Patent ID: 7781824

Claim:
A memory cell of a nonvolatile semiconductor memory comprising: source/drain diffusion layers formed separately on a surface part of a semiconductor substrate; a first insulating film whose principal constituent elements are Si, O and N, formed on a channel between the source/drain diffusion layers; a charge storage layer whose principal constituent elements are Hf, O and N, formed on the first insulating film; a second insulating film having dielectric constant higher than that of the first insulating film and formed on the charge storage layer; and a control gate electrode formed on the second insulating film, wherein when a composition of the first insulating film is defined as (SiO 2 ) x (Si 3 N 4 ) 1-x (where 0<x<1), a composition of the charge storage layer is defined as (HfO 2 ) y (Hf 3 N 4 ) 1-y (where 0<y<1), and further valence band offsets of a silicon oxide film, a silicon nitride film, a hafnium oxide film and a hafnium nitride film are represented by φ V (SiO 2 ), φ V (Si 3 N 4 ), φ V (HfO 2 ), and φ V (Hf 3 N 4 ), respectively, correlation between a compositional ratio x of the first insulating film and a compositional ratio y of the charge storage layer meets: y < 7 ⁢ ( 1 - w ) 7 - 4 ⁢ w ⁢ [ where ⁢ ⁢ 0 < x < 1 , 0 < y < 1 ] w = { ϕ v ⁡ ( SiO 2 ) - ϕ v ⁡ ( Si 3 ⁢ N 4 ) } ⁢ 7 ⁢ ( 1 - x ) 7 - 4 ⁢ x - { ϕ v ⁡ ( SiO 2 ) - Φ v ⁡ ( HfO 2 ) } { ϕ v ⁡ ( HfO 2 ) - ϕ v ⁡ ( Hf 3 ⁢ N 4 ) } and, in the case where trap energy levels due to oxygen vacancies in a hafnium oxide film and a hafnium nitride film are represented by E t (HfO 2 ) and E t (Hf 3 N 4 ) which are evaluated in such a way that band edges of respective conduction bands are defined as reference points and direction within band gap is defined as positive direction, the compositional ratio y of the charge storage layer meets: y > 1 1 - 3 7 ⁢ E t ⁡ ( HfO 2 ) E t ⁡ ( Hf 3 ⁢ N 4 ) .