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.
Vibration Casting for Brittle Materials

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.
Advantages of the Vibration Casting Process for Sputtering Targets

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.
Gold-Tin and Gold-Germanium Sputtering Targets

Gold-Tin (AuSn) and Gold-Germanium (AuGe) sputtering targets are used by the microelectronics industry to deposit the solder onto thermal management packages and other devices for attachment to printed circuit boards. The development of a fine microstructure in PVD targets has been shown to improve the sputtering performance of the target.
Microstructural Development in Sputtering Targets

In order to develop this fine microstructure in sputtering targets, the cast billet is typically thermomechanically processed by either cold or hot working to break up the cast grains. The subsequent heat treatment recrystallizes the grains. The object of this process is to recrystallize the grains without any additional grain growth.
Production of Gold-Tin and Gold-Germanium Sputtering Targets

Two solder alloys, 80%(by weight) Gold (Au) 20% Tin (Sn) and 87.5% Gold (Au) 12.5% Germanium Ge can not be made by these traditional methods. These alloys are very brittle due to their heterogeneous microstructure of the eutectic composition. They crack and break up when mechanically worked at cold temperatures. AuSn solder is successfully produced as strip by rolling the solder at an elevated temperature with small reductions between anneals. This method will not develop acceptable grain size due to the inability to achieve significant reductions.