Synthesis of SiON films by helicon-wave plasma and their characteristic analysis

Abstract

SiON becomes a kind of new functional material because it has many excellent mechanical and chemical properties such as high hardness, corrosion resistance, oxidization resistance. It is reported that the coating of SiON has many important applications in optical device. For example, it can be used as the protective layer of Edmund optics, touch panel of mobile phone, waveguide tube et al. the Mohs hardness of SiON is about 9H. In addition, the transmittance of the coating is 98% in the visible region. Lately, lots of researchers are interested in the biomedical applications of SiON coatings due to its favourable mechanical properties and the good hemocompatibility of the material. Such as hip implants, it can help patient recover soon because the coating is smooth and the Si–N and Si–O–N chemical bonding are more to the hydrophilicity than Si–O or Si–Si bonds. There is also lots of significant application of SiON films in the field of microelectronics. According to the reports, SiON has the inhibiting effect on hot-carrier injection, impurity diffusion and water vapor permeability. As the dielectric layer, SiON also possesses better electronic mobility and the trap densities of electron. So far, the main synthetic method of SiON is plasma enhanced chemical vapor deposition (PECVD) including inductive coupled plasma source (ICP), capacitive coupled plasma source (CCP) and microwave electron cyclotron resonance (ECR). It is found that selectivity of PECVD is bad along with the further study of it. In addition, the SiON dielectric layer contains impurities unavoidably, for example, it will affect the insulation and dielectric properties if adding H atom into the dielectric layer, which can restrict application in large scale integrated circuit. Helicon wave plasma source (HWP) comes to the notice of many researchers because of its high density (about 1013 cm-3) at low pressure (0.1~10 Pa). Chen said that “Interest in helicon discharges stems from their unusually high ionization efficiency: plasma densities n achieved are almost an order of magnitude higher than in other discharges at comparable pressures and input powers.” During the discharge, high-energy electron collides with gas particle adequately. In this experiment, it can divide N2 into N2+ efficiently along with steady-state helicon wave discharge. In addition, there is no impurity element mixed in the SiON (such as C, H) which can improve the quality of the SiON films. In this experiment, SiON films were synthesized by nitridation on the surface of Si sputtered by N2/Ar helicon-wave plasma. During the mixed helicon-wave discharge, the mass flow ratio of N2 and Ar was different. X-ray photoelectron spectroscopy (XPS) showed that the SiON films were constituted of Si–O–N and Si–N. Atom force microscopy (AFM) indicated that the surface of the film was very flat and smooth, and the RMS was less than 1.2 nm. We collected Plasma discharge parameters by optical emission spectroscopy (OES) when the Si wafer was sputtered using N2/Ar helicon-wave plasma, and studied the relationship between the particle in the plasma and structure of SiON films.