Link between hot electrons and interface damage in n-MOSFETs: A Monte Carlo analysis

Typical measurements on n-channel MOSFETs show that interface damage, causi ng threshold and transconductance shifts, tends to peak when V-GS approxima te to 0.5V(DS). In such conditions, more impact ionization (substrate curre nt) is measured. At higher gate voltage, one expects that channel hot elect rons would impact the interface at increased energy and numbers. Therefore, it has normally been assumed that hot carriers in the channel cannot direc tly contribute to damage, and impact-generated holes must be injected into the oxide for damage to take place. However, there is increasing experiment al evidence that hot electrons should be able to remove hydrogen atoms whic h passivate interface dangling bonds, even through a multiple collision pro cess, at energies below oxide-injection threshold (typically 3.0 eV). A det ailed full-band Monte Carlo analysis shows that in a typical 0.25 mu m gate device there are, indeed, more energetic electrons hitting the surface whe n V-GS, = V-DS than at the condition of maximum impact damage V-GS approxim ate to 0.5V(DS). However, the electrons impact the surface at much shallowe r angles, with lower chance of perpendicular momentum transfer to the inter face. This analysis reconciles damage measurements with the physical pictur e suggesting direct damage generation by energetic electrons. (C) 1999 Else vier Science B.V. All rights reserved.