| CPC H01L 27/092 (2013.01) [H01L 21/28088 (2013.01); H01L 21/823821 (2013.01); H01L 21/823842 (2013.01); H01L 27/0924 (2013.01); H01L 29/401 (2013.01); H01L 29/4966 (2013.01); H01L 29/66545 (2013.01)] | 20 Claims |

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1. A semiconductor device comprising:
a substrate having an N-type region;
a gate stack over the N-type region of the substrate and comprising:
a gate dielectric layer;
a bottom work function (WF) metal layer over the gate dielectric layer;
a top WF metal layer over and in contact with the bottom WF metal layer, wherein dipoles are formed between the top WF metal layer and the bottom WF metal layer, and the dipoles direct from the top WF metal layer to the bottom WF metal layer; and
a filling metal over the top WF metal layer; and
epitaxy structures over the N-type region of the substrate and on opposite sides of the gate stack.
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