Dual-type CMOS gate electrodes by dopant diffusion from silicide

Dual work function gate electrodes have been implemented in a 1-μm CMOS process. Dopant atoms were implanted into tungsten silicide simultaneously with the source-drain implantations and subsequently diffused into the underlying polycrystalline silicon layer by rapid thermal annealing. Physical analyses showed that arsenic and boron could easily be incorporated in the polysilicon to concentrations greater than 10²⁰ cm^-3. Capacitor and transistor measurements confirmed that n⁺ and p⁺ silicon could be obtained, with a difference of about 1 V between the respective flat-band voltages. By comparison with conventional n-type gate MOSFETs, it was verified that significantly improved subthreshold characteristics were obtained with p-type PMOS gate electrodes