| The subject investigated in this thesis is deposition of hafnia (HfO2) and zirconia (ZrO2) thin films and research on their properties. We have developed a new method for deposition of hafnia (HfO2) and zirconia (ZrO2) films, which is plasma assisted reactive pulsed laser deposition (PARPLD). We also determined the films' optical properties and electrical properties, which include the structure of films, the interfacial qualify between the film and the silicon substrate, the optical constant, the band gap, the capacitance-voltage curves and the leakage-voltage curves. We also determinate the effect of annealing in the N2 ambient at different temperature and evaluate the thermal stability as well as the change in properties of films.We use electron cyclotron resonance (ECR) microwave discharge to generate highly activated oxygen plasma. In this reactive oxygen plasma environment, hafnium or zirconium target was ablated by pulsed laser to form hafnium or zirconium plasma, which react with oxygen and then generate metal oxide precursor, then the precursor transport to substrate and formed hafnia (HfO2) and zirconia (ZrO2) films. There was no additional heater applied to the substrate holder, and the bombardment by the low-energy plasma stream slightly heated the substrate whose temperature stayed below 80℃. The method of pulsed laser deposition is based upon the characteristic of laser that it can ablate the target to generate the plasma, which moves to the substrate, condenses and forms films. This method has been carried out successfully and is called pulsed laser deposition. ECR microwave discharge is a process that could generate plasma of high density and high ionization, and the plasma is uniform in large space. We have combined pulsed laser deposition and electron cyclotron resonance to create a novel film deposition method, which is called plasma assisted reactive pulsed laser deposition (PARPLD). This method is useful to synthesize thin films and to avoid oxidation and formation of interfacial layer.The hafnia and zirconia thin films have many excellent optical properties, including high transparency in a wide spectral range, relatively high damage threshold, excellent thermal and mechanical stability, so that they are attractive candidates in optical field. Moreover, hafnia and zirconia thin films are promising materials in microelectronics, for they have medium dielectric constant K, wide band gap, and reasonable band gap offset with silicon, as well as good thermal and chemical stability on silicon at high temperatures. Especially, they are regarded as the substitution of conventional SiO2 to be gate dielectrics in the next generation of complementary metal-oxide-semiconductor (CMOS) devices. Hafnia thin films have already been applied in CMOS devices successfully.Based on successful fabrication of HfO2 and ZrO2 films by our new method, we characterized the structure, optical and electrical properties of the as-deposited films. We also evaluate the effects of post-annealing in the N2 ambient at difference temperatures. The structure and the interface of the deposited films on silicon were characterized by means of Fourier transform infrared (FTIR) spectroscopy and Raman scattering spectroscopy. The result reveals the predominantly monoclinic phases of HfO2 and ZrO2 in the films with a small amount of amorphous matrix which gets crystallization after high-temperature annealing. No interfacial SiOx is observed for HfO2 and ZrO2 films deposited on silicon and the films appear stable at temperatures as high as 900℃. Annealing near 1200℃results in the formation of a SiOx interfacial layer. The spectroscopic ellipsometry technique was used to characterize the optical properties of the films, the thickness together with refractive indexes and extinction coefficients of the films was derived, and the result reveals an improvement in the optical properties by high-temperature annealing. The films deposited on fused silica plates show excellent transparency in the range of 250-2500nm, the transmittance was above 80% especially in the near infrared. There is a sharp ultraviolet absorption edges at about 200nm, according to optics band gap determination we can deduce that the film have direct band gap structure, the band gap of HfO2 and ZrO2 films are 5.65eV and 5.95eV respectively, which change according to the annealing process. We measured the capacitance-voltage curves as well as the leakage-voltage curves to get the dielectric value, the flat band voltage and the density of leakage. These properties were improved after annealing in spite of leakage.In this thesis, a novel method is developed to fabricate hafnia and zirconia thin films. Because of the advantage of this method, the films have very good optical and electrical properties as well as thermal stability, and are free from SiOx interface between the film and the substrate. To make the thin hafnia and zirconia films suitable for the application in the optics and micro-electronics, we will refine our method of fabrication and improve the quality of the films. |
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