What is target poisoning?

　　The factors of affecting target poisoning are mainly the proportion of reaction gas and sputtering gas, which can lead to target poisoning.

　　Once reactive gas is introduced into a process chamber it reacts with the un-passivated surfaces, such as chamber walls and sputtering target. Consequently the surface of the sputtering target converse to a compound, for instance, Ti target changes its surface to TiO2 when oxygen is introduced into a sputtering process.

　　Poisoning of the target surface is associated with a number of effects, of which the following two have great importance:

　　1) Change in secondary electron emission, which results in a change of the discharge impedance. Consequently, at the same discharge power, the current and voltage can change substantially as reactive gas is introduced.

　　2) Drop in sputtering rate due to typically lower sputter yield of elements from a compound. For example Al2O3 sputtering rate is an order of magnitude lower than that of Al.