Preparation And Characterization Of Atomic Layer Deposition-derived High-κ Thin Films For Microelectronic Applications

With the aggressive development of the microelectronics industry, the feature size of integrated circuits (ICs) are scaling down constantly, which makes a lot of traditional microelectronic materials and technologies face enormous challenges.Atomic layer deposition (ALD) is a kind of modified chemical vapor deposition (CVD) technique suitable for manufacturing inorganic material layers with precision and simple thickness control down to a fraction of a monolayer for potential applications in fabrication of deep sub-micron ICs and nano-structures. The precursors which meet ALD requirements are very scarce at present, so the development of metalorganic precursors and related materials growth processing suitable for microelectronic industry is an important and urgent task in ALD technology.With continuous shrinking of metal-oxide-semiconductor field-effect transistor (MOSFET) devices, gate dielectric oxide gets more and more thinner, resulting in larger tunneling current and degraded performance. High dielectric constant (high-K) materials have been investigated intensively and extensively as a replacement of Sio2in Si-based ICs, is an attractive solution to breakthrough the performance limits caused by devices miniaturization. It is another promising approach to replace conventional Si with the high mobility semiconductor channel materials in order to obtain high performance MOSFET devices.Floating gate devices, as a kind of non-volatile memory, have drawn more and more attention because of its fast operation speed, long retention time, low cost, and high reliability. Since the concept of nanocrystal memory was proposed in1995, it has triggered tremendous research efforts due to its advantages in scaling down.This thesis focuses on the fabrication and characterization of ALD high-K materials for microelectronic field applications. Using home-made metal-organic precursors from Nanjing University "863" project MO source center etc., several kinds of high-K thin films have been prepared by ALD. GaAs surface passivation, interface structure, and electrical properties of ALD high-K materials were characterized deeply. The structure and storage performance of the Hfo2HLO/Alo3/Si stacking structure deposited by ALD were investigated. Main results are summarized as follows:1. Using Hf(NMeEt)4(or Hf (NMe2)4), Zr(NMeEt)4, La[N(SiMe3)2]3, and Gd[N (SiMe3)2]3as precursors from Nanjing University "863" project MO source center etc., HfO2, ZrO2, La2O3, and Gd2O3films were successfully deposited by ALD, verifying the feasibility of home-made ALD precursors. Hf(NMe2)4, Hf(NMeEt)4, and Zr(NMeEt)4sources have lower bubbler temperature of75°C,120°C and110°C with corresponding ALD window of200-250,250-300°C and200-250°C, respectively. Their deposition rate is about0.9-1A/cycle, and the film thickness is linear with the number of cycles. The films on Si, GaAs, and Ge substrates are extremely smooth with smaller surface roughness ranging from0.2-0.5nm (RMS) depending on the film thickness of3-10nm. HfO2films deposited on4-inch Si wafer show good thickness uniformity with standard deviation (1-o) of only1.4%. Gd[N(SiMe3)2J3and La[N(SiMe3)2]3have higher source temperature of175°C and173°C, respectively. They exhibit relatively larger surface roughness. The RMS value of Gd2O3and La2O3films are1.08nm and1.45nm, respectively. The larger roughness of La2O3is related to the high deposition rate (2.6A/cycle) of La source.2. The impact of chemical solution passivation on GaAs surface, interface structure, and electrical properties was studied carefully. Four kinds of H2SO4solution, HC1solution, HBr solution, and NH4OH solution were used to remove native oxides of GaAs and (NH4)2S solution as passivation agent. The experimental results reveal that the pretreatment of HBr+(NH4)2S solution can obtain smoothest surface of RMS value of0.5nm with less Ga and As native oxides at GaAs/Al2O3interface. The corresponding GaAs/Al2O3/Pt MOS structures exhibit the most excellent electrical properties such as higher accumulation capacitance, less capacitance hysteresis, and smaller leakage current density. The pretreatment of HBr combined with (NH4)2S solution is a better choice for GaAs surface passivation.3. The effect of various ALD pulses of TMA pulse and TMA+TDMAH pulse on S-passivated GaAs substrates, interface structure, composition, and electrical properties of GaAs/Al3/HfO2stacking films were compared carefully. The results indicate that the TMA+TDMAH pulse can more effectively remove the native oxide of GaAs surface than TMA pulse, reduce the interfacial layer thickness (only0.2nm), and improve the electrical properties. The mechanism can be explained by the ligand exchange interaction. With optimal TMA+TDMAH pulse pretreatment, sample GaAs/Inm-Al2O3/2.8nm-HfO2/Pt shows larger accumulation capacitance of2.29uF/cm2with the capacitance equivalent thickness (CET) of1.5nm.4. The stacking structure of HfO2/Hf-La-O(HLO)/Al2O3/Si as nanocrystal memory has been prepared by ALD. After700°C and800°C annealing, separated nanocrystals are formed in trapping layer of HLO with a size of about3nm, and the pure HfO2barrier layer is also crystallized. Electrical measurements show that the memory window is linear with applied voltage, and doesn't change with frequency. Compared with700°C annealed samples, the800°C annealed samples have larger memory window (9V when sweeping between±11V) and relatively better retention characteristics. It can be ascribed to more body defect traps and fewer interface traps in Hfo2/HLO/Alo3/Si after higher temperature annealing. The charge density of nanocrystals for800oC annealed samples is about2.5x1013/cm2.