Methods of forming dual gate semiconductor devices having a metal nitride layer

A method of forming a dual gate, comprising:

• providing a semiconductor substrate having a first region of a first conductivity type and a second region of a second conductivity type;
• forming a mold insulating layer on the semiconductor substrate;
• patterning the mold insulating layer to form a first gate groove in the first region of the semiconductor substrate and to form a second gate groove in the second region of the semiconductor substrate;
• forming a gate insulating layer on the semiconductor substrate and the first and second gate grooves;
• forming an initial metal nitride layer on the gate insulating layer, opposite to the semiconductor substrate, wherein the initial metal nitride layer fills the first and second gate grooves;
• planarizing the initial metal nitride layer to form a first gate electrode in the first gate groove and a backup second gate electrode in the second gate groove;
• and
• implanting nitrogen ions into the backup second gate electrode to form a second gate electrode, wherein a work function of the second gate electrode is higher than that of the first gate electrode.