Influences of structure around gate-edge on high electric field strength in MISFETs with high-k gate dielectrics

In this paper, dependences of electric field strength around gate-edge in gate dielectrics of MISFETs with high-k gate dielectrics on design parameters are studied. It is newly found that locations of sidewall/gate dielectric interfaces relative to gate electrode edges are critical to electric field strength of high-k MISFETs. Electric field can be as high as 4 MV/cm, which could have large influences on the yield of large scale integrated circuits (LSIs) with high-k gate dielectrics. An explanation of this phenomenon is given by considering discontinuity in electric field at interfaces between two materials with different dielectric constants. It is clarified that an electrical potential of side and top surfaces of gate dielectrics is strongly affected by the discontinuity of electric field strength at interfaces. As a result, electric field strength around gate electrode edges critically depends on locations of sidewall/gate dielectrics interfaces relative to gate electrode edges. Based on the physical considerations, a structure, in which gate sidewalls are also made of high-k materials, is studied from the viewpoint of electric field strength around gate electrode edges. It is shown that this structure effectively suppresses electric field strength around gate edges.