Reseach On Microstructures And Electrical Properties Of HfO₂ Films

The rapid development of integrated circuits promotes semiconductor materials and technology upgrading, and the MOS device gate dielectric materials are also put forward to higher requirements. Conventional SiO2 gate oxide layer has been gradually not fit process requirements so that high-K oxide materials become a hot research field. In this paper, high-K gate oxide is set as an application background, and three groups of HfO2 films on Si substrates are prepared by RF reactive magnetron sputtering method under process parameters of oxygen flux, sputtering time and sputtering power. X-ray diffraction analyzer(XRD), atomic force microscopy(AFM), X-ray photoelectron spectroscopy(XPS), IV / CV tester, electronic thin-film stress tester are used to do analysis of the component structure, surface morphology, electrical properties and residual stress of the HfO2 thin film samples. The performance characteristics of HfO2 films and their interrelation are summarized, effects of different parameters on the performance of films are discussed, and the results are as follows:First, the residual stress and electrical properties of HfO2 thin films are closely linked to the surface morphology. It’s important to seek the effects on the mechanical and electrical properties of surface morphology by varying the process parameters. A more uniform and dense film has a better surface roughness, as well as the residual stress and electrical properties. AFM analysis shows that,(1) as the oxygen flux increases while maintain the other parameters, the surface roughness of the films reduce. Defects reducing make films become more uniform and dense.(2) Changing the sputtering time alone, due to the physical thickness of the HfO2 films, the surface roughness increase first and then decrease.(3) Changing the sputtering power alone, with the sputtering power increases the average roughness of HfO2 films become larger.Second, microstructure has a direct link to the electrical properties of thin film, amorphous films have better electrical properties, and crystallization in the films can reduce the dielectric constant and increase the leakage current. XRD patterns of the three groups HfO2 films show that all the films are amorphous, only monoclinic HfO2 diffraction peaks with small intensity and large FWHM are showing in the spectrums. With the increase of oxygen flux, sputtering time and sputtering power, all the films exhibite slightly increasing monoclinic.Third, the leakage current is one of the key indicators of the gate oxide films, and different process parameters affect leakage current characteristics of the films through influence on surface morphology, microstructure, etc.(1) When the gate voltage is negative, with increasing oxygen flux traps in HfO2 films are reduced, so is the leakage current density of the films; when the gate voltage is positive, as oxygen flux increases, the leakage current of HfO2 films show a certain tendency to increase.(2) As the sputtering time increases, the leakage current of the thin films decreases. Although the surface of the films become more smooth and the degree of crystallinity increases, due to the sputtering time increasing leads to an increasing thickness of the films, which is the main reason for the reduced leakage current.(3) As the sputtering power increase, the deterioration of the surface roughness and the crystal phase of the films both increases, which causes the leakage current of the film increases.Fourth, the oxygen flux comparing to sputtering time and power has a more significant influence on the structure and properties of the HfO2 films, therefore an independent discuss of how oxygen flux affects the chemical composition, C-V characteristics and the residual stress of HfO2 films is carried out.(1) As the oxygen flux increases, the content of oxygen vacancies in the HfO2 thin films correspondingly decreases so that the O/Hf ratio increases. The O/Hf ratio obtained increasing from 1.653 to 1.683 gradually by calculated.(2) With the increase of the oxygen flux, the dielectric constant of HfO2 films increases from 16.1 to 19.2 gradually, and C-V curves of HfO2 thin films gradually move to the axis of positive voltage, which shows the density of oxide layer charges and interface states in the MOS structure have been reduced.(3) With the increase of the oxygen flux, the surface roughness of the films decreases, the average size of surface particles becomes larger, and a more uniform and dense structure leads to a decreasing trend of residual stress of the HfO2 films.