Electrical Characteristics of the Uniaxial-Strained nMOSFET with a Fluorinated HfO₂/SiON Gate Stack

Area of Science:

• Materials Science
• Semiconductor Physics
• Device Engineering

Background:

• Uniaxial tensile strain from SiN CESL improves nMOSFET electrical performance.
• Integration challenges and reliability concerns in advanced gate stacks require investigation.

Purpose of the Study:

• To investigate the combined effects of channel fluorine implantation (CFI) and SiN CESL on strained nMOSFETs.
• To evaluate the impact of fluorine incorporation on strain effects and device reliability.

Main Methods:

• Fabrication of n-channel metal-oxide-semiconductor field-effect transistors (nMOSFETs) with HfO₂/SiON gate stacks.
• Integration of SiN CESL for strain engineering and CFI for reliability enhancement.
• Electrical characterization and reliability testing including constant voltage stress (CVS) and channel hot electron stress (CHES).

Main Results:

• CFI integration with SiN CESL-strained nMOSFETs did not alter transconductance, subthreshold swing, or drain current, indicating strain effects are unaffected.
• Fluorine incorporation in the HfO₂/SiON gate stack improved resistance to channel hot electron stress by forming stronger Hf-F and Si-F bonds.
• Both SiN CESL and CFI processes led to reduced charge detrapping, with stress-induced charges remaining in the gate stack.

Conclusions:

• The strain effect in SiN CESL-strained nMOSFETs is independent of fluorine incorporation via CFI.
• CFI enhances the reliability of strained nMOSFETs against hot carrier stress by mitigating interface degradation.
• Further research is needed to fully understand charge trapping mechanisms in these advanced transistor structures.