The distribution of radiation-induced charged defects and neutral electron traps in SiO sub 2 , and the threshold voltage shift dependence on oxide thickness
- Microelectronics Center of North Carolina, Post Office Box 12889, Research Triangle Park, North Carolina 27709 (US)
As insulated gate field effect transistor dimensions continue to decrease, and fabrication sequences rely increasingly on processes that involve ionizing radiation, it becomes essential to understand the radiation-induced threshold voltage shift ({Delta}{ital V}{sub {ital T}}) dependence on gate-insulator thickness ({ital t}{sub ox}), since threshold voltage tolerances are required to scale with device dimensions. In the present study, {ital n}-channel insulated gate field effect transistor devices were fabricated with gate-insulator thicknesses ranging from 6--50 nm, and were then exposed in an unbiased state to Al{ital K}{alpha} x-ray radiation to simulate process-induced ionizing radiation exposure. Gate-oxide Coulombic defects and neutral electron traps were measured before and after irradiation using optically assisted electron injection. Following irradiation and injection, the measured voltage shifts indicated that the extrinsic'' defects are localized near, but not at, the Si/SiO{sub 2} interface. For oxide thicknesses where the top gate electrode lies in the region above the extrinsic defect volume {Delta}{ital V}{sub {ital T}} is found to be linear in {ital t}{sub ox}; at thicknesses where the top gate electrode encroaches upon the defect region, {Delta}{ital V}{sub {ital T}} is found to be quadratic in {ital t}{sub ox}, and for very thin oxides, {Delta}{ital V}{sub {ital T}} is observed to approach zero. A defect distribution model that applies to process-induced radiation exposure is formulated to explain this behavior. This model also provides a unique and simple method for determining the defect centroid in gate insulators that have been exposed under such irradiation conditions.
- OSTI ID:
- 6910100
- Journal Information:
- Journal of Applied Physics; (USA), Vol. 67:6; ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SILICON
PHYSICAL RADIATION EFFECTS
SILICON OXIDES
CRYSTAL DEFECTS
FIELD EFFECT TRANSISTORS
INTERFACES
SPATIAL DISTRIBUTION
TRAPS
X RADIATION
CHALCOGENIDES
CRYSTAL STRUCTURE
DISTRIBUTION
ELECTROMAGNETIC RADIATION
ELEMENTS
IONIZING RADIATIONS
OXIDES
OXYGEN COMPOUNDS
RADIATION EFFECTS
RADIATIONS
SEMICONDUCTOR DEVICES
SEMIMETALS
SILICON COMPOUNDS
TRANSISTORS
360605* - Materials- Radiation Effects