Calibration Of Phase Modulation Spectroscopic Ellipsometer And Characterization Of HfO₂ Ultra-thin Films

With the increasing demands of semiconductor devices and the maturing of thin film preparation technology, scientists’ research directions have gradually transformed from the conventional thickness HfO₂ film to ultrathin films, which thickness less than 10 nm. The physical characterization of HfO₂ ultra-thin films is the basis of all the research work. Only the exact physical characteristics of HfO₂ ultra-thin films, can guarantee the further study of the performance of HfO₂ ultra-thin films and performance improvement carried out smoothly. Then make performance features of the ultra-thin films more stable. Meanwhile, accuracy characterization of HfO₂ ultra-thin film is the basis of process improvement of film preparation. Accurate physical characterization of HfO₂ ultra-thin film can provide reliable reference for the process improvement of the preparation. According to improvement of the preparation of ultra-thin films, we will obtain higher quality film. In this paper, characterization of HfO₂ ultra-thin films were implemented, the thickness, structure and composition of the film were obtained.To ensure the accuracy of the film thickness characterization, Phase Modulation Spectroscopic Ellipsometer was calibrated before the experiment. The optical path of light, optics element and parameters were adjusted to make the instrument achieve the best state. After calibration, a number of SiO2 standard reference samples were used to test the measurement results of Phase Modulation Spectroscopic Ellipsometer. The results show that the thickness of SiO2 standard reference sample measured by calibrated ellipsometer are within the uncertainty range, indicate that the status of the ellipsometer are great.After calibtation, the factors of the thickness from standard substance transfer to Spectroscopic Ellipsometer were studied. And Spectroscopic Ellipsometer’s measurement data was traced to the SI International Unit.The results showe that use SiO2 standard substance as measurement objedt, central location are equivalent when transfer the standard thickness from standard substance to Spectroscopic Ellipsomete. And the measuring area, measuring position, measuring time and operator have no effect to the measurement result.The HfO₂ ultra-thin film samples were measured by calibrated Spectroscopic Ellipsometer. Fitting models were used to obtain the thickness and optical constants of the film. Analys is of the cross-section of the sample by High-resolution Transmission Electron Microscope, to verification the thickness values obtain by calibrated Spectroscopic Ellipsometer. The thickness of HfO₂ film of the sample A is about 2.60 nm, and the refractive index is 1.951 at 632.80 nm laser wavelength; The thickness of HfO₂ film of the sample B is about 2.70 nm, the thickness of the interfacial layer between the substrate and HfO₂ film is about 1nm, and the refractive index of HfO₂ film is1.886 at 632.80 nm laser wavelength.To obtain the structure and the thickness of each layer, X-ray Diffraction was used to measurements the samples, IMD software was used to fitting the measurement data. The layer structure of the sample A is : two parts contaminated layer, the interface layer 1, HfO₂ layer, the interface layer 2; the layer structure of the sample B is : two parts contaminated layer, the interface layer 1, HfO₂ layer, the interface layer 2 and the natural oxide layer.Cleaning and X-ray Photoelectron Spectroscopy were used to determine the component of the layers of the HfO₂ film. There are thicker contaminations existed on the surface of the films for both sample A and sample B. These contaminations are carbon particles and little amounts of organics. These pollutants can be removed by ultrasonic cleaning with isopropanol. After three times ultrasonic cleaning, these contaminants can be removed effectively. There determined bond Hf-Si-O between HfO₂ layer and the Si substrate for the two samples. Since the natural oxide layer SiO2 was wiped off prior to the preparation, HfSixOy hafnium s ilicate film was not formed. But for sample B, the HfSixOy hafnium silicate was already formed, which formed by the reaction of natural oxide layer SiO2.