Ultra-thin C-N-Si Protective Films Prepared By Plasma Enhanced Deposition

In recent years, the magnetic storage density of hard disks has been increasing rapidly. An effective method to increase the magnetic storage density is to reduce the flying height, which is the distance between the read/write head and the hard disk. As a result in the near future the thickness of ultra-thin protective films, which are deposited on both the read/write head and the hard disk, need to be below 2 nm. At the same time the ultra-thin film should provide good wearable properties and good corrosion resistance. In this thesis, ultra-thin Si-C-N films meeting these requirements were prepared by microwave ECR plasma enhanced deposition techniques.In this paper, the DLC and CN_x films used as proctective coatings at the present time were studied. DLC films were prepared by plasma immersion ion implantation and depositon, which was a good way to increase bond strength of the films. DLC films were smooth, dense and had a low friction coefficient. The films were amorphous and thickness levels was in the nanometer range. With the increase of the H₂ flow rate, deposition rate, RMS and friction coefficient decreased. The minimum RMS was 0.159nm, and the minimum friction coefficient was 0.044. The adhesion between DLC film and Si substrate was good, but there was a wide transition section in adhesion. Ion implantaton would destroy the substrate, which was not suitbale for use as a protective film on hard disks. However, it has a many possibilities in MEMS applications.CN_x films were prepared by MW-ECR plasma enhanced unbalanced magnetron sputtering technique. With increasing carbon target power, the RMS increasd; but the deposition rate, the ratio of sp³/sp² and the nitrogen content in the film decreased. The increased target power improved the transformation of sp³ bonds to sp² bonds, which caused the graphite like structure in the film to increase. Thus, film properties were not good enough. As for the increasing flow rate of nitrogen, the content of nitrogen and sp³/sp² increased. Their tribology properties were also improved. These improvements were due to the the doped nitrogen breaking the hybridized sp² bonds and increasing the sp³ bonds. The plasma density decreased to a certain extent because of the small sputtering target and the large vacuum chamber. This caused the film growth rate to be slowed due to the volatilized radicle of CN, which cannot bind with N₂ or N2⁺. The bias voltage on these substrates corraded the films and caused the properties of films to degrade and not reach physical requirements. High quality Si-C-N thin films were prepared by an MW-ECR plasma enhanced unbalanced magnetron sputtering technique. We used these methods to obtain films which met the physical requirements, such as, increased contents of carbon and nitrogen, and rectified the silicon content and substrate bias voltage on the structure. The best parameters found were: a carbon target voltage of-600V, a silicon target power of 250W, an N₂/Ar flow rate of 0.067 and a substrate voltage of-150V. A high quality ultra-thin film, with a thickness of 1.8 nm, was obtained. The ultra-thin film showed good anti-corrosion properties (immersed in 0.1mol/1 oxalic acid for 12h) and tribology (GCr15, load 400mN, to and fro sliding for 20min) properties, which can withstand a hard disk driver environment. The results showed that the carbon content in the films increased with the carbon target voltage, and C-N bonds were also increasd. During the process of film deposition, the increasing N₂ flow made the bombardment of Ar⁺ decrease while the silicon target was poisoned, causing the film to have insufficient density. As the silicon target power increased, the silicon content also increased. Also, a too large of a target power caused in increase in the number of Si-Si bonds, which is detrimental to a films mechanical properties. The proper bombardment energy on the substrate could promote a film's properties. The hardness and the optical properties of the films were determined by the contents of C-N and Si-N respectively. XPS results show that the N/Si atom ratio was near 1.33 in Si-N bonds, as in the stoichiometry of Si₃N₄; the C/Si atom ratio in Si-C bonds was near 1 as in the stoichiometry of SiC. Thus, the structure of the film can be considered as tetrahedral structures composed of silicon nitride and silicon carbide and bonded with carbon. It's chemical model was (Si₃N₄)-(SiC)₂-C₆.