How does the relative density and porosity of the target affect the coating quality?

The relative density of the target is the ratio of the actual density of the target to the theoretical density, the theoretical density of the single-component target is the crystalline density, and the theoretical density of the alloy or mixture target is determined by the theoretical density of each component and its content in the alloy or mixture. proportion is calculated. The thermal spraying Tungsten Sputtering Target has a loose and porous structure, high oxygen content (even if it is vacuum sprayed, it is difficult to avoid the generation of oxides and nitrides in the alloy target), the surface is gray, lacks metallic luster, and the adsorbed impurities and moisture are the main The source of pollution, which hinders the rapid acquisition of high vacuum, easily leads to discharge during the sputtering process, and even burns the target.

At the same time, the instantaneous high temperature on the sputtering surface of the target can easily cause the loose particles to fall off, contaminate the glass surface, and affect the coating quality. There are clear regulations for the point-like release on the surface of coated glass. The regulations are shown in Table 1. The higher the relative density, the faster the film formation rate and the more stable the sputtering process. According to the difference of the target preparation process, the relative density of the casting target should be guaranteed to be above 98%, and the powder metallurgy target should be guaranteed to be above 97% to meet the production requirements. Therefore, it is necessary to strictly control the density of the target material to reduce the occurrence of slag removal. The spraying target has low density and low preparation cost. When the relative density can be guaranteed to be more than 90%, it generally does not affect the use. The SiA1 targets currently used are all spraying targets.

In addition to the density, if the target is abnormal in the production process, such as large particles falling off or shrinking cavities due to heat, more pores (internal defects) will be formed, and larger inside the target (casting target>2mm, spraying target> 0.5mm) or denser holes will cause discharge due to charge concentration, affecting use. Targets with low density and pores are prone to chipping during subsequent processing, handling or installation. The target material with high relative density and few pores has good thermal conductivity, and the heat on the surface of the sputtering target material is easily and quickly transferred to the inner surface of the target material or the cooling water in the liner, and the heat dissipation is good, thus ensuring the stability of the film formation process.