Discussion on splashing process of DVD9 aluminum layer
DVD9 is composed of two different substrates, both of which have their own splashing coatings. These two layers are called 0 layer and 1 layer of DVD9 respectively (Fig. 1). In DVD players, layer 0 is close to the laser reading head of the player, so layer 0 must be a semi reflective layer, so that the reading laser beam can penetrate layer 0 to layer 1. Like CD, 1 layer is a total reflection layer, which is also made of aluminum splash coating. The semi reflective layer of DVD9 is usually splashed with gold or silicon. Although in theory, the semi reflective layer can also be splashed with aluminum, it is not feasible in the current actual production
dvd9 has the same aluminum layer as CD, but there are obvious differences between DVD9 and CD. The reading beam of CD passes through the transparent substrate and reads information on the aluminum reflection layer, while the DVD player actually reads the back of the first layer of DVD9. Although this is not a major problem, it means that the actual pit size will be slightly smaller for the reading laser (how much depends on the thickness of the splashed coating), And this problem needs to be compensated when making a motherboard (Figure 2
another problem is that the increase in the thickness of the splashed coating in the whole pit is inconsistent. In the splashing process, more aluminum will be deposited on the substrate, which will increase the friction force on the flat surface, that is, the pit bottom and platform, while the pit wall is less. This factor must also be considered, otherwise the electrical signal will change.
the design of the cathode of the splashing machine is also very important, and effective design is needed to reduce the base The change of sputtering thickness on the film is also an important difference between DVD9 and CD sputtering processes. For CD, the different thickness of splashed coating on the pit wall and bottom, and the sampling position and experimental preparation of mechanical properties of splashed gbt2975 (1) 998 steel and steel products; The uniformity of the whole layer is relatively unimportant. As long as there is enough aluminum deposition layer to meet the requirements of reflectivity, the thickness is only a matter of cost rather than technology
the reflectivity of layer 0 and layer 1 was initially set to%, but now it has been reduced to%, because the reading laser beam must pass through layer 0 to layer 1. The thickness of layer 0 directly affects how much light will actually reach the next layer. When reading 3. Pendulum lift angle: when the 90 ° laser beam is reflected back to the player through layer 0, it also has the same effect on the signal intensity. The attenuation of signal strength is not only related to the thickness of sputtering coating, but also changes with the difference of sputtering material
the sputtering thickness of aluminum has a narrow deposition window (Fig. 3). It is difficult to design such a cathode to achieve the required consistency within the service life of the target, which is why aluminum is not suitable for use in production at present. Although gold is a very expensive material, it can provide a much larger process window (Figure 4), and silicon nitride (SIN) and silicon carbide (SIC) can also be used (its process window is shown in Figure 5)
(to be continued)