Preparation Parameters On Hafnium Oxide Thin Film Stress And Optical Properties Of The Impact

Hafnium dioxide(HfO2) is a high quality anti-damage threshold thin film material, it is the first choice high refractive index material which to produce high-power laser system thin film devices. Hafnium oxide has good adhesion, mechanical properties and thermal stability characteristics, from the near ultraviolet to the infrared spectrum(230nm-10000nm) has perfect permeability. In addition, chemical stability of hafnium dioxide is also very good, so it is often used as protective film for aluminum, silver and other metal film. Hafnium dioxide in the optical, optoelectronic devices, laser systems antireflection film, and gas, magnetic field detectors are widely applied, is the thin film materials research focus in recent years.The stress produced during deposited films has significant impact on the optical properties and strong resistance, excessive stress even induce the film cracked and off. Electron beam deposition is the most commonly used method for fabricate HfO2 thin films, so research different preparation parameters of electron beam deposition on the HfO2 film stress and optical properties has important practical values.We prepared HfO2 thin films by electron beam deposition under different deposition temperature, oxygen pressure, deposition rate and annealing temperature, Systems researched different deposition parameters on the HfO2 films,s mechanical and optical properties. ZYGO interferometer was used to study the stress of the samples which fabricated under different conditions; Used UV3101-PC spectrophotometer and the Essential Macleod thin film software researched the optical constants of tha samples; Used D/MaxIIIA X-ray diffraction apparatus and JSM-6700F type cold field emission scanning electron microscope studied microstructure and surface morphology of the HfO2 thin films that fabricated under different deposition conditions.The full text mainly includes four chapters given as follows.In the first chapter, we introduce the optical thin films widely used in optical devices and systems, current research situation on thin film stress have been summarized, and described the research content of the issue.In the second chapter, introduced the basic principles on thin film stress and optical constants. Described the development history of quantitative calculation of thin film stress, stress models and the main measurement methods, used strain energy method derived the stoney formula for calculation the stress of thin film deposited on circular substrate; Derived the thermal stress formula based on the principle of strain compatibility. Introduced the envelope extreme value method for calculate the optical constants and the dispersion models that commonly used in the fitting of the refractive index.In the third chapter, described the preparation process of hafnium dioxide thin films under various conditions. Introduced the vacuum coating equipment, HfO2 thin films material, the clean-up method of substrate and coating machine before deposite thin film and the deposition parameters of fabricated the HfO2 thin film sample.The fouth chapter is the core part of the research, this part is experimental results and analysis. We divided this charpter into five parts. In the first part, the main instruments used in testing and analysis have been introduced. The second, third, fouth and fifth sections are the deposition temperature, oxygen pressure, deposition rate and annealing temperature effect on the HfO2 film stress and optical properties. Every section of the study include:researched the stress characteristics of HfO2 thin film by ZYGO interferometer and gived the microscopic explanation; used UV3101-PC spectrophotometer and Essential Macleod thin film software studied the optical properties of the HfO2 thin films that deposited under different conditions, and the refractive index formula is given; used D/MaxIIIA X-ray diffraction apparatus studied microstructure of the HfO2 thin films; the JSM-6700F type cold field emission scanning electron microscope is used to collected the surface morphology image of the HfO2 thin films, and compared with the RMS values measured by ZYGO interferometer. Summarized variation of stress and optical constants of HfO2 thin film deposited at different conditions, and find the best preparation parameter of HfO2 thin films.1. In the research of selected of selected deposition temperature, the HfO2 films are amorphous structure at selected deposition temperatures, residual stress and intrinsic stress are tensile stress, when the temperature is lower than 220℃thermal stress plays a major role on the residual stress, and the intrinsic stress plays a key role on the residual stress when deposition temperature is higher than 220℃.The HfO2 film has minimum residual stress at 220℃. The refractive index became higher with the increasing of deposition temperature and refractive index are normal dispersion. The HfO2 film has the best flatness at 220℃. The results provide reference for making high-quality HfO2 films.2. In the research of selected of selected oxygen pressure,all HfO2 thin films are amorphous and residual stress is tensile stress under our selected conditions. Residual stress is increase and then decrease with rasing oxygen pressure. The samples has minimum stress at oxygen pressure 1.0 x 10-2Pa. low-oxygen environment can prepare low dispersion HfO2 thin film. The HfO2 film has the best flatness at 8×10-3Pa and 10×10-3Pa.3. In the research of selected of selected deposition rate, all HfO2 thin films are amorphous and residual stress is tensile stress under our selected conditions. Residual stress is increase and then decrease with rasing oxygen pressure. The samples has minimum stress and fine flatness at oxygen pressure 1.0 x 10-2Pa. low-oxygen environment can prepare low dispersion HfO2 thin film.4. In the research of selected of selected annealing temperature, the HfO2 films are amorphous structure under our experimental conditions. The residual stresses are tensile stress, with annealing temperature first decreases and then increases, the HfO2 film has minimum residual stress at 300℃ annealing. The refractive index increasing with annealing temperature, and the dispersion decreases. Annealing under low temperature can decrease the film roughness, but high temperature annealing will increase the surface roughness.