Effect of sputtering condition on dynamic characteristics and microstructures of magneto-optical 5.25 in. SiN/TbFeCo/SiN/Al disks for 532 nm recording media

Abstract

A systematic study of the effect of sputtering conditions, for each layer of the magneto-optical SiN 500 Å/TbFeCo 200 Å/SiN 200 Å/Al 600 Å disks, such as power and Ar gas flow rate on the noise levels (NL) and carrier-to-noise ratio (CNR) was performed for the 532 nm high density storage media in this work. The NL dropped to its minimum value of −71.3 dB as the sputtering power for the first SiN increased from 0.5 to 1.5 kW. With a further increase in sputtering power to 2.5 kW, it sharply increased to −64.5 dB. This was ascribed to the smooth and dense surface of the first layer at 1.5 kW, as was observed in the atomic forces microscopy images. The spherical, isotropic, fine grains with a diameter of about 0.2–0.7 μm at 1.5 kW were found, while the longitudinal, directional granular features with a length of 2.5 μm were seen at 2.5 kW. The highest CNR of 46.3 dB was observed at 0.6 kW with a constant sputtering Ar gas flow rate of 25 sccm for the magneto-optical layer. The sputtering conditions for other layers are as follows: 1.5 kW with sputter Ar/N2 gas flow rate of 30 sccm/11 sccm for the first and third SiN layer, and 0.6 kW with 25 sccm of Ar for the Al reflection layer. This is due to the smooth surface morphologies of the magneto-optical layer at this optimum sputtering pressure, as previously reported in similar research. To obtain a high readout signal, the phase compensation for the elliptic laser beam has been considered.