Paper EL-TuP10
Bonding Chemistry of Alternative Gate Dielectrics: Is there Really an Alternative Gate Dielectric that can Meet SIA Roadmap Expectations for Performance, Reliability and Process Integration?
Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D
This paper presents a new classification scheme for non-crystalline metal oxides that have been considered as replacements for SiO@sub2@ in Si devices with channel lengths < 100 nm.. The scheme is based on relative bond ionicity, and the scaling parameter is the difference in the Pauling electronegativity, @Delta@X, between the oxygen, X(O), and metal (semiconductor), X(M), atoms. This approach distinguishes between three groups of non-crystalline elemental oxides with different bonding micro-structures: i) @Delta@X < 1.6 - covalent random networks such as SiO@sub2@, B@sub2@O@sub3@, and P@sub2@O@sub5@, ii) 1.6< @Delta@X < 2.0 - random amphoteric networks with interstitial ions such as Al@sub2@O@sub3@ and Ta@sub2@O@sub5@, and iii) @Delta@X > 2 - random close packed ionic structures such as Zr(Hf)O@sub2@, and Y(La)@sub2@O@sub3@. This approach has been extended to binary oxides and alloys. Systematic trends in atomic bonding arrangements and thermal stability with increasing @Delta@X are addressed for i) elemental oxides such as Al@sub2@O@sub3@, Ta@sub2@O@sub5@ and ZrO@sub2@, and ii) binary silicate alloys, such as (ZrO@sub2@)@subx@(SiO@sub2@)@sub(1-x)@ that span the entire range of @Delta@X. As @Delta@X increases, the atomic coordination of the metal atom increases, and thermal stability with respect to crystallization decreases. Three factors limit application of alternative oxides/silicates with @Delta@ X> 1.6 as gate dielectrics in Si devices. These are i) reactions with Si substrates, and/or intentionally-grown thin SiO@sub2@ interfacial layers that occur during film deposition and/or annealing, ii) thermal stability against chemical phase separation and/or crystallization which limits post-deposition processing temperatures, and iii) an inherent ion polarization contribution to the frequency dependent conductance that can degrade high frequency electrical performance.