Enhanced electron trapping near channel edges in NMOS transistors

Charge trapping in the gate oxide of NMOS transistors due to constant-voltage Fowler-Nordheim injection was investigated. Results from several different measurement methods consistently indicated strongly enhanced electron trapping in the gate oxide near the channel edges and in the gate oxide overlaps above drain and source, although net positive charge was observed in the bulk of the channel. The edge trapping effect could increase the electrical channel length by as much as 0.5 mu m and is independent of the channel length. Possible reasons for the observed phenomena are discussed.