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High frequency CV curves of HfSiON with a TaC metal gate with and without a Gd capping layer. The EOT is 1.15 nm for MOSFET without a Gd capping layer and 0.9 nm for that with a Gd capping laye. Normalized CV characteristics of both samples are almost identical, as shown in the inset.
Flatband voltage vs EOT characteristics on terraced oxide capacitors. The Gd capping layer induced over 300 mV of EWF shift. TaC metal gate with Gd capping layer had lower EWF (4.2 eV) than the TaC metal gate without a Gd capping layer (4.54 eV).
Backside SIMS depth profiling of the gate stack with a Gd capping layer. The Gd signal indicates the Gd atom diffused through the gate stack and accumulated in the bottom of gate dielectric. This may be a primary cause of EOT reduction and EWF shift.
shift due to RE doping varies with dopant EN (see Ref. 9). The schematic explanation of a RE–O–Hf dipole model is shown in inset (see Ref. 9).
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