The main performance requirements of the target:
purity
Purity is one of the main performance indicators of the target, because the purity of the target has a great influence on the performance of the film. However, in practical applications, the purity of the target material is not the same. For example, with the rapid development of the microelectronics industry, the wafer size has grown from 6”, 8” to 12”, and the wiring width has been reduced from 0.5um to 0.25um, 0.18um, or even 0.13um. The previous 99.995% target purity The process requirements of 0.35 umIC can be satisfied, while the preparation of 0.18 um lines requires 99.999% or even 99.9999% of the purity of the target.
Impurity content
Impurities in the target solids and oxygen and moisture in the pores are the major sources of contamination of the deposited film. Targets for different purposes have different requirements for the content of different impurities. For example, pure aluminum and aluminum alloy targets used in the semiconductor industry have special requirements for alkali metal content and radioactive element content.
density
In order to reduce the porosity in the target solids and improve the performance of the sputtered film, the target is usually required to have a higher 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, the better the film performance. In addition, increasing the density and strength of the target allows the target to better withstand thermal stresses during the sputtering process. Density is also one of the key performance indicators of the target.
Grain size and grain size distribution
Usually the target is a polycrystalline structure, and the grain size can range from micrometers to millimeters. For the same target, the sputtering rate of the fine-grained target is faster than that of the coarse-grained target; and the thickness distribution of the sputter-deposited thin film of the target with smaller (uniformly distributed) grain sizes is more evenly distributed.