Achieving Conduction Band-Edge Effective Work Functions by La₂O₃ Capping of Hafnium Silicates

Conduction band-edge effective work functions (φ_m, eff) are demonstrated withTaCₓand TiN by means ofLa₂O₃capping ofHfSiOₓin a gate-first process flow with CMOS-compatible thermal budget. WithTaCₓ, a 10--thickLa₂O₃cap results in aφ_m, effof 3.9 eV with a low equivalent oxide thickness (EOT) increase (1–2) and unaffected electron mobility. With TiN, non-nitridedLa₂O₃capping results in a smallerφ_m, effreduction at a larger EOT increase, while with post-cap nitridation, the TiNφ_m, effis lower at a smaller EOT increase. Results show that the choice of metal and nitridation conditions have significant effects onLa₂O₃capped stacks.