The Lanthanum oxide capping layer induced flat-band roll-off behaviors in high-κ/metal-gate NMOSFETs with 28nm CMOS technology

The Lanthanum oxide (LaO_x) capping layer induced flat-band voltage (V_FB) roll-off behaviors for a high-κ/metal-gate n-MOSFET prepared by the 28nm CMOS technology are investigated in details. Experimental results show the V_FB roll-off increases with EOT scaling down. With EOT =1 nm, 10 cycles and 20 cycles ALD LaO_x capping layers cause significant V_FB roll off ~282 mV and~ 550 mV to result in threshold voltage shift ~292-mV and ~543-mV, respectively. Systematical analysis including gate C/V, gate I/V and V_FB vs. EOT were applied to study the significant V_FB roll-off behavior. In addition, the related mechanism is explained comprehensively with a proposed model.