ABSTRACT
This chapter introduces the most promising mastering technologies for the high-density optical disc in the future. These technologies are electron beam recording (EBR), UV, and deep UV (DUV) recording, near-field optical recording, laser thermal recording and stimulated emission depletion (STED) recording. The chapter illustrates in detail the methods and processes of these technologies and summarizes their features and maximum resolution capabilities. 6.1 IntroductionBlu-ray disc (BD) is the third generation in the optical disc family. One of the greatest advantages of read only memory (ROM) disc reproduction is the ease preparation and low cost. Compared with the digital versatile disc ROM (DVD-ROM), BD-ROM has much
smaller track pitch and data mark, which of the 25 GB BD ROM are 0.32 µm and 0.149 µm, respectively (Table 6.1). A next-generation optical disc system after BD is expected to have a capacity of 150-500 GB/layer (100-350 Gbit/in2), and the corresponding pit size is estimated to be approximately 40-70 nm [1]. This suggests that a considerable improvement in recording resolution will be necessary to fabricate such high-density patterns. Table 6.1 Main performance parameters of CD-ROM, DVD-ROM, and BD-ROM
CD-ROM DVD-ROM BD-ROMDiameter 120 mm 120 mm 120 mmCapacity (SL) 0.65 GB (SL) 4.7 GB (SL) 25 GB, 27 GB(DL) 50 GB, 54 GBLaser wavelength 780 nm 650 nm 405 nmNumerical aperture 0.45 0.6 0.85Cover layer thickness 1.2 mm 0.6 mm 0.10 mm (L0, SL), 0.075 mm (L1)Track pitch 1.6 μm 0.74 μm 0.32 μmECC modulation CIRC (C3/2/1)EFM, RLL (2,10) RSPC PI × POEFM+, RLL (2,10) LDC + BIS 17PP, RLL (1,7)Min./max. mark 3T/11T 3T/14T 2T/9TMinimum mark length 0.83 μm 0.40 μm 0.149 μm for 25 GB, 50 GB 0.138 μm for 27 GB, 54 GBChannel/user bit rate 4.32/1.4 Mbps 26.16/11.08 Mbps 66/35.965 MbpsRotation CLV CLV CLVReference velocity (1×) 1.2~1.4 m/s 3.49 m/s 4.917 m/s/4.554 m/sThe mastering of the DVD-ROM is generally realized using maskless laser writing based on organic photoresist, which is the same as that used in the lithography for semiconductor. The pattern dot or pit size depends on the laser spot size and the parameter
K, which is a parameter to characterize the contrast of photoresist
during the exposure and develop processes; the resolution of various types of photoresists on the same laser beam recorder (LBR) can be valued by K, while the laser spot size is determined by laser wavelength and numerical aperture (NA) of the objective lens.Laser spot diameter, D = 1.22 l/NA.Pattern dot or pit size, Pw = 1.22 l/NA × KThe main process steps of DVD-ROM mastering include photoresist coating, photoresist exposure, chemical developing, metallization, and electroforming (Fig. 6.1). The traditional laser writing process with organic photoresist for mastering was considered to be the most flexible and precise approach to the control of pit morphology, and played important role in the DVD-ROM’s prosperity in the past.
