Accurate Method For Measuring Thickness Of Nanoscale HfO₂ Films And Development Of Standard Materials

With the increase of integrated circuit integration,the development of material preparation technology and the needs of industry,the thickness of the gate dielectric layer for semiconductor films has been gradually developed to the nano-level.The traditional SiO₂ semiconductor material can not meet the industrial needs due to its low dielectric constant which leads to the dielectric layer breakdown.HfO₂ has the advantages of low leakage current,stable chemical and thermal properties,wide band gap width as well as high dielectric constant,which is the preferred material to replace the traditional SiO₂ gate,and excellent optical properties of HfO₂ makes it valuable.The popularity of nanometer-scale materials causes the HfO₂ film to become thinner,and thus accurate characterization of thickness of HfO₂ ultra-thin film is particularly important to ensure device performance.The grazing incidence X-ray reflectance technique is considered to be an accurate and non-destructive means of obtaining a film thickness,but it is not widely used in industrial production because of its time-consuming operation.Although the spectral ellipsometry can be easy and nondestructive to detect the film thickness,but it is subject to the parameters of the fitting,dispersion model and other conditions,and nano-scale film thickness characterization is difficult to obtain a reliable value.Therefore,from the point of measuring the thickness of the film by using the spectral ellipsometry,the spectral ellipsometry model of 1.2 nm HfO₂ films is established accurately by using the grazing incidence X-ray reflection technique.The thickness of the nano scale HfO₂ film is calculated by using the spectral ellipsometry and the relationship between the optical property and film thickness is studied as well.The development of standard materials ensures an accurate measurement of ellipsometry.When the thickness of HfO₂ film reaches the nano scale,both the optical properties of the film and the fitting model of the spectral ellipse will change.The spectral ellipsometry dispersion model of 1.2 nm HfO₂ film is Tauc-Lorentz 3.The spectral range of ellipsometry is 3.45-4.35 eV.The porosity ratio of the surface contamination layer is 60:40.In order to study the effect of different thicknesses on the optical properties of nano scale HfO₂ films,an Al₂O₃ layer in 10 nm thickness as the interface buffer layer was firstly prepared on Si base,and then the HfO₂ thin film with the nominal thickness of 2 nm,5 nm and 10 nm was deposited on the Al₂O₃ layer respectively.The thickness of each layer was measured by GIXRR measurement of the HfO₂-Al₂O₃ film by grazing incidence X-ray reflectometer,and the thickness of the interface layer was fitted by spectral ellipsometry.In the laser wavelength of 632.80 nm,the refractive index of 2 nm–thick HfO₂ film,5 nm–thick HfO₂ film and 10 nm–thick HfO₂ film is 1.901,2.042 and 2.121 respectively.The refractive index of the HfO₂ film increases with the increase of the film thickness,and the extinction coefficient of the three different thicknesses is zero.In order to provide standard samples for spectral ellipsometry measurements,the HfO₂ film standard material candidates was determined and then the thickness of HfO₂ film was confirmed by using grazing incidence X-ray reflection technology.According to "standard material value of the general principles and statistical principles"?JJF1343-2012?,the uniformity and stability of the HfO₂ film thickness of the standard materials were examinated by using the spectral ellipsometer and the grazing incidence X-ray reflectometer.The uncertainty of the reference material is analyzed and the characteristic values and uncertainties of the reference substance are determined.