-J. King, and C. Hu, "Metal Gate Work Function Adjustment for Future CMOS Technology," Symp. VLSI Technology, Kyoto, Japan, June 2001.

[3]

R. Lin, Q. Lu, P. Ranade, T.-J. King, and C. Hu, "An Adjustable Work Function Technology Using Mo Gate for CMOS Devices," IEEE Electron Device Lett.,, Vol. 23, 2002.

[4]

M. Qin, V. M. C. Poon, and S. C. H. Ho, "Investigation of Polycrystalline Nickel Silicide Films as a Gate Material," J. Electrochemical Society, Vol. 148, 2001.