High Temperature, Pb-Free, Metallic Sputtering Target Bonding Using Reactive Multilayer Foil
September 19, 2013 12:00 am
Sputtering targets used in physical vapor deposition (PVD) processes are bonded to compatible backing plates to promote cooling and to extend the life of the target material. There are several bonding methods used in the sputtering target manufacturing community: diffusion bonding; elastomer bonding; silver-filled epoxy bonding; and metallic bonding, typically using indium or tin-based alloys. The bonding method varies with the choice of target material, backing plate material, and intended bondline temperature during the deposition process. Metallic bonds provide excellent thermal and electrical conductivity, but are limited by the relatively low melting point of the solder material used - 157°C for indium or 217°C for tin-based alloys. This limits the power input, which in turn limits sputtering rates and final film properties. There is a desire for a higher temperature (> 300°C) metallic bonding process that can produce flat, stress-free target assemblies, enabling targets to run at higher temperatures for longer periods of time. This paper demonstrates a metallic bonding process using reactive multilayer foils and a high temperature alloy with melting temperatures as high 380°C. This process is compared with typically-used traditional Sn-based solders, specifically comparing shear strengths, void analysis, and cross-sectional analysis.