Purity is one of the main performance indexes of the target material, because the purity of the target material has a great influence on the properties of the film. However, in practical application, the purity requirements of the target are not the same. For example, with the rapid development of microelectronics industry, the size of silicon chip has been developed from 6 ", 8" to 12 ", while the wiring width has been reduced from 0.5um to 0.25um, 0.18um or even 0.13um. Previously, 99.995% of the target purity can meet the process requirements of 0.35um IC, while the preparation of 0.18um line requires 99.999% or even 99.9999% of the target purity.
Impurities in the target solid and oxygen and water vapor in the pores are the main pollution sources. Different target materials have different requirements for different impurity content. For example, pure aluminum and aluminum alloy targets for semiconductor industry have special requirements for alkali metal content and radioactive element content.
In order to reduce the porosity in the target solid and improve the properties of sputtered films, the target is usually required to have a high density. The density of the target not only affects the sputtering rate, but also affects the electrical and optical properties of the film. The higher the target density is, the better the film performance is. In addition, increasing the density and strength of the target can make the target better withstand the thermal stress in the sputtering process. Density is also one of the key performance indicators of the target.
Grain size and distribution
The target material is polycrystalline, and the grain size can be from micrometer to millimeter. For the same target, the sputtering rate of the target with small grain size is faster than that of the target with large grain size, while the thickness distribution of the film deposited by the target with small grain size difference (uniform distribution) is more uniform.
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