Study of Scanning Electron Microscope Irradiated Damage to Gate Oxides of Metal Oxide Semiconductor Field Effect Transistors

Abstract

Damage induced on typical structures of n-channel metal oxide semiconductor field effect transistors (MOSFETs) by irradiation from a scanning electron microscope (SEM) has been studied. It is observed that up to a critical SEM beam energy of 7 keV the devices are not affected. The maximum damage to the gate insulator occurs for an energy of ∼10 keV above which the extent of damage reduces. Therefore, depending on the device structure, this sets an upper limit on the beam energies during the processing sequence at ∼7 keV. Hot electron injection method used to fill up the traps in the SEM irradiated devices showed that in short channel devices (<3 µm) all the traps do not get labelled due to loss of hot electrons into the bordering field oxide regions. Hence, the threshold voltage does not come back to its unirradiated value even after the hot electron injection procedure, thereby restricting the injection method to devices of channel lengths greater than 3 µm.