Composite silicon nitride sidewall spacers for reduced nickel silicide bridging

摘要

Bridging between nickel silicide layers on a gate electrode and source/drain regions along silicon nitride sidewall spacers is prevented by employing composite silicon nitride sidewall spacers comprising an outer layer having reduced free silicon. Embodiments include forming composite silicon nitride sidewall spacers comprising an inner silicon nitride layer, having a refractive index of about 1.95 to about 2.05 and a thickness of about 450 Å to about 550 Å, on the side surfaces of the gate electrode and an outer silicon nitride layer, having a refractive index to less than about 1.95 and a thickness of about 350 Å to about 450 Å.