The relative density of the target material is the ratio of the actual density of the target material to the theoretical density. The theoretical density of the single component target material is the crystallization density. The theoretical density of the alloy or mixture target material is calculated by the theoretical density of each component and its proportion in the alloy or mixture. Thermal spraying organization target material is porous, high oxygen content (even vacuum coating, also hard to avoid alloy oxide and nitride) in the target material, the surface appears grey, lack of metallic luster, impurities and moisture adsorption is the main pollution sources, prevent high vacuum quickly, easy to cause discharge sputtering process, and even burn out of target.
At the same time, the instantaneous high temperature on the sputtering surface of the target material is easy to make the loose particles drop off, which pollutes the glass surface and affects the coating quality. The higher the relative density is, the faster the film forming rate is and the more stable the sputtering process is. According to the difference of the preparation process of the target material, the relative density of the casting target should be above 98%, and that of the powder metallurgy target should be above 97% to meet the requirements of production and use. Therefore, it is necessary to strictly control the density of the target material to reduce the occurrence of slag dropping. Spraying target density is low, the preparation cost is low, when the relative density can ensure more than 90%, generally does not affect the use, the current domestic use of SIA1 targets are spraying target.
In addition to density, if the target material appears abnormal in the production process, such as large particles falling off or heating shrinkage cavity, will form more pores (internal defects), the target material inside the larger (melting and casting target >2mm, spraying target >0.5mm) or more dense holes will appear due to charge concentration and discharge, affecting the use. Target materials with low density and pores are easy to fracture during subsequent treatment, handling or installation. The target material with high relative density and few pores has good thermal conductivity, and the heat of sputtering target surface is easy to quickly transfer to the inner surface of the target material or the cooling water in the liner, so as to ensure the stability of the film forming process.
