Physics of trap generation and electrical breakdown in ultra-thin SiO2 and SiON gate dielectric materials


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Nicollian, Paul Edward (2007) Physics of trap generation and electrical breakdown in ultra-thin SiO2 and SiON gate dielectric materials. thesis.

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Abstract:This work spans nearly a decade of industrial research in the reliability physics of deeply scaled SiO2 and SiON gate dielectrics. Our following original contributions include:

• Below 35Å, the dominant mechanism for stressed induced leakage current in the off-state is tunneling via interface traps. Traps at both top and bottom interfaces participate in the transport process.

• A conclusive experimental proof showing that breakdown is voltage rather than field driven in ultra-thin oxides. This work has been instrumental in ending the long running controversy in the industry on breakdown models.

• Experimental verification that anode hole injection through minority ionization remains a plausible breakdown mechanism down to 3.6V. However, anode hole injection is eliminated as the mechanism for breakdown below 2.7V.

• Plasma nitridation of oxides extends the reliability scaling limit of SiO2 based films. Trap generation rates are minimized and reliability is optimized when the nitrogen profile is uniform. These films are now widely used in volume manufacturing.

• Reaction-diffusion theory applies for PBTI stress of ultra-thin NMOS SiON films. This finding enables the determination of the mechanisms for trap generation and breakdown. Two species of hydrogen (H+ and H0) are released from the anode in two separate anode reactions. H+ and H0 both create interface traps at the poly interface. After migrating into the dielectric, H+ creates bulk traps while H0 creates interface traps at the pwell interface. The hydrogen species that controls breakdown is voltage dependent. The mechanism transitions from hole induced H+ desorption to electron induced H0 desorption below the 2.7V threshold for vibrational excitation of Si-H bonds.

• Bulk traps control breakdown in SiO2 below 30Å. In SION, below the 2.7V threshold for vibrational excitation of Si-H bonds, the rate limiting step is the generation of interface traps. A minimum of two traps is required to cause breakdown in SiON films down to 10Å EOT and at least must be a bulk state. The SiON bulk trap diameter is 4Å, which is smaller than earlier estimates and results in the Weibull slope remaining greater than 1 down to the 12Å physical thickness limit.
Item Type:Thesis
Faculty:
Electrical Engineering, Mathematics and Computer Science (EEMCS)
Research Group:
Link to this item:http://purl.utwente.nl/publications/58722
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