Technical Papers

Vibration Casting of AuSn and AuGe Sputtering Targets

Abstract

The development of fine grain size in PVD sputtering targets has been shown to improve the processing performance of the target in the sputtering chamber. Fine grain size is most commonly developed in a metal through the introduction of mechanical work and the addition of heat to allow recrystallization of the metal into small grains. Some alloys due to their brittle nature are not able to be processed by traditional metal working techniques without experiencing cracking and material failure.

A novel approach to obtaining fine grain size in PVD sputtering targets for brittle materials has been developed. Gold-Tin (AuSn) and Gold-Germanium (AuGe) are two brittle alloys formed into targets used to deposit the solder layer on the device surface. Neither of these two alloys tolerate appreciable mechanical work. AuSn and AuGe are produced at near-eutectic composition leading to the formation of a heterogeneous microstructure. Traditional cast targets exhibit a large varying grain size and a large eutectic structure that is detrimental to the performance of the target. A method to introduce vibration energy during casting was developed. The energy of vibration is introduced into the molten metal leading to small grains being formed. The size of the grains formed is a function of both frequency and amplitude.

The vibrational manufacturing process develops sputtering targets that have a smaller grain size and more uniformly distribute the heterogeneous structure throughout the target. The vibrational casting process decreases the grain size from 5 mm to 0.5 mm and the eutectic structure by an order of magnitude. The smaller grain size targets produced by vibrational casting give improved performance in the chamber.

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