Method and structure for work function engineering in transistors including a high dielectric constant gate insulator and metal gate (hkmg)

Abstract

Adjustment of a switching threshold of a field effect transistor including a gate structure including a Hi-K gate dielectric and a metal gate is achieved and switching thresholds coordinated between NFETs and PFETs by providing fixed charge materials in a thin interfacial layer adjacent to the conduction channel of the transistor that is provided for adhesion of the Hi-K material, preferably hafnium oxide or HfSiON, depending on design, to semiconductor material rather than diffusing fixed charge material into the Hi-K material after it has been applied. The greater proximity of the fixed charge material to the conduction channel of the transistor increases the effectiveness of fixed charge material to adjust the threshold due to the work function of the metal gate, particularly where the same metal or alloy is used for both NFETs and PFETs in an integrated circuit; preventing the thresholds from being properly coordinated.