Effect of strain on p-channel metal-oxide-semiconductor field-effect-transistor current enhancement using stress-modulated silicon nitride films

Abstract

The stress in chemical-vapor-deposited silicon nitride films (∼100nm thick) is modulated by an ion implantation technique. The tensile-strained silicon nitride film is deposited on the back and front sides of a Si wafer. After implantation of P+, As+, Sb+, or BF2+ ion species, the stress of the silicon nitride film becomes compressive on the front side. It can be explained by strain relaxation of Si–N bond on the front side and highly tensile-strained Si–N bond on the back side of wafer. The compressive stress is increased with a double-implantation process because of more atomic collisions in the silicon nitride film, as well as more strain relaxation of Si–N bond on the front side of wafer. After a thermal annealing process, the compressive stress in the silicon nitride film with P+, As+, or Sb+ implantation is reduced, while compressive stress is increased for BF2+ ion implantation due to formation of the B–N bond in silicon nitride film. To justify the stress-modulated silicon nitride film by the ion implantation technique, the p-channel metal-oxide-semiconductor field-effect transistor (p-MOSFET) is fabricated. The drive current of a p-MOSFET is improved by 7–13% for implanted silicon nitride films, due to the compressive strain-induced effective mass lowering in the channel.