Fabrication And Properties Study Of Novel Hf-based High-k Gate Dielectric Thin Films

Presently, the novel Hf-based high-dielectric constant (high-k) materials have beenextensively investigated and are considered as one of the most promising candidates asalternatives to SiO₂/SiON gate dielectrics due to high dielectric constant, thermal stability,excellent interfacial properties, wideband gap, low leakage current density and lowfrequency dispersion.This thesis is focused on the hotspots in the field of Hf-based high-k materialsresearch. Si, N and RE (Gd and Ce) doped HfO₂thin films were synthesized via dual ionbeam sputtering and magnetron sputtering method, and its structure, electrical propertieswere investigated. The following is the major results:1, After Si and N doping into HfO₂gate dielectric thin films,crystallizationtemperature of HfO₂films increases, which indicated that the thermal stability of thedielectric film is improved. Changes in the structure of HfSiO and HfSiON dielectrics withdifferent annealing temperature occur, the value of K is decreased due to the formation oflow K oxide layer which increase the lower interface layers thickness. As the annealingtemperature increase, the leakage current of gate dielectric films have declined, which wasattributed to lower oxide-charge density. The assisted ion beam of lower energy activatethe substrate surface atoms, enhance the film contact and adhesion, and the maximumdielectric constant and the smallest Qoxand gate leakage current are obtained atAIE=100eV. In the high field domain, the Al-/HfSiO/Si MOS capacitor is fitted by a FNlaw, and the Au-, Ag-/HfSiO/Si MOS capacitor are fitted by the Schottky emission law,the distinctive behavior between Al/HfSiO/Si and Au (Ag)/HfSiO/Si capacitors imply thatthe top metal/HfSiO interface plays an important role in the conduction process.2,After Gd and Ce doping into HfO₂gate dielectric thin films, band gap E_gandcrystallization temperature of HfO₂films have a large increase, which bring a largeimprovement from the thermal stability of the dielectric film. Meanwhile, HfGd(Ce)Ocould effectively inhibit the growth of the oxygen vacancy. HfGd(Ce)O dielectric thinfilms exhibit a stable cubic structure after900℃PDA, which is attributed to the increaseof K and decrease of Vfbshift. The leakage current density of Ce and Gd-doped HfO₂films is two-orders of magnitude lower than that of pure HfO₂films, which was attributed to (1)increase in band gap as well as the reduction in oxygen vacancies after the Ce and Gdincorporation,(2) the lower electro-negativity and larger atomic raddi of Ce and Gd. Dueto the crystallization of gate dielectric films and decrease of band gap after900℃PDA,there are two-orders of magnitude different in leakage current density between before PDAand900℃PDA. In addition, Ce-doped gate dielectric films have lower gate currentdensity is because that the tetravalent Ce is more effective to inhibit the generation ofoxygen vacancies than trivalent Gd.3,After Ce doping into HfSiO gate dielectric thin films, gate dielectric film continuedto maintain a high crystallization temperature, high thermal stability and a small increase inthe band gap. Ce doped HfSiO gate dielectric film can effectively suppress the generationof oxygen vacancies, reducing the formation of SiO_xclusters which from the oxygen atomsdiffuse into the Si substrate, making the interface layers thickness decrease and the value ofK increase. The formation of the stable cubic structure after1000℃PDA will make thevalue of K further increase. The leakage current density of Ce-doped HfSiO films isone-orders of magnitude lower than that of HfSiO films, which was attributed to a smallincrease in band gap as well as the reduction in oxygen. Due to the crystallization of gatedielectric films and decrease of band gap after1000℃PDA, there are one-orders ofmagnitude different in leakage current density between before PDA and1000℃PDA.4,The theoretical results show that Gd-doped HfO₂could effectively inhibit thegrowth of the oxygen vacancy. Theoretic verification that RE-doped HfO₂could inhibit theformation of the oxygen vacancy, and there is a good match in experiments with thetheoretical values.In a word, it is thus proposed that RE element doped novel Hf-based high-k materialis one of the most promising candidates as alternatives to traditional SiO₂/SiON gatedielectrics for45-32nm technology node CMOS devices.