The Properties Of Ultra-thin A-SiN_x Films Prepared By Microwave ECR Magnetic Sputtering

It has been more than 50 years ever since IBM shipped the first magnetic disk in 1956. In recent years, the magnetic storage density is increasing at 100% per year, because of the using of GMR, and MR technologies. Furthermore, people's dependence on computer has been increased to ever-higher levels. All those require disk devices should have much larger storage density, longer using life, and more reliability. One of the crucial issues to increase the storage density is the reduction of the fly height, which is the distance between the disk and the read/write head. As the result, the thickness of protective layers, which were deposited on both the disk and the read/write head, needs to be reduced correspondingly, for example, it should be less than 2.5 nm when the storage density reaches 1T bit/inch² in the near future. To prepare such ultrathin continuous layer with excellent anti-corrosion and antifriction and tribology properties to protect the underlied magnetic layer is one of the main challenges in the present magnetic storage R&D areas.In this thesis, the ultra-thin a-SiN_x film with acceptable properties was deposited by MW-ECR plasma enhanced unbalance magnetic sputtering system. The MW-ECR plasma characteristics and the film properties have been studied systematically. The results are summarized as follow:(1) The Si target sputtering yield was independent of MW power, but only related to the sputtering radio frequency power. The plasma density and N ion/active radicals density increased with the increasing of MW power. On the condition of keeping Si target sputtering power and N₂ flow rate constant, the N ion/active radical density was the key parameter that influenced the component, structure, and properties of a-SiN_x films. In order to deposit the films with acceptable properties, keeping high MW power was necessary which makes the Si atom/ion react with N ion/active radical sufficiently.(2) Si target sputtering power and N₂ flow rate were the key parameters. On the condition of keeping other parameter constant, Si atom/ion sputtering yield increased with the increasing of the sputtering power. The films deposited with 350 W sputtering power and 2 sccm N₂ flow rate displayed good stoichiometric, structure, and mechanical properties, such as stoichiometric of 1.33, 94.8% Si-N bond content, 23 GPa hardness, 0.18 nm RMS, and excellent anti-corrosion property. But the a-SiN_x films deposited with high N₂ flow rate displayed poor mechanical properties because of rich N structure in film.(3) The a-SiN_x film thickness was linear with the deposition time. The film growth rate was 4.7nm/min, which was deposited at the optimum deposition parameters. 5 nm thickness a-SiN_x film deposited on Si substrate displayed acceptable anti-corrosion property and anti-wear property. 2 nm thickness a-SiN_x film deposited on a-Al₂O₃/Si substrate could stand the stringent corrosion test. The thickness limit with sufficient protection for the magnetic layer of a-SiN_x film could reach 2 nm, lower than that of DLC film and CN_x, film (4 nm).(4) On the condition of keeping other parameter constant, the plasma potential and electron temperature T_e decreased monotonously with increasing the N₂ flow rate. The plasma density increasd with N2 flow rate and reached maximum when the N2 flow rate was 5sccm, this increase of plasma density could be attributed to the Ar^*-N2 collision process since the density of Ar metstable active state density was high when N₂ flow rate was less 5 sccm. So N⁺ and N₂⁺ density increased with increasing the N₂ flow rate proportionally, and reached to the peak value at 5 sccm N₂ flow rate. At the same time, Si atom sputtering yield decreased monotonously with increasing the N₂ flow rate, because of target poisoning phenomenon. These two factors resulted in the a-SiN_x film with the excellent structure and properties when N2 flow rate was set at 2 sccm. When N₂ flow rate was higher than 5 sccm, the density of Ar^* decreased tremendously, N₂⁺ was the main component in plasma. Combining with the serious target poisoning phenomenon, the a-SiN_x film was N-rich structure and displayed poor properties. The Si atom density and the N⁺ density were two crucial parameters which influenced the a-SiN_x film structure and properties.