Study On The Structural And Annealing Characteristics Of High-k Dielectric Stacks

The continuous development of semiconductor industry requires further decrease of technology node.When technology node comes to 45nm or smaller,the high-k gate dielectrics begin to replace the traditional gate dielectrics for suppressing the increase of gate leakage current.Recently,the Al₂O₃ and La₂O₃ are both high-k materials which are considered by researchers as the most promising gate dielectrics candidates.The Al₂O₃/La₂O₃ dielectric stacks and ternary oxide La AlO₃ demonstrate excellent properties such as high dielectric constant and good interface properties.In this work,the impact of annealing conditions and structure differences on the properties of Al₂O₃/La₂O₃ dielectric stack and LaAlO₃ gate dielectrics are investigated.The major contributions are outlined as follows:Firstly,the Al₂O₃/La₂O₃ dielectric stacks with different structures have been deposited by ALD,then annealed in different conditions.A negative shift of V_FB has been observed for thinner single layer,higher annealing temperature or longer annealing duration.Then,the possible reason of negative shift of V_FB has been studied.It has been concluded that it is the variation of dipoles at the high-k/Si interface,not the fixed charges or dipoles located in other places leading to the V_FB shift.The XPS results indicate that for thinner single layer,higher annealing temperature or longer annealing duration,there will be more La₂O₃ diffusing into the high-k/Si interface,forming more Si-O-La bonds.La has weaker electronegativity than Al?La¹.11,Al¹.61?,which means a larger electrostatic potential,leading to the increase of band offset then the V_FB shift happens.Moreover,The Al₂O₃/La₂O₃ dielectric stacks and LaAlO₃ gate dielectrics have been deposited by ALD,and annealed at 600?and 800?.Then the interface state densities have been figured out by the electrical parameters of prepared samples.The results reveal that a smaller interface state density of Al₂O₃/La₂O₃ dielectrics stacks can be obtained for a higher annealing temperature,which can be attributed to more recombination of dangling bonds at high-k/Si interface for a higher annealing temperature.Furthermore,higher interface state density has been observed in LaAlO₃ gate dielectrics than Al₂O₃/La₂O₃ dielectrics stacks.Finally,the energy band offset between high-k gate dielectrics and Si substrate has been investigated.From XPS results,the band gap of Al₂O₃/La₂O₃ dielectrics stacks and LaAl O₃gate dielectrics has been obtained,as well as the valance band offset and conduction band offset between the two kinds of high-k gate dielectrics and Si substrate.In general,these two kinds of high-k gate dielectrics can both meet the requirements of gate capacitance.Moreover,I-V tests have been also employed for prepared samples,and the results demonstrate that LaAlO₃ gate capacitance shows a larger leakage current than Al₂O₃/La₂O₃gate capacitance.These indicate that Al₂O₃/La₂O₃ stacks have a better energy band structure than LaAlO₃ as gate dielectrics.