Atomic Layer Deposition Of Al <sub> 2 </ Sub> O <sub> 3 </ Sub> High-k Gate Dielectric Experimental And Theoretical Studies

With the continuous miniaturization of metal-oxide-semiconductor transistor (MOSFET),gate dielectric has become thinner,which will cause unacceptable gate leakage current due to tunneling effect.In order to inhibit the gate leakage current, high permittivity(high-k) gate dielectric will replace conventional SiO₂.And atomic layer deposition(ALD) has become more and more popular due to its precise thickness control in film deposition.However,experiments indicate that the application of high-k dielectric will cause mobility degradation.At the other hand,in order to enhance the performance of chips,semiconductor industry focuses on higher carrier mobility semiconductor as substrates,such asⅢ-Ⅴcompound semiconductors (GaAs),Ge and SiGe.Because native oxide of GaAs is not a high quality gate dielectric,which will cause high interface state density,many groups have investigated various surface passivation method to grow high quality high-k dielectrics on GaAs substrate.In this work,we discuss the ALD growth of high quality high-k dielectrics on GaAs,GeSi and Si substrate.The main content and results of this thesis are summarized as follows.1.We investigate the effects of surface(NH₄)₂S pretreatment and surface (NH₄)₂S+thermal nitridation(TN) pretreatment on GaAs surface and we investigate the interfacial characteristics at Al₂O₃/GaAs using the XPS methods.——From the XPS analysis,surface(NH₄)₂S pretreatment can form Ga-S bond at GaAs interface;effectively suppress As-O bond at Al₂O₃/GaAs interface;Ga-O and As-As still exists at Al₂O₃/GaAs interface.——surface(NH₄)₂S+TN pretreatment can effectively incorporate N at interface and form Ga-N and As-N bond;effectively suppress Ga-O,As-O and As-As bond at interface.This indicates that as compared to surface(NH₄)₂S pretreatment,surface(NH₄)₂S+TN pretreatment will have better surface passivation effect on GaAs.2.Based on quantum chemistry calculation,Gaussian 03 has been used to investigate the initial surface reaction of atomic layer deposition of Al₂O₃ on H-passivated GeSi substrate.——We use the Ge-Si dimer and Ge-Ge dimer to model H-GeSi(100)-(2×1) surface.——Through the quantum chemistry calculation,compared with the Si-Ge dimer, we can explain that TMA adsorption proceeds most efficient on Ge-Ge dimer because of lower activation barrier and larger adsorption energy.Therefore,it is beneficial for Al₂O₃ growth on Ge-Ge dimer,which is in accordance with the experimental results.3.In order to investigate the effect of N₂ and NH₃ anneal,HfAlO films with different Al:Hf atomic ratio are deposited on Si substrate in an ALD system.——We can deposit various HfAlO film with different Al:Hf atomic ratio through different ALD process.With the decrease of Al:Hf atomic ratio,the accumulation capacitance density will increase.Furthermore,with the decrease of Al:Hf atomic ratio,the flat band voltage will shift negatively,indicating the decrease of negative charge in the film.——After the annealing in N₂ or NH₃,the capacitance equivalent thickness(CET) will decrease;decrease fixed positive charge density;effectively passivate bulk traps in the film and decrease the hysteresis.